Sustainer Ideas

[curtisa]

Back from the weekend! Had a shot at trying to connect the driver to the LM386 circuit with a transformer with a 1:1 ratio. Results - needs more testing. It seemed to work, but I got carried away with other experiments and didn't get a chance to see if isolating the driver from the circuitry made any real difference to noise levels.

Also had a play with different arrangements for the buffer feeding the LM386 circuit. The Fetzer/Ruby arrangement surprisingly made things worse - EMI feedback was far too extreme to be usable. There's obviously way too much gain in the Fetzer for me to use. I found the best performance when I used a single FET-input op amp, a TL071, as a non-inverting buffer. The buffer added no extra gain to the LM386 circuit.

Finally got a chance to hear the sustainer amplified too, and also got the opportunity to hear the EMI fuzz everyone's mentioned. I found that I had quite a lot less fuzz when the buffer at the front end of the LM386 circuit had no extra gain. Also tried adding compressors and EQ's to the signal path for the driver - still had better performance with all of it left out and running direct: op amp buffer -> LM386 -> driver.

I'm curious to see what happens if we add positive feedback to the LM386, as shown on the Ebow drawing much earlier in this thread. Has anyone tried this to see what effect this has on sustainer performance?

Cheers,

Curtis.

[col]

...Also had a play with different arrangements for the buffer feeding the LM386 circuit. The Fetzer/Ruby arrangement surprisingly made things worse - EMI feedback was far too extreme to be usable. There's obviously way too much gain in the Fetzer for me to use. I found the best performance when I used a single FET-input op amp, a TL071, as a non-inverting buffer. The buffer added no extra gain to the LM386 circuit.

The fetzer was never intended for this application - its supposed to simulate a preamp valve stage.

Is it possible that the discrete fet is more sensitive to stray EMI than the op-amp?

Finally got a chance to hear the sustainer amplified too, and also got the opportunity to hear the EMI fuzz everyone's mentioned. I found that I had quite a lot less fuzz when the buffer at the front end of the LM386 circuit had no extra gain. Also tried adding compressors and EQ's to the signal path for the driver - still had better performance with all of it left out and running direct: op amp buffer -> LM386 -> driver.

The fact that more gain at the input stage means more fuzz tends to suggest that the noise is getting in prior to the circuit (or at that gain stage). So its likely to be the leads and/or pickup/driver coupling.

One of the bigest problems with my dynamic range inverter circuit is related to gain. The concept works really well, but with my limited electronics knowledge I can't get the correct response in the AGC circuit without putting quite a lot of gain on the input, and then attenuating the output. So the gain magnifies the crosstalk noise, and then the attenuator brings in more noise (any unnecessary resistors) prior to the LM386.

The current setup is a vast improvement on the posted circuit - it's much more controllable, but the noise is just as bad. If I can't get rid of the crosstalk soon, and I still have the energy, I will have a go at re-implementing the DRI idea using two LDR/LED pairs - basically a bog standard LDR/LED compressor hacked so that there is a second stage. Instead of the second stage being controlled by feeding back its own output, it is controlled by 'feed forward' - splitting the control signal from the first stage and using that... so I won't need two rectifiers, just an extra amp and an extra LDR/LED pair...

...

what kind of compressors and eq did you try, and in what way were they worse? worse noise? or just worse sustainer action?

I'm curious to see what happens if we add positive feedback to the LM386, as shown on the Ebow drawing much earlier in this thread. Has anyone tried this to see what effect this has on sustainer performance?

When I saw the feedback in the ebow circuit it made me think... the idea that you could use feedback to somehow squash interference between pickup and driver (they are so close in the ebow that there must be interference). So, the signal from the pickup would contain current generated by the string vibrations and current generated by coupling from the driver.... Could feedback be used to remove some of the parasitic driver signal leaving the pickup signal intact ?

Right now I'm going to go and try making some Inter-8 weave cable (minus the shielding )

like this:

cheers

Col

[www.5zhi.com]

Anyone any thoughts on the stacked driver ideas? Not sure if I had completely thought that one through!

hello www.5zhi.com, sorry we only have english!

I would be trying this on perf board or vero board, not a PCB. It is expensive ($$$) and difficult to change things. It is very easy to make a mistake. The on switch is only good for single pickup guitars. Your switches are fixed in one place so that the circuit and the switches must be mounted in one place which might be a problem if you don't have room in the guitar.

....

Thanks PSW.Circuit because I did not know, with pickup device can replace DRIVE?

I made a one-day experiment, but without success.

[curtisa]

The fetzer was never intended for this application - its supposed to simulate a preamp valve stage.

Is it possible that the discrete fet is more sensitive to stray EMI than the op-amp?

I think what's more likely is there's just too much gain, and the resultant extreme emphasis of the upper harmonics because of the introduced distortion just makes the whole system unstable. I tried the same thing with the TL071 by making it a high-ish gain non-inverting amp and got similar results.

what kind of compressors and eq did you try, and in what way were they worse? worse noise? or just worse sustainer action?

Compressors tried were an 1176 clone and the bog standard one in my Digitech RP6. EQ used was again the one in the RP6. Noise wasn't the problem with the compressors, just no real improvement in the sustaining action. And the EQ's only added extra "peakiness" to the sustainer - depending on the EQ settings it just made certain notes sustain harmonically instead of fundamentally, kinda like a cross between harmonic and normal modes. Obviously boosting certain frequencies pre-driver "encourages" the strings to sustain at the harmonic that is accentuated by the EQ boost.

I also tried incorporating distortion (again the RP6) but ended up with an extreme version of the sustainer in harmonic mode, no matter what note I played.

I'm finding that once the note has started, provided the sustainer can excite the string it'll happilly sit there for ever and a day singing away. Adding extra processing in the signal chain seems to change the way the strings want to sustain, but not always in a good way.

When I saw the feedback in the ebow circuit it made me think... the idea that you could use feedback to somehow squash interference between pickup and driver (they are so close in the ebow that there must be interference). So, the signal from the pickup would contain current generated by the string vibrations and current generated by coupling from the driver.... Could feedback be used to remove some of the parasitic driver signal leaving the pickup signal intact ?

My thinking is that perhaps the positive feedback is some sort of AGC control - the smallest-level input to the LM386 will immediately force it to start swinging it's output as hard as it can. Any further increase in input level results in no appreciable increase in output level, as the output cannot swing any further.

I can see building a foolproof circuit will in some ways be just as tricky as the driver itself, mainly because the biggest variable in the whole system is the most important one - the driver. We all currently experience different levels of success with our drivers, even with the same circuits. The one big difference is that we cannot control exactly how we're constructing our drivers, and we're all ending up with something slightly different that works better with some circuits than others.

Tricky

Cheers,

Curtis.

Edited October 9, 2006 by curtisa

[curtisa]

One more thing before I sign off for tonight - when I was doing my tests I was leaving the pickup leads for the combo driver/pickup disconnected. When I shorted the two pickup leads together, I could change the pitch of the EMI feedback. It occurs to me that with a combined driver/pickup sharing a common core, what we have here is a transformer, with a primary of around 100 turns (the driver) driven by the LM386, and a secondary (the pickup) with a few thousand turns generating voltage determined by the ratio of primary to secondary turns. Shorting the pickup leads together is obviously shorting out the "secondary" of the transformer and resulting in excess, and wasted energy in the primary and secondary windings. Leaving the "secondary" open gives us a pair of leads radiating all sorts of who-knows-what into our sensitive guitar electronics.

