curtisa Posted October 13, 2006 Report Share Posted October 13, 2006 In the LM13700 AGC app note, there is a 250k resistor in series with the input. If you reduce this - say down to 10k, Then the internal gain of the first AGC stage is enough to get a useful effect. Unfortunately, using a smaller resistor in series with the input seem to pull the dc levels of the preceding stage out of whack (depending on what that stage is). My (probably naive) assumption that if the output impedence of the preceding stage is low (? guessing) enough, then it would still work ok. e.g. when i use the smaller 10k resistor feed it directly from a unity gain input(from the guitar) buffer, it doesn't work. however when I stick my switchable inverter/non-inverter between the two, it seems to work ok. My thinking is that high value resistor (250K) is used to prevent the signal current flowing into the LM13700 from the previous stage from throwing off the gain reduction function of the linearising diodes. You'd probably get better performance if you used the LM13700 in the configuration shown in the app note on page 8, figure 2. However you'll need more support circuitry to use it in this way - the control signal is completely different to the one you're currently using. You'd need a precision rectifier to properly generate the control voltage to apply to pin 1 (labelled "gain control" in the app note). I had a look at the SSM2018, looks useful although its a shame its not any smaller than an LM13700. There are other smaller ones yet. Thing is they cost even more. I'm waiting on some free samples of the THAT2181 which is an 8 pin SIP package VCA. have a look at this article on single supply op-amp design. At the end there is discussion of a configuration for 'phantom ground'. using an op amp to create a +4.5 -4.5 from a 9v might be good for us if we can find an op-amp that will cope with the current requirements... The other thing in that paper I was looking it with most interest is using zener diodes to provide more stability and better PSRR. What do you think about this? Would it be possible to use one zener diode to probide the ground reference for the whole system, or would it have to be one per device? I reckon the buffered voltage divider is the better way to go (page 88, figure 7). Seeing as we're looking at running the sustainer from battery supplies we want the "mid point" of the battery to remain at exactly half the supply as the battery drains. With the zener earth reference, as the battery starts draining the earth starts falling relative to the positive side of the supply, which will bugger up the earthing of the system - you might start out with a 9V battery with 4.5V in the middle (+4.5V, 0V, -4.5V, but after a couple of hours of playing your battery has sagged to 7V and you're left with a supply sitting at +2.5V, 0V, -4.5V. Not so good. At least with the circuit shown in Figure 7, if your battery discharges to 7V, your supplies are still divided equally around earth. Current shouldn't be too much of a problem, there are plenty of opamps capable of sinking/sourcing enough current to work a few stages - NE5532, NE5534, LM833, even the good old LM741 would probably work OK. We're only supplying the earth for the preamp section afterall (light duty stuff), the LM386 will look after itself with just a single 9V supply. Cheers, Curtis. Link to comment Share on other sites More sharing options...
col Posted October 14, 2006 Report Share Posted October 14, 2006 My thinking is that high value resistor (250K) is used to prevent the signal current flowing into the LM13700 from the previous stage from throwing off the gain reduction function of the linearising diodes. You'd probably get better performance if you used the LM13700 in the configuration shown in the app note on page 8, figure 2. However you'll need more support circuitry to use it in this way - the control signal is completely different to the one you're currently using. You'd need a precision rectifier to properly generate the control voltage to apply to pin 1 (labelled "gain control" in the app note). I'll have to a have a play around with different input resistors again with your suggestion in mind. As far as the other app note, the thing that drew me to this particular circuit was the simplicity.... I think if I was going to have to set up a recitfier, I'd probably have gone down the LED/LDR or FET route.... I had a look at the SSM2018, looks useful although its a shame its not any smaller than an LM13700. There are other smaller ones yet. Thing is they cost even more. I'm waiting on some free samples of the THAT2181 which is an 8 pin SIP package VCA. Have you checked out the LMH6502 It has voltage controlled gain for AGC, and can drive a low impedence load with enough current for a good sustainer circuit(assuming AGC is included). Could be a good option... maybe the circuit could be just that and a dual op amp with a few supporting components.. have a look at ... I reckon the buffered voltage divider is the better way to go (page 88, figure 7). Seeing as we're looking at running the sustainer from battery supplies we want the "mid point" of the battery to remain at exactly half the supply as the battery drains. With the zener earth reference, as the battery starts draining the earth starts falling relative to the positive side of the supply, which will bugger up the earthing of the system - you might start out with a 9V battery with 4.5V in the middle (+4.5V, 0V, -4.5V, but after a couple of hours of playing your battery has sagged to 7V and you're left with a supply sitting at +2.5V, 0V, -4.5V. Not so good. At least with the circuit shown in Figure 7, if your battery discharges to 7V, your supplies are still divided equally around earth. after another look, the diagram there looks wrong? it seems like the + and - supplies are connected to ground... oops (that doc is a pdf version of one I found elsewhere, and I didn't check it). Am I correct in thinking that the idea is that the battery -ve terminal is not connected to ground, and that the buffered Vs/2 is so that the half supply is also the 'real' ground? in which case it would not sit well alongside the LM386. I have been modelling my circuit with a similar setup where the op-amp is just buffering a standard divider... Fig.2 in this doc. cheers Col Link to comment Share on other sites More sharing options...
