Hank McSpank

I can certainly relate to that...I'm new on the thread, but even this early on, there's been at best a dismissive (bordering on patronising) response to initial posts. I'm sure there are a lot of folks who pass through this thread that haven't got the faintest idea about electronics or the technology & just want to build a cheap sustainer - but that doesn't mean everyone is clueless. For what it's worth (& *without* wanting to sound dismissive myself!), I think the basic design promoted here is a fantastic starter sustainer - & cheap as chips, but I'd imagine it's not where most want to end up. (even though it seems to yield decent results). An earlyish observation - it seems most attempts have been to use a driver based loosely on a pickup format ...I'll be taking a different tack based on some related info gleaned from totally unrelated sites (& in the best tradition upheld on this very thread...I'll keep that particular tack to myself for now!) I haven't got all the way through the 280 odd pages, but as of yet, I've seen no indication/data as to how much electrical power each string needs to get it to 'excite' satisfactorily (ie open string through highest fret per string). This is a little surprising....without such info, the resulting circuit proposals would seem to be very much 'hit & hope'! (sure, I'm aware that there are variables...driver efficiency, core type used etc - but I've not not even seen a general ballpark figure) I'd pondered this myself (even posted the coil resistance a couple of pages back), but even though I have an old GK2A lying around & could readily experiment - I doubt I ever will, because 1. I just can't see those six small coils (with the limited amount of copper & tiniest of magnet) ever being able to handle enough current to drive a string! And 2. Once again, it's a pickup design...& at this stage, I don't think that's the best way to go (design wise). Re Variaxes... very current, I have several related mini projects relating to Variaxes pending (once the weather warms up here in London & I can venture into my workshop without freezing my Nads off). He's my Variax carcass, which I knocked up some circuitry to drive midi synths... (I also added a magnetic pickup to the guitar ...the aformentioned bespoke circuit allowed a mix of piezo & magnetic pickups). I intend installing the original removed Variax guts in a standalone floorboard & ultimately driving these guts from a midi guitar (no need to carve up the intended guitar then) Anyway, we're veering off! Re your VG-99, fed via a GK2A. Hmm....the GK-2A is a tradtitional magnetic pickup design (albeit six mini ones!) -& therefore it's going to suffer from the same problems that traditional magnetic guitar pickups have by being placed in too close in proximity to the sustainer. You might have a bit of a win here, because a GK pickup being so narrow & placed so close to the bridge, puts more physical distance between the driver & the GK2 - distance is good!

For fundamental frequencies, I reckon this is the band of frequencies (for a 24 fret neck)... String 6 E = 83Hz open string thru 332hz (highest fret) - however to allow for alternate tunings, say 70Hz thru 400hz String 5 A = 110Hz open string thru 440hz (highest fret) - however to allow for alternate tunings, say 85Hz thru 500hz String 4 D = 146.8Hz open string thru 552Hz (highest fret) - however to allow for alternate tunings, say 110Hz thru 600hz String 3 G = 196.0Hz open string thru 784Hz (highest fret) - however to allow for alternate tunings, say 150Hz thru 820hz String 2 B = 246.9 Hz open string thru 987.6Hz (highest fret) - however to allow for alternate tunings, say 210Hz thru 1050hz String 1 E = 329.6Hz open string thru 1,318Hz (highest fret) - - however to allow for alternate tunings, say 290Hz thru 1480hz but for a sustainer, you'd obviously want the octave harmonic, so when factoring for filters, you'd need to double those figures above.

Yes I know...but remember, I'm going to try a string driver that has a higher impedance (the aim being lower power per string) & this particular chip can drive low loads (unusual for an opamp), eg... http://www.elecfree.com/electronic/portabl...fier-by-ne5532/ In that circuit it provides 50mW RMS @9V into 32 Ohm (with very low THD), which doesn't sound like a lot, but if I can get a really focused string driver it may work ....if not, perhaps crank the VCC up (it goes as high as 22V) to suck more power out of it. Ultimately, if I have no success, I'll get 30p's worth of fun out of it by leaving it upturned on my wife's favourite seat ;-) Like I say, I reckon for a hex pickup to work, each individual driver (& circuit) will likely need to be per string 'customised' & should be driven with the least power that I can get away with!

You're asking me to post up driver design...when at this stage, I've not even had a chance to fail miserably in the privacy of my own loft! My initial plan is to use 38 SWG wire to try and wind a single string test driver to something in the order of 40 Ohms. I'm thinking of first trying a NE5532N to drive it - I'll feed a test circuit sine wave from a signal generator & keep cranking up the amplitude (& if necessary, the circuit's VCC) to hopefulyl get a high E string stimulated sufficiently on a test rig single string guitar. I reckon if I can get each of the string just past the edge of being stimulated, then there'll hopefully be enough separation (additionally, a large part of the separation strategy comes from the fact that a driver will only be active when its corresponding string is being played) I'm envisaging that each string will possibly need a different driver characteristic (and possibly circuit!)....it's very early days, I'll probably fail - but it's not a strong enough argument *not* to try because others haven't totally nailed it. If it works...the possibilites are quite exciting.

