Hank McSpank

Unfortunately, within an active preamp scenario, you can't apply the same rule. The preamp buffers the piezos and to all intents & purposes converts their (very) high impedance characteristic to an output signal that has a low impedance. It's not clear where you are thinking of changing the pot? As Elmo says, we'd have to see the specific circuit you're talking about to see where the pot lays in the overall signal path, but in all likeliehood, within an active preamp circuit you'd not hear a whole lot of difference between using a 25K pot and a 250k pot.

Syn ...a preamp typically doesn't power a speaker ...a preamp normally feeds into a power amp which then feeds the speaker. An example is an LM386 - that's a power amp (albeit a small one @circa 1W !) ...it can connect to a speaker (or in this case, a sustainer driver coil). A preamp is normally used, because without one, the characteristics of a power amp chip will (normally) load your guitar's pickup ....making your guitar sound awful. Do you mean coil dimensions? Well, I've made (lots of) them tall, squat, slim, wide.....I've tested each one of them extensively (with proper test kit) ......so long as there's not an outrageous difference in the driver's basic config (number of windings & DC Resistance...and behind the scenes 'inductance ', but don't worry too much about this latter one, your inductance will be in the ball park)....in my testing there hasn't been a whole lot of difference... Tallish (7mm high) & slim coil (wound with 0.28mm wire)... Taller (10mm high) & wider coil (0.315mm wire) .... Squat (3mm high) and widish coil (0.28mm wire) .... http://www.youtube.com/watch?v=W5JlPbkQYhs the point to take home is that for all the driver talk of efficiency & being 'phase aligned' (a misnomer - unless you have a one note guitar), the coil - within reason - for a DIY sustainer is the least of your worries (certainly for a first attempt) .... it can be wound big small, wide - whatever fits your guitar. At the end of the day, it's a passive device, and as such there's not a whole heap you can do to make it cater for the multitude of permutations/conditions a sustainer needs handling. IMHO - the circuit you mate the driver with is where the magic happens.

Mustn't bite, really mustn't bite, oh dammit.... what I view a bringing hard cold facts to the forum you view as trolling? The only conclusion I can draw is that you're very keen to perpetuate the "one eyed man being king in the valley of the blind" stance. You've got everyone blocking off their bobbins to make a 3mm driver - it's just not necessary (& adds that little bit of extra heartache to a lot who struggle with getting a bobbin together) you've got everyone thinking that 0.2mm is the only gauge works - well, not on my test bench it isn't! you call your driver thin & efficient....but you have no way of backing up 'efficient'. (& as a techie, I wince whenever I see you write it - I'm sure others do) You say your driver doesn't need phase correction - well, unless you've re-written the rules for phase vs frequency (or play a one note guitar?), that's total bunkum (& just reveals a lack of grasp on the basics) You've got folks across the globe making DIY sustainers to your subjective thoughts/hunches! (& not even so much as a scope in sight - I'm not wanting to come across as test equipt elitist, but you go to war, you need tanks, you go to the moon you need a rocket, to glean hard cold facts about sustainers you need more than an ohmeter and a hunch or two) Re circuits - ahem, hello you never actually published your own end finished circuit ....I smell a rat. I'm still active wrt sustainer & have circuits in spades...but they're all on breadboard (why stop to Eagle them up until I've finished all the tangents I head off on). Yep, I'm still active, whereas you prefer to frequent a forum for guitar building to talk (at length) about your personal affairs....(we use pubs over here for that type of stuff - they work surprisingly well). You recommend the Fetzer Ruby - I (& others) say the LM386 is sub par (I have outlined what I think is better (though still basic) - a tilman pre into a TDA7052A...but hey, at least I was clear, when I said it - ie it'll still perform relatively poor on the two open strings - I wouldn't want to mislead folks) There are driver winding tutorials aplenty on the net now - I've nothing to add (my issues aren't with the tutorials, but the bold erroneous technical claims)...furthermore, any such tutorial would likely just dishearten folks. I took time out to make a CNC machine and a CNC winder to help me with this project - for example this bit of acrylic was nothing more than a bit of rectangular block of acrylic until 2 hours ago.... (I've resurrected my Variax project - a PCB is going on the other edge of that bobbin tomorrow) what would be the point of me showing how it was done to a beginner? (I'd have to an associated tutorial on CAD, CAM, GCode, CNC operation (Mach3), coil winding...and so on. Most folks starting out on this, have access to a junior hacksaw and some empty jewel cases...so I don't think my tutorial would be relevant? I've offered up heaps of advice on here (alas a lot of it conflicts with your own) - I even did my own bit to hold the 'sustainer' fort when you went off in a huff for 8 months...so don't confuse others helping newcomers with advice that may confilct your own as simply 'trolling'....if anyone is trolling to get a rise, they're not in the northern hemisphere I can see how we ended up at loggerheads ...not only did you patronize me way back (& believe me, you picked the wrong blunt gruff northern English bloke to patronize), but the cycle is starting all over again - first with Elmo' the other week - and now here with syn. He seems to have grasped very quickly all that he needs to push on and make his first DIY Sustainer, but you're all but belittling him before he's even out the starting block!

I wouldn't say that at all...you've grasped the important elements. Re winding the driver - you've got it. Don't get too caught up wrt which lead is ground - as long as you end up with the start wire, and end wire which you can hook up to your circuit...that'll do! One wiring config from the amp IC to the driver coil will give you (mainly) 'fundamental note' based sustain' - with the wiring reversed you'll get (mainly) 4th harmonics ...it's not possible to say which wire will be which until you put the driver in situ (unless we all start winding drivers the same way...eg clockwise, put our magnets in the same way eg north side up etc, make sure we all have the same circui - inverting/non inverting etc!) If you've already got a PCB for the FR, I'd say roll with that - you'll get sustain, which as your first attempt will make you chuffed to bits....but then you'll want better.

