psw Posted October 25, 2006 Author Report Share Posted October 25, 2006 Excellent... This will be great, and I hadn't thought about that but the 4 ohm coils would take half the time and be easier to wind....alowing the use of quick epoxy like this...hope you wore rubber gloves!!! How we use these coils is another matter...finding appropriate materials and working out the magnetics could be a problem. I have a feeling that small rare earth magnets could play a role in a rail or othe dual coil device that would keep the device very small (well at least "slim") but I am not sure if we could make it small enough to fit under the strings in the mid position of a guitar like a LP...there really isn't that much space there if we were looking at surface mounting the thing. Anyway, good work... pete 1 Link to comment Share on other sites More sharing options...
unklmickey Posted October 25, 2006 Report Share Posted October 25, 2006 hey Pete, i just happened to be in the neighborhood, and saw the number of replies you had. since this will be #2001 (a pretty cool number) i thought i'd say hi. cheers, unk Link to comment Share on other sites More sharing options...
psw Posted October 25, 2006 Author Report Share Posted October 25, 2006 Cool...I missed the milestone, but at least I got #2000 and #2002!!! Thanks unk and thanks to all those contributors... pete Link to comment Share on other sites More sharing options...
curtisa Posted October 25, 2006 Report Share Posted October 25, 2006 Many guitar amps produce a thump when switched off - others don't. I imagine that there will be some circutry for this that we could borrow - assuming that the pop is still an issue when using a dual core driver. In guitar amps they usually place a high voltage ceramic capacitor across the poles of the power switch (and/or standby switch) to suppress the pops. Don't know if this can be adapted to our purpose with the same degree of success? The monitor amp in my studio is completely silent when turning on and off, and that's without any fancy power-switch-capacitor malarkey. And it's a DIY job too (another Silicon Chip special). I've been playing some more with FET based compressors converted to feed-forward topology. The orange squeezer is ok, however its frequency response isn't really good enough for our purposes - particularly when you try to reduce the attack and decay times. That's a shame - just last night I was breadboarding up the "Tangerine Peeler", but ran out of components before I could try it out. Maybe I should abandon it before I get too carried away? The problem is that the feedforward version limits the signal asymetrically - in the feedback circuit, the negative feedback removes most of this asymetry. What this means (I think) is that there will always be lots of harmonic content an less fundamental for the low notes, which menas no nice stable fundamental mode for the sustainer. Yes, that's something I noticed when I sim'ed the Tangerine Peeler gain cell - there was an optimum range of control voltages that seemed to work best with the FET's available, and it tended to be quite non-linear. I suspect that the two FET's in the gain cell probably needed to be quite closely matched, which is probably more trouble than it's worth for us. The only fix I can see that might work is using the fet attenuator in the negative feedback loop of an op-amp gain stage - could this fix the asymetry ? I have tried to set this up, but so far unsuccessfully. Edit: here is a doc with a FET attenuator something like I'm thinking of Now that looks much more appealing, and reduces the component requirements down too. One FET, one (stage of an) opamp and a handful of resistors and caps. Might be time to give this one a go. Another possible option would be the LA Light compressor, this is a feedforward design based on an LED/LDR combo - which makes it difficult to simulate, so I've not tried it yet. EDIT: at last I found a link to the LA-Light schem HERE Difficult to say. The light/resistance characteristic of LDR's can vary quite a bit from piece to piece, which means that our DIY'ed compressors will probably vary in performance from one to another. Cheers, Curtis. Link to comment Share on other sites More sharing options...
psw Posted October 25, 2006 Author Report Share Posted October 25, 2006 The orange squeezer is ok, however its frequency response isn't really good enough for our purposes - particularly when you try to reduce the attack and decay times. Given that we don't know the characteristic of the driver and what it does to the signal...are frequency responses based on audio quality valid do you think? Or, does it not respond within the guitar's range (plus harmonic range) do you mean? Difficult to say. The light/resistance characteristic of LDR's can vary quite a bit from piece to piece, which means that our DIY'ed compressors will probably vary in performance from one to another. OK...but again, the driver styles, quality of construction, installation and the guitar itself are all variables too...is this so important given the nature of the project? Also, could not an optochip be used to function in this way and provide more consistancy and ease of construction? While there maybe an optimum performace criteria, there could well be a lower threshold that provides acceptable performance. The fact that notes below C on the g string on my guitar morph into a consistant octave above with sustain is actually quite appealing, if it would do it over the whole neck I'd be quite happy . I guess it depends a little on the musical application you have in mind and it would be nice to sustain low drones, I could settle for "less"! Also, the fact that the signal is distorted...is that really so much of a problem. My signal must be totally twisted given the gain in the preamp, running the LM386 at max (notorious for distortion as it is) and the unknown response of the driver and it's action on the various strings. Yet it does "work", so even a non-linear response in the compressor may still be an improvement. Or, am I missing something here? Do you have a schematic for the orange peeler or similar with just the feed forward components? Could the Aussiemart compressor be adapted to a feed forward design do you think and provide the signal to the driver cutting back on components there...or some other variation. Perhaps the pop will be addressed with a dual coil design, a popless amp replacing the Lm386 or some other kind of amp (BTL) or some combination. Mine is not a huge thump you understand, but it is not silent. The temptation is to leave it on and control it with the sensitivity control...but you still can't regain pickup selection unless it is switched off so not really a solution. Anyway...keep at it, admiring your tenacity... pete Link to comment Share on other sites More sharing options...
