col

why? Because of magnetic permeability. Say, neodymium magnets have low permeability, but high coercivity. In other words, if you compare the inductance of the same coil, wound on a neodymium magnet and a piece of nail of the same size, there will be a huge difference. Yes, however once you get above one or two mH inductance, you start to kill the high frequency response, and the driver can't drive the higher string/fret combos. (impedance due to inductive reactance rises with the inductance) inductances that are too high to be usable are possible without high permiability cores. (It is possible (I think - still to try), to use a combination of two or more coils with different properties combined with some passive impedance balancing LCR networks, to get some success with slightly higher inductances, but they are still well within the realm of what is possible with an air core. I am looking at a 6 string 6mH coil combined with a 3 string 1.2mH coil. The impedance is nearly the same from 82Hz through to 1200Hz with acceptable phase distortion throughout that range. The idea is that the 6mH coil will get more current at low frequencies while the 1.2mH coil gets more (~65%) of the current at higher frequencies. The 6mH coil has more magnetic pull, but it's response falls off rapidly after about 300Hz. The 1.2 mH coil is tweaked to provide good drive from 300Hz to 1200Hz, and due to its smaller size will drive the strings above it harder than if it had to drive all six. So if I can get the practical stuff to work, this is my next attempt at getting more magnetic power from the same current without compromising the high frequencies.) cheers Col

why? I can see some point in this, however it is not possible to 'correct' the physical phase difference between driver and pickup - the only way to preserver the true vibration of a guitar string is to have the pickup and driver in the same place (eg. optical pickup / magnetic driver). The reason for this is that when a string is picked, two 'kinks' move lengthwise in opposite directions on the string - 'correcting' the phase difference for one kink will increase the phase difference of the other. With a well designed circuit/driver system, any other phase distortion should be low enough to be acceptable. (It is true that - as mr McSpank has stated - a guitar sound morphs into something like a sine wave. However, the initial part of the sound, which is what gives the sound it's character, will be altered by a 'standard' sustainer... even with the driver and pickup in the same place, there will be problems. A guitar string vibrates in 2D (up/down and left/right), the sustainer has to overcome this natural vibration and force an up/down 1D movement. This effect is also likely to have an impact on the sound of the note's 'attack') Piezo is an ideal way of reducing/removing some of the unwanted noise that might be introduced by a magnetic pickup/driver based system. Unfortunately, a piezo pickup ain't going to give you a truely authentic vintage wailing guitar sound. (even with fancy digital modelling IMO). I'm not so sure about the value of a finger mounted driver. A sustainer is VERY sensitive to the distance between driver and string (the pull of the magnet is inversely proportional to the square of the distance). That's why the ebow has a setup whereby the strings either side of the sustained one are used to position and guide the driver. cheers Col

Here's your reason: If you have 8ohms of 0.2mm wire wound around a steel or iron core, the inductance will be considreably more than the same 8ohm of 0.2mm wire wound around a ceramic magnet - about 60% more in my experience with the steel I use for cores, YMMV. Using 60% as a example, that means that if your steel cored driver had 120 turns of 0.2mm, your magnet cored one would need about 150 turns to have the same inductance (instead of 0.2mm you would probably use 0.23 to get a similar DC resistance). A few calculations show that the magnetic pull of the *same* coil without a steel core will in this case be 20% less that with the core. The extra 30 turns fixes the disparity. The reality may be a little bit away from this ( a few turns one way or the other depending on the non linearity of the core material, and the quality of the winding), it also depends on the dimensions the core and the type of metal - so the only really sure way is to measure the inductance, then wind to match it with a thicker gauge of wire. cheers Col