As has been discussed as of late, IMHO that IC is not a great choice, but hey, you gots to use, what you gots to use I guess. Re measuring the coil resistance. The point of me posting up that bobbin winding calculator in my last post, was so you don't even need to have access to an ohmmeter - enter your bobbin's dimensions, enter your enamelled wire size (it does imperial too), select 8 Ohms - it'll then tell you how many windings you need to wind - so long as you can count as you wind, you're good to go! What I'm also saying is that an ohm either side isn't that significant & not worth fretting about.

Yes, but since some are saying that simply breaking the neck pickup 'hot' wire may cause issues(I can't confirm one way or the other wrt this as I've a different setup), you should therefore short the neck hot to ground when the sustainer coil is live. Correct. Correct again. What is it you want to know? There is much made of getting the DC resistance correct, but most audio amplifier ICs are quite forgiving of the DC resistance (within reason!) - what I consider is more important is getting the correct of ampere turns (basically the amount of current through the driver coil multiplied by the number of coil turns), at this early stage I'd simply say don't get too hung up on the winding aspect. Elmo recently did a nice pictorial about winding a driver which will give you a start (there are other tutorials on Project Guitar too).... http://freespace.virgin.net/e.macdonald/index.htm To help you establish how may windings to do for your given wire gauge (much is made of 0.2mm being the only wire type that works, but this is not the case - my testing has revealed you can pretty much use anything from 0.17mm - thru 0.4mm, depending on you preferred end DC resistance for the IC you're matching it with), here's a great online bobbin winding calculator... http://pickups.myonlinesite.com/pickup.php...=ohms&avo=8 So for that particular bobbin size, to get 8 Ohms using 0.24mm wire, you'd need to wind 149 turns. I'd say for your first bobbin - providing you use a robust output IC (ed the TDA7052), for a 9V supply circuit, shoot for somewhere in the region of 180-200 turns for a coil with a DC resistance of between say 6.5 & 9 Ohms. (I've filled the fields in to give you an idea, but obviously tweak those fields to bring your own bobbin dimensions & wire gauge into play)

Towards removing sustainer myth, legend & mystique, I reckon it's better to offer up a solution once it has been identified..... & Elmo recently offered one up that will work for that very situation - short out the neck pickup while the sustainer driver is selected - job done.

Mike, I'm sorted now, but that seems like an excellent deal for someone who wants to avoid the beginners pitfall of using basic threaded rod - if anyone is starting out Stateside, they should take your hands off! It is a massive learning curve...it took me about a month of nights trialing & erroring to get my simple CNC machine built, but then the real time sump arrives - how do I drive this darned thing!! (which means learning a CAD program & the CNC s/w itself...eg Mach3). IMHO, that needs about the same amount of time again to get to a level where things start falling into place. In the beginning, I too was somewhat intimidated by something as basic as positioning a simple shape & gettting it located in a place that my CNC would know where to go! (I was cacking that my spindle would try to go flying off past one of the Axis extremeties, lol)..you need to start thinking in coordinates & 'origins'. Additionally, I couldn't get away at all with some CAD programs at all (I tried the AutoCad demo - euuugh). Wrt CAD, once you've got past the basic s/w familiarity hurdle (eg "I just want to create a semi-circle damnit!"), you'll soon realise you've got to start thinking 2.5D & creatively pondering how to achieve the end result in the most efficient (or do-able) way. For example - eg to knock up a proper pickup bobbin on a 3 axis machine - not possible, but if you get creative & start thinking in 2.5D you can use your CNC machine two make two separate identical parts & join them together in the middle (where the copper winding hides the joint!) - I'm now using bits of my grey matter that have lain dormant for years! In general, I think it's just one of those things where you have to go through the pain of giving yourself a simple intial goal & plodding away & being a pain asking simple questions until you get there...then setting the hurdle a little bit higher - the penny eventually drops & it all becomes real fun after that. (BTW the CNC Zone is good because there are so many targetted/focused sub forums - so you're almost sure to get an answer to a basic question there). But it's worth the effort - CNC machines....every man should own one! (it's a birthright ) Re a tutorial ....it would need someone who has your chosen CAD s/w & Cut2D to do that (have you tried the obvious place - youtube ? - there's normally someone gracious enough to take the trouble & upload a video to help others on there). I know Vetric software is considered very good, but I'd think there's a possibility that you might outgrow Cut2D quite quickly - it looks to be ideal for 'easing you in' wrt toolpaths etc, but personally I'd rather go with a more 'integrated' package (by this I mean CAD->Toolpaths->Gcode all in the one application)

Completely agree about the organization. I'd have thought a FAQ on page 1 might have evolved after 5 years?!! Seriously, I'm wading through treacle with those first 120 pages. i reckon if you took out the repetition (& also had a FAQ), then you could easily slim those first 120 pages down to about 25 pages....if I was cynical, I could have have almost thought the thread was being kept purposely long for the Kudos?! Col, about me wanting more technical info...I didn't mean in isolation (you are correct ....technical info on it's own isn't a whole lot better than just trial & error results!). But we've had the trial & error (lots of it) , we have the theories (some good...some waaay bad!)...surely after 5 years, it's time to give the project a little more disicplined scientific approach?