curtisa Posted October 25, 2006 Report Share Posted October 25, 2006 Given that we don't know the characteristic of the driver and what it does to the signal...are frequency responses based on audio quality valid do you think? Or, does it not respond within the guitar's range (plus harmonic range) do you mean? I think it will matter if we want any hope of driving the high strings in high positions, or in harmonic mode. If the circuit is incapable of reproducing anything over a couple of kHz you'll never be able to excite the higher notes on the guitar into sustain, no matter how good the driver. OK...but again, the driver styles, quality of construction, installation and the guitar itself are all variables too...is this so important given the nature of the project? Also, could not an optochip be used to function in this way and provide more consistancy and ease of construction? What we want is an opto coupler. There's only one style that I know of. It's made by Vactrol, and it's not easy to get. VTL5C1 and VTL5C3 are examples of them - they're just an LED and a selected LDR encased in a sealed epoxy cylinder. A lot of amp manufacturers use them for channel switching and tremolo circuits. There's only one place I've found here in Oz that stocks them and they're 15 bucks a pop...if they have them at all... Also, the fact that the signal is distorted...is that really so much of a problem. My signal must be totally twisted given the gain in the preamp, running the LM386 at max (notorious for distortion as it is) and the unknown response of the driver and it's action on the various strings. Yet it does "work", so even a non-linear response in the compressor may still be an improvement. Or, am I missing something here? Well, I'm actually getting better, more-consistent performance with clean, compressed signal. For me the distorted signal worked, but introduced a lot of unpredictability into the sustainer - excess microphonics, harmonic sustain when in fundamental mode, excess EMI... Do you have a schematic for the orange peeler or similar with just the feed forward components? Could the Aussiemart compressor be adapted to a feed forward design do you think and provide the signal to the driver cutting back on components there...or some other variation. That schematic of the Tangerine Peeler is pretty much it, just set the "FF/FB" switch into the "FF" position and you're away. Mind you, it does say on the diagram that it's an "untested trial design". I'm going to have a closer look at that FET/Opamp article that Col found over the next couple of days - long weekend for us down here, going to make the most of it! Interesting side note - I tried the sustainer with my acoustic last night. It's got a piezo bridge pickup and preamp all built in. With the feed-forward limiter and clean drive I could get plenty of sustain on the 1st and 2nd strings, but almost nothing on the 3rd-6th strings. Probably due to the bronze-wound strings having less magnetic material to play with. And I could move the driver all the way to the bridge where the piezo pickup is located and got absolutely zero feedback (driver didn't work so well here though as it couldn't "move" the string as efficiently). Cheers, Curtis. Link to comment Share on other sites More sharing options...
psw Posted October 25, 2006 Author Report Share Posted October 25, 2006 Mind you, it does say on the diagram that it's an "untested trial design". Yes...well whatever design works will be untested till it does! I am a little concerned that unless we have a good deal of efficiency, we will have to have a lot of headroom to drive this thing cleanly. Perhaps we do need to consider phantom power to achieve this.... I could move the driver all the way to the bridge where the piezo pickup is located and got absolutely zero feedback (driver didn't work so well here though as it couldn't "move" the string as efficiently). Well done, I never did get around to this experimentation. I suspected that steel string would need to be used. Looking to the future of the instrument, the Line 6 modeling guitar has some intriguing aspects and runs from piezos. Perhaps the future holds software modeling for recording and perhaps performing instruments. If so, this type of device is still well placed as it becomes an addition to the instrument itself, not just a processor. The sustainer would still be a valid contribution to such an instrument and would be an interesting propersition. I sought to make drivers that would work from the bridge. I find it fascinating that such a powerful sustain can be achieved at the highest frets, just shy of the neck driver, effectively stopped like the bridge but from the other end (as on my guitar) and that such a placement would solve a lot of the discrepencies caused by fretting action. Alas, I think the magnetic bridge pickup will not be overthrown easily in the near future and is what we currently have to contend with. Eventually I will attempt to make a driver run from the neck pickup however...it will be interesting to see the effects of such a device even if it weren't entirely practical in the end for most... The mid coil driver is of course my comprimise position... pete Link to comment Share on other sites More sharing options...
