Hank McSpank

zfrittz6 - my driver coil is different to everyone else's - I'm using a small single string driver...I find this is extremely useful for flushing out specific issues, because I can hone in on a string at a time. What I've now established, is that with a single ended 5V single supply combined with 1x 8 ohm driver coil, it's not possible to 'excite' a string sufficiently when the string is more than 4mm distance away from the driver. Having slept on this, I have a few plans of attacks... 1. Increase the VCC of the sustainer cct (I'll take this up to 7V...as then we're into 2 x Li-ion batteries in series or midi guitar +7V supply territory) 2. Reduce the impedance of the coil (probably split the difference & go for 6 ohms)) 3. A chunkier output IC (2W?) & if those two don't work, then 4. Start thinking about having two coils 'rowing together' in parallel I'm therefore thinking of resurrecting my TDA7053A, if steps 1, 2 & 3 don't work...then feed the TDA7053A the just one mono signal into both strereo channels .....& then out to two separate coils. This ought to put a *lot* more firepower at the business end on demand A big win here, is that the TDA7053A has a more flexible logarithmic DC volume control (vs the TDA7052A) - so rather than mess about with JFETs - which, even though work admirably with my PIC ...they're not linear within their ohmic region (you can linearize them, but then you lose a lot of dynamic range - http://freespace.virgin.net/ljmayes.mal/comp/vcr.htm )...which makes for somewhat fierce fluctuation in gain. It makes sense to try & take advantage of the hard work done by the chip manafacturer! BTW In a moment of madness/frustration/puzzlement I did at one stage last night revisit the LM386 ...it's a truly awful little piece of junk. Bearing in mind there's very little cost difference between it & other poweramp chips...based on what I saw on my scope, I'd urge everyone to avoid it like the plague!

Ok, having failed to get my sustainer to yield a constant, predicatable, grip of 'distant' strings - I went back to basics tonight - I took the AGC temporarily out of circuit, just a simple two stage preamp (on non inverting, into an inverting)...feeding into the TDA7052A & a single string driver coil at 8 ohms 1.2mH ....I used a sine wave into the preamp (& tuned the guitar until it was totally resonant with the sig gen) ....then tuned for maximum smoke the bottom line is, my particular power stage combination is not up to the job of getting enough grunt out to the thinner strings when they're more than 4mm away from the driver. by this I mean if I place the driver 5mm+ away from, say the the G string, the TDA7052A does not have enough firepower to get the string moving sufficiently with an 8 ohnm coil (4mm is its 'distance' limit ....I'm using different sized drill bits to establish the gap between the string & the driver coil!). I'm summising here that this is because I'm only using a 5V single supply in combination with an 8 Ohm Coil. I scoped the signal across the coil...it was 3V max (if I put any more into this chip, the output gets ugly)...no matter what I tried, I couldn't get anymore out of this combo....if my TDA is limited to 3V peak to peak output @5V rail, then to get more grunt, I either I need to take the supply voltage up, or the impedance of the coil down. My preference is to take the coil's resistance down to 4 ohms (but then doubling up the wire gauge to maintain the winding count at about 150 turns), so that's what I'll be doing in the next night or two. (it's becoming clearer why most Sustainers use 9V supply & have a discreet push pull output stage!!) It really is going to be a very tricky task to design a sustainer circuit that can cater for the (relatively large) extremeties of power needed to excite from say a 'top fretted' bottom E string thru an Open Top E string (at least certainly for a guitar where the action is high!!)

Ok, I've sussed my problem (though haven't been able to implement the fix yet)....sometimes you can get so close to the wood, you can't see the trees! It's my mistake...due to my fixation on tweaking the AGC so much, I overlooked the fact that I'd tapped off the AGC feed from the wrong point in the overall signal flow chain! This messy sketch of my block diagramexplains it all... Essentially where my AGC is (soon to be 'was'!), it's not monitoring incoming the incoming input signal level...it was purely focusing on making sure the output level of my 2nd stage preamp always remaning the same (& a damn fine job it does of that too!). I now need to move AGC's the tap off point to be just after the first preamp stage ...the AGC's control voltage still feeds to the second stage to alter the gain to suit. It's been a bad day in McSpankland!!! zfrittz6...that's not an obvious choice in chip - it's fully integrated ...ie a preamp & output amp are combined...its input impedance is way too low to attach to a magnetic guitar pickup directly...it'll suck come life out of the natural guitar signal. You'd need to front end that chip with a buffer....& hey, if you're going to need to make a buffer, then why not just go the whole hog & make it a preamp (dispensing with the integrated monolithic solution.. It also looks a little over spec'ed power wise (ok, so if the power isn't needed, it won't be used...but that's a little akin to going to Wal-Mart in a Formula One car!) & the external component count is quite high too. Point taken about the Class D - there must be a way of getting it to work becuase the Sustainiac uses class D (if not, no matter... I've received about 10 different Class D samples....so they're all free anyway!)