Hi Fresh, Well, I hope to have meaningful power levels per string at my next run of tests (which hopefully will recommence soon, just after I bottom out these other sideline projectettes ...target date - about a fortnight) Re using the PIC for switching - I'd pondered that already...it makes sense as it'll save a lot of battery power (& I'll likely be using output ICs with 'standby' pins on them, therefore the PIC should dovetail well with such a method). Re the type of Hex input - I have both to hand (an old GK2 pickup & an old electronics debowelled Variax that still has a Hex piezo bridge) Re the technical data...I understand what you're saying about variants (which is why I propose trying to remove as many as possible!), but it might be suprising how aligned everyone's results turn out - we'll not know until people start taking such measurements & posting them up! Having some ballpark power levels per string (either with 'six string' drivers or 'single' string drivers) will be essential & if this project is to be nailed once & for all ....it's the only way to go (else we'll all just be trialling & erroring until the cows come home!). I suspect that there just aren't enough techy types with measurement tools tuned into this thread to get any meaningful 'depth of data'...which ultimately means most will come to this thread, build the driver that's been derived mainly from trial & error...connecting it up to a circuit whose only attribute being is that it's readily available, easy & cheap (the Fetzer Ruby!) & then getting very average results. There's only one way to tackle this project - technical data, else ....we're all just following the lead of those who have trialled/errored ...& how does that proverb go again? "The one eyed man is king in the valley of the blind....?" "MMF ...it's where the stimulation is!"

Hi Fresh, I'm definitely having some finger trouble with those RMS conversions! (I keep tapping 400mV peak to peak into online calculators, whereas it should be 200mV peak!) Ok, first the bad news - that 400mV peak to peak signal I mentioned was just an example. That said, 400mV peak to peak figure I gave is probably from an actual reading I took (I seem to recall that's the type of signal level I was seeing across my driver ... during my first 'stint' of sustainer experimentation, I did a lot of initial experiments with my associated notes scribbled on the back of scrap paper ...I really must get more disciplined with my notation this time!) Alas, at the moment I can't double check - my sustainer 'REDS' facility (Research, Experimentation , Development Stop. ) is out of action at the minute ...due to a hulking hobby CNC machine I'm building taking over *all* my bench space. Now, to your specific questions... (bear in mind, I'm still on single string drivers until my CNC is complete, then I can start cutting some bobbin top/bottoms that'll hold six of my individual coils wired in series) "I. How fast does your sustain set in? I can imagine that when you use that little power it can take some time to achieve a sustaining tone. I hate to wait for sustain to happen." You may not recall, but I'm using a PIC to digitally sample a rectified incoming pickup signal. Once sampled, my little PIC program can determine how much gain is needed & how fast....therefore it's possible to have the sustainer kick in as fast as required , but as it goes I prefer to fade the sustain in, as the string's natural sustain ebbs (with the 'melding point' level set to my preference)...it's all pretty seamless. BTW, I have no fizz whatsoever in my sustained notes....clear as a bell. I've got to go back & revisit the supporting analogue circuit again once my CNC is ceremoniously launched (dumped!) from my bench...I have a whole heap of new analogue ICs to play with. There's still a lot of work to be done, but I'm striving towards the bare minimum of potentiometers or presets at all (hopefully none - aiming to be all done digitally with just a couple of small push buttons. I'm still someway off from that...my main focus is the 'patent applied for' McSpanKStainer complete in the shortest time! II. How focussed is the magnetic field? If you bend the string do you still have sustain? And I'm curious how you solve that issue with bending strings. Is that a matter of PIC, like when you play the high E-string your E and B driver work. (I don't know if that makes sense, I'm not familiar with PIC). Or do you build drivers with some sort of overlap (when a string is bent it is still above the driver). Or are you fully focussed on sustaining chords? Ok, this is an interesting one. You must bear in mind that I set out on this journey with a Hex driver in mind. My tests showed that with a single string driver scenario, the string can be bent a good way from the small driver & the sustain would still 'hold'. Too allow this, it needs a fast AGC circuit & a sufficiently powerful enough output stage (that said, when you're only dealing with one string...the driver's power needs drops significantly). So, as the string moves away from the area of driver flux 'focus', my circuit really is designed to crank up the gain fast & spam out a bit more flux & keep that string sustaining. III. There is a chance that when your sustainer is operational the drivers could have a negative effect on one another. You stated that you needed 400 mV pp for your E-string, but what if your B-string is sustaining at the same time? It could be that because of interference of the 2 signals it's a lot harder to get good sustain. There's every chance...but when you think about it...most of the time , guitarists have a 'mono' sustainer requirement (occasionally 2-3 strings for a fleeting moment)..ie this being when a guitar player is soloing. Therefore at any one time, there will normally be just one dominant note played by the guitarist...in a hex driver scenario, that'll map to one dominant driver 'ruling the roost' for that moment in time. For chords, I'm not so sure that driver interaction will be so benign. I'm hoping that string/driver resonance plays a large part. eg, the driver will only impact on the string it's getting a feed from (assuming a hex input) ...the other strings because they aren't resonant...will hopefully disregard. It may well be that there won't be as much focused MMF (not a porn term in this instance :-) ) presented at the string due to inter-driver flux fights...but at the end of the day it'll be very much a case of suck & see. I'm presently creating some simple CAD designs for holding multiple single coils to be held at exactly the string's mid point...I now only have the Dremel tool holder for my CNC machine to complete & I can then finally start cutting these driver holder CAD designs out of acrylic.... The screen shotABOVE just a simple CAD/CAM 2D representation of the top/bottom six coil holder design, (the dotted red box represents the acrylic it'll be cut from....BTW I'm being tongue-in-cheek with the wording!!!). It's full single coil in size...why? For no other reason than my benchtop guitar is a strat has a big hole where the neck pickup used to be...therefore I'll fill it with this shape! I'll be scaling the driver down to suit once I have definitive coil dimensions. I'm now up to page 110 of this (somewhat highly repetitive thread! Each page is like Groundhog Day), but as of yet, I haven't read of anyone back then using hex drivers with a hex pickup feeding six channels into the driver circuitry. The big stumbling block I have with the 'standard issue' driver that has been adopted by many on here, (ie a one coil driver breaching all strings), is that for most 'sustainer' situations (certainly when soloing) - at any one time, you really only need a dominant string to be sustained ...but the driver adpoted by many here, presents the required one note across all six strings - highly inefficient & which I reckon is wasting a lot of scarce battery power as the driver attempts to sustain strings which aren't meant to be sustained ....far better to find a way of 'routing' the dominant required note for sustaining to the correct string(s), therefore two options I can think of.... 1. Take a bog standard merged/mono guitar pickup signal & bandpass filter it to get the right frequencies 'routed' to the right strings (obviously there'll be some overlap, as for example a high 'B' could come from the B string itself or the two strings below fretted high up) & have six drivers (and preamps/power amps) or (far better)... 2. Take a hex input feed from the likes of a midi/hex pickup etc. I may pursue a non Hex input solution (too many 'decision point forks' with this project ....& I blow hot & cold as to which path to beat first!) ...but if I do go with a 'driver across all six strings' approach, one avenue I'll certainly explore is to customize the 'turns' needed per string across the strings by using six coils below in series ...less turns on the coils for the lower strings....more turns for the higher strings. This won't save power, but at least it'll help get the string balance right. Re the power need for your driver...I can't say what's best in your case - but that's the whole point of my 'call to arms' for those of us ith scopes. If you can scope the signal across your driver for each open string in turn, at a known distance (eg use a drill bit to slide between driver top & sting bottom to establish the distance) where you just get past the edge of sustain (a subjective term, but can be described where the sustain is just enough to keep the string sustaining)...with sufficient data we should be able to glean how much power is needed per string etc. This will at least allow us all to address the "My top two strings don't sustain at all" type posts we see. It's a little puzzling to me how a thread can be this old & yet still have no meaningful technical data! I'll not pretend to be a clued up electronics wizard with lots of Formulae waiting in the wings to solve all sustainer problems (& after all, I've calculated some RMS voltage levels erroneously twice!), but I'm sure that discussing/applying the basic stuff (power levels, impedance, inductance, 'ampere turns' etc) will go along way to finally solving this sustainer conundrum that (unless I've missed it), still hasn't been satisfactorily nailed in all that time?! Sure there are DIY sustainers a plenty out there, but everyone I've read of seems to have a problem-ette of some sort (distortion/fizz, weak/no sustain on some strings/fret positions, no harmonics, bad EMI, pop problems etc). There's only so many times I can read "0.2mm wire is the magic ingredient" without any explanation why, or "it's the thin efficient coil you see" - without anyone even trying to establish its efficiency. There must be about 20% of all posts in the first one hundred pages alone harping on about pva vs epoxy vs superglue vs wax during the winding process (sure you don't want the coil vibrating, but purlease!!)- but few are chiming in & questioning the technical aspect of the driver ...ie power levels, turns required per string (note: not the the driver turns in total across all strings), inductance blah blah...nope, everyone appears to follow the you need to wind the magical 0.2mm gauge wire thinly until you get 8 ohms! line! Yet everyone seems to have a hiccup of some sort with their sustainer?!!

