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Sustainer Ideas


psw

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The demise of the Gizmotron was the inconsistency of performance - it needed constant fiddling to keep it working anywhere near correctly, and apparently Lol was the only person who ever got really good at playing it. Strangely enough, it was the Musitronics owners' massive investment in the Gizmotron, and the subsequent sell-off of Musitronics (to ARP, who promptly went broke and disappeared), that led to the disappearance of the Mu-tron line, not the other way around. Even Bob Moog (who was hired by Gizmo Inc after his contract with Norlin/Gibson ran out) couldn't work out the problems with it.

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SUSTAINER TUTORIAL POSTED!

I just wrote up a tutorial with pictures on how I made my sustainer:

http://projectguitar.ibforums.com/index.php?showtopic=16984

As I said in the tutorial, this is certainly NOT written up to say "we did it and here's how to build it", it's more meant to say "here's an easy way to build it so everyone can start improving on it". So let's see some working sustainers out there, and everyone report in on how their experimenting goes.

Thanks PSW, thanks lovekraft, and thanks everyone who has added to this stuff. Let me know if you think I should change anything in the tutorial or if anything is unclear.

Let's keep this thing going. Personally, I'm going the PSW route and I'm going to start integrating this into a guitar. I'll check in and report as I find out more about this sustainer beast.

Mike.

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UPDATE: WORKING SUSTAINER!

So I wound a new driver and wired up a simple opamp preamp. The new driver uses rare earth magnets that I took out of a hard drive. I slipped it under the strings of one of my guitars, and it works like a dream!

With one exception:

The 386 seems to give out in intervals. I pluck the string, it goes into a beautiful sustain, it builds up to a level and then the Ruby circuit cuts out and the string dies down a bit, then the Ruby kicks back in and it starts building back up. This is about a 8 second cycle with 5 seconds of great sustaining and 3-4 seconds of cutting out. I'm gonna try replacing the 386 chip and hopefully that will fix it.

If this small glitch is worked out this will be an excellent system! I went all over the fretboard and every string held excellent infinite sustain except for the high E. The guitar I'm trying has a bit of a quite high E due to pickup alignment, thought, so that may be the problem. But seriously, when the Ruby is working it is flawless. I love it. I was just touching the string without picking and the sustain would kick in and I could slide it all around.

Any suggestions on the cutting out problem would be really appreciated. As soon as I work out that bug I'm planning on posting schematics, driver winding instructions, and sound clips.  I really think this is something that anyone with any soldering capability can easily do.

Thanks again to PSW and everyone else that has contributed to this. Let's keep it rolling, it's almost there.

Mike.

Thank Mike...nice, brief and too the point...Me...the king of the Mega-post, I'd have trouble editing myself down...EXCELLENT.

Just a few things in your "general comments: 1" it should read "without a neck pickup" not bridge as it currently says!

I'm a little disappointed that there's nothing new on the preamp...you promised:

I made another circuit, it works much better.

My first circuit would only give good sustain with hot humbuckers, but this second circuit has enough preamp gain to work with just about any guitar.

You seem just to have just posted the Ruby...so how do you get more gain from the preamp stage...I kind of got the idea that you'd made a new preamp stage...perhaps with an opamp. As I said in reply:

I'm so keen to see your op amp preamp. I tried and tried but I can't work out why I couldn't get the results I was after...

Maybe I got the wrong idea :D D'oh! Sounds like I'll have to go back to the drawing board on that one...still I would have thought the ruby buffer stage could be modified to provide more gain. My two transistor preamp can have the gain modified by simply changing resistors in the circuit...anyone want to put their mind to it!

Anyway...thanks for putting the current state of the DIY Sustainer where more people will see it without the confusion of all the different stuff discussed in this huge thread...it can be a bit misleading.

psw / pete

BTW: thanks Mutron...that's interesting about the tape heads, I thought it must be something like that. You couldn't use tape heads as drivers though as you'd soon burn them out and the impedance would be way too high.