BTW, I'm being a bit slow...I know why this is causing me so much grief - it's because my present AGC has to be set with an 'optimum' string level (& it does that wonderfully) The problem of course...the optimum level for one part of the fretboard is *not* the optimum level for another part! Doh. (I should be forgiven this very simple lack of foresight on the basis, that I've only just brought all my sustainer 'pieces together' ....you kind of have to make that journey to realise!) A bit like painting the floor then realising your in the corner with your back to the wall & can't get out of it without walking over the freshly painted floor!) What you describes, sounds to me like a bog standard AGC approach with threshold ...ie cranking the drive when the incoming note is low & vice versa (or am I missing the salient point?!). My problem isn't getting low notes up...but getting the sustainer to 'get a grip' on a normal strength plucked note (but one where where it was plucked where the action is high). In this scenario, the string comes in as a healthy enough signal (& my PIC AGC just thinks "Aha...here's an incoming note...& it looks like the incoming signal is healthy...I'll therefore go through my normal gain adjustment routine"...my program is slick, because the PIC can talk to itself ) , but because the action is so high & therefore the string that much further away, what it really needs is for the drive seen at the coil to ramp up *very* quickly, in order to get a 'grip' on that string before it fades past the point of no return. This is why I was pondering the concept of monitoring how quickly the sustainer is 'getting a hold' of the string (ie the deviation I spoke of...if the deviation between 'optimum' level & present incoming level' is narrowing fast, then nothing to worry about...if it isn't than that must mean the action is high - and the string further away - therefore more firepower needed at the coil pretty darn quick!) So, would it be fair to say that the biggest challenge facing DIY/Hobby sustainer designers...is perhaps not phase, not frequency, not the type of output chip or whether it's 0.15mm, 01.9mm, 0.27mm gauge wire, etc - but making sure the overall solution can cater for the chunky range of power requirements needed for the wildy varying scenarios between a high Open E (a lot of drive needed) vs low E string fretted towards the top of the fretboard (not much 'drive' needed at all) I guess what the perfect sustainer needs, is a fretboard location & string dependent 'drive' circuit!!! (but how can we give it this info?!!) I have to admit...for now I'm genuinely stumped as to the immediate solution. I reckon a look up table will only work if there's a 'unique' condition coming in at the input (eg if I could tell the PIC...this particular incoming note means the string has been plucked at a where the action is high - go get 'em floyd)....but the PIC doesn't have enough grunt to analyse so many note in real time to derive this info (eg was the action high or low action when the string was plucked) I guess with a one driver per sting approach (Hex solution), I could have the preamp use frequency based gain - eg for an 'A' string driver, a 110Hz note *must* be an open string, therefore this is where the action is known to be high, therefore ensure more more gain is applied, right up to 440Hz at the top of the fretboard for the same string - less gain required). Then use an output stage correlating voltage to current. This could be done with discreet components. Hey ho...needs a bit of thought...ideas welcome!

Ok, I'm just about there ....but this last hurdle is proving to be a significant one. What I've got ticked in the box thus far... 1. A Single string driver design (my inductance meter arrived from China yesterday ...allowing me to finally measure the string driver that I've having the most success with ...a 0.15mm variant - I was surprised to see that it has a surprisingly high inductance ....2.95mH. I will address this using with less turns, taking the DC resistance down a little, but for now it works) 2. A reasonable ballpark preamp circuit (it may not be totally optimum, but it's good enough for now) 3. Digital AGC (this one is proving to be a blinder - I'm getting visual feedback as to what's going on with incoming digitized string level readings as my digital AGC adjusts preamp gain to suit in in real time) 4. A poweramp chip that is 'ok-ish' (for now)** My 'test guitar is a particularly bad strat 'catalogue' copy with high action ( my logic being if I can get it to sustain well, then that should cover most bases! Accordingly I'm using .009 gauge strings) The Problem? - the variation in sheer amount of power needed at the driver, towards getting the highest fretted notes vs the open strings to sustain. At the moment, for convenience of access, my driver is held in place *above* the stings, therefore open strings are closer to the driver then those fretted higher up the fretboard. Having tried driver placement everywhere, I'm sure those that have gone before me know that there really is only one good solid location that yields a constant, nice, clean sustain - that happens to be around the neck pickup region (as I move the driver closer to the bridge end, too many 'odd' harmonics are introduced, resulting in the loss of that bell like quality). The problem with driver placement at the neck end, is that that's where the difference in action is at it's greatest! (& like I say this test guitar is a particularly bad actioned guitar - something in the order of 8mm-10mm action!) As I recall, there's some equation the goes something along the lines that power needs to be applied logarithmically with distance (or perhaps what I recall is more something along the lines o f 'that sound pressure drops off logarithmically with distance...I digress!). Anyway...how are others dealing with the seemingly *huge* variation in output requirements to 'excite' those string that are close to the driver & those that are far away? I'm struggling here to rationalise how this will even be possible & *not* have a current hog of a poweramp 'beast on board'. I can only think of one solution at this early stage - have the AGC to become more 'intelligent'. At the moment, I simply set the optimum string level & if after plucking a string, the incoming level is too high , it starts adjusting a PWM duty cycle to suit (this is essentailly an altering DC output that I use to control a JFET)...like I say, within bounds it works extremely well...but when the action is too high, it can't get enough 'grunt' dispensed quickly enough. therefore perhaps what I need to do next is have some form of decision making based on how well the AGC is 'wrestling control' of the string. Something like this.... (Deviation = a 'number' respresenting the difference between incoming level & a user preset optimum level') 1. String gets plucked 2. String gets AtoD'ed 3. PIC assesses this incoming string level (sample 1) to establish the 'deviation' number. 4. PIC Adjusts preamp gain circuit up 5. Again PIC assesses this incoming string level (sample 2) but then calculates how quickly this deviation is narrowing in percentage terms "If the deviation hasn't narrowed by at least X%...then start bringing in some major artillery at the power amp end" Whereas, at the moment, I have this... 1. String gets plucked 2. String gets AtoD'ed 3. PIC assesses this incoming string level to establish if it's above/below optimum (as it goes, it'll always be above just after plucking, but I've put the 'iff too high' condition first so it always acts on this aspect first) 4. PIC Adjusts preamp gain circuit down 5. Again PIC assesses this incoming string level - establishes if too high or too low 6. Adjusts preamp gain again. & continue (it's a little more refined than I've explained, as there's the concept of initial coarse adjustment then finer adjustment as the incoming string gets closer to the optimum level) So, things still to do... 1. Solve this big power 'window' problem. 2. Make something that'll hold a few of my smaller drivers (I'm thinking here that probably three drivers might be a good balance between component count, power drain & yet still give very good control) Step 2 is the only fly in the ointment ...& the subsequent test after I have the 'holder' it's likely to be a Biggie - ie inevitable ineraction between adjacent drivers. If it's too bad...hey ho, nothing ventured etc...I'll just then hone in on a six string driver! (watch out Pete...I comming at ya! ) My new Class D Power amp chip arrived in the post this morning (MAX9700) ...it won't need a whole lot of solder (& probably best I stay off the coffee for a day or two before I try!)