Catch 22?

Over and out

Curtis.

[psw]

Here are some details of how my strat is wired and switched...

This is the wiring for the complete guitar...

This is what my driver loosks like...

I did have problems such as you described (and some still as you can hear) but these were mostly solved by a complete bypass of all the electronics (selector, neck and bridge pickups)...the unusual thing was that it was not enough to simply short or open the circuit, the pickups hot and ground leads needed to be lifted...

This guitar was made as a test bed for a lot of ideas. I had to comprimise the esoteric phase/mid pickup phase to avoid an even larger switch!!!

Yes...the pickup/driver does potentially work as a transformer, it may even be some backlash from this that is causing my "pop" on switch off. I even wondered if putting a little signal into the pickup coil would aid or shield it in some way (similar to the stacked driver idea but with a massive diffence between the two coils).

I am even hoping that if the "pop" is related to this backlash from the driver coil, or induced in the pickup coil (and thus the earth on reconnection) that the RWRP coils of a HB driver may help or solve this...

You can see that the implementation is tricky. A three pickup strat is certainly a problem...a single pickup guitar like col is playing with, should be much easier...but apparently still a problem. Primal's LP worked ok, but perhaps the JB is more powerful or sensitive or something. I'm a little baffled!!!

Tim suggested that we get a bit into the implementation part of it, so I guess this is a start....

My future project is to modify an actual rail pickup...kindly donated by shawn/spazzy...into a twin coil version of what I am using now.

First will be to test it as a direct replacement for the driver pickup currently in use.

Second to see if I can run it...or modify it to run...in the mid position and gain the use of both of the other pickups... (a side result maybe the first multi driver guitar if I leave the other one in!!!)

The first step will give a direct comparison between the two technologys...the second will see if there is a significant improvement in EMI problems.

One of the attractions for me of the mid driver is that it may aid in installation. Only the driver's pickup part need be isolated...or if not fussed about a mid-pickup...omitted so as to be installed as if a single pickup guitar. (this would leave the original wiring largely intact).

I am prepared to experiment in some low tech shielding options. I have made driver coils incapsulated in a thin layer of iron impregnated epoxy. I am prepared to even shape the finished driver coils in some kind of putty to completely eliminate vibration and create some shielding. I would even consider som side fins if necessary...but I still want to keep the project simple and approachable. Exactly how I am going to get the coils onto the bobbins is yet to be detirmined...I have a few cunning ideas...but they will have to wait till I see the pickup and get some time and materials to actually do it.

I'm finding that once the note has started, provided the sustainer can excite the string it'll happilly sit there for ever and a day singing away. Adding extra processing in the signal chain seems to change the way the strings want to sustain, but not always in a good way.

Hehehe...way back I posted some embarrassing stuff about this thing potentially being a kind of "natural synthesiser" (a term coined by ebow btw) by adding in effects into the drive chain...but in a good way. I have even tried it and some things are interesting (flanger is just weird), an auto wha would be interesting... But ultimately, it is really about the guitar and far more can be done in processing the guitar's signal than can be done by processing the drive signal and trying to vibrate the strings in some un-natural way.

LK and I did have a debate as to whether a square wave or sine/natural signal wave would be best to drive a string. That is, a clean or distorted signal. I liked the idea of clean and built a compressor/limiter preamp version to test this idea. I think now that the driver itself (and the LM386) will generate distortion and clipping anyway. My current preamp has a temendous amount of gain (much more than a fetzer) and will be pushing a very clipped and compressed overdriven signal into the amp and driver. I think it does effect the way it is driving the string, but once the string is being driven hard...it is naturally being physically distorted (or is that tortured)!

So the jury is still out on that...and practically...what can we use...to run clean with power would take a lot of headroom...

As to why my guitar works as well as it does...I'm just not sure. Col in particular replicated pretty much my driver and simple amplification before moving on to the AGC and rail driver stuff. It is not simply a matter of overambition or anything. I'm just sorry that I can't exploit (at the moment) what this guitar of mine was built for...the testing and comparison of such ideas in a working instrument...but it does work pretty well as you can hear.

I really must track down or get some reports on the fernandes or sustainiac equiped guitars...they seem to be rare here...I've never even seen one. Are they completely noiseless? And what about the ebow...they suggest a potential distortion and cancellations as a featured effects at some locations near pickups (rubbing it over the magnetic fields of a HB will produce a tremolo effect)...why does this not suffer from these types effects. Even if isolated by it's own internal pickup...placing it over the guitar's pickup surely generates some kind of signal/distortion/feedback?

Anyway, more than enough from me for now... pete

[col]

I think what's more likely is there's just too much gain, and the resultant extreme emphasis of the upper harmonics because of the introduced distortion just makes the whole system unstable. I tried the same thing with the TL071 by making it a high-ish gain non-inverting amp and got similar results.

The preamp stage of my circuit has gain variable from about 3x to about 10x. At max, the noise/fuzz is worse than at 3x. However, even at max, only the louder 'attack' parts of the signal will be haevily clipped. The noise I get happens mostly on low level signals. This is because more gain is being added further down the chain by the AGC. So the worst noise in the system happens when there is no(or at least much less) hard clipping). Bascically, when you bring a weak guitar signal up to a reasonable level, you have to bring the noise up by the same multiplier...

what kind of compressors and eq did you try, and in what way were they worse? worse noise? or just worse sustainer action?

Compressors tried were an 1176 clone and the bog standard one in my Digitech RP6. EQ used was again the one in the RP6. Noise wasn't the problem with the compressors, just no real improvement in the sustaining action. And the EQ's only added extra "peakiness" to the sustainer - depending on the EQ settings it just made certain notes sustain harmonically instead of fundamentally, kinda like a cross between harmonic and normal modes. Obviously boosting certain frequencies pre-driver "encourages" the strings to sustain at the harmonic that is accentuated by the EQ boost.

I thought you may have been using 'stomp box' or other external effects for this. I would be surprised if you got useful results this way - particularly with the digital box. The success of the sustainer is so heavily dependent on keeping phase distortion to as low a level as possible.

For an obvious improvement in sustainer action, the compressor would have to be on an extreme setting - fast attack and delay with extreme compression ratio - even then it will only help even the string balance out a little - it can even out the signal going to the driver. it can never adjust for some of the strings/frets being more exitable at the same level than others. Its not enough evening out the laval, you have to make the out put louder for weaker inputs and softer for inputs - dynamic range invertion

I also tried incorporating distortion (again the RP6) but ended up with an extreme version of the sustainer in harmonic mode, no matter what note I played.

I wonder how pete gets his setup to work - he is adamant that he uses tons of gain in his preamp section.

I'm finding that once the note has started, provided the sustainer can excite the string it'll happilly sit there for ever and a day singing away. Adding extra processing in the signal chain seems to change the way the strings want to sustain, but not always in a good way.

Yep - its great isn't it

I think (as I'm sure you know from reading the thread) that the trick with any additional processing is it only comes into play when its needed - and it's only there to adjust levels and/or improve phase response.

My thinking is that perhaps the positive feedback is some sort of AGC control - the smallest-level input to the LM386 will immediately force it to start swinging it's output as hard as it can. Any further increase in input level results in no appreciable increase in output level, as the output cannot swing any further.

wouldn't this bring in loads of issues with noise and (bad)feedback ?