I played the Gizmotron too when it came out here :D . Paul McCartney was a bit of a convert too as I recall. It was pretty wacky...100's of tiny picks on wheels. I got a similar effect back then by cutting a slot in the head of an electric toothbrush and pushing a pick in there. I could only play in G cause that was the key of the motor's interferance buzz through the pickups B)

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Speaking of Preamps....I found this one that would work but seems to have a pretty high parts count:

Bob Blick Op-amp Preamp

And...I've noticed a lot of trafic to to Mike's Sustainer Tutorial...from a lot of Guests. Who are these "Guests" anyway???

pete

Oh Yeah....and here's some shameless cross promotion to my Outside pentatonic Theory in the Player's Section:

THE SECRET LIFE OF PENTATONICS

Also...here's a site that discusses D class Amplifiers:

D Class Amplifiers

Edited by psw
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...You seem just to have just posted the Ruby...so how do you get more gain from the preamp stage...
Take a look at the input stage - they've replaced the source follower in the original Ruby with a Fetzer gain stage.

Mike, any idea about how many turns of wire it took to get to 8 ohms?

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Thanks for clearing that up about the Gizmotron, lovekraft...

I'd remembered later that Arp bought Musitronics...and then subsequently went bust over the Arp Avatar guitar synth fiasco..

If ARP had acted quickly enough they could have targeted those Avatars at keyboard players as well...they were after all, just keyboardless versions of an ARP Odyssey...with a hex pickup section (that worked badly) Because they had CV and gate inputs they worked fine as a synth expander (I had a few in my synth studio)

Then to save their bacon, ARP threw all their resources into the Chroma poly-synth...which was a great synth...but it was too late.They ended up selling all Chroma rights to CBS in an effort to stay afloat

I'm not surprised the Gizmotron failed...it was just too ricketty and plastic...it looked like it was gonna break at any minute...heh

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A-ha LK...so what kind of gain is that pre-amp giving out then...looks like what we were looking for all the time then...yeah :D

BTW...everytime I made one...I think three like this...I lost count but with my 0.2 mm wire it was about 100-150 turns. You really have to measure it as you go though, especially towards the end as the ohms rise fairly rapidly as the coil gets thicker.

So is the perf-board layout the same as the Ruby but with different values...whats the go there!

psw

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Hi. I discovered this thread two weeks ago and yesterday I finished my first sustainer driver. 5 mm iron core, 220 rounds of 0,3 mm wire, DC resistance 7,3 ohm, ceramic magnet from old single coil pickup. I tested it quickly today using DI Box -> Mixer -> old stereo amp -> driver as a sustainer circuit.

I found out that sustainer effect was much more powerful on lower strings. On low E, the whole guitar was vibrating massively and on high E there were hardly any effect at all. Slightly varying driver height didn't make much difference. My first impression was that the sustain was vary similar than what can be achieved with a loud amp.

Is there any experience about the driver design which would give more even response from different strings? As I'm sustaining through mixer, it's easy to test if compressing or eq'ing has any effect on behaviour.

I'm going to build an amp with preamp based on TL071 and power amp based on ruby. I'll report back when it's done.

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to drive mine i have gone back to the original sweet overtone producing distortion pedal that i fell in love with and was one of my first reverse engineering projects. the blues pearl perplexed.

what i didint' know is this.

1st stage is a mosfet not a transitor however i like the transisor configured in this way.

heres the scheamtic.

http://www.geocities.com/radu_teppes/Revisedperplexed.htm

some of the changes i have done to make this a beastly pedal are as follows

use a .15uf input cap. .47uf C1 50k push pull pot wird as a 25k pot when in down posistion. 1uf C3 5k R2 560k R6

1uf C9 and i dropped it all off at the R7 resistor and jsut used a standard guitar tone pot.

that gave me the option to use screaming distortion to really freak out everything which dimed will give something like 1.5minutes of sustain before it starts into feedback. or if you roll the gain pot downalmost all the way it has a nice compressed feel to it that is really open if that makes any sense.

now this may seem like a daunting build but its really quite easy if you take into consideration we are loosing the tone stack completely.

i am now going to be using the nice little LK trick on the vbias to loose some parts there. it can be made somewhere in the neighborhood of 15 -30 minutes or so if you have all your parts laid out and ready to go and the iron is hot.

of course then again this is my time as i build everyday so if you don't then well your build time may vary. :D. soon i will have boards for these.

i do have a few extra 386 boards on hand set up for input and output caps gain pin controls v+ grnd and diode clipping on the output stage as well available if anyone wants to try one out.