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!) There's some good stuff in there that'd be a good starting point for discussion! (eg more current through the coil might be 'the more the bbetter', but not if you're running off batteries, where you just want the bare minimum current possible to get a good 'grip' on the strings) Incidentally, I've been in relative radio silence...not because I've lost interest - far from it - but more, life is getting in the way! (also, I've spent an inordinate amount of time getting my PIC based coil winder running with 'bells & whistles' not to mention that darned CNC machine - TOP TIP....DON'T EVER BUILD ONE!). Anyway, I'm getting to the point where I can start getting back to sustainers tagain. I'd like to try & stimulate some discussion around ampere turns/ magnetomotive force (OR MMF which, which as it goes, I don't know a whole lot about). I'm slowly wading my way through this thread hoping that the odd pearl will surface (I jumped in at about page 30 & I'm up to about page 75 - woaah....what a lot of repetitive woolly 'noise' there is in there too ...in just about every other post!). I find it surprising - .bar one poster back then - that MMF hasn't been discussed much at all (certainly not up to page 75 anyway!). Ultimately it's the MMF that's going to produce magnetic force which will make our drivers physically move the guitar strings ....a common theme seems to be "My sustainer works on the lowest 4 strings fine, but not the top two" ....then surely we need to establish roughly how much MMF these strings need to get them sustaining well? (removing some of the 'variables' where possible - eg distance between driver & string etc). From my understanding, those drivers that span six strings generally have the following 'known' characteristics (I say 'known'...not 'best')... About 150-200 turns A DC resistance of 8Ω (this is the figure that everyone seems to focus on & I'm puzzled why - it's the least important!) An inductance of about 1mH (this one is certainly more significant) The variables we can't remove are ... type of magnet core material ..because a lot of folks will simply use what they can get or have to hand! Variables that could be removed are (for the purposes of collecting data)... Distance between sting & driver (ie if when taking measurements, we all ensure we use the same distance - eg 3mm) pickup feeding the circuit - use a Sig generator to feed into the circuit (as opposed to a pickup) There hasn't been a huge amount of technical data put forward wrt the measured signal levels across the driver which results in good sustain (I realise this term is subjective, so perhaps it's better to talk about the 'edge of sustain' ....this being where the driver has just got enough grip of the string to start sustaining it). In my opinion, unless we can start getting some of this data together, then we're all just shooting in the dark & making clones of a supposed 'efficient' driver (& that term actually gets my goat, as without some meaningful technical data to back it up, it's just people bigging their own driver up). So this is a call to all those of a more technical ilk, that have access to a scope, to start noting down & posting up some meaningful data!! Once we know the current running through the driver *and* the number of turns of the driver...then we can start talking 'ampere turns' & MMF. For example, let's take a single string 8 ohm driver, 1mH of about 200 turns as an example with 3mm distance between string & driver (you can slot a drill bit in between the gap to confirm the actual distance) let's say that to get the 'edge of sustain' for the top E string, that 400mV peak to peak sine wave is needed. Bear with me on this bit as I may have my figures wrong..... Firstly 'ampere turns' is meant to be DC current related (and measured in a vacuum!)...& what we're dealing with here is AC current (& no vacuum)...but let's park that pesky fact for now! If @200 coil turns it takes a 400mV peak to peak 'drive signal' to move a top E string at the 'edge of sustain', then assuming a coil of 8 ohms we can summise... Impedance is 8.264 Ω (top E = 330Hz, coil inductance = 1mH, DC resistance was 8Ω) RMS voltage is 282mV (ie our 400mV peak to peak) Therefore driver current is 34mA (282mV/8.264Ω) Therefore our 'rough & dirty' ampere turns figure for the 'E' string is 6.8aT (200 turns x 34mA) Once we have figures for two highest strings, then we can start honing drivers that will cater for these troublesome strings (one idea ...if you didn't all have solid cores running through the entire core length of your driver, is simply to wind a few more local turns at the higher string end of the driver - that'd put more ampere turns at the end causing the problem) Thoughts / Comments?

