Fresh Fizz

No, they are switching at the frequency of 30 kHz. Compare it with a movie projector which projects images at a rate of 50 (?) frames per second. When the thing works you're watching a movie, not a 50 Hz frequency. Exception: dither -> interference between the movement on screen and the 50 Hz thingie. Like when wheels seem to turn the wrong way around. That's one reason why the switching frequency has to be high. I can't give you a brand name or schematic but I've seen a schematic with a switched resistor. Then there is a mosfet switch in series with the resistor of the RC part of the allpass filter. (Most of the time it's a fet or photocell/diode in parallel with the resistor.) So when the switched is closed 50 % of the time the resistance will be twice as big. The problem is the lousy performance of our output stages. It's the combination of phase shifting and high cut. (My first and not so short contribution) Sustiainac's current drive will work much better in harmonic mode. But what you can do and what I've seen in a patent is use a high boost for harmonic mode. Which means more switching troubles. Another option is to use the current drive principle together with the lm386. This is what the theory says. There's not much more to it than steal a bit of figure 11 of the patent. R26 and feedback loop to C9 into opamp "U1b" (IC U1b should read U2b). By the way figure 10 contains an error, 1001 is in the (negative) feedback loop. Cheers Fresh Fizz

Don't worry too much about the switching frequency. Basically it's analog in, analog out (+ distortion). The Mosfets which work like switches don't dissipate power, if they are open there's no current flowing through the mosfet, if they are closed there is no voltage across the mosfet. Now if only one of the mosfets could be closed there would only be 2 analog states, 9 volt and 0 volt. The comparator and switching signal are a way of creating the analog states in between by means of duty cycles. For instance if the top mosfet would be opened for 50% of the time (of a "pulse") the analog state of the output signal would be 6.75. It must be clear to everyone that through this process the signal becomes distorted. (50% of the time 4.5 volt, the other 50% 9 volt). That's the trade-off, more efficiency, less high fidelity. Maybe some of you know the phase shifters built from opamp allpass filters that use mosfet switches (switched resistors) instead of fets. Same principle. Fresh Fizz

I don't want to ruin this great thread, but do you know that all the information can be obtained from freepatentsonline? It would be a pity if everybody started to copy the sustainiac. On the other hand I've seen some thingies that could be usefull to us. Like a current-source amplifier to deal with impedance and phase shift, a drive current limiter (to minimize fizz?) and the class D amp. The patent I'm referring to has a three pickup configuration with the driver in the mid position. The switching of this version appears to be active (don't know if that's any good to you, Pete), the driver has it's own preamp to turn it into an active pickup. If you create a free account at freepatentsonline.com you can take a look at the patent images. Taste the forbidden fruit if you wish. Cheers Fresh Fizz

That was my very first sustainer project. I thought I could get sustain without a magnet. I used a single power darlington pinched off in class B, the driver coil as some sort of emitter resistance. It was a total failure. Lack of power, no decent sustain possible. Instead I got cricket-like sounds. Changing the bias of the darlington in class A didn't improve the performance. Except that my transistor and driver started to get really hot. FF

The danger is that once you're start copying a part of sustainiac's device you might need to go all the way and you'll finally end up copying the complete sustainiac. That's not exactly the spirit of DIY. I'm only interested in that tiny part in the sustainiac that reduces the fizz. If the bilateral driver is the solution than I will build one, if I could only find some decent magnets. So I'm awaiting the results of UI's, Col's and Curtisa's projects. In the meantime I'm reading a bit of the boring patents hoping to find something fizz-related. Good luck to you all Fresh Fizz

For my driver I used some left-over 3 layer strat pickguard material. I can understand that people find it too thick, but it's easy to saw and when sanded it can be superglued easily.

Tda7231 or tda7231A 's quiescent current is 4mA at 9 volt. That was the best thing I could come up with. Makes a great kill switch though. Don't you want a stutter effect à la Gibson Les Paul? Another idea of mine: a small resistor in stead of the wire to connect the S2a and S1b neck pup connection. When sustainer is switched on it'll give bridge pup with neck pup in series. In combination with the harmonics switch it'll give bridge with neck pup in series out of phase! I think that there are two approaches. One is the hi fi type of approach. Make phase and frequency response as flat/neutral as possible. The other is the musical approach of letting the ears decide (what utopian isotope is doing with the use of an eq). I think that the hi fi approach is a good starting point, especially if you're in the process of setting up agc and/or overdrives. At the beginning there just are too many parameters to take into consideration. Now I'm arrived at the point that I'm going to experiment a bit with different eq to see if there is an improvement in sound and feel of the sustain effect. Why don't you use a simple connector for the outboard power supply. I use a plastic female 6,3 mm connector. Then you have the option of using the power supply or a battery in a small box attached to your guitar strap. Fresh Fizz