Ok then (& btw, I'm not throwing away anything!).... 1. Massive synergies with midi guitars (which I'm into big time!) 2. Much *much* lower power in use for the majority of real world playing scenarios (=less emi flying about)...lower power per string also means potentially less interaction of the magnetic fields between strings. I'm seeking an incredibly small tight focused electromagnetic field, with the driver very close to each string in turn....I reckon this can only be achieved with a hex solution. 3. Better 'control' per string, which in turn avoids a one size fits all approach to sustaining for example chords. A nice tight frequency band for each amp circuit (on account you're only handling one string of limited frequency band - open string to highest fret) 4 I actually need polyphony for a cunning idea I hope to exploit once I get there with a good working hex driver! The particular mono driver you've researched, may be an efficient driver & yield the required results, but when you think about it, when soloing spewing a dominant note across all the strings isn't such an efficient approach?! If a string isn't being played then why whack it with the same magnetic force as the sting that is...far better to have a much lower power focused driver only being active if the corresponding string is being played. There's certainly a beauty in the simplicity of your design (driver & circuit) & the research you've done is the best available anywhere on the web....but there's always going to some of us are going to want to head of in different directions...not to be awkward or throw away the invaluable research that's gone on here, but just to see if it's a viable concept & see what it can bring to the sustainer party. I'm not trying to reinvent the wheel...I just want to add more wheels! There doesn't appear to be a whole lot of people who've tried to get a working hex driver ...but I'm very interested in surmounting the unique problems associated with a hex driver. Thrill of the chase, I climbed it because it was there blah blah** ** Insert your own cliche to suit.

Having mulled this a while, I'm sticking with the LM386 format as it can be physically condensed easier (as the chip is available in SMT). Ideally, I'd like a stereo 9V 1w power amp chip in SMT format...but I haven't one as of yet. Why stereo? Well, I still intend pursuing the Hex pickup route & then I'd only need three ICs (and space is of a premium) Just one comment about the AGC - I'm pretty sure this is *not* the correct circuit needed for a sustainer's preamp circuitry. I reckon what you really need is a limiter. An AGC will try & boost the incoming signal when it's low...but with a Sustainer, you're going to have incoming signal in spades from the off! What you really need is a way of limiting the output to a fixed limit. Here's how I'll be tackling it... 1. Make up the LM386 power amp stage first (breadboard) 2. Make initially one single string driver (though ultimately six needed) 3. Using a Sig Gen & scope, drive the amp stage direct to see what signal level the LM386 needs for best performance at each string's limits (open sting & highest fret) 4. Design *individual* string preamp circuit to fulfill the signal level info derived from step 3. (ie six 'per string' dedicated preamp circuits) My line of figuring here is that each string requires different amount of physical 'drive'. Also each string has a limited band of (fundamental) frequencies. Therefore it follows that each string will need a different amount of gain &/or driver for the unique frequency range it's capable of producing. I'm only upto about page 70 of this long thread.... so can anyone tell me if it's discussed exactly how much power is required to move a string? The datasheet shows that an LM386 typically yields about 500mw at 9V @8 ohms, but that 'power' will be dispensed across all strings. I'm intrigued to know how much power say a top E string needs to get it moving sufficiently. Ok, so there's a lot of variables (efficiency of driver, type of string, distance from the string), but how about for a typical situation? (ie a reasonably efficient driver, fairly close to the string etc)....what type of electrical power are we talking? I'm thinking that's it's actually likely to be quite low (say 200mw-300mw?). Such info would help greatly in working out some hex cicuit & coil prototype variants!

Donovan- thanks for taking the time to draw up your circuit. Re signal polarity, I see with your preamp, that your signal feeds into a non-inverting input then onwards to an inverting input. This means the signal driving your amp chip will be 180 degress out of phase to the original input. Does your final amp chip right that? psw (or anyone). Is the LM380 phase inverting or not? (or somewhere in between!) Re the orientation of the coils & subsequent electromagnetic field...I've still to read a lot more, but I'm thinking here that the electomagnetic field from the driver will be pulling down & up on each string - is this correct? (ie this force being 90 degrees removed from direction the string moves when plucked by the player)

The bit about a pickup not being a driver is coming through loud & clear! Since I'm no expert on driving speakers (though I'm fine with the concepts), i guess I need to do a lot of reading (& prototypes!). Re downloading the whole thread - it's far easier than you'd imagine... At the top of each page for the thread, there's a drop down menu entitled 'Options' - from there select 'Download this topic'...you'll then have two actual downloadable formats to choose from - I chose MS Word. It's all pretty self explanatory from there. After opening in Word, I opted to select 'all text' & then made all the fonts therein the same size, type & colour - makes it a whole lot easier on the eye!