Oops...my bad - you are of course completely right!

As an aside, your scope trace shows the peak to peak voltage nearer 7.5V, (5.3V RMS)...which works out at 662mA into an 8 Ohm coil = 3.5W - positively nuclear!

Well that scope trace signal is looking a lot cleaner than the crud I saw on my scope (unfortunately, I didn't take a screenshot of my LM386 results). I can see evidence of JFET induced distortion on that trace ...but what's with the vertical lines on the final two positive cycles (the falling slope)....is that some kind of oscillation? (or just a bad screen shot!) RE the heat...I'm not surprised you're getting a hot chip - it's nothing to do with that specific chip per se .... but more the fact that you're pumping 5Vpp across an 8 ohm coil (or is yours 4 ohms?). If my maths serves me right 5Vpp, is 3.536V RMS, therefore @8 ohms that means about 440mA = 1.56W!!! To put this into context, I'm getting good sustain on the lower 4 strings with an 8 Ohm driver @ about 0.7Vpp! (5V is insane!). I reckon you'll be able to move your driver a few metres away from the guitar & still see your strings sustain! (I hope none of your relatives visit with a pacemaker fitted when you're testing that circuit

Well, there's your problem. Four hundred turns of wire is going to give you a fairly big inductance. I've just checked & established that 30AWG is about 0.25mm...so if you halved the wire diameter size (0.125mm), you'd need approximately 200 turns to get the same DC resistance - but that amount of turns is still perhaps a little too much. From recollection, with my sewing machine bobbin, I used about 140 turns of 0.15mm (approx 34AWG), which yielded a DC resistance of about 4.2 ohms (which is fine for my particular output chip) & an inductance of 1mH. You really only have two options... 1. Stick with your 30AWG but you must make big coils (eg rectangluar & with the longest bit at least 60mm), that way you get to nail your amp's required DC resistance fine yet witout too many turns. 2. Buy some thinner wire! [pedant alert] You keep speaking of impedance but it's actually DC resistance you appear to be referring to. Impedance does matter (a lot), but the impedance is not the DC resistance of your coil...I'll not bore you (there's plenty of info about) & there are some good calculators where you can extrapolate the interaction of each (but it won't tell you the wire length). For example http://pr.erau.edu/~newmana/imped.html [/pedant alert] No, don't go there...you've already got a volume pot in your guitar. If you start putting other pots in, you're going to get some interaction going on. The 5-10K pots I spoke of are for use within active circuits - you can't just drop one into a passive guitar wiring circuit with some *major* impact.