spazzyone Posted October 14, 2006 Report Share Posted October 14, 2006 Hey Col i take it your a David Gilmour fan as the middle of the demo sounds a little like Run like hell the clipping is no worse than what i experiance. at this point convinced its a byproduct of all sustainers as the floyds clipped and in the demos for the fernandes there is also some clipping the poping is all would worry about and by ossilations i take it you mean that little bit of worbble near the end? i wouldn't mind hearing some more without the delay ill post some more stuff in a day or so as i have been writing something aroundthe sustainer thats pretty neat. this sustainer sounds great using tremolo but i dont want to let anymore cats out of the bag yet Link to comment Share on other sites More sharing options...
col Posted October 14, 2006 Report Share Posted October 14, 2006 Hey Col i take it your a David Gilmour fan as the middle of the demo sounds a little like Run like hell not especially the clipping is no worse than what i experiance. at this point convinced its a byproduct of all sustainers as the floyds clipped and in the demos for the fernandes there is also some clipping the poping is all would worry about and by ossilations i take it you mean that little bit of worbble near the end? No, thats just operator error, the oscillations I'm talking of are likely to be happening above the range of human hearing...related to bad circuit design probably of course theres every chance that its something else thats causeing the problem. i wouldn't mind hearing some more without the delay soon cheers Col Link to comment Share on other sites More sharing options...
curtisa Posted October 14, 2006 Report Share Posted October 14, 2006 (edited) I'll have to a have a play around with different input resistors again with your suggestion in mind. As far as the other app note, the thing that drew me to this particular circuit was the simplicity.... I think if I was going to have to set up a recitfier, I'd probably have gone down the LED/LDR or FET route.... Yeah, that's what I figured too - all the extra components make it less attractive, but I guess we're after repeatable, reliable performance..? Have you checked out the LMH6502 It has voltage controlled gain for AGC, and can drive a low impedence load with enough current for a good sustainer circuit(assuming AGC is included). Could be a good option... maybe the circuit could be just that and a dual op amp with a few supporting components.. I'll have to have a look, thanks for the tipoff after another look, the diagram there looks wrong? it seems like the + and - supplies are connected to ground... oops (that doc is a pdf version of one I found elsewhere, and I didn't check it). Nah, it's just really poorly drawn. Remove the earths at the top right (just below the 110K feedback resistor), and the output of the opamp (labelled "Vs/2") and it'd work fine. The supply bypassing isn't quite right either - the two caps on either side of the opamp supplies should either be drawn with their "earthy" ends sitting off the Vs/2 output, or straight across the battery terminals (omitting the negative side of course, as it's not doing anything bypassing itself). I can redraw it for you if that sounds a bit confusing Am I correct in thinking that the idea is that the battery -ve terminal is not connected to ground, and that the buffered Vs/2 is so that the half supply is also the 'real' ground? The battery terminals become +Vs and -Vs, and the Vs/2 becomes the new ground for the opamps that require it. Special IC's (like the LM386) that require no ground are designed to look after themselves. Connecting one circuit up with it's Vs/2 ground to another with it's -ve battery ground will present no problems provided you capactively couple the inputs/outputs. All we're doing with the Vs/2 output is providing a reference voltage around which our audio signals "wiggle" around on. The same thing happens with dedicated split supplies (eg, +15V, 0V, -15V) - you could argue that the whole thing is one giant 30V supply, but the difference is that we already have our midpoint ready to go thanks to the more elaborate power supply/voltage regulators, and that we can source/sink a lot more current than the opamp vs/2 supply. Righto, off to have a fiddle with this sustainer thingy! Cheers, Curtis Edited October 14, 2006 by curtisa Link to comment Share on other sites More sharing options...