a sustainer driver is nothing more than a electro magnet you need iron pole peices to make it work. thats about all the help i can give you. That is nonsense ! A sustainer can only work if there is a reasonably strong permanent magnetic field (try it without if you don't believe me). Also, you don't actually need iron or steel core at all - just a permanent magnet and a coil. However, a coil with a good core can have more power with the same number of turns - or the same power with fewer turns. Some reasons why a permanent magnet is needed: reason #1 The field developed by the electromagnet is weak, so it can't generate enough power to align enough of the the magnetic domains in the steel of the strings. The permanent magnetic field aligns far more of the magnetic domains in the strings so the strings become far more sensitive to the pull of the tiny electro-magnet reason #2 Without permanent magnetic field that is much stronger then the electromagnet, the alternating current in the driver coil would cause the magnetic field to have its polarity reversed every cycle. This would mean breaking down and re-forming the domains in the string and also destroying and reforming the drivers magnetic field - both things take mucho energy and time. Having a permanent magnetic field means that all the sustainer does is alternate between a bit more pull than the permanent magnet alone, and a bit less pull than the permanent magnet alone. No destroying and reforming of magnetic domains or fields is required One of the tricky parts of designing a sustainer driver is getting the permanent magnet just right. To weak, and not enough of the domains in the strings will be aligned, too strong and there will be too much pull on the strings affecting tone - above a certain point, where most of the domains are already aligned, adding more permanent magnet force will not help, only hinder. @ al S, I can't see any reason why rare earth magnets wouldn't work. As long as the field at the strings is not too strong or too weak and the domains are aligned in the correct orientation. cheers Col

If you were correct, then humbucker pickups wouldn't work, or would have a low powered response. Instead, they are the ultimate for anyone wanting a high powered output - the only passive pickups that can cause an amp to break up a bit without a booster of some sort.... Maybe, but every indication is that there has been little research or knowledge yet about the requirements of such an undertaking... It's still for him to say not you ! He has asked for help, I - among others - have provided him with information. For you to come in and state that the information presented is too difficult or technical for him is extremely patronizing. ...... Please don't take this the wrong way Pete, but this isn't the old 'Sustainer ideas' thread, and huge posts that contain very little of relevance to the thread don't help anyone. cheers Col

I think it's for the OP to decide what's too technical for him ? I was slightly wrong with my explanation, but didn't have time to edit. The width between cores of my old dual driver was the same as with a humbucker - dictated by the magnet. The difference is that the humbucker has much deeper cores, so the overall distance the flux has to travel is considerably more, spreading out the flux over a bigger area reduces its density, and therefore the field strength. The extra core mass may also contribute to eddy current losses. They are correct as far as I understand for Magneto Motive force. Whether they provide a more efficient pull on the guitar strings will depend on the physical design and layout of the driver. Personally, I feel that it might be possible to get a better than 40% improvement over a simple single coil driver, but not without a lot of R&D, and maybe access to a gauss meter (a not so simple single coil driver on the other hand could be better than a simple one - I've posted about that before). cheers Col

Can't EDIT previous message, so here what I was going to add: EDIT: the basic idea is that magnetomotive force (proportional to field strength) is I x N (current times number of turns). So two coils set up so each has twice the desired overall inductance and resistance should give roughly (not taking into accoulnt that they will interfere with each other somewhat depending on how closely mounted they are): if 1 core at 1mH takes 120 turns, then a 2mH coil will be 170 turns (in this hypothetical case, we would choose wire so that 170 turns gives 16 ohm or as close as possible) Lets say we had 100mA going through our single core 120 turn driver, that would be 12 ampereTurns of magneto motive force. now with two coils of 170 turns, each with 50mA we get 17 ampereTurns. So we get an increase in magneto motive force of just over 40% Now, it is important to remember that the field strength is the magneto motive force divided by the 'effective path length'. This means that for a given magnetoMotiveForce, the further the flux has to travel, the weaker the field will be. I think the best approach with this in mind is compact coils (another point for you Pete ). It also helps if we have core material everywhere but at the strings, as the field will build up in the 'air gap'. I guess this is why my old dual core driver worked well. It also explains (one of the reasons) why my more recent driver built using standard humbucker bobbins wasn't so good - too big, with too big a gap between cores. So to reiterate, I'm going to build a compact driver with two 16ohm cores wired in parallel, aiming at a combined inductance of around 1.2mH. This worked out at 0.18 or 0.19 wire being the closest to optimal. I'll fiddle with core specs to fine tune the inductance. cheers Col