It's reasonable....but what's going to be key here is the coil characteristics & how you connect them all together. For example an inductance figure of 1mH (circa 150 windings) & a DC resistance of 8 ohms seems to be the ballpark for a general purpose driver ...the inductance figure is derived (in the main) from the number of windings your driver coil has. Therefore if you want to connect say 12 drivers in series, you'd want to shoot for 1/12th of those figures per coil (therefore each individual coil should be about 0.66 ohms & 83uH!). You'd need to experiment with differing coil gauge as you'd be beating a trailblazer's path there! My gut feeling is that a coil of 83uh, that the wire would need to be very thin to be able to get 150 turns - so thin, I reckon it'd not handle the current needed to get a higher frequency type string 'excited' sufficiently. I'd also have to assume that trying to span/excite so much string real estate with one 'virtual coil' (12 mini coils in series) would need a fairly chunky driving amplifier. if you don't need individual control per string (as per the EMPP), then I'd go with your 12 drivers connected in parallel or a combination of series/parallel (You'd still need to be careful with your coil characteristics, but they'd be more do-able vs pure 'series' connection) Well, I tried a couple more designs. One was a thin steel core, 4" long, wired with 30 AWG to 8 Ohms, solidified with PVA glue, with a ceramic block magnet attached to the blade. Another was like you suggested, wire wound around a plastic sewing bobbin, again potted with PVA glue, with a bolt in the middle of the bobbin and a neodymium magnet attached to the bolt. Both worked okay, not great, although using the glue eliminated the direct sound I had been getting with my earlier attempts. However, neither was nearly as good as the Radio Shack Miniature Audio Output Transformer, I cores removed and E cores aligned, with a neodymium magnet attached. This driver is by far the best of those that I've tried thus far. So...thinking aloud, would it at all be reasonable to wire up 12 of these transformers in a combination of series and parallel like: 7 in series 3 in series 2 in series and those three groups connected in parallel? With 8 ohms per transformer, that combination seems to yield a total impedance of 8.1951 ohms. Of course, this doesn't consider inductance. EDIT: I had incorrectly assumed that the transformers had an impedance of 8 ohms. In fact, after measuring, they have an impedance of 1.5 ohms each! So, how does that effect what I should do? IMHO, you're focusing on the least important aspect of making a driver (the DC resistance!). Re the sewing machine bobbin...what wire diameter are you using? The problem you're going to have is, unless you know the inductance & the total winding count of your own particular coils, then you really are going to be in the dark - & walking a (very) solitary & uncertain path. You can put the coils in any combination you wish, so long as the DC resistance matches whatever your final power amp wants to see *but* it may not sustain - what's absolutely key with sustainers, is not so much the DC resistance (that bit merely placates the needs of your power amp chip), but the delicate balance of number of driver windings (a bit like the three bears...this one has too many, this one not enough this one is just right!), strength of magnet (again three bears!), type of core etc. If you read through this thread you'll keep coming up with posts that wire gauge X is the most suitable - however such recommendations apply only to coils of a similar design. For example, many on here have established through trial & error, that circa 0.20mm diameter copper wire works best with a single driver breaching all six strings (I've seEn it said often on here that 0.2mm diameter wire is the only size that works ....this IMHO is quite incorrect *unless* we are all making drivers of exactly the same style/dimesions). theredfore 0.2mm wire gauge is the one to go for *if* (& only if) you are making a driver of similar proportions as the one most talked about on here. That said, what's been generally established on here, is that (for the main) a driver with about 150 windings & an inductance of about 1mH (maybe a little more) is about right. Therefore for my part, where I've been making single string drivers, to keep the winding count circa 150 turns & the inductance about 1mH, I have to use thinner wire than most (about 0.12mm-0.15mm)...your mileage will certainly vary. Therefore in summary...if you're making your own coils towards a different end goal, then you're going to need to find the wire gauge that suits your own situation (ie that satisfies the aforementioned characteristics). You'll be on forever & a day with the trial & error route...so I strongly I suggest you invest in a cheap inductance meter from China (mine cost a mere £14 delivered to my door from the far east! http://www.tinyurl.com/ompaon ) Mock duck - I can't comment about bass guitars (I don't use 'em) my gut feeling is that you won't need any extra oomph...because the strings that sustain best on a normal six string guitar are the lower frequency ones anyway! There's certainly a lot more ferrous material in the bass string for the sustainer coil to act upon Also the strings aren't as taught, so again I reckon this (in theory) ought to mean that no extra power will be required. re where to place the sustainer 'intensity' pot - that depends on the particular solution you decide to deploy, but it's probably fair to say that in the main, the intensity pot would best fit between the preamp output & the power amp input. Re its 'resistance' ...that depends on the optimum load that your preamp wants to 'see' but pots in the region of 5k-10k upwards are normally in the general ballpark

Firstly, your wiring signal flow chain is fine. Re your bridge pickup query - a sustainer will work with a single coil in the bridge - after all, a guitar signal is a guitar signal (ie analogue...low level) - it's got to go into an active circuit anyway , where it can be 'treated/handled' according to the characteristics of the incoming signal ...ie single coil more gian, humbucker, less gain needed etc (my test/workshop guitar is a cheap strat copy...& its bridge single coil feeds my sustainer ciruit just fine) ...I can only imagine they recommend a humbucker, to help reduce some of the EMI spillage from their driver - can anyone else explain why they suggest a humbucker only in the bridge?

That's now how it works here - you have to read the whole thread! I'm not sure I've ever seen a bill of materials for the Fetzer/Ruby, here's a site that comes close (I gather has simply 'pulled stuf from this thread as it credits Pete & Col )... http://diy-fever.com/index.php?project=sustainer re your wiring diagram...someone may have something diagrmatically to hand (I don't), but it's as simple as can be - you simply tap off your bass pickup signal either at your guitar's 1/4" jack output socket (which is simple - but not ideal as the sustainer will then be fed a 'manipulated/filtered' signal) or more preferably tap off the full unadulterated pickup signal as it appears at the input lug on your guitar's Volume pot.