col Posted October 16, 2006 Report Share Posted October 16, 2006 I posted this in the diystompboxes forum while this one was down, but I figure I should post it here as well I think there is a better way of achieving the goal that my circuit was intended to tackle. The fundamental idea is that we want the sustain level and response to be even no matter which string is played and which fret it is played on. There is an enourmous difference in response depending on the magnetic mass of the string and it's tension. Playing higher on the neck makes any string more responsive because it will be closer to the driver - this effect is magnified by a higher action. Using a normal compressor/limiter circuit doesn't help much because the best it can do is even out the signal sent to the driver - unfortunately the more responsive string/fret combos will obviously respond much better to the same level of driver signal.... My 'Dynamic Range Inverter' circuit was an attempt to solve this by trying to break the restriction imposed by the feedback loop of a compressor type circuit. The 'better way' that I'm working with now is: Rather than trying to 'beat' the feedback loops tendency towards equalizing the signal output - why not incorporate the driver/string/pickup part of this system into the feedback loop (seems obvious now heh.).. So instead of rectifying the output of the compressor and feeding it back to the start.... take some of the input from the guitar pickup, rectify that and use it to control the AGC amp... This should work ok assuming the overall phase shift isn't big enough to cause instability ? The biggest problem I can see is that the initial attack from a hot pickup could be larger than the circuit would deal with when it has settles into a steady feedback state... so how to protect the circuit from that initial attack without too much additional circuitry (it has to be as small as possible)... An additional benefit of this approach over the last on is that it makes adjustment of the response (via a knob on the guitar) much simpler - in the original design, just naively boosting the driver signal would just cause the AGC to limit it further... Anyway - thats the new plan. cheers Col Link to comment Share on other sites More sharing options...
psw Posted October 16, 2006 Author Report Share Posted October 16, 2006 Thank Goodness were back!!! Sounds like a good plan col... Using a normal compressor/limiter circuit doesn't help much because the best it can do is even out the signal sent to the driver - unfortunately the more responsive string/fret combos will obviously respond much better to the same level of driver signal.... This really is a problem. On my guitar I have had to set the action to even out the responses to this. Another reason I'm seeking a mid driver...closer to the bridge differences in action are less acute (at the bridge it is nil, right!). I had not thought there was any way to achieve an evening out of this effect. The only circuit that I could think of is an auto-vol (like a Boss slow gear) but this will only respond to distinct new attacks (spaces between notes) in order for it to reset to the next one, so it wouldn't work for that... I listened to your sound clips too col...your system does seem fairly quiet as it is from that example, but it's dynamic range seems to be a little too resrained for my tastes. Certainly it does sustain a string, but it does not continue to drive it louder and louder as mine does...of course that is the intention. I'd like to see some medium or adjustment between the two. What would be the effect of adding more power (bridging 1 & 8 on the 386) with the circuit you are presently using? Anyway...I hope people are all ok out there and that PG didn't suffer any damage from whatever happened... pete Link to comment Share on other sites More sharing options...