Ok, so I've made a start reading the thread at page 1! (a bit less onerous, once I realised it's possible to download the whole thread into a Word Doc)...it's going to take a while though! Funny how all the stuff in my head is making an appearance as I progress throughout the thread (phase lock looping etc!) Last night I ventured into my loft - still *way* too cold to make a start, but while up there I was able to measure the DC resitance for each individual string coil of an old Roland GK2 pickup I had lying around. Alas, each coil measures 54 ohms (I'd hoped it would be 8 ohms....voila instant hex driver to start working with!). Still, I guess all six coils could be wired in parallel, which would yield a resistance of about 9 Ohms. Anyway, I thought this little bit of info worth posting up as without a doubt the biggest stumbling block for most will be making up a driver .....if we can use Roland GKs (which some - like me - may have lying around, or there's always Ebay!), then so much the better!

Actually at this early stage I'm just spewing out thoughts for others to comment on....the simplest form of regulator is a zener, but I'd be inclined to use a proper regulator transistor. I'm more of a tinkerer than designer, though as I mentioned a couple of posts back I was trained in Electronic fault finding by the RAF....so I can handle the usual associated test kit fine (eg I have a USB Digital storage scope, which might be handy for comparing phase differences between the original & driver signal) Having slept on it...I'm inclined to dispense with a single rail opamp solution altogether - this will obviously mean I'll walk a solitary path on the circuit aspect, but my reasoning being is that I'm into midi guitars...they already provide dual rail to the guitar (+7V & -7V) & I've already done a fair bit of experimentation with the TL series (to get my own DIY Midi guitar interface working with piezos) - my guitar will never be used on stage, so I've no need for a portable solution - & batteries suck! Therefore at this stage I'm thinking of a TL072 front end preamp (dual rail power supplied externally) driving a Fetzer Ruby amp variant. I'll also possibly head off on a path of individual driver per string (hex) as there may be some synergies with other ideas I have ...I'll therefore probably focus on just getting a small driver working for the top E string initally (as it goes I doubt I'd ever need a driver for the A & low E - for my needs, I only really need the sustainer for the high end). Since 8 ohms is not a variable for the fetzer Ruby & I need to condense the driver (becuase of one driver per string), then I'll need to go down much lower in wire gauge...becuase less cross section = more resistance, which means less coil turns, which means the single string driver can be made smaller (which is very necessary if you're going to have six drivers!) My problem here is my workshop is in my attic - & there's no heating up there ....it's freezing here in the UK right now...so this is just a fact finding/canvassing mission right now until the spring, when I can start this in earnest.

Everyone talks of the Fetzer Ruby & how common it is on the net...therefore I googled it & found the basic schematic. looking at the board layout on p280 (which has the requisite mods?), I reckon the modified FR schematic might look like this? Have I missed anything (Harmonic switch aside!) or made any errors? re the wire...I'm hearing 0.2mm is paramount, but by the looks of it here in the UK at least, it's also rare. Best I can find is 0.19mm ...does 0.01mm matter that much? re going the opamp route...if stability is paramount, how about a dedicated single supply opamp (eg http://focus.ti.com/lit/ds/symlink/opa340.pdf) with a regulated VCC @5V? Sure, you're not saving much in the way of components, but biasing an opamp with a resistor network is a bit rough & ready...therefore you could dispense with that aspect & use the component space savings for a simple VCC regulator? As the battery life wanes, you'll still have a solid 5V ...this ought to be better where constant dependable results are the end game.

Just a thought...has anyone constructed a one string 'plank guitar' as a test bed? I'm thinking here a plank of wood with a hole drilled at one end to thread say a high E string through from underneath - the string then goes over a pseudo bridge (a small piece of wood lying on the aforementioned plank!) - at the other end of the plank -equi-distant to a typical guitar neck length - would be another piece of wood similar to the one used in the pseudo-bridge.....& then into a guitar tuner (machine head). An old pickup as the...erhmm - pickup...to feed the driver circuit Voila the makings of a guitar! The benefit here being... 1 you can get easy access under the string (to place the driver - asure I know you can hold the driver from above...but not steady & you have to remove the neck pickup first etc)) 2. Being able to quickly hold the driver securely in place ...at the optimum/preferred height from the string (nobody minds screwing test drivers into a plank of wood!) 3. The pickup electrics are stripped to a bare minimum - simplifies things. 4. No damage to your own guitar (I know from experience how testing stuff on your guitar ...eg hand held driver over the guitar can end in marks, scratches etc. Of course this only works if you have a spare pickup & tuner lying around (I do)...but thought it worth mentioning anyway, as I'm sure the amount of in & out at the R& D stage would get a little tiring on a restricted access normal guitar. Likewise for the circuit...I'd imagine a breadboard has got to be the way to go for fast prototyping of the circuit (http://www.tinyurl.com/86aezg - components can get whipped in & out very quickly) & how about this for brilliance - http://uk.youtube.com/watch?v=ZfNGYTT1IM0 (yes, I've read the "best wound by hand" comments...but I'm pretty confident that Fernandes don't!)