I can see building a foolproof circuit will in some ways be just as tricky as the driver itself, mainly because the biggest variable in the whole system is the most important one - the driver. We all currently experience different levels of success with our drivers, even with the same circuits. The one big difference is that we cannot control exactly how we're constructing our drivers, and we're all ending up with something slightly different that works better with some circuits than others.

Yes and no, I found not a huge difference between my single coil driver and one half of my dual core driver - the core width and wire guage are all they have in common. I think that a lot of the difference in success from person to person is a combination in equal parts of guitar setup, pickup, circuit and driver. After doing an install, I thing that a huge part of it - in terms of noise at least - is the position and size of the control cavity and the routing for the pickup and driver cables. Also the layout and connection of the circuit is probably much more crucial than I had first thought.

I'm on a steep learning curve - right now its the various types of noise than can be introduced by grounding design faults... and magnetic shielding technology (I built one of those inter-8 weave cables, its mostly a proof of DIY potential as the cable is too fat to go in the guitars cable holes - will need to buy some thinner wire to use. They're pretty easy to make if you go about is the right way.)

One more thing before I sign off for tonight - when I was doing my tests I was leaving the pickup leads for the combo driver/pickup disconnected. When I shorted the two pickup leads together, I could change the pitch of the EMI feedback. It occurs to me that with a combined driver/pickup sharing a common core, what we have here is a transformer, with a primary of around 100 turns (the driver) driven by the LM386, and a secondary (the pickup) with a few thousand turns generating voltage determined by the ratio of primary to secondary turns. Shorting the pickup leads together is obviously shorting out the "secondary" of the transformer and resulting in excess, and wasted energy in the primary and secondary windings. Leaving the "secondary" open gives us a pair of leads radiating all sorts of who-knows-what into our sensitive guitar electronics.

Catch 22?

Sounds like yet another potential bug to throw in to the mix - part of the reason I decided to work with just the bridge pickup and a driver with no stacked pickup or other pickups to get in the way... KISS (says the guy with the complex AGC circuit) lol

cheers

Col

[psw]

I wonder how pete gets his setup to work - he is adamant that he uses tons of gain in his preamp section.

Yes I do....

It occurs to me that with a combined driver/pickup sharing a common core, what we have here is a transformer, with a primary of around 100 turns (the driver) driven by the LM386, and a secondary (the pickup) with a few thousand turns generating voltage determined by the ratio of primary to secondary turns. Shorting the pickup leads together is obviously shorting out the "secondary" of the transformer and resulting in excess, and wasted energy in the primary and secondary windings. Leaving the "secondary" open gives us a pair of leads radiating all sorts of who-knows-what into our sensitive guitar electronics.

Ahhh....so, I am getting the strings to sustain and producing energy....hmmmm

Me thinks laterally...so this energy, which I assume is some kind of high voltage, could it be used to return and recharge a battery or power the circuit to an extent while in operation? This energy...is it adversly effecting the driver in some way? Could this energy be configured to power some kind of active shield (a shielding coil)? How does shorting the coil waste energy?

I have made two coils the same, one on and one sans pickup with no appreciable difference in the drive performance.

I was always concerned that the complexity of the circuitry of some of these things to induce frequency dependent "lags" for phase correction just added another layer of complexity and lag itself that would need to be compensated for. My aim has been to make driver designs fast enough not to require it...

The success of the sustainer is so heavily dependent on keeping phase distortion to as low a level as possible.

I am not yet convinced...is possible as a guess. I am still not sure that the noise is a factor was ever a concern in these phase correction circuits...they only suggest string response concerns.

I use a high gain preamp. The result is a clipped, compressed mush of a signal I am sure. What I'd like is some kind of limiter that would cut back the gain (to a set point) when the string is vibrating hard enough. We are creating a feedbackloop with the physical vibration of the string being a part of it. At some point the strings large physical vibration reaches the maximum possible (so it crashes into the frets usually, or can't vibrate any harder in any case) but I'd like to cut back the power before this.

A small signal is enough to get this feedback loop to start up and set the string vibrating and the increased volume created by this vibration, is feed back to the string and round it goes, building and blooming from almost nothing to maximum physical potential. A more refined response would be as col describes and aims for with his circuit. Maximum drive need only occur when there is small signals (the string is barely vibrating) and none at all when the string is flapping about (when picked hard or when sustaining past a given point, or at least beyond it's physical capabilities).

I think (as I'm sure you know from reading the thread) that the trick with any additional processing is it only comes into play when its needed - and it's only there to adjust levels and/or improve phase response.

Is this really a traditional compressor or limiter effect? Could there not be some kind of electronic switch (transistor?) that would cut power once the input signal reaches a certain level? The driver would then only be operating when signals fall below set limits. This is more the kind of thing I am contemplating, and something simple should be able to be devised surely. Such a scheme coulod reduce EMI and decrease battery consumption perhaps...but what I am really interested in (since my guitar works) is a more refined response potential (I still like the runaway effect sometimes )

I'm finding that once the note has started, provided the sustainer can excite the string it'll happilly sit there for ever and a day singing away.

Yep - its great isn't it

This is the most salient point...even the most basic and crude experiments that achieve the "effect" of driving the string will provide this thrill of seeing a driver in action. I will never forget the reaction of my young daughter when I ushered her in to see this happen just after I got such a thrill. She help this little 1cm disc above a string and the thing just sang. Everyday for a week she asked or sneaked in to witness it again...

I still get a thrill with the idea obviously...I encourage all to experience this nad for those who have to continue to develop it further to it's full potential... pete

[spazzyone]

I really must track down or get some reports on the fernandes or sustainiac equiped guitars...they seem to be rare here...I've never even seen one. Are they completely noiseless? And what about the ebow...they suggest a potential distortion and cancellations as a featured effects at some locations near pickups (rubbing it over the magnetic fields of a HB will produce a tremolo effect)...why does this not suffer from these types effects. Even if isolated by it's own internal pickup...placing it over the guitar's pickup surely generates some kind of signal/distortion/feedback?

Anyway, more than enough from me for now... pete

If someone has the january 2006 issue of Guitar world with the bonus cd

there is a video reveiw of the Fernandes Dave Kushner ravelle with the sustainer system

its the only disc im missing im looking but no luck....ill keep at it though

i know its somewhere (i have about 4000 disc's to go through)

here is a link to the written reveiw (yes i know magazine's are bias'd)

as they dont want to piss off advertisers

http://www.guitarworld.com/archives/2005/0...r_world-ku.html

Edited October 9, 2006 by spazzyone

[col]

...

Ahhh....so, I am getting the strings to sustain and producing energy....hmmmm

Me thinks laterally...so this energy, which I assume is some kind of high voltage, could it be used to return and recharge a battery or power the circuit to an extent while in operation? This energy...is it adversly effecting the driver in some way? Could this energy be configured to power some kind of active shield (a shielding coil)? How does shorting the coil waste energy?

I guess the coil will dissipate energy as heat, magnetic and electric field radiation...

I have made two coils the same, one on and one sans pickup with no appreciable difference in the drive performance.

I guess If you have enough gain in the system that the strings rattle off the frets and the LM386 is run at or near max output, you're not going to miss the odd milliwatt here or there

The success of the sustainer is so heavily dependent on keeping phase distortion to as low a level as possible.

I am not yet convinced...is possible as a guess. I am still not sure that the noise is a factor was ever a concern in these phase correction circuits...they only suggest string response concerns.