I agree that the initial guitar signal is *very* rich in harmonics...but you'd be surprised how quickly these settle, resulting in something more akin to a sine wave. There is no sustainer in existence that can do anything other than stimulate a string & *not* yield a sine wave type string output (this is why sustainers have a slighty different tone in the tail to the guitar's initial attack (it's not much of a problem in reality though ....Roland worked out that us humans decide what it is we're hearing mainly based on the 'attack' portion of a sound - Roland released LA synthesis to take advantage of this aural illusion! http://en.wikipedia.org/wiki/Linear_Arithmetic_synthesis). The only way around this sinewave-esque tail, would be to have the sustainer circuit 'sample' the string sound just after the attack (as it's initially *too* rich in harmonics then) & then loop that sample back to the string driver...that's an awful lot of processing & specialist h/w (& we're probably some way off that level of sustainer detail!) That's the point...we're all - in the main - restricted by parts count (even SMT to an extent)...that's what makes this a difficult project! It'd be a doddle if we we're all upright double bass players! (plenty of room in one of those puppies!) I don't think that'll be possible with PICs for a good while. the only option then is something akin to a Variax board - take your guitar signal, AtoD it using dedicated AtoD chips, a chunky motorola DSP & do it all in software ....end result? A board that's fairly big - oh, yeah...it'll cost you £200+ to make! re the Scope - yes...certainly if you want to come up with your own 'design', I'd say you definitely need some visual feedback wrt what's going on with your breadboarded circuit ...it needn't cost a lot (anything?) - there are plenty of soundcard based 'software oscilloscopes' on the net - more than up to the job of monitoring guitar frequencies. BTW: I finally got round to using MultiSim last night...very cool, but it can only take you so far - for example, that TDA7052A quirk i mentioned earlier...I doubt a simulator would ever be so 'customised/detailed' to simulate that one...& without a scope, how would I have known why my guitar output suddenly sounded awful? I genuinely find it amazing that so many DIYists have spent as long on their sustainer journey without one.

Pretty damn tricky though. How would you do this? Dead bug style ? Maybe not so bad if you have cnc, or all the kit for etching your own pcbs. Any suggestions for the rest of us? Sure.....an adapter board... http://cgi.ebay.co.uk/Surface-Mount-SMT-SM...A1%7C240%3A1318 re soldering pins that are only 0.65mm apart ....well, for a start if you've shaky hands, just flood all the pins with solder, then use copper braid to get the excess off thereby removing 'bridges' (the capillary action of the braid will lift the solder off...except the solder that's underneath the pins) - there are plenty of tutorial youtube videos about, you can get the idea here... (from about 3m46sec in). Another method is to buy some solder paste (eg http://cgi.ebay.co.uk/SOLDERPLUS-LEAD-FREE...A1%7C240%3A1318 - you normally need a syringe, but you could get away with dabbing a needle into the container & then dabbing it on to the pin pad) .. place a small amount on the pin pads, mount the chip (the paste holds it in position) & whack it in your oven (got to use the right temp!) - the paste morphs into solder - no bridges with this method. A lot of folks are put off by SMT, but all the best & latest variants of chips are often only available in SMT nowadays.....going this route sure beats the hell out of rolling your own class D amp! (ie 90p for the Class D chip & £2.00 for the adapter - cheaper than a Marks & Spencer sandwich!) By the way, a CNC ain't much use when it comes to SMT (unless you throw £££££££s at the CNC build - mine was made from scrap!)....at best all I can expect from it, is to make a larger 'experimental' board & things like coil bobbin cutouts. Edit: I've been using a TDA7052A as a poweramp chip ....I feel it's worth posting up details of a TDA7052A 'quirk' (just in case anyone else uses this poweramp chip). This particular chip performs admirably when the peak to peak signal feeding into it is under 3V (the exact level I can't be sure as I noted it down at home ...i'll update this post when I get home)...ie no visible distortion. However, once it get's above a certain level...the output signal seen across the driver goes really whacky. It's as if the frequency has doubled (a bit like an unsmoothed full wave rectifier output)...it's not a clean representation of the input at this double frequency - no clipping though. This has proved to be a real bummer for me, as I really needed the full 5V swing heading into the power amp chip (for the most flexible AGC)- I guess what I really need is a unity gain voltage to current converter as the output stage. Incidentally, last night was the first chance I've had to try & integrate my 'digital PIC AGC' with my analogue sustainer electronics - as a first run, it went *very* well. I have full digital control over... 1. How quickly the sustainer kicks in after a string has been plucked (ie how quickly the sustainer takes up the slack as the string fades out.... the idea being towards a seamless 'marriage') 2. The 'starting level' gain for the AGC (else each time the 'sustainer start' string threshold is breached, it has to start getting to the correct 'gain region' from scratch, which can pose a problem wrt hitting the 'time deadline to wrestle control of the string before the string fade below the 'point of no return'!) 3. How quickly the AGC reacts to incoming signal variation (ie how quickly it adjusts the JFET ...which in turn changes the gain), both... i) Initial 'coarse' AGC (ie to get to the approximate gain 'region' real fast) & once it gets 'in the zone' ', then... ii) Final 'fine' AGC (this takes over from above coarse AGC, to stop it 'hunting'/pumping' ..this is where the sustain 'drive' level ramps up/down as the AGC coarsely tries to get 'hit' the preset optimum gain setting) 4. Sustainer 'enable' threshold (I can cease the sustainer's 'hold' on the strings by slightly damping them - once the string level falls below a certain level...the AGC gets disabled, and therefore the sustainer is curtailed) 5. Release period - I can either have my sustainer 'hold' a note forever at the same level, or fade it out over a preset-able period (eg...slowly fade over 60 seconds) 6. Intensity level. ...I'm chuffed to bits! The mind boggles though as to how the commercial manafacturers got their's working using discreet components! Some difficult choices lay ahead soon, do I... 1. Stay focused on a six channel sustainer (Hex...which is how I started out this journey!) 2. Have a sustainer for six inputs (hex), six AGCs ...but then sum them into one driver (much lower component /driver count...less power) 3. Have one standard mono guitar input & tweak what I've done to suit! (the lowest component count of them all...but not likely to be as 'controlled' due to the wider & combined frequency band)