col Posted October 25, 2006 Report Share Posted October 25, 2006 I've been playing some more with FET based compressors converted to feed-forward topology. The orange squeezer is ok, however its frequency response isn't really good enough for our purposes - particularly when you try to reduce the attack and decay times. That's a shame - just last night I was breadboarding up the "Tangerine Peeler", but ran out of components before I could try it out. Maybe I should abandon it before I get too carried away? when I say the response is not good enough - I mean it's not balanced. Below a certain frequency - about 200hz but dependant on component values obviously - it doesn't limit as much so the sustainer would drive harder.... If you try to squish this problem, you end up with loads of harmonics and no decent fundamental (I think) The problem is that the feedforward version limits the signal asymetrically - in the feedback circuit, the negative feedback removes most of this asymetry. What this means (I think) is that there will always be lots of harmonic content an less fundamental for the low notes, which menas no nice stable fundamental mode for the sustainer. Yes, that's something I noticed when I sim'ed the Tangerine Peeler gain cell - there was an optimum range of control voltages that seemed to work best with the FET's available, and it tended to be quite non-linear. I suspect that the two FET's in the gain cell probably needed to be quite closely matched, which is probably more trouble than it's worth for us. I've been more attracted towards the 'fast FET limiter circuit'..., and after a load of fiddling I'm wondering if the asymetry of the compression in feedforward mode is due to the resistance of the fet being dependant on the forward source/drain voltage keeping it in its 'triode region'... I guess this is only happening during half of the wave ? which would explain my asymetrical result - one side of the wave sqaushed a lot, the other a little. On this page, it is explaines that "In the saturation region the drain current is almost entirely independent of the drain-source voltage (Vds) whilst in the ohmic region the drain current depends on the drain-source voltage." The variable resistor attribute of the FET works in the 'ohmic' region, and the ac signal that we're trying to attenuate with the FET resistor also pulls Vds up and down. Either the circuit needs to be tweaked so that this effect is minimised (can this be done?) OR it would require some cool but more complex (parts availablility dependent) tricks using a pair of FETs one N-type and one P-type, like in this circuit (anyone here speak russian ). The only fix I can see that might work is using the fet attenuator in the negative feedback loop of an op-amp gain stage - could this fix the asymetry ? I have tried to set this up, but so far unsuccessfully. Edit: here is a doc with a FET attenuator something like I'm thinking of Now that looks much more appealing, and reduces the component requirements down too. One FET, one (stage of an) opamp and a handful of resistors and caps. Might be time to give this one a go. Unfortunately, (for me) this exhibits the same asymetry issues - just much worse Another possible option would be the LA Light compressor, this is a feedforward design based on an LED/LDR combo - which makes it difficult to simulate, so I've not tried it yet. EDIT: at last I found a link to the LA-Light schem HERE Difficult to say. The light/resistance characteristic of LDR's can vary quite a bit from piece to piece, which means that our DIY'ed compressors will probably vary in performance from one to another. could this be handled with a multiturn trimmer for tuning ? It seems that that final versin of the LA-light has been tweaked especially to prevent the asymetry problems from occuring. Cheers, Col Link to comment Share on other sites More sharing options...
col Posted October 25, 2006 Report Share Posted October 25, 2006 The orange squeezer is ok, however its frequency response isn't really good enough for our purposes - particularly when you try to reduce the attack and decay times. Given that we don't know the characteristic of the driver and what it does to the signal...are frequency responses based on audio quality valid do you think? Or, does it not respond within the guitar's range (plus harmonic range) do you mean? It's based on looking at a virtual Oscilloscope attatched to a simulation of the circuit The best I could tweak the circuit, it would have given more drive on the bigger strings - which is exactly what we are trying to avoid. Difficult to say. The light/resistance characteristic of LDR's can vary quite a bit from piece to piece, which means that our DIY'ed compressors will probably vary in performance from one to another. OK...but again, the driver styles, quality of construction, installation and the guitar itself are all variables too...is this so important given the nature of the project? Also, could not an optochip be used to function in this way and provide more consistancy and ease of construction? I think that it may be worth investigating an LED/LDR solution - would require some trials with differen combos of LED and LDR in order to get a circuit that can work with a variety of them. An opto chip would be good, but all the 'opto-couplers' I've found have been opto transistors rather than opto resistors, I'm not sure how to use these yet (or if its possible for our requirements). I'm aware of 'vactrols' as described by Curtis, but as he says, they are expensive and difficult to get. While there maybe an optimum performace criteria, there could well be a lower threshold that provides acceptable performance. The fact that notes below C on the g string on my guitar morph into a consistant octave above with sustain is actually quite appealing, if it would do it over the whole neck I'd be quite happy . I guess it depends a little on the musical application you have in mind and it would be nice to sustain low drones, I could settle for "less"! Also, the fact that the signal is distorted...is that really so much of a problem. My signal must be totally twisted given the gain in the preamp, running the LM386 at max (notorious for distortion as it is) and the unknown response of the driver and it's action on the various strings. Yet it does "work", so even a non-linear response in the compressor may still be an improvement. Or, am I missing something here? I want to be able to choose between true fundamental mode, and 'mixed' mode where notes bloom slowly (although mixed is my favourite) cheers Col Link to comment Share on other sites More sharing options...
col Posted October 25, 2006 Report Share Posted October 25, 2006 I'm going to have a closer look at that FET/Opamp article that Col found over the next couple of days - long weekend for us down here, going to make the most of it! Before you do, check out what I suggested a couple of posts up about the signal varying the Vds of the FET... It may be that we just cannot do clean FET attenuation without feedback (or a more complex circuit) Maybe some trick involving using a half wave rectifier instead of full wave could help.... or some way of allowing the FET to 'float' more easily so that it's Vds is less dependent on the signal voltage.... (just hopeful guessing with these ideas) Interesting side note - I tried the sustainer with my acoustic last night. It's got a piezo bridge pickup and preamp all built in. With the feed-forward limiter and clean drive I could get plenty of sustain on the 1st and 2nd strings, but almost nothing on the 3rd-6th strings. Probably due to the bronze-wound strings having less magnetic material to play with. And I could move the driver all the way to the bridge where the piezo pickup is located and got absolutely zero feedback (driver didn't work so well here though as it couldn't "move" the string as efficiently). Its a shame that it didn't work so well on acoustic... maybe some other type of string would work better ? phosphor bronze instead of bronze ? Col Link to comment Share on other sites More sharing options...