Not true! If people go only on the number of turns, then they must use exactly the same dimensions of core made of exactly the same material to get the same result as a driver they are copying. e.g. A 52mm 2mm thick core wound to 8ohm with wire with very thin enamel will have about 136 turns A 56mm 4mm thick core wound to 8ohm with wire with thicker enamel will have about 122 turns if the 136 turn is optimal - for this hypothetical example lets say that's 1mH, then the other will be underpowered by 20% at 0.8mH Can you see that that is significant (and probably more than you would expect from the slight changes in specs. Now that difference may be offset by the extra mass in the 4mm core, but then there would also be significantly more losses due to eddy currents in the larger core - and the core material would come into the equation. In the end, the only way to be sure is to get the DC resistance AND the inductance right. String gauge is only one factor in achieving that goal. (It would be better to match the inductance exactly and have the DC resistance vary somewhat - anything form 7ohm to 9 ohm should be fine) It is simple, but very inaccurate. That conclusion doesn't take into account how the effectivness of a driver depends also on the path length of the magnetic circuit and the flux density at the strings. All these things could easily conspire to give you similar result from different core specs. Without measurements and data, drawing the conclusion that core specs don't matter while string gauge does is silly. Misinformation is when someone provides information that is false an that may in some way make things more difficult for the recipient of the information. One such example is saying that only DC resistance and wire gauge are important, and the the rest can be ignored. All that might be true IF The system that was presented and has been recommended was a complete system. Unfortunately, the driver is only part of the system, and your driver specs are only optimized for the rest of your system which AFAIK has always been secret ? If someone provides a complete design with exact specs - including stuff like core materials, wire manufacturer and type and (significantly) circuit diagram with parts list, then it can be cloned be someone else without needing knowledge and calculations. Otherwise, knowledge is needed for success. Unless folks are willing to go through months of trial and error spending loads of money in the process. So, if you aren't willing to give folks the design for your complete system, you should probably keep quiet about it unless you are willing to accept that they will need the knowledge required to tweak the driver to match the rest of their system (which is unlikely to be the same as your secret one) No need for complexities of inductance, just a cheap inductance meter would do. No more difficult than measuring resistance. In fact, it would be really useful if you would measure the inductance of your driver as that would give folks a target to aim for. Yes, its an interesting path. I have been tinkering with this approach for a while. At the moment I'm waiting for Maplin to get 0.19 wire back in stock. then I'm going to wind two 16ohm coils and wire them in parallel. this will give 8ohm DC, and the combined inducance will be roughly 1.2mH. The current through each coil will be half, but the magneto motive force (therefore field strength) should be plenty more then double, so should provide a more powerful magnet while still preserving the correct input impedance.... Theres a big post about the idea lost somewhere in the old ideas thread. cheers Col

The important factors are DC resistance and Inductance. The number of turns is the most crucial factor in getting the correct inductance, followed by core specs. The 'correct' wire gauge is just a by-product of this. It has been demonstrated that it is not difficult to use the 'correct' wire guage and wind to 8ohm and still get a driver that doesn't work well. This isn't just down to bad construction or luck. It's also down to the fact that inductance and flux density at the strings are the important factors for drive (DC resistance is important for optimum power amp performance). Using the 'correct' wire will give people a better chance of succeeding, but unfortunately they can still follow your instructions and fail. I'm not saying that folks shouldn't use the 'correct' wire, or that they will make a great sustainer if they understand about inductance. However, the more people know and understand about how the thing actually works and about what is actually important and why, then the more chance they will have to get a result, or at least work out why they didn't get a result. Spreading misinformation like "don't worry about turns" is just unhelpful. better to say something like: "if you don't have access to an inductance meter, you should get *roughly* the correct inductance by sticking to 0.2 or 0.23 wire - be prepared to try different core materials" cheers Col

No, its wrong. You are correct that roughly 34 turns of 0.1 will give you an 8ohm DC resistance. The problem is that the fewer turns you have, the weaker the magnetic force of the driver will be, and unfortunately, this is not linear with number of turns. If 300 turns gives an inductance of 2mH (miliHenries) then 34 turns will give you (2 /sqrt((300^2)) * (34^2)) which is 0.026mH - 100 times weaker !!! if you are using an 8ohm single coil drive with an LM386, then you want roughly 1 - 1.2 mH. any less means not enough drive. any more means fizz and distortion will become more likely, and high frequency response will get worse. What you discribe suggests that your coil is not 'potted' properly, so some of the windings are vibrating. This is BAD. it is important to make sure that all the windings in the coil are solidly held together with some sort of glue, and that the bobbins and magnet are also held firm. Otherwise you will get vibrations that can cause various problems, and will reduce the efficiency of the driver. What FFs suggestion would do is to use a doubled strand of 0.1 wire as though it were a single strand of 0.15 wire. To get it to behave like 0.2 wire, it would need to be a 'quad' stranded approach. There is another way you could try to use 0.1 wire. You could try making 4 separate coils each of 32ohms (~120 turns). Then wire them in parallel. This is nothing like optimal, but you will be left with an 8ohm dc resistance, and the inductance will be maybe 0.3mH. Not ideal, but a lot better than what you would get with a single coil driver. You will also get a much better performance with this than if you used a single coil 0.3mH driver! The min difficulty (apart from having to construct four good coils) is to get them all wired up correctly so that they are in parallel and the magnetic fields are all in the correct orientation. My advice would be to get some 0.2 or 0.23 wire and make a single coil with 120 - 150 turns. When you have that working, try other stuff. cheers Col