col Posted October 16, 2006 Report Share Posted October 16, 2006 I listened to your sound clips too col...your system does seem fairly quiet as it is from that example, but it's dynamic range seems to be a little too resrained for my tastes. Certainly it does sustain a string, but it does not continue to drive it louder and louder as mine does...of course that is the intention. I'd like to see some medium or adjustment between the two. Thats the problem with my original circuit - it can be set up for a louder overall response, but its not as simple as turning up the gain on the LM386, the AGC would have to be setup with multiple settings tweaked. Thats one of the good things about this new idea (assuming it works). What I've found is that using a clean tone, my current setup is quiet, but when you add in plenty of rock distortion, that brings it back up to a good level, and you get the feel of an apm feeding back.... would be better if it were controllable with a single knob though. I wonder if Curtis can help design a new circuit based on this idea cheers, Col Link to comment Share on other sites More sharing options...
psw Posted October 16, 2006 Author Report Share Posted October 16, 2006 Ah...yes, it is a little like that with mine, a little dirt brings back the harmonics even in the fundumental vibration and gives it more guts...but it doesn't need to be full on metal or anything. Perhaps it is in part the way this thing works, it is not driving at the true sound of the string and it is no longer a "natural vibration" once the string is vibrating itself... pete Link to comment Share on other sites More sharing options...
curtisa Posted October 16, 2006 Report Share Posted October 16, 2006 The 'better way' that I'm working with now is: Rather than trying to 'beat' the feedback loops tendency towards equalizing the signal output - why not incorporate the driver/string/pickup part of this system into the feedback loop (seems obvious now heh.).. So instead of rectifying the output of the compressor and feeding it back to the start.... take some of the input from the guitar pickup, rectify that and use it to control the AGC amp... Errr...I think you've just described exactly how a compressor works. The compressor needs to use the input signal to control the AGC, otherwise it won't compress! Have a look at this appnote by THATcorp: http://www.thatcorp.com/datashts/an100a.pdf Ignoring all the unnecessary detail, the way the compressor is constructed is exactly the way you're proposing - The input signal (Vin) is split and goes through the VCA chip (218X), and also into the sidechain (2252, OA2, OA3). The output of the sidechain feeds the gain control pin of the VCA (pin 3) and the output signal is buffered by OA4. I think the only difference between what you're proposing and what you've used in the past (the LM13700) is that we're changing the compressor topology from feed back to feed forward control. The thinner/tauter strings will require more drive and the thicker/looser strings require less drive. The comrepessor, by it's very nature should naturally even things out anyway, regardless of what compression topology is used. Thinner strings will naturally generate a smaller signal (due to mass, vibration amount etc), which causes a smaller control voltage to be generated for the compressor, resulting in less compression (perceptibly louder), whereas the thicker strings will generate a higher control voltage and more gain reduction (perceptibly softer) for a given compression threshold. Cheers, Curtis. Link to comment Share on other sites More sharing options...
spazzyone Posted October 16, 2006 Report Share Posted October 16, 2006 I thought Pete was going to post this but i dont see it.....have a look does the driver look familiar also take note of the sheild on the front its something i dont need even in the middle position. but i would on a homade driver the needed info is in the middle of the page http://www.vintagekramer.com/company52.htm Link to comment Share on other sites More sharing options...
psw Posted October 17, 2006 Author Report Share Posted October 17, 2006 I thought Pete was going to post this but i dont see it.....have a look does the driver look familiar also take note of the sheild on the front Ah...yes, sorry shawn...quite right! So...it seems the rail driver already exists!!! However, although there is nothing new in this world, I still have never seen any thin coil desighs, rail or otherwise...hahaha Shawn definitely has somethin unusual happening with his approach to all this...running from the middle position is itself an achievement, no matter how it is done...still not sure how or why it is working but it does appear to work...hmmmm pete Link to comment Share on other sites More sharing options...