It's reasonable....but what's going to be key here is the coil characteristics & how you connect them all together. For example an inductance figure of 1mH (circa 150 windings) & a DC resistance of 8 ohms seems to be the ballpark for a general purpose driver ...the inductance figure is derived (in the main) from the number of windings your driver coil has. Therefore if you want to connect say 12 drivers in series, you'd want to shoot for 1/12th of those figures per coil (therefore each individual coil should be about 0.66 ohms & 83uH!). You'd need to experiment with differing coil gauge as you'd be beating a trailblazer's path there! My gut feeling is that a coil of 83uh, that the wire would need to be very thin to be able to get 150 turns - so thin, I reckon it'd not handle the current needed to get a higher frequency type string 'excited' sufficiently. I'd also have to assume that trying to span/excite so much string real estate with one 'virtual coil' (12 mini coils in series) would need a fairly chunky driving amplifier. if you don't need individual control per string (as per the EMPP), then I'd go with your 12 drivers connected in parallel or a combination of series/parallel (You'd still need to be careful with your coil characteristics, but they'd be more do-able vs pure 'series' connection)

Hmm...I had high hopes in 'porting' the principles used in the Electro Magnetically Prepared piano over to a guitar sustainer - but in my (albeit brief) experimentations...it wasn't very successful. I reckon they're successfully doing this by chucking a fair old chunk of 'power' at each string...because they don't have to worry about EMI (on account the piano sound is 'acoustic' & not needing to use electric pickups like an electric guitar). IMHO, you'd be better off making a single driver more akin to the many variants on here but in a scaled down version for one string. (I suggest a sewing machine plastic thread bobbin, like these http://www.brother-usa.com/usaimages/Acces...Large/sa155.jpg, winding your copper around...about 150 turns of 0.15mm wire, dip it all in molten wax then let cool to solidify the windings , find an old drill bit that fits into the hole snug, cut the drill bit to length & pop it in the hole - now place a 3mm-5mm diameter rare earth magnet on the end of the cut drill bit - voila a single string driver!) One thing though....you shouldn't hear any sound from your driver at all - if you can, it suggest the wire windings are moving &/or the magnets....everything needs to be totally solid/rigid.

Sorry I can't help you there... at this stage, I'm only winding smaller one string drivers...at the risk of appearing a little blunt....it's not that tough a task to wind a coil...why not have another go? Next time, I'd say don't bother with the glue ...at least this way, you can always unwind the coil again if it hasn't turned out as you'd imagined (once you're happy - simply pot it with wax afterwards)

Fresh fizz...thanks for posting up all the details of your build. That's quite an elaborate (Rollys Royce?) of limiters...I wasn't familiar with it, but a bit of Googling certainly shows it's a good 'un - it doesn't suprise me that it works well (a more technical explanation of the circuit is here - http://www.geofex.com/PCB_layouts/Layouts/d&rpub.pdf ) A couple of questions... 1. Why did you choose a 12V rail? 2. What made you choose that particular output chip? 3. You say in your accompanying notes that you circuit really needs a scope to assist setting it up ...is this same scope not helping you eliminate your two string fizz? (in other words, is you fizz not visible on a scope - what does you rsignal look like across the driver if you feed a sine wave into the circuit?) Edit: By the way...your limiting method 'after' the gain controlled amp, sort of falls into the same trap that I made with my AGC circuit (when I placed it inadvertently in the wrong part of the overall chain)...the CA3080 is essentially acting as a VCA (albeit in this case a 'current controlled' amplifier using pin 5)...the signal at output of the CA3080 is rectified & then fed back into itself on pin 5. In my opinion, the sustainer circuit will work better if the signal is monitored/assessed before the CA3080 & then the gain of the CA3080 altered to suit. Else you'll need to set the whole circuit's gain to cater for the worst case scenario (thin string/high action) & ensure the limiter is set to allow that condition through - of course, this means the thicker, lower actioned strings will likely have too much gain (which could cause probs). I guess the Ross compressor designer didn't have to cater for the fact our input can grow back into a large signal (ie the Ross compressor was designed for a standard decaying guitar signal), hence their decision to limit after the CA3080. Just my opinion of course! (& anyway, you're getting good results, so we can therorize all day long - the proof is in your pudding!). As it goes this Ross compressor circuit has intrigued me sufficiently to pickup a CA3080E chip on my way home today (my first contact with a transconductance opamp!) ...I'll have a tinker with it over the weekend & see how it interfaces with my PIC's AGC output. Anyway, once again great work (btw: it's too high a component count for me! And perhaps a bit 'high maintenance') ....is that your first sustainer build? It's fairly quiet my end...I've been plodding on with my CNC build (which is a real time sump too - but it's getting to the stage where I really need it, to cut acrylic into a suitable shape to hold the multiple single string drivers I have!). Alas, the courier delivering the latest 'Sustainer' project components attempted to deliver twice...nobody home! So I'm kind of stuck for now (hopefully they'll succeed tomorrow which might allow further dabbling over the bank holiday weekend). This downtime has given me time to ponder how to nail that 'high action' excitation problem (or lack of) & I'm now thinking that one plan of attack of attack is possibly a 'reserve coil' only to be brought into play when the AGC circuit hasn't managed to get control of the string within a set time. I'm now thinking along the lines of a sustainer 'driver' that has three separate coils (ie two strings per coil) & one coil that could be used as backup & which bridges all strings**. I can then use the PIC to decide & enable/ bring the extra firepower online on demand....hopefully the extra coil 'rowing in parallel' will quickly coax the most reluctant high strings into action. Does anyone know how the commercial units perform wrt higher actions? (or is it just a general case of "You want a Sustainer? Then you'll have to tolerate some notes not kicking in if your action is too high") I've also just sorted my coil winder program out...which up until two night ago, I hadn't realised had a bug, which meant that the winder was miscounting the coil revs! (Oops!). Anyway, I've just wound a corker - 150 turns of 0.15mm wire...1.2mH @4 Ohms ...we'll see how that one performs over the weekend. ** The other option is two coils - one for Low E thru G strins plus a coil dedicated to the High E & B strings - which I'm beginning to think really need 'special' treatment! (especally to coax .009s into excitaition when the action is high)