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This is Great...it's fantastic to see some research and experiment being done outside my ability and resources :D at last!

Pekko...that's fantastic about the TL071....I made several preamps with this and the TL072 but failed to get them to work right simply because I don't know what I was doing. They would be ideal and have plenty of gain potential with the LM386 amp. With a dual or even quad opamp you could also add distortion diodes if it were to turn out that a more squarewave signal is benificial.

I'm a little concerned that you're using a stereo amp...there's way more power there than the 1 watt or so being produced by our little battery powered devices. You may want to consider something from my first ever post on this thread:

Sustainer Ideas

Many years ago I wound a crude coil and ran the guitar output to both my amp and a trashed hi fi amp. The output of this went directly to the coil placed beneath the strings. It worked!!!!!!!!!!!! However some notes better than others, but still it worked!!!!!!!!!!!

Only one drawback. Within minutes the coil heated up like a bar radiator and proceded to melt the electrical tape holding it together. The strings really heated up and the whole thing threatend to catch on fire! Still it worked!!!!!! I've got some recordings somewhere to prove it. Would make a great stage act!

Check you're not putting too much power through it...if your lower strings are bouncing around that much I suspect you are. Remember that although it's a starting point...you'll have a hard time in reality fitting all that gear in your guitar...in otherwords, it's not a real life experiment. .

Try reducing the power and you may even get a better response from the higher strings. The high E seems to be a universal problem, even for commercial systems (look at out early discussions on the patents and phase compensation). Also...try accentuating the treble to send more signal at the higher frequencies and such...if you've got an equalizer on that mixer perhaps cut all the very high frequencies to cut high frequency noise that can cause squeel (oscillation). But it's tricky, simply more treble does not necessarily produce better high string response...you may find that you're driving the low strings at a higher harmonic...that's very typical.

There are ways to address these problems...for a long,long, time I was using separate drivers for each strings...the so called Hex Drivers...to address these problems, to get a better response on chords and to reduce size. Eventually, I came round to realizing this approach was not really a DIY project and, although I had visions of selling my driver technology, it really didn't help you guys and would probably amount to nothing for a lot of time spent developing it. That's why I cut my losses and went back to the very basic single coil driver and simple amp setup. But there is a lot I've learn't along the way and together I'm sure everything will only get better. Meanwhile, this incarnation does produce a very usable result all the same.

Lovekraft suggested (a loooong time ago) that I concentrate on the driver design and I think he was right. For instance most of my Hex designs made use of ferrite and quite happily drove high strings.

5 mm iron core
Now I don't know if you mean simply steel or actual iron but some materials just simply dont have the ability to respond at high frequencies. This is where the experimentation really is...the circuitry is secondary I think. BTW my circuitry works perfectly well. The preamp uses two transistor stages and it's gain can be tweaked with some resistor swapping. It's cheap too but it's a little larger than I had hoped for...a simple opamp preamp on the same board as the LM386 would be far more elegant and easier to install, that's all.

Ansil...

i do have a few extra 386 boards on hand set up for input and output caps gain pin controls v+ grnd and diode clipping on the output stage as well available if anyone wants to try one out.

I'd be interested :D . Are you able to make or easily get boards made? Perhaps you should look into this a bit more and design something...maybe when we get a better idea of what we're doing...with a simple opamp preamp and LM386 etc as a kind of universal circuit kit...might be some $demand$ for it.

Now...can anyone draw up the means by which, with a single switch you can turn the sustainer power on and select the bridge pickup so I can install it in my test guitar...I'd be really greatful...

Anyway...it's all good to see everyones input and interest resulting in...well, some results :D

heartwarming

psw B)

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can anyone draw up the means by which, with a single switch you can turn the sustainer power on and select the bridge pickup so I can install it in my test guitar...I'd be really greatful...

I guess you could use a superswitch for that purpose.