How shall I put it? In my switching system the pickup selector has priority over the sustainer switch. When the Neck, Mid or combinations are selected there will be no feedback. Only when bridge pup is selected there will be feedback depending on the sustiainer on/off and power standby/off switches. These 2 switches could be combined into a single switch, but personally I think it makes more sense to have 2 switches. The quiescent current is low, around 4 mA. When using only 1 switch you have to deal with spikes, pops every time the sustainer is switched on and filter cap(s) are charged. Then it could be something like this: Thanx Col, but I'm doing my own calculations in Excel. I haven't updated my schematic yet but the old one is not here. That's because the input impedance of the lm386 is only 50kOhm. You need a bigger capacitor. In my schematic there is a voltage divider on that spot which takes care of that problem. I have been looking at the lm836 national semiconductor datasheet. I saw that there is an easy way to get a 6 dB low boost with only 2 components. That's pretty cool! (see amplifier with bass boost) Cheers Fresh Fizz

Very nice samples Pete. Your sustainer device sounds definately more refined than mine. Did you use one setting per sample or have you've been adjusting settings while playing? To me it seems that you don't need more compression or output level there is more than enough feedback. And those tapped notes seem to go into feedback with ease. Maybe your driver is more efficient than mine. Or a compressed signal is more obedient than a distorted one. I presume that you were using fundamental mode all the time. The strength of using agc is that it gives you a classy sound. But to me it seems that the fizz is more noticable when it occurs. With overdrive there is allways some background nasty-ness but it sounds more creamy. I only need to find a way to make my sustainer not to react so aggressively right after the attack. Could you perhaps make a sample of a problem area of mine? A single G note 3rd fret on high e-string (on my guitar I get a weak, fragile 3rd) I've thought about your switching troubles. How about this one (what's missing) ? Fresh Fizz

That 50 degrees phase shift is caused by the output cap. And you probably included the Zobel in your simulation I think that Pete has allready found out by trial and error. Thicker wire -> more turns of copper windings needed to get 8 ohm -> higher inductance. For low and mid frequencies this means a gain in efficiency but the highs stay where the are. It works the same as with overwound pickups. (Loosing the twang.) I use a pretty strong ceramic magnet. But I use rather thinny blades as cores. I wonder whether if the blades get saturated they will produce harmonics. And for that reason: 1. have a tendency to build feedback on a harmonic rather than the fundamental 2. because all of us don't use a core as thick as sustainiac's could this saturation be the cause of fizz? Fresh Fizz

Fortunately this is not something I have to deal with. Apart from the fizz the sustainer device doesn't seem to change my tone. So you're saying that because of the overdrive I use my device is acting rather nervously, my sustainer is responding too soon, too intense? It's not that it's functioning badly but I want to know if there is any room for improvement. From what I'm reading from you my sustainer could well be a little one dimensional. So I'm waiting for the new soundclips from you. COOL! Even if I wanted to install another pickup there would be no place to do so. The circuitboard is placed in the mid pickup hole. I want to get more involved in solving problems which are specific to a more complex pickup/switching configuration but from where I am now at the moment it is a luxury problem. And you have to be prepared to answer all kinds of silly questions. OK, one for now, why is the sustainer switch positioned before the pickup selector switch? Who am I to want 2 pickups if he only has one? cheers Fresh Fizz