col Posted October 25, 2006 Report Share Posted October 25, 2006 (edited) ...and after a load of fiddling I'm wondering if the asymetry of the compression in feedforward mode is due to the resistance of the fet being dependant on the forward source/drain voltage keeping it in its 'triode region'... I guess this is only happening during half of the wave ? which would explain my asymetrical result - one side of the wave sqaushed a lot, the other a little. On this page, it is explaines that "In the saturation region the drain current is almost entirely independent of the drain-source voltage (Vds) whilst in the ohmic region the drain current depends on the drain-source voltage." The variable resistor attribute of the FET works in the 'ohmic' region, and the ac signal that we're trying to attenuate with the FET resistor also pulls Vds up and down. Either the circuit needs to be tweaked so that this effect is minimised (can this be done?) It seems like it can be done After some more fiddling, I've reduced the asymetry to what might be an acceptable level - needs tested on a real circuit now. One problem was that the circuit was designed for a different JFET to the one I'm using... I'm trying to get it working with a J201 which is the only JFET I can get locally, and is also the most common one in guitar fx circuits - so seems like an ideal choice... Another issue was that the signal I was trying to attenuate was too strong - of course reducing the signal prior to the VCR then boosting is after add noise and components, but it also reduces distortion.... well, anyhow, it seems like I have circuit that with a few tweaks, could be a goer. EDIT: Another discovery that seems obvious now is that when I change from a full wave rectifier to a half wave rectifier, I get the same 'low frequencies are louder' issues that exists with the Orange Squeezer circuit - I guess this is because at low frequencies, larger caps are needed to filter the control signal produced by a half wave rectifier. Maybe modding the Orange Squeezer circuit to use a full wave rectifier would help it. There is still a major advantage to the 'fast FET limiter' circuit and that is it reacts MUCH more quickly to changes in the signal amplitude, So I'm going to stick with it for now. Edited October 25, 2006 by col Link to comment Share on other sites More sharing options...
onelastgoodbye Posted October 25, 2006 Report Share Posted October 25, 2006 update.. What you see is the same jig from the animation a few pages back, albeit in a less fancy form. I wanted to keep things as diy as possible; this is about as easy as it gets (scraps of wood and LOTS of tape). The jig itself is the thing indicated in red. The blocks of wood on top are only there to clear the bolt in order to make the clamping (in the vise) easier. After I've wound the driver (which is sitting between the two shiny l-profiles in the pic, notice the epoxy oozing out in the middle) I put the jig in a big vise to prevent the core from pushing the bobbins apart (the bolt and wire arrangement, seen here only provides sufficient clamping force for the winding process itself, but when you slide the side clamps in, you need something bigger, hence the vise). There's a little procedure for this: First, the side clamps (the aluminium l-profiles) are slid in (just a tad, they aren't compressing the windings yet) to space the bobbins correctly. Then, the vise gets tightened. After that, the side clamps are pushed in all the way ( I used screws) Finally, the vise is tightened some more and you wait till the epoxy sets. The winding and clamping take about 5 min total. You have to be pretty fast though, If you've never done this I wouldn't use the 5 min epoxy stuff (more like 15 minute stuff) because you have to get those clamps on before it sets. Now you can pry the thing apart. This is the hardest part. The trick is to use low-stick tape on all parts that get epoxy on them (the bobbins, the side clamps, the core). That way, if you pull the jig open (gently!), the tape will let go sooner than the epoxy, because it sticks less than the epoxy. I used vinyl tape prior to this, but it wouldn't let go..resulting in a gooey mess and broken windings. Here you can see the jig with the top bobbin removed. Notice the yellow tape on the side clamps. The yellow stuff left and right of the coil is epoxy squeeze out.The black thing is the rubber core (cut it frome some hard rubber sheet) If you look closely, you can also the two screws that clamp the sides. My wire reel is on the left. 5 € for about 10 drivers worth. Here is the jig with the side clamps removed. Note the layer of yellow low stick tape on the bobbin. The screw holes are clearly visible too. Here everything is removed (it's essentially the bottom bobbin. There's an indexing pin for the core in the middle, and two small holes for the clamping wire to go through. The grey stuff is heavy duty tape. You can add more layers of tape to control the width of the bobbin, and thus, the width of the driver. The finished product . Maybe i should make this a pic too? Damn picture rules. I'm sure psw 'll quote it . Tim Link to comment Share on other sites More sharing options...
psw Posted October 26, 2006 Author Report Share Posted October 26, 2006 You guessed right! Simply superb...solid without the wacky paper reinforcement that I perscribed no side bulging at all Now, for the core...this could be slipped over the blades of a rail pickup and back filled with epoxy. Another option could be to fill the core with iron fillings (you can get pure iron powder from magnet shops btw), put a magnet below to hold them down and align them beneath some plastic, then soak in superglue which will be absorbed by the wick effect...instant powdered core! This is great also because the technique is so adaptable...you could make half sized coils for bilateral type drivers, as I have posted lately, just by changing the core length and depth...or single coil driver's like I have in my guitar now. Stack two and see how that goes... I love how compact it has made them...no loose windings and very small. This can only help with efficiency and reduce EMI. The small, thin driving coil, concentrated as much as possible directly below the strings and maximising the number of overlapping windings is a strategy seemingly ignored by the commercial propositions...possibly for ease of manifacture, possibly because it wasn't thought of previously... It is so minimalist, I think I am in love! Nothing but the coil...fantastic...but the way it was achieved so simple, makes me want to make one for myself... Seeing it on the pickup like this... You could imagine a driver like this with internal magnets being built into a slightly enlarged pickup ring for instance. Would, with more development, a low impedance pickup made with similar techniques and a driver work within a HB sized device...like a miniture fixed ebow? Be afraid sustainiac... ...the day of the DIY sustainer is coming...mwhahahaha Congratulations to everyone, 2000+ contributions approaching 70,000 visits and still making progress, we should all be proud ... Once this sustainer is done, perhaps we should start a new thread...DIY world peace, DIY global warming solutions, DIY housing modules... I really admire the spirit and tenacity people are approaching this project with and the mixture of skills and talent it has drawn together, quite remarkable... keep it up... pete Link to comment Share on other sites More sharing options...