Phase distortion is just distortion of phase - eg phase of output is not the same as phase of input. It doesn't decessarily have anything to do with fuzz, or similar 'guitar distortion'. If the phase of the output is too far removed from that of the input, the sustainer function less efficient and less predictable... So we would like to keep phase distortion as low as possible (and then manipulate the phase intentionally for effects like the 'harmonic mode')

I think (as I'm sure you know from reading the thread) that the trick with any additional processing is it only comes into play when its needed - and it's only there to adjust levels and/or improve phase response.

Is this really a traditional compressor or limiter effect? Could there not be some kind of electronic switch (transistor?) that would cut power once the input signal reaches a certain level? The driver would then only be operating when signals fall below set limits. This is more the kind of thing I am contemplating, and something simple should be able to be devised surely. Such a scheme coulod reduce EMI and decrease battery consumption perhaps...but what I am really interested in (since my guitar works) is a more refined response potential (I still like the runaway effect sometimes )

I think a threshold switch would be problematic - the signal would home in on the threshold, and then you would probably get weird oscillation - possibly at a high pitch - as the switch turned on and of rapidly... If you designed some hysteresis into the system, you might then get some sort of warbling effect... I think from your description, what you need is a limiter. And a simple limiter circuit is already approaching the complexity of my AGC circuit.

btw, I got hold of some Light dependent resistors and an led today, so somtime soon, I'll have a go with that tech... If it works, I should be able to get somthing going that takes up less room on the stripboard... and the parts will be easier to come by... don't hold your breath though

Oh, and I got some thinner wire today, so I'm going to make another length of diy 'inter-8 weave' and see if it makes any difference.

cheers

Col

Edited October 9, 2006 by col

[curtisa]

Ahhh....so, I am getting the strings to sustain and producing energy....hmmmm

Me thinks laterally...so this energy, which I assume is some kind of high voltage, could it be used to return and recharge a battery or power the circuit to an extent while in operation? This energy...is it adversly effecting the driver in some way? Could this energy be configured to power some kind of active shield (a shielding coil)?

No, I don't think you could "use" this energy for anything much. The transformer action of the driver/pickup combo might be stepping up the voltage through the pickup windings, but it would have an extremely low current capability. At best you'd get (winding ratio) x (max LM386 output) volts, with a current delivery maximum of (volts) / (winding resistance of pickup). Probably somewhere in the vicinity of a few volts at a couple of milliamps, depending on how you've got it loaded up.

How does shorting the coil waste energy

Because you've shorted the secondary of the transformer. With the secondary shorted out there is zero resistance across the terminals. Ohms law will tell you that V/R=I, and in this case secondary volts / 0 ohms will equal lots of current. The transformer will try to put out this current, but won't be able to do it (due to winding resistance and other losses) and will just heat up. The short on the secondary is reflected back to the primary by the transforming action of the device and you have excess current in the primary, heating that up aswell. With the combo pickup/driver you're probably not going to damage anything, but I would think that you'll get pretty poor driver response and a heavily distorted output from the LM386 with a shorted "secondary".

I was always concerned that the complexity of the circuitry of some of these things to induce frequency dependent "lags" for phase correction just added another layer of complexity and lag itself that would need to be compensated for. My aim has been to make driver designs fast enough not to require it...

That could be one of the reasons why the Ebow uses such a simple circuit compared to the Sustainer - with the Ebow you have the option of moving the device up and down the length of each string to find the best place to get things going. With the Sustainer you're stuck with an immovable driver in a fixed location. Each string probably has different "sweet spots", and the resultant phase differences from string-to-string at a given driver location may dictate the use of complex phase correction networks to keep the whole thing running?

The success of the sustainer is so heavily dependent on keeping phase distortion to as low a level as possible.

I am not yet convinced...is possible as a guess. I am still not sure that the noise is a factor was ever a concern in these phase correction circuits...they only suggest string response concerns.

Yes, I'm thinking that too - I can get excellent results by moving my driver up and down each string to find the "sweet spot", and I get passable results with the driver in a fixed position. By moving the driver up and down the string I am effectively tweaking the phase relationship of string-to-driver in subtle ways which makes a big difference to the overall effect.

I use a high gain preamp. The result is a clipped, compressed mush of a signal I am sure. What I'd like is some kind of limiter that would cut back the gain (to a set point) when the string is vibrating hard enough. We are creating a feedbackloop with the physical vibration of the string being a part of it. At some point the strings large physical vibration reaches the maximum possible (so it crashes into the frets usually, or can't vibrate any harder in any case) but I'd like to cut back the power before this.

Which is where Col's circuit is useful aswell. Dynamic range limiting/reducing can help, both in string response and power consumption of the driver circuit, but I reckon there's more to it than just that. I'm sure the Fernandes Sustainer is complicated because it has to be to work reliably, which is a bugger for us DIY-ers!

Yep - its great isn't it

This is the most salient point...even the most basic and crude experiments that achieve the "effect" of driving the string will provide this thrill of seeing a driver in action. I will never forget the reaction of my young daughter when I ushered her in to see this happen just after I got such a thrill. She help this little 1cm disc above a string and the thing just sang. Everyday for a week she asked or sneaked in to witness it again...

Hehe...yes, I agree. I could've gone out an bought a brand new Ebow for $250, but I've built one that works for the cost of one IC. Now THAT'S cool.

Experiments shall continue!

Curtis.

[spazzyone]

im such a dumbass

has anyone watched these?

http://www.fernandesguitars.com/media.html

Edited October 9, 2006 by spazzyone

[curtisa]

Col,

I'm just trying to get my head around your work-in-progress AGC circuit that's been posted a few times. I've found the entry in the LM13700 applications note that describes the AGC element you've used in your circuit. The way it describes the action of the element is to act purely as a limiter, ie output voltage is kept at a fixed level regardless of any increase in input voltage.

A few queries/ideas:

What is the function of your second stage of LM13700 in your circuit (on the far right of the diagram), and what is the purpose of feeding it the same control voltage that the first stage uses?

The 10 ohm/47nF combo on the output of pin 8 forms a low-pass filter with a cut-off frequency of circa 30kHz. The one in the app note uses 50 ohms/20uF giving 160Hz. Is it possible that by applying different combinations of filtering (or even inserting an EQ in the control voltage path in the feedback loop between pin 8 and pin 2) might affect the operation of the AGC element so that it's more responsive to input signals based on frequency content? For example, by adding a high frequency boost to the control voltage the AGC will respond by clamping down the input voltage harder if it's a high frequency sound (or has high frequency content). That could have implications for evening-up the string-to-string response by changing how the AGC responds to pitch.

[col]

Col,

I'm just trying to get my head around your work-in-progress AGC circuit that's been posted a few times. I've found the entry in the LM13700 applications note that describes the AGC element you've used in your circuit. The way it describes the action of the element is to act purely as a limiter, ie output voltage is kept at a fixed level regardless of any increase in input voltage.

A few queries/ideas:

What is the function of your second stage of LM13700 in your circuit (on the far right of the diagram), and what is the purpose of feeding it the same control voltage that the first stage uses?

I'll try to explain.... The acg in the app note works by feeding back a current into the 'linearizing' diodes at the input of the amp stage... so if the output is louder, the control signal is stronger and the gain is reduced... in essence it works just like any other compressor.

The thing with a compressor though is that because its in a feedback loop the best it can do is make all input signals come out at the same level... any signal weaker than the threshold is amplified, any signal stronger is attenuated.