A little addition explaining why 300 turns of 0.1 wire is over 70ohms to start with lets state that 125 turns of 0.2mm wire around a 55mm core is 8ohm (this is roughly correct) Firstly the wire: 0.1mm wire is not (as may seem intuitive to some) half the size of 0.2mm wire. This important thing is how much copper there is per unit length of wire - this is proportional to the area of the cross section of the wire. Assuming the cross section is a circle. The formula for area of circle is PI * radius squared So half the size of 0.2mm wire would be sqrt( (0.2^2)/2 ) = ~0.14. So in reality, the nearest guage to 'half' of 0.2mm is 0.15mm not 0.1mm ( ^ means 'to the power of', so 0.2^2 is the same as 0.2squared) 0.2mm wire is actually 4 times the size of 0.1mm wire ! this means that 0.1mm wire has 4 times the resistance of 0.2mm wire (for the same length of wire) ( 0.1^2 / 0.2^2 = 4) Secondly the turns: 300 is 2.4 times the 125 turns from the 0.2mm driver. so lets take our original 8ohms and multiply it in turn by the turns ratio and by the wire guage ratio. 8 * 2.4 = 19.2 (so even using 0.2 wire, 300 turns bumps the resistance to 19.2 which is already too much for an LM386) 19.2 * 4 (wire gauge ratio) = 76.8 These results closely match the results you get inputting these coil specs into the Ziegler pickup calculator So although it seems initially that there shouldn't be much difference between '125 turns of 0.2mm' and '300 turns of 0.1mm', the difference is actually very significant. cheers Col

The buffer is there for a reason. If you don't have a buffer, the low input impedance of a LM386 based amp iwl 'suck tone' from the output. The fetzer/ruby is not ideal for a sustainer as it was designed as an amp to give a warm valvy tone, not to provide optimum buffering and drive for a sustainer, there should be no squeal. the harmonic mode should work without moving the driver closer to the pickup. The gain of the amp is not really relevant. what matters is how much current it can supply before distortion sets in (over the frequencies we are interested in). The LM386 is designed to feed into an 8ohm load. that's roughly 150 turns of 2.0mm - 2.3mm wire. if you get much lower than 8ohms (e.g. 6 or less) you will get distortion and overheating. if you get much more than 8ohms (e.g. 12 or more) you will get a lot of distortion if you are pushing the amp near it's limits. unfortunately - assuming you are using a core about 55mm long and a few mm wide - 300 turns of 0.1mm wire gives a dc resistance of ove 70ohms. Thats WAY to high. It's important that you ignore the folks here who are suggesting that lots of coils will work, and that it doesn't really matter what wire or core you use - that is ignorant misinformation from people who don't understand what's going on. Different wire will work, but only in a configuration that is carefully designed and in which that particular wire gauge is optimal. For a 55mm long core in a single core driver being driven by an LM386, a good starting point is 0.2mm or 0.23mm wire, and wind it until its DC resistance is about 8 ohms. you NEED a DMM (digital multi-meter) for this. It should work out at about 150 turns. If you decide to use a bi-lateral or a bi-longitudinal multiple coil conficuration, then you might need to use a thinner wire guage - I think for bi-longitudinal 0.18mm is about optimum. 0.15 may be too thin (I'm going to find out soon though) If you have a more powerful camp/circuit that can handle a wider range of output loads without distortion, then you could go with more turns of a heavier guage - say 0.28mm or 0.31mm. do remember that there is a significant difference between even 0.2 and 0.25 wire. so going from 0.2 to 0.1 is an enormous difference. cheers Col

Great clip the AGC really does make a huge difference - gives that otherworldly quality to the effect. plus lovely clean tones. can you refresh my memory about your driver specs and what power source you are using. cheers Col

Yes, that would be a good approach. That's certainly what I did, and obviously what elmo7sharp9 also did (hehe).