I'd considered a THAT VCA...but I've not quite wrapped my head round how it'll integrate with the Virtual Earths we're using?!! (also these THAT VCAs will definitely need a 9V supply, as they need a +ve...earth...-ve & the minimum spec for these is 4.5V...not sure what happens to the VCA when the battery life starts fading away?!) I've all but written off controlling the JFET with my PIC...sure, it works, but the JFET is *not* linear...meaning if my PIC increases the gate voltage by set 'predictable' steps in voltage, I don't get predicatable 'steps' of JFET resistance change - this plays havoc with the gain structure of my variable gain 2nd stage preamp. For example, if the signal coming in is below 'optimum', the PIC increases the gate voltage by a certain amount.... the preamp gain then increases by a certain amount, this feeds into the power amp & I get an increased signal across the coil by the required amount. However, after few more steps of this (ie analysing the input, increasing the gate voltage), the JFET resistance then leaves it's linear range' & therefore the its Source-Drain resistance is not proportional to the predictable 'voltage steps' I've applied. The gain of the opamp then whacks up...this can result in a whacking great increase in signal fed into the poweramp stage, ultimately vibrating the string stronger in almost 'step up' fashion, the resulting larger guitar signal then feeds straight back into the sustainer circuit, where the the AGC thinks "Whoah, DECREASE THAT GAIN SHARPISH!!!)...so this all results in it taking longer to 'lock' the AGC gain at optimum (also hunting/pumping enters the fray). Sure, there are articles which show how the JFET can be linearized, but it seems you then lose a large portion of the controlable JFET range....meaning ultimately the gain range of the variable gain opamp (ie dynamic range) is hampered ...I reckon we need to control of almost the full rail-rail range of incoming signal. So, (stating the obvious) unless we have a totally, predictable linear AGC, then it'll be a real struggle to get our Sustainer 'tuned' well. Also, I've not quite wrapped my head whether we need a logarithmic gain structure or linear for the circuit driving the coil. I suspect we need logarithmic (on accountwe hear logarithmicly)....if so, this is even more reason to use the THAT type VCAs (or an output stage with a logarithmic volume control). Does anyone have anything more definitive on this last aspect?

Hi Col, I'm not suggesting the LM386 is not capable of producing clean sustain, but what I'm seeing on a scope across the driver coil is downright ugly (since you ask, I was using a 330uf cap in series with the coil - that was the largest I had to hand). What my line of thought is....is that *if* the poweramp stage is adding distortion (not meant in the more common 'grunge/clipping' sense, but more just 'changing the signal' vs the original)...then overall, it's going to be a struggle - because most JFET based AGC circuits are also adding their own little bit of JFET based distortion into the mix ...therefore adding these two 'distortions' together results in a final signal appearing across the driver that's different by some margin to the the original incoming string signal. If it's not an exact copy of the original signal, then this can only mean the sustainer have to work that much harder at 'exciting' the string (meaning less efficiency = more battery drain) Re the PIC....what you say is do-able...but the problem is the initial signal transient varies wildly (I can see the transient levels in real time on my PC screen as reported by the PIC) - in my opinion, AGC's really needs a less volatile input signal (else you'll only end up with more 'hunting'/pumping)...also, the transient 'fade time' varies greatly between strings - a low E's transient doesn't appear to fade as fast as a high E - therefore it'd be hard to base an AGC 'gain needed' decision on these initial transient levels .....far better to wait a portion of time (say 200ms), for the string to establish a more meaningful 'average level find its 'average level - & then have the AGC act...but the problem then of course is that there's much less time for the sustainer to wrestle control of the string before it fades past the point of no return! The 'dynamic' sustainyou're proposing...is a nice touch, but I'll lleave that for my MKII version (I'm not even at MK 0.5 yet!)...that aspect is probably just best left to an 'intensity control' pot for now! A predicatable, controlled AGC for high action'ed guitars really is one outrageously tough balancing act! I'm now searching for a chunkier output poweramp - & the TPA0252 - http://focus.ti.com/lit/ds/symlink/tpa0252.pdf - now looks like the latest contender (now winging its way to me) Benefits include... Digital Volume Control (controlled up/down via pulses ....this will dovetail well with my PIC signal level analyser...therefore, I'm hoping this digital volume control will make for a good, lazy man's AGC!) A much chunkier 2W Stereo capability (therefore potentially driving two separate coils). A low 5V supply (PIC friendly) A Low current draw @8mA (& only 150uA in shutdown! Muxed inputs (therefore I can feed both inverted & non inverted guitar signals into the chip & have either the PIC or a simple SPST switch select between the two - that ought to make for a very & easy harmonic mode switching solution!) Very low external supporting component count. It remembers where the Vol control was last set after coming out of shutdown mode (useful for making sure the volume level is 'in the ballpark' right out the starting gate) A low THD @0.3%-ish. Very Small!! (though you might view this as a problem if you're put off by SMT!) Cons include... Quite costly in comparison to other poweramp chips. Very small! :-)