To Col It's nice to see that somebody finally took interest in my phase shift "thing". (For me it's only a tool, a test to perform after having constructed a driver. There could be a lot of other things wrong with the driver but not it's electrical properties.) What is important to realize is that with the guitar pickup it's not about power but voltage amplification. For the most efficient power transfer the load that's been connected up to the pickup would have to be equal to the pickup's impedance. But in case of voltage amplification we can afford to keep the current low. Which means the pickup sees a high impedance as load. To do the calculations right you have to take this load in series with the dc coil resistance of the pickup. If you do the calculations now you'll see that there is hardly any phase shifting. You undoubtly know what happens if you connect your guitar to a low impedance amplifier circuit. You loose all the highs. You could look at it from a power perspective, lots of phase shift which means that a lot of the energy is backfired to the pickup, or from a voltage perspective, voltage attenuation because of high reactance of the pickups coil and low input impedance of amp. Not necessarily the fundamental, it could be a harmonic. It's more a survival of the fittest, there allways seems to be one heavy favorite. It would be nice if we could create some sort of bi-state where two frequencies were equally ...favorite (?). Would two agc's or two overdrives in parallel with separate eq be a possible way of achieving this? to Utopian Isotope (in dutch it's even a greater word play: utopische isotoop) Because I overdrive a fet I know exactly what it's maximum signal is. That signal that's passed to my power IC is attenuated in such way that the IC never is overdriven. Meaning my IC doesn't produce distortion and never goes over the limit. (also been checked on oscilloscope). My device produces a lot of distortion and power but so far that hasn't harmed my driver. Doing this way it's possible to take the highs out of the distorted signal before the power IC. If the IC gets overdriven there is no way to do this. For some reason my pickup with it's ceramic magnet puts a lot of emphasis on higher harmonics especially on the plain strings. Or maybe it's the maple neck. Too bad... Greetings to you all Fresh Fizz

What you really want/need is a method to convert the pickup signal into driver signal. Something like a computer programme that recalculates per string, per frequency the amplitude and phase shift for the occuring string movement. In fact simulating a pickup that's situated on the driver's position. The best solution would be to have both driver and pickup at the same position. Like Pete has been trying to do. Could it be done with an optical pickup and a magnetic driver? I think that no matter what you'll allways end up with a sine wave. But it would be nice if it was possible to get a different harmonic by changing the way you pick the string. But in my case it's allways the same, 3rd harmonics low, fundamentals high on the fretboard. And I want 2nd harmonics as well! I would like to rely more on another feedback principle: fingers to ears and vice versa. Stick a volume pedal in between pickup and F/R amp. And decide by hearing when the sustainer device has to be set into action. I tried to get fundamentals below the 12th fret. Therefore I used a fet to boost the low. This way I was able to get fundamentals on my wound strings but it made my plain strings sound even thinner by comparison. And it didn't feel right. When playing on my g-string I felt the wound strings shaking insanely. Anyone knows how the commercial guys get good fundamentals on all positions? Is it eq, all-pass filters or is it their trick of trade? Cheers Fresh Fizz

I don't think that the phase issue is a big problem. It can be split up into 3 areas: pickup, driver and electronics. For the driver I allready gave you a way to calculate phase shifting. Here is my document to calculate the phase shift of the driver. For the pickup you could do the same calculations, but it's a waste of time. Any decent pickup well extends the range of 1100 Hz. Unless you have some kind of superdistortion very ugly metal humbucker. What electronics concerns, if the signal is only amplified without any toneshaping (eq) there won't be much phase shift. About Helmholtz: I found this interesting link. I think this and also this links show the real problem to solve to achieve fundamentals below the 12th fret. The java applet shows that the fundamental is around 10 dB weaker than the 3rd harmonic (pickup at some 2" from bridge). So the fundamental cannot compete with the 3rd. I fully agree with you. Something out of control, like driving off a cliff. How about slew rate limiting? 1 , 2, 3 No, it's a prehistoric version the name scope unworthy. I bought it for my at 286 (remember ?). It won't work under Windows. I need to boot if from floppy without the himem.sys and no chance to read my harddisk partitions. Well my sustainer device produces a lot of "dirt" but I think that they are 2 different phenomena: harmonics created by overdriving the fet + clippers and the fizz. I think Col's description of fizz comes very close. No they are in parallel. Mind you, all the trouble to squeeze in an extra cap only to get less fundamentals? Question answered by Setain. I was thinking Pete, have you ever considered of skipping the neck pu. Why don't you use the driver as pickup? What you need then is a noisefree microphone amplifier. And the switching system had to be rock solid of course. You don't want a few volts on your microphone amp. But maybe you want to keep it passive. I think that is what the commercial guys have done. Somebody mentioned a transformer, I think it is a step-up transformer for the driver. But I am not sure I have never seen a sustainiac in my life! Cheers Fresh Fizz

I did some tests with my Handyprobe (oscilloscope on PC). I found out that the appearing wave forms are pretty much sine wave. So even with a lot overdrive the feedback will settle in a more or less sine wave-y tone. I did the test only for fundamental mode. There is no harmonic mode on my guitar. Maybe it is due to the overdrive but I only get 3rd harmonics below the 12th fret position. Above the 12th fret it's all fundamentals. Is that normal? I would have expected positions on the fretboard with a 2nd harmonic. I use a 660u (2 x 330u) output cap. One thing about the fizz. I found out that the fizz is most anoying when you hit the string softly. Then the driver causes some sort of volume swell which sounds very fizzy. Cheers Fresh Fizz