fresh fizz....I agree about the biasing of that FET.... as battery voltage starts decreasing, then so does the biasing. Not good. Whilst all very interesting, I'm not quite understanding the pursuit of 'power modulation' ideas, when perfectly good Class D power amp chips exist that cost pennies.... http://uk.farnell.com/jsp/search/productde...jsp?sku=1648680 (ok, so at 3mm long, it's small, but this isn't insurmountable & is surely going to far exceed the results hobbyists could achieve switching the rail on/off quickly!)

[Here are some 'real world' USB Scope screen scrapes which shows the type of distortion I'm seeing controlling a JFET. To explain where my JFET sits, firstly look at this simplistic diagram for reference... I'm actually using 2 x Rin ....as opposed to the more normal 'one' seen above. My JFET is placed 'across' (in parallel) with one of the Rins - when the JFET is gated on, it bypasses (shorts out), one of these Rins - therefore leaving less overall combined resistance for 'Rin' ...this increases the opamp's gain, & vice versa. Nice & simple. Firstly, this is JFET fully on...therefore crereating the maximum Opamp gain (just over 4V peak to peak.....I'm only using a single 5V rail so it's getting close to the clipping point), there a tiny amount of distortion but too little to be of a problem (certainly for sustainer circuits - not hi end audio!)... Next the JFET 'pinched off' therefore the opamp is at its lowest gain setting (in this scenario it ouputs about 1.2V), again, a tiny amount of distortion, but to paraphrase Paul Daniels "not a lot"... Finally, when the JFET is at it's 'mid bias point (half way between cutoff & full on), this is where the opamp output distortion is most pronounced (it's quite marked, in that it's starting to 'triangularize' the sine wave - but I still don't think it'll be a problem to use this as a driver output signal).... Anyway, just thought it worth illustrating the type of JFET induced distortion I'm seeing when it's being used in the feedback loop of an opamp.

That app Circuitmaker.....looks easy on the eye - I'd not heard of that it before. I really ought to do more simulation, but truthfully, I haven't the time to learn it (though I realise, if I spend time learning it - it'll save me time!) - certainly the the spice sims seem to sump a lot of time to get up to speed, so I'm just getting out the breadboard & going for it. I've just been Googling for Circuitmaker - I see that the app has gone end of life, though there are plenty versions still abounding on the net (eg student ones). I quickly downloaded/installed the student one....for the life of me I couldn't find an LM386 (I wanted to simulate that simple AGC circuit) - with it being such a common/popular chip, I'm puzzled why it's not in the library? The first circuit may have less distortion, but it's component count is getting a little chunky. I'm wondering here if the type of distortion the simpler AGC circuit introduces will even be audible (which is all we care about). When I've been putting together circuits with JFETs using a sig gen sine wave as an input, there has been some slight changing of the waverform as seen on my scope (I'm loathe to use the word distortion - even though that's what it is - becuase what I saw was mild distortion)...but no impact on the actual guitar 'sustained' output. Therefore perhaps what's important here is the type of distortion (eg clipping = very bad, gross waveforn modification = very bad, mild non square wave related distion - ok?) edit: I've just seen your 'edited' post with sim of the simpler AGC circuit - that looks quite bad...I'm not seeing any such squaring wrt the sine waves on my JFET AGC circuits. What I see is more a scooping out ofthe hollows - I'll try & get a USB Scope screen scrape next time I'm working on the circuit.

I think I've just stumbled upon the source of that AGC circuit zfrittz6 posted up a page or so ago... (full URL here - http://www.qrp.pops.net/Idaho.asp ) Therefore it was a little off to suggest it was - ahem - 'lifted' from the Aussiemart compressor thread (& who's to say Aussiemart didn't 'lift' their's from the above site in the first place!). I reckon this cct can be adapted to work with most poweramp chips ...even though it seems a little crude, I'll give it a trial with my TDA7052 soon. I'm even tempted to straighten out the pins of my 'terminated' LM386, just to see how well this cct performs with it, (this design - along with it's many derivatives - appears to be very ubiquitous.... so there must be *something* in it!)...but perhaps deriving the FET control voltage from my PIC instead of the output from the chip.

Unfortunately not - for starters the PIC doesn't have enough grunt, but more significantly, it has AtoD ability but doesn't have the reciprocal DtoA! (some folks get around this by faking an 'analogue output' with clever look up tables to replicate basic waveforms such as sine waves etc). So no hope of what you're proposing. I've not looked at the most Powerful PICs...they may do DtoA, but I've enough on my plate with this one! Re the current a PIC draws - I'm not totally sure the datasheet is vague (& as of yet, I've not measured it) - I guess being a processor with lots of IO, it'll be down to what load is asked of it. It's not a high draw though...I reckon something in the order of 20-30mA (as an aside, I had a 'doh' moment the other night when my bench PSU was showing that my sustainer breadboard 'mash up' was pulling 250mA . After after disconnecting the PIC & other stuff in my sustainer...I realised my coil winder circuit which shares the same breadboard was still attached to the rail - phew!! Re the PWM frequency...not sure either (the reason I'm not sure, is because to all intents & purposes for what I'm doing - generating a DC level - it doesn't matter. The PIC I'm using is a 16F690 - it won't be my final choice (there are many lower spec'ed versions which will be more suitable for the sustainer). The reason I'm using this variant is becuase that's the one Microchip supply with their excellent PICKIT2 starter kit (I can heartily recommend it - http://www.rapidonline.com/Electronic-Comp...source=googleps )

Yes, it's common. I mentioned a couple of posts back that using the term 'Low Pass Filter' sounds grand - but all it is, is one resistor & one capacitor(!) connected to the PWM output stream. Yes, a PWM stream would be *way* to choppy for an AGC control signal, so the LPF's purpose is to 'average out' all the PWM's 'ons/offs'. If there are more 'ons' than 'offs' (ie changing the PWM's duty cycle to have it higher for longer than it's low), the capacitor charges up more & the DC level raises - and vice versa. For my PIC, the LPF is simply a 1k resistor in series & a cap in parallel with the PIC output (at this stage, I've used 4.7uf cap - but bigger/smaller values can be used depending on how quickly you want this 'averaged' DC level to impact your AGC control) Hank.