...

emre

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Hmmm...I was hoping for a simple DPDT. One side simply connects power to the circuit. The other side to connect, in one position all grounds and on the other only connect the bridge pickup bypassing the selector switch.

LK sent me an Email where he'd worked out something like this...just can't locate it at the moment...there has been some developments and advice behind the scenes (as if this thread wasn't long enough) but it's hard to bring everything to mind when you need to.

I've pretty much decided to permanently install the sustainer/pickup prototype in my test strat...even if I need to route a new cavity (probably behind the bridge or in the lower bout from the back). Rather than go straight to a purpose built guitar...it might be worth testing the installation and I can alway's make a new driver...perhaps even better...like the one I illustrated making back a few pages.

As it happens, the pickup I used, which was ideal for the purpose, is the same as the pickup that will be replaced so I can make a direct comparison to the unmodified performance of the pickup and gain the parts to make another!

Anyway...all I need is a means to practically interface the sustainer into the guitar.

It may even be possible to use a single three position switch with a lot of poles to have off in the middle and normal one way and harmonic the other...that way it's just one switch and a knob...on a strat that could replace one of the tones if you wanted for a really stealthy installation.

So...tell me how to switch it and I'll install it ASAP!

pete

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I just wanted to check in and say that it's great to see people working on this thread so vigorously again.

PSW: As LK mentioned, I've been using the Ruby with a Fetzer valve preamp. For a while I was using a simple opamp preamp which worked pretty well, but when I went from breadboard to perfboard (right before writing the tutorial) I decided to try the Fetzer because it's already documented. I'm happy with the switch. Having said that, I'm sure that our electronic experts like LK and Ansil can improve on the electronics of this thing.

I think the biggest issue to tackle is the high frequency response. It's very easy to build this thing and get a great sustainer, but in my experience it's difficult to get the high E going. I'm going to try a new driver with a ferrite core to see if that helps.

Anyway, keep it up everyone!

Mike

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psw:

Thanks for your warning about using too much power. I didn't have to crank the stereo amp and the experiment was pretty much just to see if the driver is working or not.

Core material I used was normal black steel. I might try winding a driver around ceramic magnet or making core from transformer lamination steel plate.

This should do the trick for switching power on and selecting bridge pickup with DPDT switch ("tone" side of pickup selector not shown):

Sustainer_DPDT.gif

This will not affect tone side, so active tone controls will be selected with pickup selector.

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Terriffic...Actually I just worked it out yesterday but didn't have time to draw it to be sure...I'll install my working version as soon as I have time.

My core is normal steel too. It is only 3mm wide. I have trouble with the High E but if it's close I get a fair response on notes above the 12 fret. If it's trying to drive at the harmonic we're getting into dog whistle territory and it tends to drive at it's natural frequency. In part it could be that at the higher frets, because of the action, the string is broght down even closer to the driver (almost touching) or there maybe something to do with the physical phases of vibration.

The ways of addressing this could be:

Core Material...I know this helps...laminated, powdered, ferrite, etc.

Core shape...wider or narrower at the higher strings

Coil shape...wide or thin, shallow or deep

Coil number...separate coils optimised for each string...eg my Hex ideas

Magnet strength and placement...more/less magnets under the high strings

Magnetic Diversion..."shunts" or directing fins

Power...more or less

Filtering...processing of signal

Phase Correction....Having circuitry that changes the phase for higher freq.

These are just a few that I can think of off the top of my head that have been discussed or experimented with over the course of the last 53 pages :D ! I know there's more that I've left out and then there's all those things I've never thought of and the things that people come accross by accident while fooling around with making this stuff. That's why it's important for people to have a go and report how it's going...even poor responses give clues as to what would create a good response.

Mike....

For a while I was using a simple opamp preamp which worked pretty well, but when I went from breadboard to perfboard (right before writing the tutorial) I decided to try the Fetzer because it's already documented.

I'd still really want to see the opamp preamp...If nothing else I'd like to know where I went wrong. I think there could be some versitility to tweaking the preamp design (filtering, clipping and such) with dual or even quad opamps plus we might be able to make a super easy design for a compact circuit board...maybe we could eventually put together a kit that would make this accessable to just about anyone....ansil maybe?