So my reasoning goes that if there is a signal quieter than the threshold at the input, the control currents says 'Amplify' and if its stronger then it says 'attenuate'. Now, the output of the first stage should be pretty well compressed to the threshold level - if you then use a second stage to add the same ammount of attenuation or amplification based on the control signal from the first stage, instead of all inputs coming out at about the same level, the quiet ones come out loud and the loud ones come out quiet... Dynamic Range Invertion !

This could also be achieved using a Fet as resistor circuit, or using an LED/LDR circuit. The LED/LDR version could be nice and simple, an elegant way to get the desired effect (I think - as yet untested) is to manufacture a component comprising one led and two LDRs, basically use one of the many simple LED/LDR compressor circuits out there, bung an extra LDR in there along with another amp stage and Bobs your mothers brother... it may be that the second LDR could be applied directly to the LM386 - say, from pin 1 to ground (another way to control gain described in the datasheet...)

btw, if you want to play with that LM13700 circuit, use potential dividers on the inputs of both LM13700 stages as in the datasheet - this way you can get much more control over the response of the circuit - you can do away with the need for input gain...

The 10 ohm/47nF combo on the output of pin 8 forms a low-pass filter with a cut-off frequency of circa 30kHz. The one in the app note uses 50 ohms/20uF giving 160Hz. Is it possible that by applying different combinations of filtering (or even inserting an EQ in the control voltage path in the feedback loop between pin 8 and pin 2) might affect the operation of the AGC element so that it's more responsive to input signals based on frequency content? For example, by adding a high frequency boost to the control voltage the AGC will respond by clamping down the input voltage harder if it's a high frequency sound (or has high frequency content). That could have implications for evening-up the string-to-string response by changing how the AGC responds to pitch.

String to string response is not an issue because of the dynamic range inversion - Thats what I designed the circuit for - the battery consumption is a nice side effect. The circuit can be set so that the only intensity difference between notes anywhere on the neck is that some tend to be more harmonic than others.

The filter in the feedback loop does have an impact - depending on the cap, it will encourage harmonics more or less - although a bigger cap does help to reduce the noise problems quite a bit (I'm using values ranging from 470n to 22u - 47n is way too low). This cap also has some effect on the response speed of the AGC. The best value seems to be just at the point where the lower strings are tending towards harmonics, but there is still a good strong fundamental tone.

As far as adding a frequency 'boost' - it's not a control voltage - it's current that does the work in the LM13700, so any buffering/boosting I tried just destroyed the effect completely - beyond my electronics skills I'm afraid.

What do you know about noise due to potential difference in the grounding of a circuit ? I'm wondering if that might be one of the issues I'm having. The sustainiac installation manual talks about a seperate signal ground and power ground, and is very specific about how the power ground must be connected. I wonder if My layout and wiring are causing some problems... Where do you thing the best place for grounding and power connections would be ?

cheers

Col

[curtisa]

So my reasoning goes that if there is a signal quieter than the threshold at the input, the control currents says 'Amplify' and if its stronger then it says 'attenuate'. Now, the output of the first stage should be pretty well compressed to the threshold level - if you then use a second stage to add the same ammount of attenuation or amplification based on the control signal from the first stage, instead of all inputs coming out at about the same level, the quiet ones come out loud and the loud ones come out quiet... Dynamic Range Invertion !

Yep, I see now, thanks - stage 1 = brick wall limiter (thou shall not pass!), stage 2 = further gain reduction based on gain reduction of first stage.

...err...hang on a tic, aren't you just limiting the limited signal? That's not so much dynamic range inversion, just limiting two times over. Isn't it just as easy to run this with one stage of the LM13700, with extra gain at the input buffer (LF358), and get the same effect?. I think I need to sit down with this one and play with it. Have you tried connecting a CRO to the output to see exactly how your circuit behaves?

As far as adding a frequency 'boost' - it's not a control voltage - it's current that does the work in the LM13700, so any buffering/boosting I tried just destroyed the effect completely - beyond my electronics skills I'm afraid.

Ahh, I see. But surely if you insert buffers and whatnot into the current feedback loop to change the response, all you need to do is convert from voltage back to current again by inserting a resistor at the output of the feedback loop buffer?

What do you know about noise due to potential difference in the grounding of a circuit ? I'm wondering if that might be one of the issues I'm having. The sustainiac installation manual talks about a seperate signal ground and power ground, and is very specific about how the power ground must be connected. I wonder if My layout and wiring are causing some problems... Where do you thing the best place for grounding and power connections would be ?

I did notice that on your circuit. You actually have two different derived "earths" in your circuit - the 2x 33k voltage divider for the LF358 on the far left, and the 2x 3.9k voltage divider for the LM13700 in the middle. I would think that you'd get better performance by having one "ground" point for everything, not two different ones. IME multiple un-referenced grounds is certainly asking for trouble in almost any sort of audio application in terms of noise performance as it can create earth loops.

My thinking is that you want the whole lot referenced back to the guitar's earth, which will then be earthed back at the guitar amp, but you want to keep the sustainer/circuitry separate as much as possible and earth it back at the furthest point in the chain, which in a guitar would be the output jack.

With any audio gear that does digital and analog mixed signals (think any digital fx processor) the grounds of the digital and analog side of things are run completely separately, but are commoned at one place only - usually back at the power supply. This is to prevent/minimise any digital signal muck from being carried through the analog earths and into the audio path. I reckon the sustainer might have to be treated in this way as well - certainly sounds like the Sustainiac does by your comment above. The sustainer and it's circuitry are "dirty signals" in comparison with the natural sound of the guitar.

Cheers,

Curtis

[psw]

Great stuff guys...

I really like col's ideas and they have come a long way from a prototype circuit and I would like to see this continue. Col has been seeking just this type of discussion about the circuit and you have come along at just the right time to help develop it further. I think you have raised some important points about grounding and isolation of the circuits. It has always concerned me that the driver is connected directly to the earth and that this does not seem to be the case with D-class amps.

Such technology may be out of our league however, but until my practical work was curtailed by personal circumstances, I was about to embark on an experiment into this area. I obtained a D-class kit that could replace the LM386 amp and was about to build it when all this blew up. It will return and may have some future potential, though a bit more cost and difficulty in availability.

Further, I will be attempting experiments with a rail driver as soon as it is possible, again built on a very compact rail pickup such as spazzy's. Such a direct comparison between my present simple coil and the dual coil designs may be of important benefit.

I'd really like to try to impliment some kind of AGC control and am glad that consideration is being given to other, perhaps simpler approaches to achieving this. I have mentioned before that I built a compressor/limiter with a LM386 stage inside as a testing preamp. It was used quite a bit for the hex designs to test these very ideas. As I recall, it was used a bit in the hex designs but I don't know how much I experimented with it with these conventional coil designs. As a preamp it worked great but I didn't notice improved performance as a result of either the compressor or limiter...but then this is hardly conclusive. This was never going to be a practical circuit to build into a guitar anyway, more a proof of concept thing.

I am also aware of the size issue. This thing will have to be small, while col's circuit is not large, and just about anything could be shrunk using multi-layer PCB's and SMD's, that is a little out of our league. Unless we were going to embark on some commercial proposition, this is never going to happen. Even then, we really would need to have something significantly better to offer. More and more we seem to be heading towards the conclusions and complexity of the commercial units...a shame, but perhaps inevitable.

I'd like to think that we could develop something with a unique twist to it, but the people who make it their business to do such stuff no doubt have tried most of the kinds of things we are contemplating. If our costs and hassle increase to much we may not be able to justify this as a DIY project at all in the face of the more refined commercial units available.