Control & flexibility. A simple full wave rectifier cct, will act upon the level that it's set to - but a PIC can have some supporting 'ifs/logic' attached (for example - the PIC can be programmed , if the sustainer circuit input level is too small, and yet the JFET AGC gain is at its max, then increase the poweramp DC volume level pin up momentarily", etc - that'd make large circuit going discreet). Think of an ADSR VCA setup on a synth...the PIC allows similar degree of control. (whereas the discreet method only offers the A & R bit of an ADSR!) Remember, I set out on this journey with six drivers in mind (fed by hex pickups). I'd envisaged different operating modes. For example a 'solo mode' - the idea being here that when a player is playing a solo, he'll bend the strings a lot - not a problem for a single six string sustainer, but for a hex sustainer....as he bends out of the single coil range, then he'll have some 'fade away' going on! I'd anticpated that in solo mode, the PIC could get funky with it's switching & feed each string's input to the string driver/cct immediately above it ...for example, if a top E string note is coming in ....send it to the B string driver as well. (therefore as the E string bends out of reach of its driver, it comes into reach on the next driver up) I'm less focussed on the Hex route now, but the PIC still allows amazing flexibility. For example, PICS can sink 20ma on each of their output pins, so I could elements of the overall circuitry on/off to suit. Then there's granularity of a digital AGC - it allows 1024 'levels' to act upon - it'd be pretty darned hard to have a discreet circuit accurately act on that level of detail (eg that works out at '0.088mV' when on a 9V supply ...or if on a 5V supply as mine is, then discreet would have to handle granularity down to 0.0045mV). I doubt I'll need that level of detail though - but it's on tap. Also, as you well know, each & every JFET has it's own 'characteristics', so I can tweak the PWM to ensure it's working in the centre of it's range *very* quickly & easily (none of this having to match discreet components to suit each JFET). Another possibility , -once the data is 'digital', it allows all sorts of interfacing possibilities with sexy bespoke ICs. eg How about an 8 channel analog volume control (hex coils + EMI blocker coil) - controlled by digital input http://www.cirrus.com/en/pubs/proDatasheet/CS3308_F1.pdf ). By going digital early in the cct, there ought to be less problems with level drift too. Finally, not forgetting of course, a PIC allows plenty of 'LED bling-age!' I've just spent the guts of two whole nights trying to get my standalone PIC to tell me what its variable contents are while it is running my little AGC program. (this is one helluva steep learning curve!). I've been trying to achieve this by having the PIC send such data to a PC so I can see this info onscreen - at last, I've just got it working! For ease/speed I've previously been working on the AGC solely on the PICKIT 2 development board...but this board comes with a little pot on it that I can vary DC levels into a PIC input pin (essentially simulating the rectified input signal of a sustainer). I'd have to say it's very cool seeing what the incoming sampled DC levels are in real time onscreen as I twiddle the pot (& then seeing the DC level alter on an output pin to suit). This is a major hurdle now behind me & allows me at least now to start thinking about bolting my separate building 'blocks' together. (my driver development has been parked, pending the arrival of an inductance meter from those nice fells in China - to many whacky unknowns/assumptions without one...I need hard cold data!)

Hello gentlemen. I've recently been doing some reading about pulse width modulation using 555 timers as a means of more efficiently controlling electrical motors. The duty cycle is modulated, rather than pushing 100% of the time, it pulses power in the form of a square wave at a (for the most part) undetectable frequency. Just a shot in the dark, but could the analogy of the cruise control be realized as an AGC through the application of PWM to the output stage's power supply (or somewhere else in the signal chain) through a low frequency, say under 20Hz, with the signal amplitude modulating the duty cycle? That's pretty much the path I'm taking by using a PIC in my sustainer circuit. The PIC 'monitors' the sustainer's preamp output level & ultimately adjusts the duty cycle of its own PWM output stream to suit - if you feed this PWM stream into a low pass filter, you end up with a DC level - this DC level is applied to a 'gain control' JFET in the preamp (which adjusts the gain applied to the incoming signal to ensure a constant predefined output into the power amp)

I'm not sure I'm following the line of thought - do you mean power efficiency? If so, it has merit - & it's is one of the (offshoot) benefits of using a PIC ...ie you can program it to say for example "when the input signal level drops below X volts, then make the output pin low"...this then feeds the Power Amp chip DC volume control pin - most of these power amp chips with DC Volume controls are designed in such a way that if DC level on its Volume pin goes below say 0.4V, the power amp shuts down (& then draws microamps). This potentially will save a fair bit of juice. (the trade off being of course that the PIC itself saps juice...but I'm hoping it'll pay it's way consumption wise!) Thanks for your schematic...that's actually a very good circuit, though there's perhaps a bit too much component count going on there! Is this soley your design or is it a tangent off a group effort some few hundred pages ago?! What's your honest appraisal of where you're at with your Sustainer? (in other words, what does your design do well, & what still needs refining)