curtisa Posted October 26, 2006 Report Share Posted October 26, 2006 when I say the response is not good enough - I mean it's not balanced. Below a certain frequency - about 200hz but dependant on component values obviously - it doesn't limit as much so the sustainer would drive harder.... If you try to squish this problem, you end up with loads of harmonics and no decent fundamental (I think) Ok, so perhaps the Orange Squeezer (and others like it) are geared towards more audibly "pleasing" compression, whereas what we're after is squeaky clean "accurate" compression. I've been more attracted towards the 'fast FET limiter circuit'..., and after a load of fiddling I'm wondering if the asymetry of the compression in feedforward mode is due to the resistance of the fet being dependant on the forward source/drain voltage keeping it in its 'triode region'... I guess this is only happening during half of the wave ? which would explain my asymetrical result - one side of the wave sqaushed a lot, the other a little. On this page, it is explaines that "In the saturation region the drain current is almost entirely independent of the drain-source voltage (Vds) whilst in the ohmic region the drain current depends on the drain-source voltage." The variable resistor attribute of the FET works in the 'ohmic' region, and the ac signal that we're trying to attenuate with the FET resistor also pulls Vds up and down. Ah. Could be two things happenning here - one is, like you say, the FET being operated in the non-linear area of it's characteristic curve, but also how we're generating the control voltage. If you use THATcorp's precision rectifier circuit you're actually only using a half-wave rectifier. So for every half cycle you're generating the control voltage, and for the alternate half cycle you're generating nothing. Also it's unfiltered, so if you apply it straight on to the control input of whatever gain cell we're using, you'll only compress every half cycle of the input signal, which WILL give us bags of asymmetry and distortion. Unfortunately, (for me) this exhibits the same asymetry issues - just much worse Haha! Well I built it up last night and it works quite well! Very clean operation, and compresses quite nicely. I used a N-channel FET instead (BF256B) so I had to generate a negative control voltage instead of a positive one. No big deal, just reversed the diodes in the rectifier. The control signal had to be filtered though, otherwise I got loads of distortion and asymmetry (as above). The main problem I had was trying to get a sufficiently broad enough control voltage for the FET I was using, but this could easily be solved by using a different FET with a smaller Vgs voltage range (BF256B is something like 0V - 8V, which is too wide for 9V battery operation). could this be handled with a multiturn trimmer for tuning ? It seems that that final versin of the LA-light has been tweaked especially to prevent the asymetry problems from occuring. Probably. Maybe. Dunno. I haven't looked into the LA-light compressor yet - I've been having too much success with the FET/Opamp version to try it out! Before you do, check out what I suggested a couple of posts up about the signal varying the Vds of the FET... It may be that we just cannot do clean FET attenuation without feedback (or a more complex circuit) Oooops - too late, already have! And clean FET attenuation utilising that circuit in the pdf document, in practice, works well. Just need to tweak it to get the operation correct. Maybe some trick involving using a half wave rectifier instead of full wave could help.... or some way of allowing the FET to 'float' more easily so that it's Vds is less dependent on the signal voltage.... (just hopeful guessing with these ideas) Full-wave rectification will probably help in that we'll get more accurate compression operation (we're generating the positive AND negative half cycles of the input waveform. I suspect that careful selection of the attack and release times will help aswell (filtering the control voltage). Sounds like we're on some sort of race - you take the LED/LDR route and I'll stick with the FET/Opamp system. Onelastgoodbye will take care of the drivers and we'll meet somewhere in the middle! BTW, nice work with that driver construction there, Onelastgoodbye Cheers, Curtis Link to comment Share on other sites More sharing options...
psw Posted October 26, 2006 Author Report Share Posted October 26, 2006 Hey fellas...what a great day today... Let's go backwards...I just got home to find a rail pickup in the post...thankyou spazzy, won't be able to test it just yet, but the quality is really good...very impressed! Just sent a roll of wire to bancika...should be with you in about 10 days mate...so then well have some winding going on, on this... I got a really nice email this morning from Tim/onelastgoodbye who allowed me to reply at length...hope I didn't burden you too much and things will move forward for you... And...after much frustration and rejection...I have found somewhere to live and will be moving in a few weeks...Hooray!!! This will be a difficult move and a lit of other $h*t is happening in my life right now, but it is a new start and while smaller and not the facilities to do much (making guitar's may be difficult, and I don't know where I will put the grinder to make driver blades and such) but it means that I can do some practical work in the near future on this and other projects.... Most of all, it may allow me more time with my children, especially my beautiful and very musical daughter who I miss enormously. Hopefully I will have both her and my son around more often than I do now. I just came back from seeing her for a few hours after school and her face just lit up when I told her I was moving.... It is a big and daunting step for me but very important in the circumstances...it will be a trial to keep all the balls balanced but in my quieter moments I will enjoy doing things with my hands and making these ideas a reality and seeing how the dice rolls as to their success. Fortunately the sustainer project is a small scale proposition and cheap to do (money will be tight) but perhaps when things are ironed out some production or supply of materials to get more people involved will come of this. There are other guitar projects that I could tinker with...I have a pickup winder and large reel of pickup wire to get back...so there is a whole other, yet related project. There are two strats in pieces waiting to be put back together and sustainerized that play a lot better than this thing here... And perhaps I will get to play a bit more guitar and make some music again. This has been serverely restricted in recent times, but the essence of music is to create and to share and moving will allow that from which I can draw inspiration. The guitar has been good to me, it has been a constant companion and freind for many, many years...while I left school early to join bands that never when anywhere, my ability to play allowed me to return and study music at university. It is a part of my being that I have missed and neglected greatly....and while there is much else in life (children, work, food, shelter) if nothing else, there is still the guitar to accompany one on this road. So...changes that may take a while to come to a stable state...at least things are changing, and for the better I'm sure... pete Link to comment Share on other sites More sharing options...