Anyway...got to run...great contributions guys!

pete / psw

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It always looks a little strange at PG when the Sustainer Thread slips back to the 2nd page doesn't it.... :D

Well not a lot happening here just now...still thinking of doing an install into my test strat, looking like a rout through the back of the guitar under and around the input jack for the circuit battery and the controls...knob just aft of the bridge and the two switches just below. I'm thinking of making space for another preamp,knob and switch under the sustainer control for a piezio system. The battery could be made accessable by just removing the two screws of the strats jack plate.

I'd still like to know what Mike used for his original opamp preamp, but the "fetzer valve" is probably a simple and compact solution...I'll have to test it out with my drivers and test guitar and see how it compares...here's the schemetric from the Tutorial

On alternative preamp designs....here's a guy named HiFiJohn

HiFiJohn's Guitar Stuff Page

He's got a simple single opamp distortion box with 4 controls that might be of interest because the circuit could be built really small and the controls be internal trim pots...here's the schematic:

fxschem.gif

Meanwhile...Ansil has circuitboards for a LM386 onboard guitar booster. It measures about an inch square and could easily be used as the power amp section for this project with a little mod (linking pins 1-8 for 200x amplification).

Here's the link to the fetzer valve circuit from runoffgroove:

Fetzer Valve Details

and the Ruby

Ruby

I'm not sure why they have that trim pot on the fetzer valve circuit and not just a resistor. It might be worth having the "gain" control on the Ruby as a trim or it could be omitted to a simple link for max gain, the 10k "volume" pot is the sustainer's sensitivity control...other than that...use Pekko's DPDT on/off switch, Led and resistor (LED color of choice...I've got a blue one), I'd add a diode across the battery inputs to avoid problems in case you accidentally put your battery in backwards, a simple phase reverse DPDT on the output wires (going to the driver) makes the harmonic switch.

Anyway...this might get us well on the way to a "standard" circuit for the DIY sustainer...

If you haven't seen it yet, check out Galaga Mike's Tutorial in the Tutorial Section (where else) and look back a few pages to see some other drivers by onelastgoodbye(Tim) and my pickup/driver pictorial...

check you later

psw

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For Reference...here are diagrams and pics from Mike's tutorial...hope the moderators don't mind the excess pics too much....This is kind of a follow up to my last post on circuits and such...

flow_chart-driver.jpg

Amplifier:

The guys over at runoffgroove.com have a circuit for a small 386-based amplifier called the Ruby which is very well suited to our needs here. I built this and found that it worked great with hot pickups but did not have enough gain for lower-output pickups. Fortunately, they also have a preamp design called the Fetzer valve which is enough of a preamp to get sustain with about any pickup I've tried. The schematic is given below, and more info and troubleshooting tips can be found in the forum at runoffgroove. Thanks to runoffgroove for allowing the use of this circuit in this tutorial. The only difference here is that our "speaker" will be our driver, which is discussed next.

fetzer-ruby.jpg

Driver:

The driver took me a couple of hours to wind and is probably the most labor intensive part of this build. Still, it's really not too difficult.

My driver was built from a stainless steel bar that originall measured 6.2x6.2x61mm as the core. I rounded the edges of this so the corners wouldn't hurt the wrapping wire. I then cut two bobbin pieces (top and bottom) from the black plastic from the back of a CD case. Just cut them in a pickup shape as you can see in the pictures below, then cut out a little rectangle in the middle for the steel bar to poke through. The steel bar and the bobbin top and bottom are then all epoxied together to make the bobbin structure on which the wire is wound.

I used 30AWG wrapping wire from Radio Shack for the windings. I squeezed some Elmer's glue all in the bobbin and then started wrapping the wire, keeping it tight. The glue squeezes up through the windings as you proceed and this hopefully pots the driver and avoids squealing. Just wrap it until you get around 8 Ohms, and then solder some wire on to the ends of the wrapped wire. I epoxied this connection into the bobbin, too, just so that the wrapping wire does not flex too much and break.

DSCF0039.jpg

After you have the winding, just stick a magnet on one side of the steel rod. I used some rare earth magnets that I salvaged out of an old hard drive.