To chime in on this 'Compressor' discussion.... Firstly, Col is right, the MOSFET in the compressor schematic recently posted is *not* being operated as switch but acting as a Variable resistor (sure, you can use a MOSFET as a switch, but in this particular circuit the results would be terrible!). Personally, I think the compressor being discussed is fairly crude ....all it's really doing is 'limiting' the output of the LM386 . Therefore, the only way to be sure that smaller input signals will 'excite a string' sufficiently is to have a high gain arrangement either at the LM386 (or more likely - feeding into it), which is going to cause you all sorts of problems....think of it along the lines of nailing a car's engine at 10,000RPM with lots of torque readily available at the wheels, but then merely controlling the car's speed with the brake only - not good. What we need is a good cruise control! (AGC). I guess 5 years is a long time for a thread to run & there'll be repitition along the way as new entrants mention stuff that was posted 274 pages ago! A quick search, reinforces this point, here's a perfectly good circuit posted up by CurtisA some 2.5 years ago.... (CurtisA's original post with circuit explanation here - http://projectguitar.ibforums.com/index.ph...t&p=295401) That type of circuit is *far* more elegant. Unlike the, the aussiemart compressor - which is really just a signal shunter (ie when the LM386 output gets too high, it starts shunting the input signal down to ground), the type CurtisA posted up actually varies the gain of the amp. It's not a unique idea...there are all manner of similar ones around the net. I've used a similar 'concept' in my own design (though quite different to CurtisA's schematic) Re the aussiemart compressor - IMHO, for all bar the most basic of sustainer solutions - it's probably a case of move right along folks , there's nothing significant to see here" WRT my own explorations...well, all my separate sustainer 'building blocks' work fine now (ie preamp, PIC AGC/Threshold cct, power amp, driver) - I now just need to 'bolt them all together' & hone. On paper this is small beer, but PICs aren't too great at giving you 'in circuit' visual information (eg "I wonder what the PICs AtoD'ed input level is at present" etc), so I'm now having to knock up a way of getting the PIC to talk to my PC's COM Port so I can see what AtoD levels are going on inside the PIC (via Hyperterm) while it's running in conjunction with the rest of my circuit. I'd have to say at this point that I salute anyone who's designed an all encompassing sustainer AGC circuit using just discreet analogue components - you're all Electronics Demi Gods! Last night's testing revealed something new (I think!) - that even with a good AGC circuit (ie wide output range & no visible distortion on the scope), that there's a tiny bit of 'fizz' just at the point where the power amp chip needs sometimes a little quick 'coaxing' to get the output up a little to get the string to vibrate enough. It's almost as if the output stage is groaning when a quick burst is asked of it ....to use the car analogy again, think of when you're doing 30mph in 4th at the foot of a hill & you put your foot down to try & accelerate quickly...for most cars, it doesn't happen - you just get engine groan. Therefore, I'm now pondering if the driver needs a supporting powerchip that can get supply enough current into it very quickly. Col - I see your schematic uses a transconductance opamp....which is a pretty new area for me (I'm aware they yield a current output directly linked to the voltage input)...care to say why you went the transconductance route & what the win is wrt sustaining devices?

Exactly - as an aside, just about all decent AGC Circuits I've seen require a dual rail approach - The lazy/simple approach would be to go the Quad VCA SSM2164 route, but alas even that in single ended mode, still needs at least an 8V control voltage (& I'd prefer to stick with my 5V rail), that's why I liked that simple AGC - it's works with 5V & it's simple ....the 'detail' wrt my AGC comes from the PIC (there's lots of decisions going on in there!). There is a new fantastic 5V 8 channel digitally controlled audio fader chip that would interface wonderfully with my PIC - http://www.cirrus.com/en/pubs/proDatasheet/CS3318_F1.pdf ...but it's 48 PIN SMT (& bloody expensive at about £20) That's a good point, but with my intended route, the reaction time (in this instance the JFET's controlling DC level) will be controlled by altering the duty cycle on a PIC PWM output stream - this ought to make for a little quicker control. What I did notice last night is that when increasing the power amp gain level (manually), there's a critical point where the whole circuit 'bites' & it starts exciting the string well, but that *very* rapidly runs away & turns into squeal....the conclusion here being is that any AGC will need to be somewhat 'clever' & lightning quick to get to that point of 'bite' but back off quick enough so that the squeal doesn't kick in. In my opinion, that's a tall order for the DIY discreet component route (though it's obviously do-able as there are already commercial solutions out in the market). I also have a hunch, that the driver can be 'right' next to the other pickups, *if* you can control that AGC well (& darned quick)...I reckon the squeal isn't so much a by product of EMI (though obviously it is changing magnetic flux ffields that are the conduit), but more a by-product of unecessary power being applied to the driver (& across all strings) resulting v quickly in uncontrolled positive feedback...in short, I reckon if you nail the AGC (ideally with a smaller drivers ...eg three string, two string or one string variants)), you're well on the to full 'squeal control' , which leaves you with a lot more options with respect to driver placement. btw, I can't open the snazzy last cct, as I'm just getting spammed with adverts, & it doesn't take me past them - even when I click on the "Take me to, blah blah")), or at the very least most need a 9V rail (in order to get enough headroom to get into a JFET's pinchoff area).