col Posted October 26, 2006 Report Share Posted October 26, 2006 (edited) ... Haha! Well I built it up last night and it works quite well! Very clean operation, and compresses quite nicely. I used a N-channel FET instead (BF256B) so I had to generate a negative control voltage instead of a positive one. No big deal, just reversed the diodes in the rectifier. The control signal had to be filtered though, otherwise I got loads of distortion and asymmetry (as above). The main problem I had was trying to get a sufficiently broad enough control voltage for the FET I was using, but this could easily be solved by using a different FET with a smaller Vgs voltage range (BF256B is something like 0V - 8V, which is too wide for 9V battery operation). Thats good news. As I mentioned, I've managed to get better results with a FET circuit, although I've not gone back and re-tried that 'Fet in -ve feedback' one yet. One thing I wondered about your results: Are you getting an output that drops of to zero or very low as the input goes above the threshold ? This is what we want to happen, and I'm finding that the best I can get is minimum output is about 20% of maximum - I was hoping for better. As it stands, my best results with a FET circuit are very similar to what I was getting with my original LM13700 circuit ! Before you do, check out what I suggested a couple of posts up about the signal varying the Vds of the FET... It may be that we just cannot do clean FET attenuation without feedback (or a more complex circuit) Oooops - too late, already have! And clean FET attenuation utilising that circuit in the pdf document, in practice, works well. Just need to tweak it to get the operation correct. Yeah, I already have too , although I would say cleaner rather than clean - it does exhibit more distortion around the threshold :-| Maybe some trick involving using a half wave rectifier instead of full wave could help.... or some way of allowing the FET to 'float' more easily so that it's Vds is less dependent on the signal voltage.... (just hopeful guessing with these ideas) Full-wave rectification will probably help in that we'll get more accurate compression operation (we're generating the positive AND negative half cycles of the input waveform. I suspect that careful selection of the attack and release times will help aswell (filtering the control voltage). I did get a marginal improvement by messing around with the symetry of the rectifier, but not enough to make the extra complexity worthwhile. I have been using a precision op-amp based full-wave rectifier, and using this with the 'fast FET limiter' gives very quick response with acceptable (I hope) distortion. Sounds like we're on some sort of race - you take the LED/LDR route and I'll stick with the FET/Opamp system. Onelastgoodbye will take care of the drivers and we'll meet somewhere in the middle! I'm not on a race - just posting the results of my expreiments, and trying to understand them. At this stage I'm starting to feel that this last wave of development is not going to offer much of an imprevement over my LM13700 circuit. I'm certainly not for or against any approach - just want to find one that works well, is simple, repeatable and uses readily available cheap parts. LED/LDR, FET based, and LM13700 solutions all pose problems here - the first two are variable and/or difficult to find, the LM13700 is bulky and will probably soon be difficult to get hold of. The issues I have with my current development: There is some asymetrical distortion, and it is most extreme at or near the point where the sustainer equilibrium will be. It uses too many op-amps signals above the threshold will still recieve some (although much lower) drive. signals below the threshold will recieve progressively less drive - so if the threshold is set high for a loud sustain, it is likely that the High string/low fret issues will sill be apparent. In order to limit the distortion, I've attenuated the signal prior to the Fet attenuator.... so it will need more gain in the post AGC stage(s), this will add even more noise to what is already a noisy circuit... I fear all that noise could cause problems ? It will certainly make the circuit more sensitive to EMI I have some ideas for how to deal with this, but nothing concrete enough to post at this stage. would you be able to set up that 'FET in the op-amp feedback' to work with a J201 ? I got it to kinda work, but as I posted, It wasn't anywhere near usable. EDIT: I have this working better now. There is very little asymetry, the problem is that the range is not wide enough. If its set to squish the high levels (around 2v), then it won't bring the level up on 200 - 300mV... also, I've not yet managed to get the compression ration as high as I want (ideally, high level squished to near zero) right now it just about levels everything between about 400 and 1000 mV cheers Col Edited October 26, 2006 by col Link to comment Share on other sites More sharing options...
zfrittz6 Posted October 26, 2006 Report Share Posted October 26, 2006 (edited) This it is the circuit that I am using by far better result than lm386. I do not use preamplifier I I use single the power stage. and enough good goes. Edited October 26, 2006 by zfrittz6 Link to comment Share on other sites More sharing options...
col Posted October 26, 2006 Report Share Posted October 26, 2006 This it is the circuit that I am using by far better result than lm386. I do not use preamplifier I I use single the power stage. and enough good goes. can you post a less blurred/reduced image? or some details please. Col Link to comment Share on other sites More sharing options...
zfrittz6 Posted October 26, 2006 Report Share Posted October 26, 2006 the scheme This in datasheep of tda 2822 is that not like extending it, excuses. Greetings Link to comment Share on other sites More sharing options...
