Replies to This Discussion

Permalink Reply by BrianQ. on April 4, 2013 at 4:28pm

Look up Compressor pedal- MXR Dyna Comp , I've used it for both magnetic & piezo, U can get some pretty lengthy sustain, I don't think U would want a Pickup that close to an amp,it would howl like crazy(feedback). Behringer DC9 goes for $24.99 if yer on a budget.Also Rogue Compressor goes for $29.99. Hope this helps.

Permalink Reply by mike smith on April 5, 2013 at 7:11am

no help at all. i'm asking if an idea is possible and you're telling me to buy something. are you from google? 

Permalink Reply by Craig Mayhem on April 5, 2013 at 7:19am

They sell tiny electronics motors for a couple of bucks. Sustain is just vibrations. Butt it up against your bridge, turn it on... I'm thinking it'd vibrate the strings. Maybe 3-5 bucks for the motor, battery and switch.

Then again, that could not work at all.

Permalink Reply by Michael Recchione on April 5, 2013 at 10:11am

I've never tried it, but I don't think it would work the way you'd like it to, if what you're after is something like a commercial sustain pedal.  It would be more like a very ineffective reverb, not a sustain.  (In fact, one of the ways people used to get reverb in the old days was to put a speaker in a stairwell or hallway, and a microphone some distance away...)

But it might be interesting to try.  You'd have to make sure to keep the loop gain less than unity or all you'll get was is one of those really annoying feedback squeals.  I'm wondering what it would sound like with a gain  low enough to avoid instability ...  I think, because the distance is so small, the effect wouldn't be much.  But it still might be interesting to try it. 

The system is basically an IIR filter, with the (simplified) equation:  So(t) = Si(t) + g(So(t-d)), where g is some gain less than one, and d is the time it takes for the old output signal from the "speaker" to be picked up by the pickup.  In reality, you'll have some multi-path, so the feedback term will actually be a sum of terms.  You can see that g has to be less than one at all frequencies, or the filter goes unstable, creating a squeal at a resonant frequency determined largely by d.  (That's why PAs have notch filters...)

I think, in this case, d would be very small.  This is basically the way something like a spring or plate or room reverb works, except that they use materials (like springs or plates) to artificially increase d and introduce a lot of multi-path.

Real sustain pedals work completely differently.  The most common (and all the classic ones) work by overdrive and/or compression.  These schemes operate an amplifier in a very non-linear way, so that the output resulting from a very tiny input signal and a very large input signal are about the same - something that looks like a completely saturated square wave with the same fundamental frequency as the input signal.  The "sustain" comes because the amplifier continues to put out about the same thing even as the string vibration decays.  The side effect of this sort of sustain is that the higher harmonics of the fundamental are emphasized, so there's a lot of coloring of the sound - sometimes good (like classic tube amps), sometimes not so good (like older transistor amps).    But, in any case, you won't get anything like that from the scheme you proposed.  Still might be fun to try and see what happens. 

Permalink Reply by BrianQ. on April 5, 2013 at 7:36pm

No I work in a music store. And we sell the Fernandes Sustainer kit $259-$369 US(pricey). And I have seen what this circuit looks like,it's got close to a 100 tiny SMD components in it(2 sided circuit board),so it's a pretty difficult build.I don't think a Piezo would work with it because it only works with a special design pickup, as well as the Sustainiac system employs a special pickup. to answer yer question,not with a Piezo.