With this in mind, I will be thinking driver design, driver construction techniques and implementation options. It is possible that holy grails like extreme compactness (as the hex drivers were approaching), true polyphonic sustain response, low/no mod installation may never be able to be achieved...as was once envisioned.

But...there are tantalizing evidence that some of it can be. I would draw your attention to Dizzy's mid-pickup positioned bi-lateral driver. He thought this through and included phase correction and AGC to produce a very convincing implemention. If people have not heard it, check out this track...diablo_theme.mp3...much more realized than anything I have put up. The guitar did not feature the harmonic mode but could get different effects by the selection of the neck or bridge pickups.

There still may be some life in the techniques I developed for the hex devices. These were radically different from our conventional coil designs. They did work extremely quickly (the magnetic elements were primarily ferrite) so had less "phase distortion" and I did have one operating within 20mm for the bridge pickup on a strat that was driving it. I did have a plan where the early versions, which had a far less radical magnetic field arrangement, though still contained two magnets per string) could be built into the actual core of a conventional type pickup...but not a commercially available one. The upshot would be that I would then have to embark upon pickup design as well...hmmm (and then what would I do with it?)

I would encourage people to take a step back and try and get the thing working to a level similar to mine. So, a simple preamp and amp, basic driver design and passable results. This would provide a firm base to work on improvements. To that end the modular system would be ideal. I would like to see the ability to have the amp section close to the driver (avoiding a lot of magnetically shielded cable stuff) and to do that, a method of inverting the signal (preferably independant of the guitar's output) so that the controls can be safely be away from this high gain part of the device. Between this we could be looking at adding AGC or other parts. We can look at driver improvements too.

At the moment there is a level of complexity that has just too many variables and the problems are speculative. Each element should be proven to work at least to the best that we can make it work. Clearly, it can work in a basic form, at least I think, to a high degree. I'd like to think that it can be kept basic, cheap and approachable.

I'd like to be able to provide a greater degree of certainty in these endevours...many of the people who are trying to DIY this are not very experienced in circuits and many are put off by the prospect of coil winding (though it's far easier than many may think).

Also...This thread is about all thing sustainers....ebows too. The ebow is an elegant device and perhaps there is some room to investigate such a project too. Creating such a project may reveal things of benefit to some of our sustainer ideas. "acoustic" type sustainers such as Sustainiacs Model C are worth thinking about, as is my "power slide" which produces a quite remarkable sound. (Strangely enough, I don't seem to get a very good response from the sustainer with a slide (probably my poor technique and low action on this guitar as much as anything)). I'd also like someone to try this out with a piezo system (like an electro-acoustic)....there are a few implications there, too.

Shawn/Spazzy has obviously got something going on too that really shouldn't be ignored. Are their ways this approach could be exploited even if it does mean remote higher powered amplification. Could some kind of amp be designed to effectively drive a 14k load as found in a conventional pickup?

I am reminded that this approach appears to be the one that pioneer sustainer Micheal Brooks employed...check out this and the links infinite guitar (this is the instrument used on the famous, with or without you by U2) in particular this...manic music, brook's guitar, fernandes and a variety of other topics of interest here... Sustainiac seem to be pretty convinced of the bi-lateral driver, but I would have given due credit to Leo Fender. It is interesting to note that brook used a stacked single coil as a driver, so my concept of a low impedance stack may well have potential!

Anyway...keep exploring that circuit of col's and seeking other means to achieving such aims...and get those guitar's sustaining... pete

Would it be possible to hear what is going on with your devices curtis, col or any other's working with this...?

Edited October 10, 2006 by psw

[col]

Yep, I see now, thanks - stage 1 = brick wall limiter (thou shall not pass!), stage 2 = further gain reduction based on gain reduction of first stage.

Stage 1 is a compressor rather than a limiter - it doesn't just limit loud signals to threshold, it amplifies quiet signals...

...err...hang on a tic, aren't you just limiting the limited signal? That's not so much dynamic range inversion, just limiting two times over. Isn't it just as easy to run this with one stage of the LM13700, with extra gain at the input buffer (LF358), and get the same effect?. I think I need to sit down with this one and play with it. Have you tried connecting a CRO to the output to see exactly how your circuit behaves?

Nope - if the second stage was a carbon copy of the first ie. it's own output fed into its input then it would also be a compressor, but thats not what's happening. The second stage uses the control signal from the first, so if the first amplifies quiet signal to the threshold, the second will amplify them by the same ammount, through and beyond the threshold. Likewise if stage1 attenuates a loud signal down to threshold level, stage 2 will also attenuate the signal taking it through the threshold to be quieter.

So input louder than threshold will come out quieter than threshold, and input quieter than threshold will come out louder.

Using the potentiometers instead of fixed dividers at the inputs allows you to control where the threshold is (stage 1) and how wide the peak is (stage 2 - not quite sure why this happens) - there is some interaction between the functions of these two.

Don't have a CRO, however, I have simulated it, and it does do what I expected

As far as adding a frequency 'boost' - it's not a control voltage - it's current that does the work in the LM13700, so any buffering/boosting I tried just destroyed the effect completely - beyond my electronics skills I'm afraid.

Ahh, I see. But surely if you insert buffers and whatnot into the current feedback loop to change the response, all you need to do is convert from voltage back to current again by inserting a resistor at the output of the feedback loop buffer?

I'm sure i tried that - anyway, it works well without buffers and amplification in the feedback loop - and adding stuff in there is verey likely to add noise and other types of distortion...

What may be helpful is some sort of squelch device before the AGC - so that very low level sounds could be dumped and would not be amplified by the AGC... (this won't get rid of the crosstalk/fuzz though)

I did notice that on your circuit. You actually have two different derived "earths" in your circuit - the 2x 33k voltage divider for the LF358 on the far left, and the 2x 3.9k voltage divider for the LM13700 in the middle. I would think that you'd get better performance by having one "ground" point for everything, not two different ones. IME multiple un-referenced grounds is certainly asking for trouble in almost any sort of audio application in terms of noise performance as it can create earth loops.

unfortunately, The stages that needed a vcc/2 'derived' earth did not function if they were all supplied from the same passive divider. In the next incarnation, I will try using an op-amp to generate vcc/2 - this should allow the input buffers and the AGC (and the switchable inverter stage) all to use the same virtual earth. It's annoying having to add yet another op-amp in there though. Also note that the LM386 will always have to have a different earth to that of the op-amp based stages.

My thinking is that you want the whole lot referenced back to the guitar's earth, which will then be earthed back at the guitar amp, but you want to keep the sustainer/circuitry separate as much as possible and earth it back at the furthest point in the chain, which in a guitar would be the output jack.

Right, thats pretty much the plan anyway - what I will try is feeding the earth to my circuit as close as possible to the LM386 - to see if that helps (and other places )

Right now the guitars earth (trem/strings), the battery -ve terminal and the earth lead from the circuit all connect to the output jack. possible bugs are - the attenuator pot after before the LM386 stage is connected back to the earth track on the circuit - might be better to feed it back to a different position, or to the jack. The battery earth connection is using the stereo jack as on/off switch trick - this may also be causing problems.

Other stuff to try - I've read that using a large and small cap in parallel to filter noise from the power supply can help, maybe accross the LM386 power terminals... Also more filter caps - so each amp has one very close to its power pins...