For the sake of a bit of balance here (why so rude?), zfrittz6's last schematic, whilst *very* similar, does have quite a few different value components (and some extra ones) I read that aussiemart compressor thread from beginning to end - what a mess (about 5 different permutations, errors on the schematics etc). I'm not sure anyone got the thing working 'as expected' & looks like it eventually fell by the wayside. Who's to say that the aussiemart OP (Brett) didn't just see a similar circuit somewhere else himself & then post it up with a couple of his own mods? (my point being, in this internet age where things get posted, cross posted, modifed, rejigged, re-shared, remodified etc....it's easy to see how replication can pop up) Also some aspects of the aussiemart compessor were at best vague (MOSFET variant), whereas zfrittz6's has the MOSFET shown - maybe zfrittz6 nailed the design? I would have liked to have seen some supporting text from him, but hey, he's Spanish & if I was posting on a Spanish forum, I wouldn't have posted up much in the way of accompanying text in either! You have to remember there aren't *that* many ways to control an Opamp's level (automatically) & most decent variants use either a MOSFET OF JFET either in the feedback loop or at the opamp input (as it goes, here's one I've just found that looks promising as it works off just 5V...which is exactly the VCC level of my present line of attack - (sire from circuit posted up from - http://www.holmea.demon.co.uk/Spread/Spread.htm While I'm here, here's my first handwound 6 string driver (literally! ie holding in one hand & winding with the other - no jigs, vices etc). I used 0.15mm wire ....the core metal is about 1mm thick "L" shaped - taken & cut up from a general metal scrapbox (I think this metal was originally something to do with a PC's PCI bracket - anyway, it's ferrous!) just potted it with paraffin wax- it'll have it's first trial run tonight (I thought I'd embrace being European & place a Euro nxt to the driver to show scale) My single string drivers (0.1mm wire) are sustaining the strings well (including top 'E' & 'B' strings, just honing the supporting AGC circuitry...last night I was investigating whether the AGC works best applied at the power amp chip or the preamp chip. With the poweramp chip I'm using (A TDA7052A), AGC worked best there, but I really want to get the AGC working better at the preamp stage as that's where I'd prefer it went (better interfacing with with for example Roland GK pickup boards etc)

Here's the latest summary for my build... The story so far... LM386 - tried as a power amp. but quickly ruled it out - I saw too much distortion across the driver on a scope. I also reckon that the external component count is just too high (with chunky caps too) for a hex driver. (I should point out that I tried the LM386 very early on & it may have been me at fault)) TDA7284 - tried this chip as AGC circuit (Eeugh! Once again it might have been me, but in my opinion, this one is best left to the lo-fi cassette recorder circuits for which it was intended!) TDA7053A - a stereo power amp chip with DC Volume Control ....low distortion, but erratic results were experienced when using just the one channel (eg inter channel current discrepancy shutdown protection etc) TDA7052A - (a mono version of the above) much better, but a cheeky little gotcha with this chip (vs the TDA7053A) - the DC level for its Volume control is achieved inside the chip (using an external variable resistor - you can't just apply your own DC Voltage which you can with its bigger sibling). I'm still not 100% sold on the TDA705x chip series - the quiescent current is a little on the high side & certainly it's not that efficient when it's cranking. My next 'chip of choice' is actually class D chip ...I just need to work out how to solder 8 wires onto a package that measures just 3mm x 3mm! (I'm hoping that my 'soon to be finished' DIY CNC build will help in this area!). For now though, I'll work with the TDAs. My early conclusions are that a *decent* guitar sustainer defintely needs to produce a distortion free signal (as seen across the driver) ... the TDA705x meets that requirement, so I can push on. IMHO ...the next ingredient that's absolutely key, is a flexible (& accurate) AGC/limit & threshold circuit. Without one,, most homegrown sustainers will liekly need regular tweaking to try & get a good balance of sustain across the strings (& up/down the fretboard) After pondering this AGC/control aspect for far too long, I've decided to use PIC. So, today I've just finished a small 'AGC framework' program for a PIC16F690...this will monitor a DC level presented at one of its input pins (this DC level will actually be a 'rectified' signal level as derived from the analogue guitar signal level taken after the the preamp). The PIC converts this DC level to 8 bits digital ...this then permits *major* flexibility - because once we're in the digital domain, it's easy & quick to tweak things like the guitar signal threshold, optimum signal level (also release, attack etc). Also, using a PIC as AGC etc, still gives me hope I can still go Hex, as the component count will be quite low & the control options very flexible. The output from the PIC is a PWM pulse train - fed into a Low Pass filter (which sounds grand, but it's just a resistor & an electrolytic cap!), ultimately resulting in a variable DC level - depending on whether the incoming signal needs higher/lower gain as observed at the preamp output). I intend using this PIC o/p DC level to feed onwards to a JFET - this JFET controls the preamp gain (a VCA). I'm out to buy some JFETs today to implement this latter bit tonight (JFETs are a brave new world for me, so I'm sure there'll be some issues!). Re my driver - well, I've not given up on the single string hex driver idea yet! I've finally got *all* strings sustaining very well using a single string driver using just 0.1mm wire** - for now, this wire is wrapped around an 8mm 'cut up' nail (the nail body is 3mm in diameter - flat head). To the nail's head I've attached three very small neodymium magnets (3mm x 0.5mm). It performs well. All my testing is back to being done with a sig gen as an input to the circuit board. So why have I gone back to the Sig Gen? Well, simply to remove a lot of the 'transients' & claim back a degree of 'control' (those who have experimented & been frustated at the somewhat erratic results, should appreciate what I'm saying here!). Actually what I have discovered in using a sig gen vs the actual guitar signal, is that in many ways, it's easier to get the strings to excite with the guitar signal - because the fundamental frequency is *exactly* the same - whereas you have to be absolutely bang on with the sig gen frequency or you'll get very poor results. (the driver is still chucking out a horrific amount of EMI when being fed with a sig gen ...for reasons which I've still not got to the bottom of...I can only assume it's because a sine wave represents the 'perfect storm' from a driver's EMI perspective!) Overall, I'm happy enough with progress thus far...still a *lot* to do though! ** I'm still not conviced that 0.2mm (& above) diameter wire is needed for the six string driver - certainly for the current draw I'm seeing with a single string driver, even 'scaling up', I reckon 0.2mm wire would seem overkill), so I'll be making six string driver with 0.1mm wire over the coming days to see how that performs.

double post (no delete option?) - contents removed.