The irony is painful to my sides... You're defending your point about many different coils working and attacking me for suggesting that beginners should follow known existing designs. Then to back up your point, you describe and provide a link to your sustainer which turns out to be an almost exact copy of one of Pete's old driver designs. In addition, your sound clip is heavily distorted - show me a driver design with significantly different specs from the ones in the old thread, and provide clips demonstrating it's ability to provide strong CLEAN sustain - then you will have my attention

There's no need for you to defend your sustainer or the philosophy behind it. If you read my post more carefully, you would realize that I was referring not to your own personal driver (which I'm sure is excellent), but to the advice you were giving to the OP. You were suggesting he selected core materials based on arbitrary factors not directly related to sustainer functionality. You might also note that I am suggesting that people without the technical knowledge and equipment should base their driver as closely as possible on a 'known to work' existing design. I gave Pete's as an example, but if you were to post evidence of the success of your own design, and post the specifications, then my recommendation is equally applicable to your driver. As far as the LM386, everyone knows its not great - I listed a bunch of limitations in the thread. No-one is 'loyal' to it. However, there are very few proven existing designs out there with circuit diagrams and evidence of successful functionality that are publicly available. Some of the few that are available use the LM386, so when I see inaccurate vague advice about driver materials, and then in the same post the LM386 is being described as 'underpowered', it make sense to set the record straight. Btw, isn't it annoying when people spatter their posts with bold type. IT'S EVEN WORSE THAN SHOUTING cheers Col

So if you play a chord and let it ring, it sounds like you have a Ebow on all six strings? Or does it sound like an amp that is feeding back? I'll assume that it's working on the principle of electro-magnetic feedback since there is no speaker involved. I think his point is that there are still 2 ways it could be feeding back: #1 the good way: the driver generates a magnetic field that excites the string, the pickup senses the vibrations of the string. (sounds like ebow) #2 the bad way: the driver generates a magnetic field that is directly sensed by the pickup, bypassing the strings.(sounds like squealing feedback) cheers Col

The same number of turns of the same wire around a soft steel or iron core will give a different coil inductance when compared with using alnico pole pieces as the core. For this to work well, you need two thing in your driver: #1 enough permanent magnetism to align the magnetic moments in the string. #2 impedance and inductance values that are tailored for your driver circuit and for the frequency range you want the driver to operate effectively over. the choice of core material is an important variable in setting the inductance. Just arbitrarily choosing alnico and iron because one is 'cheaper' or one is a 'standard part' is completely missing the point. Those folks that don't understand this or don't have the equipment to measure inductance would be best to clone a 'known to work' driver as closely as possible - not to use arbitrary materials for reasons that are not relevant to the functionality of the device. That's the route to follow, if you have the time to spare That's the route to follow from the get go. going another way is just postponing the enevitable. Unless people are going to use phantom power (I already mentioned that), then they will have to at some point build a driver that is as close to optimal as is possible within their means. Or else they will be unhappy with the results they get. The closer they get on their first attempt, the better. Fair enough, it would be silly to start playing with AGC before getting a basic design up and running. However if the driver is designed carefully, or based (very closely) on an existing good design then 'tweaking' (whatever that means) should not be necessary. Similarly, preset Phase-shift (whatever that is) is unnecessary if the driver and circuit are properly designed. Alternatively, apply a little more clean power and get something that works first-time with a wide range of coils (Which is the result most first-timers are after). IMO, if you want battery powered (like me and many others) you go with a PP3 - that's the standard, and it's certainly achievable. If you're going phantom powered or umbilical, jack up the watts and use a driver with a lower inductance and a higher impedance - that way you can more easily avoid choking on the higher frequencies due to the effect of the inductive reactance. Personally, I feel that the sustainer effect doesn't add enough 'value' to a guitar to warrant the extra inconvenience of phantom power or umbilical. Col