And if nothing else works, then we'll see if an op-amp based common virtual earth will help.

Do you think it would be worth while isolating all the unused vero track ? or even using perfboard rather then vero board ?

cheers

Col

[curtisa]

Stage 1 is a compressor rather than a limiter - it doesn't just limit loud signals to threshold, it amplifies quiet signals...

The app note describes it: "...As VO reaches a high enough amplitude (3VBE) to turn on the Darlington transistors and the linearizing diodes, the increase in ID reduces the amplifier gain so as to hold VO at that level..." That to me says limiting - reducing gain to keep the output voltage at a constant level.

Still, if it's working for you...

unfortunately, The stages that needed a vcc/2 'derived' earth did not function if they were all supplied from the same passive divider. In the next incarnation, I will try using an op-amp to generate vcc/2 - this should allow the input buffers and the AGC (and the switchable inverter stage) all to use the same virtual earth. It's annoying having to add yet another op-amp in there though. Also note that the LM386 will always have to have a different earth to that of the op-amp based stages.

Hmmmm...technically the LF358 and the LM13700 need the same earth. It should've worked. It's possible that all three stages earthing through the same voltage divider was too much for it and was pulling the earth "off centre". You could try making the voltage divider using smaller reisitors, say 2x 1k to allow for a slightly better current margin.

The LM386 will be quite happy referencing back to the 9V negative terminal, just remember to capacitively couple the input to the previous stage.

Gotta dash, more later.

Curtis

[col]

Stage 1 is a compressor rather than a limiter - it doesn't just limit loud signals to threshold, it amplifies quiet signals...

The app note describes it: "...As VO reaches a high enough amplitude (3VBE) to turn on the Darlington transistors and the linearizing diodes, the increase in ID reduces the amplifier gain so as to hold VO at that level..." That to me says limiting - reducing gain to keep the output voltage at a constant level.

Still, if it's working for you...

Heres my understanding:

limiting means only those input signals above threshold are effected.

compression means input below and above threshold are both effected.

I think you're correct from a technical point of view... if you take the point at which the signal is big enough to turn on the darlington transistors as the 'threshold'. However at least from an experimental point of view (heh), it seems that the useful range is all above that level .. ?

I suppose it depends on how the circuit is set up - if you make sure that any viable input signal is going to produce an output big enough to switch on the darlington transistors, then the 'Threshold' is more of a fuzzy subjective concept depending on the output level, and on the shape of the response curve of the AGC... which is what I've spent ages fiddling with...

It's probably more complicated though, and I just got lucky hehe.

I guess it's is a combination of amplifier and limiter, but then isn't that what most compressors do? they just use a feedback loop to control gain.

Hmmmm...technically the LF358 and the LM13700 need the same earth. It should've worked. It's possible that all three stages earthing through the same voltage divider was too much for it and was pulling the earth "off centre". You could try making the voltage divider using smaller reisitors, say 2x 1k to allow for a slightly better current margin.

I'm aware that the buffers, AGC (and phase inverter) all need the same vcc/2 ground reference. However, using a passive divider doesn't seem to cut it - in the latest version of the circuit, I tried what you suggested, and found I had to go down to 20ohms before the phase inverter didn't screw up.

Surely using 20ohm resistors for the divider is going to cause other problems ? else why would most curcuits use kiloOhm resistors ? EDIT: doh - like run down the battery pretty quick

I have read that there are types of circuit in which different stages require their own dividers even though they all need vcc/2 - I know thats a bit vague and I don't have a reference handy...

The LM386 will be quite happy referencing back to the 9V negative terminal, just remember to capacitively couple the input to the previous stage.

right now I have a coupling cap on the output of the AGC, then theres an attenuating pot before the LM386. should there be another cap between the pot and the LM386 input ?

btw, thanks for your input

Col

Edited October 11, 2006 by col

[spazzyone]

added a soundclip of U2's with or without you on the sustainer sounds post

when i figure out whats going on with my recording software ill post some more

or if someone can convert a .CWB file to MP3 i can post sooner

and i have some wild stuff on tap that may change peoples thoughts about outboard

amplification and how good these rail pickups work with no mods

ive switched it into a ibanez rg with a stock pickup that sounds like poop to me

but it still shows how great it works

[psw]

Thanks Shawn...this track is probably the single most recognisable sustainer use so far and is particularly effective...sounding like nothing else.

If people follow this link to Micheal Brook's Infinite Guitar you will find an interview with Alan Hoover of Sustainiac talking about the history of the sustainer and how this guitar influenced it's development, the relation between floyd rose's system and fernandes and his companies products.

All due credit should be given to Micheal Brook for building his own DIY sustainer and for using it so extensively...here's a bit of those interviews...

We first made our acoustic type sustainer in 1986 (the Sustainiac Model T, soon followed by the Model . Then, we heard about the Brook Infinite Guitar when U2 played in Indianapolis in late 1986, as I remember. Edge's guitar tech called us, and allowed us to play a few notes on the instrument after the afternoon sound check. I thought that seemed like a neat way to make sustain, so we designed our own version of such a sustainer after looking at the I.G.

The Infinite Guitar used a regular Duncan stack pickup for a driver. Since this is a high impedance device, it requires around 100 volts of drive signal to produce adequate magnetic drive into the strings. This seemed kind of crazy to me, so shortly after that the Sustainiac GA-1 was born. We made a low-impedance driver so that the sustainer would run efficiently on batteries. The driver could be used as a pickup by attaching a transformer or amplifier to its output in order to increase the voltage output.

Technical description of Guitar Wiring and Black Box

The guitar has an Electromagnetic Transducer in the neck position. The signal from the bridge pickup (Seymour Duncan) is sent through a black box that has a circuit board inside that is an Equalizer that changes the Harmonic structure of the tone of the note(s) played. It boosts and cuts frequencies to make different overtones more or less predominant in the tone of the sustained string. Then the signal goes from the Black Box Back into the guitar and to the Bridge transducer pickup. So basically the signal from one pickup is sent into another pickup making the signal feed back into itself. This creates a feedback loop and the string is constantly vibrating once the transducer begins to move the string by itself by electronically exciting it. (Pulling and letting go of the metal string rapidly and repeatedly. So fast that you can't hear the beats of the pulse.)

-anonymous recording engineer and producer, December 1997

The 'infinite guitar' is a famous invention by Michael Brook, that is essentially his superior answer to the E-Bow. It gives the guitarist infinite sustain, with a controllable breaking point where the guitar goes into screaming overtone feedback. Unlike the E-Bow, it does not require the guitarist to hold any devices, and with both hands free great expressiveness can be achieved. Wishing to maintain the mystique, Brook is reluctant to discuss exact technical details, but apparently the infinite guitar works electronically, rather than mechanically, by feeding some of the output of his Tokai Strat back into the guitar.

To date, Brook has made two other copies of his infinite guitar system: one is owned by U2's guitarist The Edge, the other by producer/musician Daniel Lanois.

from the sound on sound interview

DW: One of the things you're best known for is the Infinite Guitar. What events lead up to the creation of the Infinite Guitar?

MB: I saw Bill Nelson playing at the El Mocambo, and he did this little thing with a device called an E-bow. I thought, `oh, I'd really like that kind of sound.' So, my girlfriend went up to his manager and said, `What is that thing, and where do you get it?' And he gave us the name of the place. So, I sent the money away, and waited.. and waited.. and waited--the guy lost my order. But I had booked into a studio to start recording what became my first solo record, so I thought `well, maybe I can make something that will kind of work like it.' Because I knew a bit about electronics. So, I worked on some things and did make something, it worked fairly well, and then my E-bow came, after I finished the recording. The Infinite was better for what I wanted to do, so it was kind of through accident, sort of.

from Varsity interview 1995

All interesting stuff...worth checking out...