Congratulations, Pete! A triple stacked coil. All pickup makers eat your heart out. utopian isotope, you did some experiments with metal sheets above your driver. If found this at the sustainiac website: 6. Metallized pickguards and guitar bodies. Also, metal pickup trim rings. These conduct electricity. The pulsating magnetic field that comes from the electromagnetic driver will produce pulsating electric currents in the pickguard or guitar body or pickup mounting rings. This will cause the bridge pickup to respond to these currents. The end result is poor sustainer performance. So, you must use a pickguard having no metal in the vicinity of the pickups (or scrape off the conductive shielding from this area). More you find here. Cheers Fresh Fizz

Yes, you're right. I'm only wild guessing. But everybody who is working on this sustainer project has some problem with fizz or grunge. It's the desire to make some progress that makes people come up with all sorts of hypotheses. I don't think this is true. You could experience that an alternative grounding system didn't improve the performance. But what if more conditions have to be met before there is an improvement? It's better to think loud. Maybe some can make good use of it. Or eventually prove I'm wrong. No utopian isotope there is no buffer, my volume pot acts the same as yours. I personally like it this way. By the way it wasn't my intention to draw a complete schematic but only the grounding issues. Fresh Fizz

I hope this makes sense to somebody.

Hi Pete, I'm going to make a drawing of how I think the mass, ground, earthing whatever works best. As soon as it's ready I'll post it. Wouldn't it be best to connect the secondary coil (= neck pickup ?) to the driver coil? (Driver coil and neck pickup in parallel). This can be done because the neck pickup has a much higher impedance. Meaning the load the lm386 sees stays allmost the same. Induction voltages are gone. ( Technically you don't have a transformer anymore, but 2 coils in parallel.) Fresh Fizz

STC is a dummy coil but humbucker style and made out of copper foil. I've put it in between driver and guitar pickup. The idea behind is that it creates some sort of flux shield. I favour an all humbucking configuration: humbucker driver, humbucker pickup, humbucker STC dummy coil. I got rid of the squeal. I'm still hearing some distortion, but I'm not sure it is the same fizz thing you are talking about. It's more that the string resonates with what it receives from the driver. And because I'm using heavy overdrive it's fundamental with a third (down the neck). It's not an unpleasant distortion it has a nice zooming quality. (Zooming as in: What would you rather be or wasp?) When I palm mute the strings and pick I have an undistorted sound (so no distortion on the pick attack). I have to focus now on another problem area which is the low part of the high e-string. If you ask me what the problem with this string is I would say that it has to do with what the guitar pickup makes of the string movement. It looks like there is too little fundamental and 2nd and 3rd harmonics. It looks like the sustainer tries to build feedback on even higher harmonics but for some reason won't make it. And falls back onto those lower harmonics. Sustaining but weak sound. Maybe that's the Helmholtz motion, Col! I have allready tried to change the overdrive character, more even harmonics instead of odd harmonics, but it doesn't make a lot of difference. Well it depends on how much use of the sustainer device you're going to make. I can remember that Les Paul even wanted to have a microphone connected to his guitar. I only have pop noise when I switch on. I'm pretty sure I can fix this. Fresh Fizz