Yep that's the one just wired everything like normal used little jumpers from the source pickup signal on the guitar's switch and one to the casing for ground and the driver i connected to the speaker - and + Think about that for a minute - 2.5 watts Now, even assuming the amp and circuit are 100% efficient (in reality it will be more like 50%) to run at 2.5 watts, it would need to draw a steady 220mA from a 9 volt battery - that's way too much. the mAh rating of alkalines drops dramatically as the power drain rises, running AT 220mA, yo probably won't get an hour out of a battery before the voltage drops to an unusable level. e.g. a graph on the everready alkaline pp3 datasheet shows that the batter provides around 450mAh with a steady drain of 100mA so you get about 4.5 hours, when the drain is 300, you're only getting about 280 mAh from the same battery, so less than an hour. Unfortunately these figures are for draining the battery until it reaches 4.8 volts which is way too low to be useful for a sustainer - assuming you want a nice clean steady signal. More likely is that the marketing for that amp module is bogus. The chip is capable of around 2 Watts, but will be set up for much less ? Probably fine for sustainer as long as you don't max it out for long stretches (unless you want lots of fuzzy sound and a flat battery Of course, switching over to phantom power would dodge this issue (and introduce others) cheers Col

A soft iron or steel core is by no means the best for rapid changes of flux there is a lot of hysteresis with iron particularly, that said, it is perfectly adequate for a sustainer driver. To suggest that iron is best then say alnico is ideal is odd considering there is no iron at all in alnico. As its name suggests, alnico is primarily aluminium, nickel and cobalt. not necessarily cheaper, and definitely more bulky, but it will make it easier to get the inductance of the magnet up to a suitable level. You are correct about using pickup wire. Unfortunately the rest is a bit more complicated. There is quite a big difference between using 0.2 and 0.3 wire when making a sustainer. They can both be used, but the design of the driver will be different in each case. If you are going to move away from Pete's basic design (0.2mm wire wound up to around 8ohm resistance) then you will need to develop a good understanding of these things: resistance vs inductive reactance inductance and how it relates to inductive reactance how inductance affects phase response. Pete got around his limited knowledge of these things by using an lengthy iterative experimental approach, and arrived at one of the 'sweet spots'. If you don't want to spent hundreds of hour and lots of money, then you either need to follow his design (or one of the other tested designs) very carefully e.g. 0.2 wire MEANS 0.2 not 0.3 or 0.15, or know (or learn) a lot of complicated stuff about how magnets and electromagnets work. Ideally you need some test equipment as well. So long as your capacitors are healthy and the correct values, I wouldn't worry too much about the material they're made of. This is not an audiophile-grade application. very true. In the original sustainer thread, I vaguely remember some discussion about using tantalum caps. I think this was purely relating to size rather than functionality. If you find the LM386 to be 'under powered' then your driver and or other parts of you circuit are sub-optimal and you should look there for some more performance. There are certainly problem with the LM386 - it's distortion characteristics are poor, so the circuit need some careful design to eliminate nasty grunge and fizz, but lacking power is not an issue - it's possible to get some of the strings rattling off the frets with an LM386, and even the 'difficult' B and E strings can be driven well with an LM386. I advise you to obtain some wire, wind some coils, build some circuits and come back here with your findings. heh - good advice cheers Col

Hmm, one thing this thread does seem to do is encourage people to keep on repeating the same old same old... they get stuck in a feedback loop . Ideally for the best chance of success, we'd need three things not one. we need to try out ideas and develop them iteratively, we need to collect data, and we need an understanding of the physics in order that we can use the data to inform the iterative development. To say that technical data is the one and only is is no better than to say trial and error is best or that you only need theory. ---------------------------- At one point, I offered to write up a document with all the most up-to-date knowledge that we had if folk were interested. Not a single person was interested, IIRC no-one even responded to the post. The vast majority of people can't get past the idea that there is something called impedance that's different from resistance - its too difficult. What folk want is a ready to go design that's easy to build and doesn't require difficult to get parts or intermediate/advanced tech (e.g. SMD, PIC). Unfortunately, that and a high quality sustainer are mutually exclusive - 'end of'. If you are looking through the thread for technical data, you are wasting your time. If you want a better understanding of sustainers and are able to wade through all the masses of crap, then it _might_ just be worth while. (but you knew all that before you posted anyway ;p cheers Col

