Help me crack this guitar signal 'phase' issue

[HankMcSpank]

Ok, what I'm trying to do is make a sustainer for a guitar (this uses magnetism to keep the string vibrating indefinetly)

I've spec'ed the driver coil & built it.

I created a simple little circuit (preamp & small power amp IC) & squirted a sine wave into (at all the six strings frequencies in turn) & achieved good sustain with all strings.

Excellent...or so I thought!

So I then replaced the sig gen with the guitar's bridge pickup output signalas the 'source signal' ...in this scenario I can only get good sustain on the three lowest (thickest) strings.

now this flies in the face of logic - when using a sig gen you have to get the frequency 'bang on' (tricky) to achieve string resonance/sustain, but using the guitar string itself removes this issue.

I'm thinking here this must be a phase issue. When using the sig gen, there is no danger of the source signal - ie the output of the sig gen - being affected by the sustainer driving the string & cancelling the source signal. But when you use the the sustainer with the guitar string & source pickup, then there's a very real possibility that phase differences can cause havoc with the sustaining.

So to my question ....say for a given frequency of 330Hz (top E String)...how can I construct a circuit where the phase can be altered tweaked to see if I can coax sustain (ie to prove that it is indeed phase that's the problem)problem?

[Wavebourn]

What happens if you increase an amplification factor, and power of your exciter?
In case of wrong phase the string should resonate, but resonate on harmonics. If it does not resonate that means feedback is too low.

But speaking of sustainers, I used ordinary compressors, with good practical results.

[cbdb]

Isnt that like using your amp to feedback the signal? (the way people have been extending sustain for forty years)

[muz64]

How about this:

http://en.wikipedia.org/wiki/All-pass_filter

Choose R and C for your corner freq (330Hz). Use a pot for R so you can tune it.

Murray

[HankMcSpank]

Originally Posted by cbdb

Isnt that like using your amp to feedback the signal? (the way people have been extending sustain for forty years)

Yes & no. The method you speak of uses acoustic feedback...& it's somewhat erratic to get right (it helps if you have a Marshall Stack turned up to '11' - not exactly what most people living in an apartment can do!)

Waveborn...the problem with cranking the power levels up...it that EMI spews out & into the source (bridge) pickup ....this gives a result akin to a microphone getting to close to the PA (positive feedback squeal)...so cranking the power up isn't an option.

I still think it's a phase issue - why else would the string resonate fine with a sig gen as the source....but when the bridge pickup is used and at similar drive levels to the sig gen - the strings don't sustain. I believe that phase discrepancies is cancelling some of the energy as fed into the string.

[Wavebourn]

I once saw a man in Walnut Creek, on a farmers' market, who played the instrument he invented. It was like an upright guitar with more strings. It seems to me it was exactly what you are trying to achieve.

[HankMcSpank]

Originally Posted by Wavebourn

I once saw a man in Walnut Creek, on a farmers' market, who played the instrument he invented. It was like an upright guitar with more strings. It seems to me it was exactly what you are trying to achieve.

i have no wish to achieve playing an upright guitar with more strings at a farmers market.

[darkfenriz]

First, increase the hight of the sustainer pickup, it should be very close to the strings and this should be no problem unless you're using a floyd rose. Possibly you can need to have it closer to higher strings (EBG) than lower (DAE).
I agree that if the system doesn't resonate at a basic harmonic it should do at 2nd or 3rd, but phase shifting can be interesting here anyway.
A one op-amp phase shifter is the circuit you may need here.
BTW are you using single coil or humbucking pickup for that purpose?

[HankMcSpank]

I realise about the sustainer height being critical (this is in testing phase - the sustainer has adjustable height pole pieces but also because it's not permanently in place, I can freely move it up/down height wise) I have the pickup located as close as psscible to the strings *but* just far enough away to avoid the strings hitting the sustainer at the higher fret positions. - so spacing isn't the issue (Like I say - heaps of resonance when feeding the sustainer a sine wave from a sig gen

What pickup am I using?

I'm using a cheap catalogue stat copy with a single coil brifge pickup as the source, for no other reason than if I can crack it with that ...then the all other guitars should be a breeze! (I believe Sustainiac or Fernandes say that theie sustainers can only be used with other humbucking pickps? Having dablled with these for a while now, I can relate to that!)

[Phostenix]

This may give you some help:
http://projectguitar.ibforums.com/in...ic=16984&st=90

Search for sustainer on that site & there are lots of threads about building & troubleshooting. The main thread has been closed, but there are still lots of others.