I'm in the mood for being long-winded again. I hope I'm telling something new to you. I kept a present for you at the end of the story! I've told you a few days ago that my sustainer device had a tendency to squeal during the note attack. What I haven't told you is that in harmonic mode the bugger was out of control screaming like an emotional pig. This might well be due to the heavy overdrive in combination with the strong output level. Both my guitar pickup as well as my driver are humbucking devices. So why is there a difference in the amount of squeal between the fundamental and harmonic mode? The only answer I can come up with is the following: I think the easiest way to explain this is make a comparison with guitar pickups. You all know the strat with its 3 single coil pickups which pick up hum easily. There is a way to buck the hum in the combined positions by using a middle single coil pup with a coil that either is been wound or connected the other way around (I don't know which one is clockwise/ counterclockwise) . The middle pup is electrically out of phase with the other pups. But that doesn't mean that the sound is out of phase. That depends on the orientation of the magnets of the pups. Only if the middle pup has a reversed orientation of the magnets the pup combined positions are in phase soundwise. This is like the fundamental mode of the sustainer device. Can we make the strat's combined positions out of phase soundwise by swapping the connections of the middle pickup or by some way inserting a signal inverting amp? Yes we can but we loose the humbucking effect. The only way to create out of phase sound and keep the humbucking effect is to reverse the magnet of the middle pup. The same goes for the sustainer device. If by switching from fundamental to harmonic mode the squealing worsens or improves it means that both configurations are not equal when it comes to bucking the hum. And this works the other way around. If we can reason that there are 2 different configurations there is no point trying to make the bad one as good as the good one. So are there 2 different configurations? I think there are. When we imagine the sustainer driver to the left and the guitar pickup to the right we could have these combinations. S and N: orientation magnet + and -: relative phase of coils What matters is the relationship of the driver coil and pickup coil that are closest to one another. 1. driver_pup SN___SN | |___ | | +-___ +- Electricaly out of phase Good for fundamental mode 2. NS___SN | |___ | | +-___ -+ Electricaly in phase Bad 3. SN___SN | |___ | | +-___ -+ Electricaly in phase Bad 4. NS___SN | |___ | | +-___ +- Electricaly out of phase Good for harmonic mode The best quiet configurations are 1 and 4, to go from 1 to 4 you need to reverse magnet! This could be the reason why the commercial sustainers use a split coil for the driver. But there is an even bigger gain by using a split coil. Because of symmetry of magnetic field created by the split coils there is a lot less inductive crosstalk induced in the guitar pup. Utopian Isotope introduced the dummy coil. I haven't tested that one but most likely it works that well because it works in an out of phase condition. I wanted to take this dummy coil thing a step further and therefore I present to you the Siamese Twin Coil . See schematic. (The circuitry still needs to be improved.) I have no problems with squeal anymore! Maybe worth trying. Bye Fresh Fizz

It looks like these tests can give us a new perspective of how to fight the fizz. Maybe a breakthrough? The dummy coil was indeed an eye-opener to me. Thanks utopian iso! So the capacitive forces are against us too. inductive emi is more likely to happen (high currents). capacitive emi is more likely to occur with high voltages. This could be the case with Pete's flat driver on top of the neck pup, where the neck pup produces high voltages. The bad thing with guitars is that everything is so high impedance there could be a problem with capacitive emi. Have you done or could you do these tests under the following conditions: 1. sheet not earthed 2. sheet earthed at guitar cable 3. sheet earthed somewhere more down the line like earth connection of wall plug, preamp to avoid currents through the guitar cable I'm looking forward to hear the results from you Cheers Fresh Fizz

I'm amazed how rich this thread is. There are so many ideas going on at the same time! You could call ourselves the sustainer think tank. Which means you're creating a second trafo-like coupling, just like your flat driver/ neck pup. This could mean more unwanted side effects. My problem is that I'm still catching up with you guys. Maybe I shouldn't have mentioned it already. My sustainer device is still suffering from diseases that you have already solved. Like optimalizing signal levels, eq, amount of overdrive/compression to fight the fizz and squeal. But I have the idea that this might be a way to address the shared earth problem. In your guitar the sustainer device is earthed means the guitarcable. But what if there is a slight resistance (because of connectors). Let's say that resistance is 0,2 ohm. It means that there will be some of the sustainer device's output voltage on that resistance. V_on resistor = V_sustainer * 0,2 / 8,2 You could say that 0,2 / 8,2 is feeded back to the guitar pickup (same earth). The sustainer device has an overall amplification that might well exceed 8,2 / 0,2 times. So there is allways a concern for oscillation/instability. Because of phase shifting of the combination of driver coil and zobel network there allways will be frequencies where the phase shifting (driver output to pup input) is not exactly 180 degrees. With the 100 ohm resistor I use the feedback is 0,2 / 108,2 The idea is that the cable of my sustainer device's power supply will serve as connection to earth. So from the power supply goes a connection to the earth of my guitar preamp. At this point it's not working this way because my adapter is not earthed. But even so it should improve the problem with the shared earth. Technically the sustainer device's ground is floating from earth but the efffect should be minimal. I remember, Pete, where you said that you got squeal when the strings touched the core of your flat driver. I think it has to do with this shared earth phenomenon. Core 's connected to earth together with eddy currents. I remember spazzyone with the outboard amp who said not to experience any big troubles with fizz. I'm a compressor junk, I don't loose a lot of volume. To me it's a very natural thing that by adjusting the volume you get more sustain. Just the same like when people use their volume pot to get more overdrive of their amp. Reason? Maybe the same why people stick safety pins in their nose. Trying to be different. In 8 ohms I should be able to get 1,8W. But I settle for about 1,2 W. I have outboard power so consumption is not a big deal. In understand that the combination of having lots of compression/overdrive and lots of output power could be too much but I was a bit concerned that my driver with the slim blades wouldn't be that strong. Better to start with too much than with too little! It prooved to be very strong. When my high e string wasn't yet at right pitch the feedback made it almost to woodpecker itself into the fretboard. Another advantage of the ic is that one side of the dil package is connected to ground. So I can use a ic socket with a peace of tin soldered onto it. It makes a perfect heat sink. I sticked my sine wave generator to it and let it run full blast for a few minutes. Kept it pretty cool. The specs talk about soft overdrive characteristics. Tubey? Pete thanks for the advice given. I'm sure that I can use some of the ideas you mentioned. More food for thought Enough said greetings, Fizz