col Posted October 17, 2006 Report Share Posted October 17, 2006 (edited) I think the only difference between what you're proposing and what you've used in the past (the LM13700) is that we're changing the compressor topology from feed back to feed forward control. Exactly - thats what I'm saying, use a compressor with feed-forward rather than feedback topology (all the simple compressor/limiter circuits I've so far found have been of the feedback variety) So insead of the compressor trying to equalise the levels at its output, it tries to equalise the levels at its input. Like I said in my post 'seems obvious now', but I figure that this is why my attempts (and those of others) to use normal stomp box compressor circuits have not given the desired results. The thinner/tauter strings will require more drive and the thicker/looser strings require less drive. The comrepessor, by it's very nature should naturally even things out anyway, regardless of what compression topology is used. I disagree, I believe that there is a difference between feed-forward and feedback in this application. Granted both versions will even things out to some extent, however, feedback will not do as good a job for us. (pardon me if any of this seems patronising, I'm just trying to explain it better than I did in my earlier post) The feedback compressor circuits use their output level as a reference. So with maximum compression an ideal compressor would give you an _output_ signal at Threshold level for any input level.... Feed that to the strings via the driver and the open high E string will be moved less by it than the G string at 14th fret.... So the signal back into the compressor will be lower for the E string... and it will give it more gain, and the G string would get less. Seems fine and dandy, however the system will never completely close the gap between the two strings/fret positions - for that to happen, the output of the compressor would have to resolve to a level lower than threshold for the G string, and Higher then threshold for the E string... no can do with a feedback compressor... so the E string will always be noticably quieter and the G string considerably louder.... The feed forward topology on the other hand doesn't worry about the level at its own output, instead it uses the level of the input signal as its reference. for many applications this won't make any difference to the final outcome, but for us it does because for us the input level depends on the output level. The feed-forward compressor will keep trying to get the input level to be consistently at its threshold level - even if this means that its output is below or above the threshold.... So in the sustainer, when the open high E string is sustaining, in order to keep its input at the threshold, it output will be higher, while when it is sustaining the G string 14th fret, to keep the input at threshold level, the output will be much lower by comparison. So assuming that we both mean the same thing by 'feed-forward compressor' it has the potential to give us a much better string/fret balance than a common or garden feedback compressor circuit. (Another way to think about it is that we need a feedback compressor, but the driver/strings/pickup combo is part of the compressors feedback line.) got any good feed forward compressor schematics? cheers Col Edited October 17, 2006 by col Link to comment Share on other sites More sharing options...
col Posted October 17, 2006 Report Share Posted October 17, 2006 Somthing like this might be ideal - shame the chip is harder to get in its DIP package, and is damn expensive. Col Link to comment Share on other sites More sharing options...
psw Posted October 17, 2006 Author Report Share Posted October 17, 2006 The 'better way' that I'm working with now is: Rather than trying to 'beat' the feedback loops tendency towards equalizing the signal output - why not incorporate the driver/string/pickup part of this system into the feedback loop (seems obvious now heh.).. So instead of rectifying the output of the compressor and feeding it back to the start.... take some of the input from the guitar pickup, rectify that and use it to control the AGC amp... Errr...I think you've just described exactly how a compressor works. The compressor needs to use the input signal to control the AGC, otherwise it won't compress! The thinner/tauter strings will require more drive and the thicker/looser strings require less drive. The comrepessor, by it's very nature should naturally even things out anyway, regardless of what compression topology is used. Thinner strings will naturally generate a smaller signal (due to mass, vibration amount etc), which causes a smaller control voltage to be generated for the compressor, resulting in less compression (perceptibly louder), whereas the thicker strings will generate a higher control voltage and more gain reduction (perceptibly softer) for a given compression threshold. Yes...I think you are right... So...perhaps again we could consider this circuit...again AussieComp LM386 compressor This thread continues to develop the idea and here is the latest version... Again...this is not a sustainer circuit, but a very simple compressor. Of interest is that it uses a LM386 and now incorporates a buffer stage on the input...the layout shows how simple and small it can be made. What I'd like to know is if this could be modified to not only compress but to provide the amount of gain we require to sustain a string...providing both compression and power gain into a simple circuit. This of course was why I built a compressor limiter, but for the life of me I can't remember using it with our conventional thin coil designs, only the Hex stuff. For that, I did,'nt notice a lot of difference except that at very high compression it may have made the EMI issues worse... Speaking of HEX stuff...I now realize how nieve I was about the interaction between the pickups and the driver since I overcame the problems associated with installing my sustainer into my guitar. I am thinking specifically about the need to completely disconnect unused pickups... I found some pics of this incarnation of a hex driver... and there were others that had internal magnets and sat next to the pickup... Because of my idealism, I was seeking to make a very low/no mod stick on type of installation. What I didn't do, was modify the guitar in any way other than to take a signal directly from the bridge pickup to driver the circuit...hmmm. These devices certainly did sustain the strings, but with enormous noise problems...these problems were overcome with my present guitar through modification of the guitar's wiring...so one has to wonder if this perhaps could have worked ok... Meanwhile...I spent a moment re-examining the osbourne/hover sustainiac patent for their never marketed mid-driver sustainiac device... Osbourne/hoover Patent Link There is a wealth of information given in this patent including the complete circuit details (including chip no#s) and some really inventive approaches to driver designs that we have not explored here and I didn't notice before; even electronic switching that I have advocated as well... I certainly have a renewed respect for the amount of research these guys have obviously put into their product and the idea in general... I am still commited to trying to make a simpler approach to the DIY sustainer, but it is quite remarkable the amount of work that has been put into this patent.... So, food for thought all round... pete Link to comment Share on other sites More sharing options...