lovekraft Posted October 26, 2006 Report Share Posted October 26, 2006 The light/resistance characteristic of LDR's can vary quite a bit from piece to piece, which means that our DIY'ed compressors will probably vary in performance from one to another. They surely can't be any more varied than JFETs! Even the best made/most expensive JFET devices (Toshiba, Linear Technologies, et al) are all over the map, spec-wise, so they're gonna have to either be sorted for suitability (buy 1000, test 'em all, sell whatever won't work on Ebay) or trimmed in circuit somehow. A trimmer in parallel with an optocoupler's LDR should be sufficient for our purposes, and probably won't even be necessary if we use a production optocoupler like the Vactrol® or Siliconix Audiohm® devices. The only major problem with LED/LDR devices is the LDR has it's own attack/release characteristics, so you'll have to pick a model that's fast enough for your design. The good news is that LDRs are virtually distortion-free, have incredible headroom, and can be treated just like a standard resistor. Just my two cents - I think most FET compressors are prized for their non-linearities rather than their transparency, but that's just me. More info here: Silonex Audiohm site PerkinElmer VTL5C series Analog Optoisolators I've got a few VTL5C2s that I can spare, if anybody wants to try one - might be a wee bit slow, but "close enough" for proof-of-concept work. PM me if interested. I'd give it a go myself, but there are already too many irons in the fire around here, at least for the next few months. A limited bandwidth (~60Hz-3KHz?) opamp "ideal rectifier" (with some gain) driving the opto looks to me like the simplest practical sidechain, but what do I know? Y'all have at it - I'm looking forward to developments! Link to comment Share on other sites More sharing options...
psw Posted October 26, 2006 Author Report Share Posted October 26, 2006 Thanks LK...good to see your still looking in... zfrittz6...that chip is rated at 3 watts! Does not the battery go flat fast? It has a 100kohm input resistance too...does it change the tone pf the guitar between switching it on and off? OK... So, here is an interesting observation. As I now have a spare pickup in Spazzy's rail, I thought at least I could tape it to a guitar lead and hold it over the guitar to test it works... With the sustainer on, it is kind of like an ebow! The wierd thing is that you don't ever get squeal out of it...even over the driver. You get distortion and an increase in gain...pulling it back a couple of inches and it is fine. Of course the guitar itself is running acoustically (is not plugged in) so the pickup is not part of the loop, but I had not expected that and did not find that in previous experiments. As a completely odd ball experiment...you can use the rail pickup as a slide with the sustainer too No real practical use I guess but an interesting phenomenon all the same... This pickup is well built to close tolerances...I am not sure if the blades will come out easily or if the coil is not wound directly around them some how...in order to get that much wire in the coils (14K) they would have needed to use thin wire and a lot of it, the bobbin would have to be thin at best...as it stands I'm just not at all sure about it. The magnet in this pickup is small but powerfull (ceramic) and with the high impedance does give out a chuncky distortion...this is not a pickup for strat lovers! There are some interesting construction details though (the base plate has a hole to put the magnet in to save on depth for instance) and the build is good and is instructive for the building of drivers. so...my first experimentation...a new pickup and some sticky tape. I was listening to the Hellecaster's track son becomes father (from escape from hollywood) in the car last night...JJ didn't use a sustainer as such, but instead pushed the headstock onto the speaker cabinet baffle to achieve a really beautiful feed back sustain effect with a nice bloom into harmonics... This is the type of effect I think I am looking for...I may post a clip of it somewhere and those who don't want to build a sustainer as such, may be interested to try it... pete Link to comment Share on other sites More sharing options...
onelastgoodbye Posted October 26, 2006 Report Share Posted October 26, 2006 My collection I now have a humbucking driver with 2 matched coils at 4.3 ohms each. 2 mm high, 14 mm wide, 56 mm long. There's a little bit of 'spring effect' to the coils; with good quality epoxy and a slightly longer core the width can get down to 12 mm. I'd like to try internal magnets but I'm afraid even the smallest neodymiums will be to powerful, given they'll be so close to the strings? Some sort of soft ferrite or low power bar magnet would probably be ideal but it's impossible to get in these sizes. Maybe the magnetic sheet would work if cut properly.. Link to comment Share on other sites More sharing options...
col Posted October 26, 2006 Report Share Posted October 26, 2006 (edited) More info here: Silonex Audiohm site Thanks for the info - Farnell have in stock an 'unbranded?' Silonex resistive isolator NSL-32SR3 with attack of 5ms and decay of 10ms for less than £2. I has a resistance from 60ohm to 25Mohm Seems like a likely candidate. I've got a few VTL5C2s that I can spare, if anybody wants to try one - might be a wee bit slow, but "close enough" for proof-of-concept work. PM me if interested. I'd give it a go myself, but there are already too many irons in the fire around here, at least for the next few months. A limited bandwidth (~60Hz-3KHz?) opamp "ideal rectifier" (with some gain) driving the opto looks to me like the simplest practical sidechain, but what do I know? Y'all have at it - I'm looking forward to developments! I wish you would have a blast at this circuit - seems like you have the relevant knowledge that I am lacking. I'm sure you and Curtis could get this sorted in double quick time. I would be interested in a sample VTL5C2 to play with, but I would be worried about destroying it. All the circuit stuff I've been doing has been simulated to hell and back before committing to real hardware in order to protect components from my ignorance . (Unless there is a model available for a resistive isolator ? I suppose I could cludge it together testing with an Led and a pot?) FWIW Here's a description of what I feel would be the ideal driver circuit: There would be a low level threshold and a high level threshold - both with a softish 'knee' rather than hard on/off Any signal below the low threshold or above the high on would be squashed. Any input between the two thresholds would be compressed to give a fixed output amplitude. The output amplitude and the low level threshold would be set with trimmers to adjust for battery life, response time, noise etc. The high level threshold would be controlled via a knob. The theory is that whatever the input level, if it is within the thresholds, the strings will be driven at the maximum power (defined by the trimpot) until the output reaches the level set by the high threshold knob... One important consideration is that the on to off slope of the high threshold must be smooth and have level frequency response and minimal distortion because the sustainers equilibrium point will be somwhere on this slope. (If Pete is right, and using a square wave to feed the driver works without causing unwanted 'effects', it could be that we use something like a comparator or a schmitt trigger to produce a driving signal with fixed amplitude...) The thing I don't know is how best to provide the low and high thresholds.... I know it can be done (up to a point) with these modified compressor circuits, but all the extra op-amps that seem to be needed to prepare the control voltage etc. are a real pain, and the result is still not ideal for the sustainer. Surely there is a simpler way. Maybe we need to go digital does anyone have any ideas about how to realize this circuit ? (please think 'outside the box', and forget about traditional compressor/limiter functinality for this - even if you think I'm barking up the wrong tree, humour me for now - think about it and tell me why it's not going to work ) (btw lovekraft, that precision rectifier you posted is the one I have been using for most of my simulations) cheers Col Edited October 27, 2006 by col Link to comment Share on other sites More sharing options...