Ok, peeps....this thread is now getting a little 'bloated' (& in recent weeks, I'm not helping!) I can see this thread is no place for my 'blog like' progress report. I can also see that whatever I bring to the table will be simply misconstrued, or used as patronising fuel....& frankly, I don't do "patronisee" - nor do I have time for the threadwarfare that ensues. Also, there aren't enough techie types posting here to stimulate meaningful, focused discussion. When I see 'wishy-washy' used as perpetual counter argument, it's time to stack the cards on that particular avenue of exploration! Therefore, I'll be going into relative radio silence ....don't take this silence as anything other than a guy who's a disappointed at the direction the thread is taking. In my opinion, the whole thread could probably be condensed into about 20-30 pages.It's puzzling why there isn't a Sticky & a FAQ...along the lines of "So you want a budget Sustainer?" with a parts list, schematic, PCB (or breadboard) layout & accompanyining A to Z 'instructable' type note (which would meet most 'just passing through' peoples' needs) I can honestly say, as someone coming to the thread 'fresh' (relatively recently) ....the chaos of disjointed information is a little overwhelming! I'll pop in now & then with the odd piccy & update ...I have a lot on the go (& can only dedicate a couple of hours, 2-3 nights per week) , but I'm setting myself a fairly ambitious target of three months starting now to have a good, predictable sustainer solution, which meets my own needs (watch this space), but for now...I'll walk the lonely sustainer path into my loft alone!

No I've not looked at any of those (but will once the kids are put to bed - though a quick look at that LT1886 sees them quoting output loads of 25 ohms....we're back into very thin wire territory again!). BTW, your DVM with inductance puts you ahead of me ...sure, I can see distortion with a scope (but you can hear that anyway), but I reckon you've got the edge with that inductance meter. When I invester in my coltage/current/capacitance meter about a year ago (it's an all singing & dancing one...does lux, temp & SPL!)), inductance metering didn't seem that necessary(!). Also, it seems if you want to go the route of a meter that has inductance, then often it's to the exclusion of something else! For example a lot of LC meters don't even measure rsistance (&/or Voltage). nevertheless, I'll be piutting this to rights soon & buying myself a meter that doesn incuctance (they're quite cheap on Ebay nowadays) wrt to component selection - I've come to this project 'fresh' as it were, & seek 'leads' from those of a technical ilk. It's becoming quite apparent though that one man's 'accessible budget Poweramp IC' is another man's 'time wasted' crock of s*** IC! Obviously, the sustainer overall 'block' model already exists! (eg that Floyd Rose schematic posted last week)....my main problem with emulating what they've done is... 1. Where's the fun in that?! 2. Component count. 3, Physical size. 2 & 3 are related, so I guess what I now seek, is a creativeway of utlising a chip whose main purpose is *not* the niche area of Sustainers...& tweak the circuit feeding it to make it work (sort of climbing a mountain...just because it's there) Re theoft quoted 'thin driver©' ...I concur with your statements about thin not being the significant discovery. Pete's found a particular combination that yields results, but his somewhat polarized stance does make it sound like it's the only combination that works - incidentally, I'm puzzled at the constant use of the term 'efficient driver' - it would take some degree of fairly involved testing/measuring to prove its efficiency. In electronics, 'efficient' doesn't mean a small, or tightly handwound while coating in PVA or thin etc - it's a bold claim to make without backing the statement up with figures. Not debasing what's he's done though...if it works, it works...who cares (but the efficiency quips does bug the nerdy side of me!). No, in my opinion there'll be heaps of combos in addition to the thin driver© ...& on paper, within reason - it shouldn't really matter *that* much what the wire gauge is ...just so long as you blend the circuit with whatever driver you come up with well. (BTW: does the constant use of 'thin driver© ' suggest Pete will attempt to 'lay claim' to anyone else making a coil sufficiently narrow to fit in a tight space - *even* if it uses toally different wire gauge & circuit?!! I doubt you can lay claim to something already invented, based on thiness alone ?!! )

From my RAF days (some 28 years ago - so admittedly not exactly fresh in my mind!), all things being equal (8 ohms of 0.063mm wire vs 8 ohms of 0.2mm) the current through the driver coil is not related to the wire size, the current through the coil is more to do with the no of windings (inductance) in combination with the VCC of the power amp. So with my .063mm wire, again all things being equal, there'll actually be less resistance to current (lower windings, less inductance = less impedance)...but nevertheless, this thinner wire will struggle when I crank up the VCC (which will increase the AC voltage signal applied across the driver & therefore current through the driver). Re the EMF...once again, as far as I can tell, that not related to the wire diameter...but more how much current you can push through the coil...again this wire being incredibly thin, probably means not a lot, before it starts melting. My LM386 has been stamped on, covered in lighter fuel & set alight (in a Jimi Hendrex-esque manner) ...I have no wish to go back there! I suspect it'll be possible use the TDA7053A to driver a lowe impedance load than 8 ohms - this will be my next tack (eg using less windings of 0.15mm wire for a driver)

There are likely two main reasons why you can't... 1. Pickup wire is incredibly thin...0.063mm (42 AWG) - this size of wire just won't be able to handle much in the way of current (& current is what we need here!) 2. On a normal pickup, the wire is wrapped around the pickup's bobbin too many times.... more windings = more inductance (which makes it hard for the circuit to pump out the high frequencies at high enough drive). I've just 'parked' my CNC project until the weekend - if you're interested, here's where I'm up to.... http://img12.imageshack.us/img12/365/cnch.jpg (it ,might not look much, but that's a solid 1.5 days work there! ...it just needs the motors mounted & I'm ready to roll) Relevance to sustainers? ....*very* easy to make an acrylic bobbin at the drop of a hat! ....so, I can do some more driver/circuit tests in the next night or two! As it goes, late tonight I used some 0.063mm wire as my latest 'test' single string driver . It's wound onto a small nail...impossibly small (8.2 ohm). It's like winding with Nicole Kidmans hair! It now just needs potting (not that there's much to pot) & therefore it'll ready to 'burn baby, burn' tomorrow night I'm expecting this driver to go 'poof' at the slightest hint of a bit of current, therefore i'll be setting the VCC on the power amp very low (at about 4.5V) & feeding the power amp a very low signal! (I just want to prove my 'less turn is good' for the high B & E Strings)