But if the that higher impedance is because of more coil turns, then ok, there'll be less 'drive' (i'm figuring you're meaning current), but all other things being equal the ampere turns will remain the same - therefore same amount of flux force at the strings? (the question mark is because I'm theorizing here!) I've been through this discussion with myself more than once. Unfortunately, It doesn't work that way. And equally unfortunately, its not simple I'll try to remember some of the details. # more coil turns means not only more inductive reactance, but more DC resistance - to counteract this effect, you can use chunkier wire, but there are practical limits to how chunky the wire can get. # As the impedance rises with coil turns, the efficiency and distortion characteristics of our basic optimized for 8ohm power amps falls away. (can we design a power stage that is better suited for driving a higher impedance load?) # the inductance and therefor inductive reactance of a coil increases with the square of the number of turns whereas MMF rises linearly with the number of turns. So for a single coil, there is a point as you add turns where the loss through increased reactance is more than the gain through increased flux. Where this point is depends on your desired highest frequency. # When there are multiple coils, it gets too difficult for me . If you could disregard magnetic coupling between the coils, you could say 5 coils has 5 times the inductance of 1 coil, but that's not going to be the reality... its probably a case of trial and measurement... as you add more coils, and pack them tighter, the coupling is going to increase, as are the limitations on the wire guage imposed by physical space restrictions... Glad to hear you're still working on this. I've been taking a break. Too many other things on just now, and I've not been playing my electric at all, so the motivation to keep working on the sustainer is pretty low. I've not given up though! cheers Col

This is probably just down to your multimeter. Unless its a very high spec unit, its accuracy down near 1ohm is unlikely to be good. You've done the right thing by connecting a few together and testing that. 5 coils in series will have 5 times the inductance of 1 coil. This meas that as the frequencies get into the hundreds of Hz, the impedance rises very quickly to the point where you won't get any useful drive. Unless you have all the specifications for the material you are using for the driver core, and have a degree in physics and maths, the only way you are going to get a remotely accurate figure for the inductance of your coil is to measure it with an inductance meter! Main things to remember if you are trying to understand how it all fits together: It's impedance that matters rather than resistance DC resistance makes up part of the impedance. The rest is a combination of capacitive reactance (mostly from the output coupling cap) and inductive reactance which comes from the driver coil. To calculate these, you will need to know your complex number arithmetic. Or else, use a meter and an online calculator. Inductance is very important: As impedance rises, the magnet gets stronger, but the frequency response gets worse quickly the ideal driver coil will have an inductance as high as it can be while still presenting an impedance that the amp can handle at the highest frequency your design intends to sustain. Current through the wire is equally important: The more current through the coil the better. In general, the higher the impedance at the output of the amp, the less current it will give you. Ideally your amp will be able to drive very low impedance loads very efficiently, allowing you to maximise the current. An LM386 doesn't seem to handle variation in output impedance very well at all hence all the talk about it being a horrible chip. If you can keep the output impedance at or very near to 8ohm, it will be fine. much higher and you get lots of distortion much lower and the efficiency of the amp decreases a lot. If you are not going to just make a driver based on Petes design, you will have to either bite the bullet and buy an inductance meter, then get to grips with the basic math and physics of coils, or be willing to spend hundreds of hours making many many iterations of coils and circuits as you try to home in on a suitable spec. OR just get really lucky. Good luck Col

Ignoring for now the 'EDIT' info, lets say each coil did have resistance of 8ohm and inductance of 1mH. Your series/parallel wiring will give an overall DC resistance of roughly 8ohm and an overall inductance of roughly 1mH => 1 / (1/7 + 1/3 + 1/2) = 1.02439. So not only will the DC resistance be the same, the impedance will also be roughly the same at different frequencies. Unfortunately, it still probably won't do what you are expecting. The problem that is still there is that the strength of the field that the coils will generate depends on the current through the wire. The three parallel branches each have a different dc resistance (7 in series is 56 0hm, 3 in series is 24ohm and 2 is 16 ohm) so each branch will get a different amount of current. Eg. each of the seven coils will get less than a third (0.286) as much current as goes through each of the set of two series coils. For this to work out in a practical system, you would need some very clever layout to take this disparity into account. This doesn't mean you shouldn't use combinations of series and parallel - just that it's going to be much easier if you ensure that the parallel branches are all equal. cheers Col

We hear logarithmically, but the magnetic pull of the driver varies linearly with current (I'm pretty sure this is correct) so the string 'hears' the driver linearly (and the pickup hears the string linearly). That meant that for 'grabbing' the string, linear control would be better IMO As far as linearising the jfet, its possible to fully linearize it an lose much dynamic range, or linearise it a little and lose a little of the range. Getting the compromise right between linearisation, dynamic range, response time and low frequency distortion is the real trick, but assuming the output amp is good enough, I think that a jfet can do the job. It might take two jfets to get closer to an ideal system, but its certainly not an unnatainable target. cheers Col