psw Posted October 27, 2006 Author Report Share Posted October 27, 2006 I wish you would have a blast at this circuit - seems like you have the relevant knowledge that I am lacking. I'm sure you and Curtis could get this sorted in double quick time. LK did contribute a significant amount earlier in the tread, but unless we could make a driver available, it may not be of sufficient interest to actually make one...maybe we could tempt him with a bass version FWIW Here's a description of what I feel would be the ideal driver circuit: There would be a low level threshold and a high level threshold - both with a softish 'knee' rather than hard on/off Any signal below the low threshold or above the high on would be squashed. Any input between the two thresholds would be compressed to give a fixed output amplitude. The output amplitude and the low level threshold would be set with trimmers to adjust for battery life, response time, noise etc. The high level threshold would be controlled via a knob. The theory is that whatever the input level, if it is within the thresholds, the strings will be driven at the maximum power (defined by the trimpot) until the output reaches the level set by the high threshold knob... I think it is worth spelling out the intentions over and again...take it back to the basic ideas and keep the details open...thanks. (If Pete is right, and using a square wave to feed the driver works without causing unwanted 'effects', it could be that we use something like a comparator or a schmitt trigger to produce a driving signal with fixed amplitude...) LK and I discussed this in the past...we even thought of driving it with a half wave...kind of pinging the string but it could play havoc with the magnets...I did a few things but nothing to write about and it was years back now! All I can imagine is that with my circuit it is clipped and so quiet signals are amped and loud squashed...the available power is limiting the extent to which it drives... As I recall, I was very much in the clean court, but I don't know if it is going to be practical, given what we are working with... Maybe we need to go digital Maybe... does anyone have any ideas about how to realize this circuit ? (please think 'outside the box', and forget about traditional compressor/limiter functinality for this - even if you think I'm barking up the wrong tree, humour me for now - think about it and tell me why it's not going to work ) Don't tempt me...the last idea I had was to use a speaker protection device that melts and resets at given voltages...they wouldn't last long even if it did work, so I was too to mention it! pete BTW...can anyone replicate what I did with a spare pickup over the strings with the sustainer on? Link to comment Share on other sites More sharing options...
curtisa Posted October 27, 2006 Report Share Posted October 27, 2006 (edited) OK, results time This works, both in simulation and in real life: The whole thing is based around quad low-voltage opamp LM324. IC1a on the far left if the virtual earth generator, providing the midpoint for the 9V battery. IC1b is a high impedance input buffer, where the guitar pickup signal is applied. IC1d and the surrounding components is the precision half-wave rectifier with filtering provided by the 10uF capacitor. Finally, IC1c and the BF256B FET form the gain reduction cell that is used to vary the amount of drive. BF256 is not the only FET you could use here either, it's just the one I had handy in my parts drawer. The "output" goes to the LM386 chip (or similar). The FET/Opamp AGC actually operate as a gain "increaser" - with no control signal applied you get maximum gain, and as the control signal gradually creeps up the gain starts backing off. It never truly reaches zero gain, but it's not hard to get a gain swing of 30dB, which is a fair bit and probably more than enough for us I would think. The AGC transfer function is not linear either, more a gradual curve - as more gain reduction is called for, the steepness of the input/output ratio increases until it's actually starting to curve back around on to itself! Col's dynamic range inversion characteristic rears it's ugly head again! There would be a low level threshold and a high level threshold - both with a softish 'knee' rather than hard on/off Any signal below the low threshold or above the high on would be squashed. Any input between the two thresholds would be compressed to give a fixed output amplitude. The output amplitude and the low level threshold would be set with trimmers to adjust for battery life, response time, noise etc. The high level threshold would be controlled via a knob. It would appear that the "curved" gain reduction curve negates the need for multiple thresholds from what I've seen with this circuit. In practice, if you really wanted to incorporate a threshold control/setting, you could just vary the 220k feedback resistor around IC1d. I found that varying the level being sent to the LM386 via a pot was enough to control the "speed" of the sustainer in getting going, and also how much harmonic bloom I could get (probably as I was starting to overdrive the LM386). In practice it works quite well with my handheld pickup/driver - the response over all strings and positions is quite even, and I can really back off the drive to the LM386 chip and maintain the sustaining action. Granted it's not as good as the SSM2018 limiter I was using before, but for a low parts-count, cheap, 9V battery operated sustainer compressor, it is a vast improvement over the raw LM386 amp I was initially using. Maybe we need to go digital Maybe... Bah! Wash yer mouth out with soap and water! Let's keep it analog at this stage before we go adding a further degree of complication Cheers, Curtis. Edited October 27, 2006 by curtisa Link to comment Share on other sites More sharing options...
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