General Comments:

3. I haven't done it, but it seems easy enough to take the output after the Fetzer valve and have an onboard boost. Kind of a byproduct of the sustainer. Just a thought.

PSW: I agree...both the preamp and poweramp could be used to switch as active boosters or distortions...

Pictures:

DSCF0030.jpg

PSW: Notice that Mike's put too full sized pots on his circuit. I'd be going for a trim pot for the gain control on the circuitboard...or simply a link via a 10uf cap...

ff9932c4.jpg

DSCF0033.jpg

PSW: You can see here that Mike's circuit board is smaller than the battery...

Anyway...we now have a few working sustainer circuits...now we need to look at improvements. Two posts back I listed some areas that could be investigated in driver design. If you look at transformers, I've never seen one with a solid steel core...they're always laminated or the newer toroid designs use powdered and ferrite cores. Likewise, this type of experimentation with core materials will probably result in more improvement than further circuit complexity.

psw

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OK...here are some of the crucial circuit details all put together:

Sustainer_DPDT.gif

For comparison...here's the Ruby:

ruby.jpg

Here's the Perf-board layout for the Ruby:

ruby-perf.jpg

And some photo's of it made up...pretty small:

ruby-comp.jpg

And the other side...nice and neat:

ruby-trace.jpg

Although these photo's are of the Ruby, you can see that the two circuits are very similar in makeup...now I think we need to make up a version with the gain control as a trim on the board, power diode, LED resistor, and clearer indications of the on/off switch and pickup selection function and the wiring of the phase/harmonic switch.

BTW...varying that 220uf output capacitor will vary the bass response. I've used that value but have also gone down to 100uf which provides a more treble drive. It could be that, as I'm already using trebly single coils to drive it that I'm getting a better high string response than the darker humbucker equiped guitars. Lowering the cap value may indeed help...a bit of easy experimentation required there perhaps.

Alternatively you could just try feeding the sustainer circuit with one of the humbucker coils...the hum cancelling function is not crucial to the sustainer as it's circuitry is not heard. In fact, a bit of background noise helps in the self-activating ebow-like swell type effects as the random noise provides a signal that will set off the strings without having to actually pick them!

Hope all this renews enthusiasm for the project...

psw

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...I'm not sure why they have that trim pot on the fetzer valve circuit and not just a resistor...
Because of the way that JFETs are manufactured, their electrical specs are inherently inconsistent - for any given model, they all fall within a specified range, but still vary widely from piece to piece. Since the quiescent bias point (and hence the maximum headroom) will vary from device to device, a trimmer is used to set the bias point slightly above 1/2Vcc to keep the headroom consistent over the range of available devices. The alternative is to buy thousands of FETs and select the one(s) that work for your chosen fixed resistor - not a problem if you're Roland or Digitech, but kinda expensive and time-consuming for us reg'lar guys! :D
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Here's a flashback to page 46...if you use really thin material for your bobbin you get a really compact coil closer to the strings, and take up less space...

driverphoto2.jpg

Looking at the circuitry again has got me enthused to heat up the soldering iron again...I've been reviewing circuit suggestions I've found plus some stuff LK sent me on some of his opamp booster designs...still like to see your's Mike G...

For those who missed it the first time round...here's a pic of one of my versions of the basic circuitry I've been using for some time..

sustainercircuit.jpg

You can see it's a little more "sophisticated" than Mike's circuit. Connected is one of my silver hex drivers...we've moved on (or back?) since that model :D

Some time ago...I posted my LM386 part of the circuit...here it is again:

champ_ampcircuit.jpg

In the photo above it takes up the left third of the circuitry, the rest is preamp. In the photographed version I put a trimpot (blue/white on the left) but now I just use a wire link as I always run it flat out!!

Now, in my "champ" circuit there are some significant differences that should probably be included in the design of Mikes. That sai though, I originally drove my early designs using Ansils Sustainer Mod Circuit which was simply the LM386 and a 100uf output cap, so....

Anyway...there is a 0.1uf cap and 10 ohm resistor from the output to ground before the output capacitor. This makes a so called "Zobel Network" to reduce the possibility of high frequency oscillation within the circuit (ie squeel!). The 10uf cap from pin 7 to ground serves a similar function. These are also advised in the chip's application note and for the sake of a few extra components may be of use...they certainly wont hurt!