psw Posted October 17, 2006 Author Report Share Posted October 17, 2006 Oh...posting at the same time as col...will have to bend my head around these two methods of compression and how they apply here... Meanwhile...it may be of interest to check out col's and my posts over at DIY stomp... sustainer circuit thread Best put is this from col... The idea is that we want the sustain level and response to be even no matter which string is played and which fret it is played on. There is an enourmous difference in response depending on the magnetic mass of the string and it's tension. Playing higher on the neck makes any string more responsive because it will be closer to the driver - this effect is magnified by a higher action. My input was mainly in reply to this post... As you can see almost all of the promotional soundclips presented by F@@nandes etc are recorded using high-gain distortion boxes or compressors. The "dry" sustainer sound is quite poor and not impressive at all, isn't it? Both col and me have advocated the virtues of clean sustain...at least from a starting off point (you can always add distortion)... In answer I linked to a couple of sound clips by me (Airie and The Yearning) that feature a very wide dynamic range in the response of the instrument that is lost in signal compresson of the actual guitar signal (as opposed to the driver signal as col is attempting) and the sound of clean sustain and it's possible uses. It is true that I have yet to see or hear a sustainer being demonstarted in a manner that fully shows of it's potential and nearly everything is shown distorted and in a predictable "lead guitar" setting. The potential of this device goes well beyond that and if you are interested, this post may interest you too... pete Link to comment Share on other sites More sharing options...
col Posted October 17, 2006 Report Share Posted October 17, 2006 hmm the SSM2165 is a microphone conditioner. It is designed for a high impedence microphone, so may not need buffering, it has feed forward topology compression, very few external parts required (3caps and a pot), and comes in an 8 pin package. Maybe just that and an LM386 with its own 3 caps + resistor would do everything we need... with surface mount components, it would be tiny. I hope I can find somewhere that still has it in a DIP package for breadboarding... I already checked all the old soundcards I have kicking around for scavanging but no luck there ... radios and minidisc next Col Link to comment Share on other sites More sharing options...
psw Posted October 17, 2006 Author Report Share Posted October 17, 2006 Nice find col...I found other preamp chips for radio and tape level control but nothing as simple as this one...now, I wonder how we could get one...hmmm, google! pete Meanwhile...to come, idea for a split blade pickup/bilateral driver design.... p Link to comment Share on other sites More sharing options...