So...although we are primarily looking into the idea of low impedance driver's like fernandes and sustainiac have developed, the oridinal sustainer guitar did use a standard pickup successfully. Just like shawn is experimenting with.

The outboard gear to run it is quite extensive and the details elusive...I did have photo's of it (now with my wife for now) so would not have been a particularly attractive proposition. He did try to patent it and that is an interesting aspect of the story for people interested in the pitfalls of patenting things, but as no patent exists no reliable information can be had of exactly what is in it (I have heard it used a very big transformer to get those kinds of voltages for instance).

Even the U2 track, With or Without You (that spazzy has posted) is under a cloud. It is certainly a very controlled sound. Some have sworn that it is an ebow and it is possible. I saw a documentary about the making of the album (unforgettable fire) and did see Eno and the edge playing around with an ebow and this is the right era. Live though, "the edge" does use a fernandes sustainer to play this track today. It still stands as an effective use of the technology, but it can do a lot more.

Certainly running the sustainer with a standard pickup is still something to explore, but at the moment I am still a little dubious as to the practicalities of the idea for a playing instrument...still, it works for Micheal Brook... pete

[custom22]

I finally got my Fetzer Ruby to make a sound. I plan on messing with drivers and such, and i've come up with an idea.

Would it be possible to use the existing magnet and bars of a pickup to wrap around wire in addition to the pickup coil? I would think it feasible, depending on where the pickup's existing magnets are. What does everyone else think?

Edited October 11, 2006 by custom22

[psw]

I am not entirely sure I have got your concept right...

If you look at the way my pickup/driver is made, that is exactly how it is done...I used a blade higher than the original to add a 3mm driver coil on top of it....It happens to have a ceramic coil below it, and I have chosen to replace the original poles with a blade (for string bending response and ease of construction mainly).

A pickup with pole magnets should work just as well...however...to get the height you would need to push the mags up above the pickup bobbin...this may be ok, but less of them will be in the pickup itself. You would need to be sure that the pickup is wound around a bobbin and not as traditional fenders are made with the pickup coil wrapped directly around the magnets...the wire in a pickup is very fragile.

Also, the magnets are usually Alnico and may be subject to some demagnetization by the driver over time (I am not sure).

If you mean wrapping a driver coil around the outside of the pickup windings (over them in effect), no this does not work. The driver coil would be too far away from the magnets themselves and the copper in the pickups coil will produce a lot of detrimental eddy currents in any case...

One could make an entire pickup driver, but that means stripping the bobbin, winding a driver, then winding the pickup coil again in a smaller space. Possible, but very difficult.

At some point I would like to make some pickups and have the equipment and materials to do this. I have much the same intentions as this for such a project, but we are still looking into other types of designs. I do wonder whether a stacked pickup/driver would not be more the go, or some kind of rail. It is important these days to have some kind of noiseless capabilities, what with computer monitors and lighting everywhere, and if I were to go to the extent of making something, I would certainly consider such things...

It is also worth noting that the cost of cheap pickups is not that great. It could be that if you don't wish to modify your guitar's pickup, or it is not entirely suitable, you would be best to find some cheap pickup to modify. If you have some guitar repairers about, they may even donate a cheap pickup that has been replaced or is broken if you explain what you are planning to do with it.

If it is the aesthetics that concern you....remember a pickup cover is cheap and will hide a multitude of sins... pete

[psw]

BTW...this is the main thread but there is some occasional stuff elsewhere such as Guitarnuts

A member there has posted a few links including this promo from fernandes...

fernandes video

pete

[curtisa]

Heres my understanding:

limiting means only those input signals above threshold are effected.

compression means input below and above threshold are both effected.

Not quite. Limiting and compression both use the same "threshold" system. The only difference is that once the input exceeds the threshold in a compressor, the output continues increasing but at a slower rate. You can have a compressor set up with a 2:1 ratio, which means for every 2dB that the input exceeds the threshold, the output only increases 1 dB.

Limiting is set such that any increase in input level over the threshold results in no increase in output, which in compression ratio terms is infinity:1.

You can add gain to the input of the compressor/limiter so that the quieter audio is louder and the louder audio is compressed - all you're doing is raising the average level of the audio by reducing the "distance" between the loud and quiet bits.

I think you're correct from a technical point of view... if you take the point at which the signal is big enough to turn on the darlington transistors as the 'threshold'. However at least from an experimental point of view (heh), it seems that the useful range is all above that level .. ?

I suppose it depends on how the circuit is set up - if you make sure that any viable input signal is going to produce an output big enough to switch on the darlington transistors, then the 'Threshold' is more of a fuzzy subjective concept depending on the output level, and on the shape of the response curve of the AGC... which is what I've spent ages fiddling with...

It's probably more complicated though, and I just got lucky hehe.

The impression I'm getting from the app note is that the threshold is defined by the 100K variable resistor (labelled "output amplitude"). It sets the absolute "ceiling" of the audio, above which nothing shall pass. I haven't built and tested this yet so I don't know exactly how it would behave in real life.

I have read that there are types of circuit in which different stages require their own dividers even though they all need vcc/2 - I know thats a bit vague and I don't have a reference handy...

It's possible I guess. Otherwise how would connecting up more than two stompboxes together work? They would each have completely unrelated earths to each other. My query stemmed from the fact that we're sharing the same common power supply

Anyway, if it works, it works

Edit: looking at your schematic, I wonder if you'd get better performance by changing the order of the buffer and preamp to:

Input from guitar -> buffer (buffered output here) -> preamp -> AGC etc...

...instead of the buffer and preamp in parallel, the way it's currently drawn? And would the shared earth work properly if it was?

right now I have a coupling cap on the output of the AGC, then theres an attenuating pot before the LM386. should there be another cap between the pot and the LM386 input ?

No, what you've got there is fine - you only need to couple once between stages.

Other stuff to try - I've read that using a large and small cap in parallel to filter noise from the power supply can help, maybe accross the LM386 power terminals... Also more filter caps - so each amp has one very close to its power pins...

Absolutely! From the National Semiconductor Audio Handbook 1977:

"...Shown or not, bypass capacitors are always required. Ceramic disc capacitors (0.1uF) or solid tantalum (1uF) with short leads, and located close (within one inch) to the integrated circuit are usually necessary to prevent interstage coupling through the power supply internal impedance. Inadequate bypassing will manifest itself by a low frequency oscillation called "motorboating" or by high frequency instabilities. Occasionally multiple bypassing is required where a 10uF (or larger) capacitor is used to absorb low frequency variations and a smaller 0.1uF disc is paralleled across it to prevent any high frequency feedback through the power supply lines..."

Whether it actually makes much of a difference in our application though..?

Do you think it would be worth while isolating all the unused vero track ? or even using perfboard rather then vero board ?

Doubt it. IME I've never had to do anything like that with vero boards. If we were playing with RF circuitry it'd be a different matter, but in our application I reckon it's more work than it's worth. As long as our finished layouts are neat and tidy (be it vero, perf or full PCB) I reckon we're fairly safe.

Cheers,

Curtis.

Edited October 11, 2006 by curtisa