My preamp...upon further study...has quite a few RF and Hum filters, etc incorporated into it, which may be influencing the results I've obtained over others efforts. My circuit's are also adapted from Kits so have circuit boards that can make them easy to build and quite compact.

Now...what I'm proposing for the preamp would be something similar to what this fellow aussie's done:

Buffer Preamp Opamp Circuit

I've had a little trouble replicating it and it would definitly need more gain but it is a simple enough circuit using a TL071 and as you can see is very small!

I'm looking at incorporating a trim pot for the gain at this stage, a trim pot in the LM386 stage (replacing the 1k resistor between pins 1 and 8 in the above circuit) and the sensitivity control pot illustrated as "volume" on the left of the above circuit (being the input from the preamp)...simple enough if you know what your doing...anyone want to have a go at drawing it up...or correcting the bugs in my circuit when I get it done? (this will be about my 3rd attempt!)

So...the result will hopefully be a simple circuit with quite a bit of flexability (3 gain control stages) and if built on two circuit boards sandwhiched together will still be about 1" square. This should be flexable enough to be adjusted to suit pretty much any guitar set up (the preamp could be adjusted right down or omitted for EMG's...Tim).

Anyway...that's going to be my little project...the "standard" sustainer circuit. I'll attempt to make it on perf-board so that it could be made without resorting to circuit board making....wish me luck :D

psw

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Sorry...didn't notice your post LK

Ok...I had heard that somewhere about the trim...but...can you explain then why the original Ruby Circuit in the post does not have such a trimmer.....hmmmmm :D !!!

Speaking of which...the "Zobel Network" I mentioned in my last post....does feature in the original Ruby Circuit diagram but does not feature in the accompanying photos, despite being indicated on the perf-board layout!!!!! Those ROG guys....they're messing with my head...arhgggghh!!! :D

And...my mistake...there is a cap from pin 7 to ground but it's smaller than mine....hmmmm...

So...Mike G and others...I'd be adding that 10 ohm resistor and 47n cap shown under the 200uF output capacitor right back in there....or substitute values from my "champ" circuit if you like...

Now...about this preamp...some unresolved business to attend to with some chips... B)

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...can you explain then why the original Ruby Circuit in the post does not have such a trimmer.....
:D Sure - the Fetzer is a gain stage, actually amplifying the input signal, so headroom is an issue that must be addressed, while the original Ruby has a source follower at the input (technically a gain stage also, but with a gain of slightly less than 1) simply to lower the impedance at the LM386's input. Since even Invaders shouldn't put out much more than 1Vrms, the maximum swing that any unity gain stage should have to swing is 707mV, making headroom almost a non-issue, since even the worst-case devices on either end of the product range would be well within limits.

Well, you did ask! :D

BTW, the Zobel is just a patch that solves a specific problem - it isn't absolutely necessary unless your layout/circuit is prone to HF oscillation. It can also be tailored for your desired frequency response if you've got the patience to tweak it out and decide what works.

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Well, you did ask!  B) 

BTW, the Zobel is just a patch that solves a specific problem - it isn't absolutely necessary unless your layout/circuit is prone to HF oscillation. It can also be tailored for your desired frequency response if you've got the patience to tweak it out and decide what works.

Quite right...and yes I did ask..... B) ...thanks LK

3 points on the Zobel....

1.why did the ROG guys put it in the circuit but leave it off the photographed prototype...if not to mess with my head...ohhh the paranoid voices :D

2.well I think that our device is prone to HF oscillation...well at least it should be attempted to be eliminated as a cause...due to the amount of trouble people have with squeel...but then I had to ask the original question!!! :D

3.why put it in the Ruby...then take it out for the Fetzer/Ruby...maybe we should go back to ansils two component model :D

Meanwhile...looking in my box of tricks I see I seem to have a few 358 low power dual opamps so I guess I'll be working on those...I found a previous design I made but I don't quite see what's wrong with it...I'll try again, shall I....

thanks LK

psw

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