I don't feel let down at all ...it just a little puzzling not to have a circuit diagram posted up for a device that uses an electronic circuit to drive it! (& whether I'd paid or not, I would have felt a little cheated to have waded through 282 pages & not see one!) Surely one of the purposes of the thread is to evolve a good basic sustainer design (from which folks could then set off on a journey/variant of their own) but for anyone to do this, they'd need to see the basic existing circuit?! Most excellent - I look forward to seeing it. (even a photographed hand drawn sketch would be great)

Duplicate post (can't find a delete post button!)

I'm certainly not after everyone to do it for me, but it would seem stupid to reinvent the wheel...hence my question about a circuit diagram ....it's surprising that the thread has got as long as it has without a couple of circuit diagram variants attached? I guess I'm just going to have to have a monster session wading through it after all! Off topic - I've recently just finished off designing my own onboard circuit which blends piezos & magnetic pickups & also drive a midi guitar unit (from an old Variax body http://uk.youtube.com/watch?v=mBYPqqGdcKg ) so I'm certainly up for a challenge!

Again...tks for taking the time to reply. I should set out my stall...I was trained in electronics in the British RAF (not in design, but repair)...so none of the sustainer concepts are hard to grasp (or circuits to read) You might think I'm being lazy, but it seems crazy that you've done **so** much fantastic work, that anyone new here still has to set off on an unecessary journey. Unless I'm missing some obvious posts...none of the links in the foot of your sig actually has a link to the latest variant of the circuit used? (sorry if that comes across a bit blunt...it's not meant to - a circuit speaks a thousand words & a 282 page thread is just too much to contemplate!). Maybe I've jyust got to start heading back from page 282 to find the 'end schematic'? What you've posted in your last post is more a board layout...sure, it's such a simple circuit I can almost visualize the circuit in my head from it...but it would have been nice to see the actual circuit diagram...mainly to see how the harmonics switch fits into the overall circuit *including your driver*. You say the harmonics switch is just changing the phase, but that'd still nice to see in circuit format (looking at the board layout wiring, it would appear to be a 180 degree phase reversal...my initial reaction is that this seems a little puzzling ......as I'd thought that'd just kill off the vibrating string pretty darned quick?) Re the footswitch...well my reasoning is that guitarists often have their hands tied up...I thought it'd be cool to have a 'momentary make' footswitch to bring in the harmonics on the fly (I'm aware that probably in a long sustain playing mode a guitarist's right hand is propably free to do any onboard switching)...but also sometimes it's just cool to have the bare minimum of switches on the guitar itself! By using a footswitch it rids you of one at least! (I'd be doing this for a studio guitar...not a live guitar, so it doesn't matter too much to me about onboard switches on the guitar...in fact less is more in my case - the less drilling on my guitar the better! I'd also toyed with the idea of a longer fade in harmonics option (user adjustable)...I may be wrong but sustainers I've seen to date tend to have a very quick impact once the harmonics switch is flicked. Therefore I thought it might be nice to have that aforementioned footswitch that once pressed the harmonics fade in over a user preset time(approximate time!). But hey...you've done *amazing* work here - I don't want to come across as some new poster turning up trying pick holes in all your good work!

Ok, thanks for the replies. Re the circuit - I see one in your tutorials...but I can't see where the harmonic switch fits into the equation? (the circuit I'm referencing is the one lifted from a small amp design driving a speaker - is there an updated one showing where the harmonic switch fits in). Without referencing this it's difficult to reply to your specific points, except I was thinking my proposed the footswitch wouldn't need to be in the actual overall signal path & could merely be used to activate a solid state relay, whose contacts in turn enable the extra circuitry needed for the harmonics) Re the piezos...point taken (& concur, as I had considered that there might be a problem generating enough energy at the bridge!!)

Obviously, by arriving here...I'm interested in a Sustainer type device, but with a slight different mod. I would like the sustainer to fade in a harmonic, when a foot switch is pressed - yes, I know this would need some wiring from the footswitch to the guitar onboard circuit, but I'm toying with the idea of a ring tip sleeve & using a stomp box to have the 'switch' (using the spare 'ring' to ground as the activation for the harmonic to kick in). ANy thoughts...comments? Also does anyone have any comments about possibly reversing the function of hex piezo bridge saddles to make them excite the strings thereby yielding a form of sustain?

Post deleted - wrong thread!