Yes, I think it has to do with the dynamics of the sound. During the attack there is a tendency to squeal. Because the fundamental is masked by all those higher harmonics string feedback doesn't happen immediately. Only after the attack the string feedback starts to build. If you mean the fast decay of higher frequencies (attack) I'm your man. I have holding back some valuable information. I use a treble booster inside my guitar (1 fet, 16 dB high boost). It serves as input signal for my sustainer. It's only after the overdrive I cut the high but overall there is still high mid boost. On my guitar there are no extra controls for the sustainer device. There is only a 6,3 mm female connector for the 12V power supply. I have 2 grounds (?) one for the pickup ,treble booster, guitar cable and another one for the sustainer device. Both are interconnected through a 100 ohm resistor. My volume pot serves as sustainer drive controll as wel. Cheap My driver is a humbucker with 2 blades, it looks a bit like those dual rails pickups. The overall impression I have of the driver is that it's good higher up the neck sustaining with a fat sounding fundamental but a bit thinnish lower on the neck. And that is almost the same on all 6 strings. Maybe a peculiarity of my driver? It could well be that I use too much gain. When I set the drive lower there is still good sustain. Some tweaking is going to happen. I'll try to get rid of the overall high boost. Fizz

Nope. A single humbucker Seymour Duncan TB5 at the bridge position of my stratocaster. The sustainer circuitry fits in the middle pup hole position. I use a frankenstein pickguard. It's been cut in 2 pieces. So we have one piece with driver and pup fitted in and a part to fit in the controls. This way it's possible to open the guitar without removing strings all the time. I only had to add to screws for the part below, that makes 13, but we're not superstitious (?). It's a way of keeping the voltage at the cap at 4,5 volt. The driver's load is 8 ohm so the 2 resistors (4700 ohm) won't have that much effect on the working of the ic. I suppose that you have a main power on/off switch to which the voltage divider can be connected besides a switch that only switches off the f/r. But to be honest I don't know if this addresses the problem. With the testing I did I only experienced problems when switching on my sustainer circuit. (Pfffeeewww in dutch, don't know in english) Switching off seemed to be quiet. So I am back om my feets again. It's a lot easier to do the theoretical blaba than to really get a sustainer system to work and be really satisfied with it. The good thing is that I've got the sustainer working. I'm using an overdrive (fet with diode clipping) into a tda7231a chip. It has tremendous overdrive and power and I get good sustain on all of my strings and all positions. At this moment I'm only using the fundamental mode which is free of squeal. The bad thing? FIZZ!!!!!!!! After closer investigation I came to following conclusions. Maybe you could tell me if you share my opinion, Pete and Col. 1. When I say that there is no squeal I notice that there is sensitivity point, a specific frequency band, where the system would like to sqeal if it only had enough energy/volts/whatever to feedback. When I listen through a compressor in front of a distortion/overdrive into headphones I imagine I can hear that frequency band in the background. When I switch off the sustainer it's gone. When I hit a low note on the low e string it seems to waken up this monster. Like it's thinking: "finally enough energy". But there's not. So it's like a short colorization of the sound (emphasizing that particular frequency band) and then going into string feedback. This is a very unpleasant sound effect (not musical sounding) 2. Crosstalk of harmonics generated by the overdrive. This is something I can live with because it doesn't sound unmusical. Surely I will try to diminish this effect as much as possible but it's like balancing off efficiency and sound quality. I'm thinking of what is the next best step Cheers The Good Fizz