curtisa Posted October 17, 2006 Report Share Posted October 17, 2006 The feed forward topology on the other hand doesn't worry about the level at its own output, instead it uses the level of the input signal as its reference. for many applications this won't make any difference to the final outcome, but for us it does because for us the input level depends on the output level. The feed-forward compressor will keep trying to get the input level to be consistently at its threshold level - even if this means that its output is below or above the threshold.... Ahhh, yes, of course! I keep on forgetting that we're not compressing blindly to set an output - the string and driver form the signal source that gets fed back into the system via the pickup. The whole thing relies on a lot of nested feedback loops to function properly. got any good feed forward compressor schematics? Yes, I have a few. Sadly they're quite overly complex for our application though. And looking through the datasheets for some of those VCA's I mentioned earlier on, most of them require at least +/-4V to run, which pretty much excludes 9V battery operation. What we're probably after is as simplified version of a FET based compressor, like the 1176. Note: Yeah, I know it's a feedback design, but you could still conceivably design a FET compressor using feed forward arrangements. In order to keep this cost-effective and keep the components in the easy-to-get basket, we're probably going to have to design (or adapt) a descrete compressor. The MXR Dynacomp might be another alternative circuit? The LM13700 will work as feed forward mind you. Figure 2, page 8 of the LM13700 app note shows you how to connect the VCA up. All you need to do is provide a precision-recitfied signal derived from the input signal, and use it to control the gain on pin 1. Setting it up "just so" for the right threshold and compression ratio settings will be somewhat tricky though. Cheers, Curtis Link to comment Share on other sites More sharing options...
psw Posted October 17, 2006 Author Report Share Posted October 17, 2006 (edited) Meanwhile...to come, idea for a split blade pickup/bilateral driver design.... p OK...another variation...this time there are two coils in a bilateral configuration...spanning only two strings each. This is built on top of a rail pickup. The split rail means that the rail of the pickup without the coil also acts somewhat as a sheild and keeps the magnetic field to some extent contained (as with a rail driver)...the bilateral coils though act to promote electromagnetc EMI across the strings. The smaller coils mean more power dedicated in a smaller area to each set of strings. Notice also that with the side by side arrangement of the driver coils they can overlap, thus avoiding a dead spot between the d and g strings as with the sustainiac's massive dual core design. Such a scheme could also lend itself to stereo amplification tailored to each set of strings. Yet another variation on the rail theme!!! pete Edited October 17, 2006 by psw Link to comment Share on other sites More sharing options...
psw Posted October 17, 2006 Author Report Share Posted October 17, 2006 (edited) OK...how about a minor diversion... This was spoken about a fair while back, but a few people brought the subject up recently, so I thought I'd bring it back again just to show that this thread is about "Sustainer Ideas" not just "sustainers" as such... Many people have tried to make their own Ebows, few with much success...the device is simple but the design is a work of art...however, for people who would like to know what it takes, this is the best I have seen so far... details can be found here... DIY ebow Link The pickup and driver's are made from pickup magnets with wire wrapped around...see the link for details. You can see that they need not be that big! The circuit is a simple as it gets LM386 with no preamp (the pickup coil is low impedance)... The problem would be making a case that would allow the pickup poles to ride the strings either side of the one being driven. Anyway...the Ebow is an elegant device even if it does restrict your picking hand to operate it! I know it could be made smaller although the distance between the driving coil and the pickup coil would be crucial. It would be interesting to see how something even smaller would interact So...a homemade ebow is possible and won't require any modification to an instrument and is completely portable. It is interesting that no one has come up with an improved ebow (other than ebow themselves now having a harmonic switch)... Just thought I'd widen the horizons a little... pete oh...here's a link to the ebow players guide and some sound samples... Ebow link Edited October 17, 2006 by psw Link to comment Share on other sites More sharing options...
col Posted October 17, 2006 Report Share Posted October 17, 2006 I've been mucking about with a few different compressor ciruits, the best so far in tems of being relatively easy to convert to feed forward is a simple circuit based on the LM13700 (heh) The biggest problem so far (not just with this circuit): It works ok within a reasonable band of input levels, say 50mV to 300mV, which is plenty for us after the sustain has started to function. However, stronger signals from about 600mV up to 2.5 volts (which is something like peak for a good hot passive humbucker) are big enough so that with the VCA of the compressor at mimimum gain doesn't attenuate them - 1v - 2.5v come through strong enough that there might be issues with the system never relaxing down to the level where the compressor can do its business... If I tweak the settings so that this doesn't happen, then the compressor functions at the wrong band of input levels... I really don't want to have to have two in one - a limiter to squish levels above about half a volt and a compressor to do the rest... Another more subtle but possibly more tricky issue is that of distortion of the waveform... This compressor produces a nice undistorted output with levels below the threshold, but at the point about half way between no compression and maximum attenuation, there quite a lot of asymetry and some DC offset in the signal. Problem here is that this is exactly where the equilibrium will be in our system. It will always settle at a point where there is just enough power in the driver to keep the string(s) going at the same level... somewhere between max and minimum, probably closer to minimum for all but the most stubborn string/fret combos... basically at the point of most asymetry and dc offset :-| So we need a circuit that behaves well at or neer its 'knee' I still have to check out that 1176LN the gain circuit look good, but the control circuit looks a bit complicated . And the FET based circuits I've tried so far have proved difficult to hack. cheers Col Link to comment Share on other sites More sharing options...
bancika Posted October 17, 2006 Report Share Posted October 17, 2006 (edited) Hello lads, Haven't started working on sustainer yet, I'm little short on $$ these days but I hopw it'll be soon. I begain quite interested in psw's driver/pickup combo. I could dissasemble (crappy) squier neck pickup and wind both driver and pickup there. My question is: pickup coil will be under driver coil. Does it affect pickup performace. Does magnet distance from string count or coil distance? Also, maybe it wouldn't be a bad idea to try dual coil design as psw suggested, with coils one below another. My question is, which winding direction should I follow for both coils? When I unwind pickup can I use same wire for winding pickup "part" of driver/pickup? Since pickup is crappy, can a wire be one of the reasons? As I understood, I'll need additional DPST switch for turning off pickup with sustainer is active, right? So it makes: one SPST for sustainer On/Off, one DPDT for polarity swap and DPST I mentioned? I'm beginer in electronics and utter beginer in sustainer theory, but I've been thinking a little about AGC "thing" and maybe someone can find it useful. In order to make string response more even maybe we could split whole frequency range on 6 zones and we'll assume that if tone of given frequency from zone 4 is played on 4th string. Zones could be determined statisticaly. I know that not all notes from one zone will be played on that note, but I consider that 50% hits is an improvement. With some combination of high pass/low pass filters input signals could be separated into 6 signals (one for each zone) and then set their level separately, mix them and then send to power amp. That way, we could amplify more notes that we assumed are played on thinner strings. What do you think about it? As for AGC and compression/inverting problem. What about one gain stage with trimmer that will amplify signal to, let's say, 1V. Trimmer will be there because pickup output range is between 80mV and 500mV so it should be able to amplify both weak single coil and some screamer hbucker to 1V. Then with some kind on hi tech mumbo-jumbo (maybe with clipping diodes, some of them clip at 250mV, some at 500mV etc) split signal into two or three signals: one below lower threshold that needs to be amplified, one above upper threshold that needs to be attenuated and maybe one in the middle that shouldn't be altered...after that just mix them and send to poweramp. I don't have a clue if any of this is possible, it's just how I see it And probably something like this has been discussed before. After all, this is "ideas" thread, little brainstorming can't hurt anyone. Btw, is 0.15mm wire ok for driver? Best regards, Branislav Edited October 17, 2006 by bancika Link to comment Share on other sites More sharing options...
zfrittz6 Posted October 17, 2006 Report Share Posted October 17, 2006 hello, to all me has been happened an idea that I have not seen that it has been proven, and it is that, that pasaria if a harvesting upon the one becomes of the center that has the guitar to use it with the conductor, totally independent of the circuit of the guitar? And to use it like in ebow, everything totally independent, podria to occur him around 1000 returns for the harvesting with fine thread, more or less like in ebow and using our conductors, or somebody has proven it? hello, bancika The thread for the coil that this giving better result is of 0.2 mm to 0.24. Greetings. PSW, in previous post you asked me for the tin that I use to cover the conductor and to isolate EMI, or rather to lead it, I have of decirte that is the one of tins of pepsi and they are not of aluminum since they are atraidas by the magnet, so, I think that iron or steel would seran of some alloy with, I am not safe, greetings and I animate because we are obtaining it. Link to comment Share on other sites More sharing options...
onelastgoodbye Posted October 17, 2006 Report Share Posted October 17, 2006 Just a quickie. I'll edit later. I know it's a picture rule violation, but it's only 25 kB Link to comment Share on other sites More sharing options...
Recommended Posts