Regenerative feedback sustainer???

[Satamax]

Hi guys!

Well, i like creamy distortion, and thought, can regenerative feedback, or local positive feedback be used to increase sustain?

Thanks.

Max.

[El Caballo]

The problem is controlling it.

With acoustic feedback, you can mute the strings. With electronic feedback, there's no way to interrupt the feedback loop, and you get uncontrolled howling.

This is why the systems I'm aware of (Sustainiac, etc.) work on the guitar strings, not the electrical signal downstream.

[blodviol]

I guess you could feed a positive reverbed signal back to increase reverb length, like in a delay circuit.

Or you could feed back a comb filter of some sort, but then i guess it wouldn't be positive as such, but out of phase. That might increase gain.

Just my two cents...

Tríste

[Rob Mercure]

The classic "E-Bow"

Rob

[bob p]

oh no! i'm having flashbacks of Black Oak Arkansas!

[Arthur B.]

Hi guys!

Well, i like creamy distortion, and thought, can regenerative feedback, or local positive feedback be used to increase sustain?

Thanks.

Max.

Aren't regenerative and positive feedback the same thing? Anyway, positive feedback is used all the time in guitar amps. Bypasing a cathode resistor introduces positive feedback.

[Bruce / Mission Amps]

Aren't regenerative and positive feedback the same thing? Anyway, positive feedback is used all the time in guitar amps. Bypasing a cathode resistor introduces positive feedback.

I never heard the before.
I can see it eliminating feedback.

[rocket]

I never heard the before.
I can see it eliminating feedback.

The cathode bypass capacitor is no positive feedback, it decreases negative feedback.

[Arthur B.]

The cathode bypass capacitor is no positive feedback, it decreases negative feedback.

How do you think it gets decreased in the first place?

[Rob Mercure]

Arthur,

I'm not sure I understand your response but an unbypassed cathode resistor creates "current" negative feedback - the current passing through the resistor creates a voltage opposite that of the plate supply lowering stage gain. Bypassing the resistor with a capacitor allows AC current flow while blocking DC. It reduces negative feedback but it does not produce "positive" feedback. While this might seem a little counter intuitive positive feedback is defined as increasing overall gain by adding back some portion of the signal in phase - not by reducing negative feedback. Or, a "negative negative" doesn't equal a "positive" if this makes sense.

You are correct that 'regeneration" and positive feedback are the same with the usual result referred to as an oscillator - but early radio receiver designs sometimes managed a controlled degree of RF regeneration to increase signal level. But since the regeneration was only the single modulated radio frequency it was easily accomplished with tuned circuits - unless you wish to have a single note sound forever it's a bit trickier with guitar amps.


Rob

[Tim Hall]

revival

I'm going to revive this topic...I had the same crazy idea as Satamax too...came accross this thread after looking for precedents.

I've been wondering what would happen if you miked some of the output back into the beginning of the signal chain with a very small delay through a volume pedal. The idea is to get sustain and controlled howling feedback without the insane volume required to re-drive the strings on your guitar.

One idea I had to accomplish this would be to butt the headstock of second guitar up to your cab - so it's constantly resonating - and mix the signal in with your playing. Crazy? Worthless idea? Maybe a pickup could be modified to work like a mic near the speaker, only produce a resonant, rather than microphonic signal?

[rathmann]

What about something like this?

http://projectguitar.ibforums.com/in...howtopic=16984

[Tim Hall]

I've seen somewhere else a similar pickup/sustainer...think it was called the sustainiak or something.

I'm think something more along the lines of a foot-switchable effect. I'm very happy with the sound of my S-S-S guitar, and prefer not to mod it...I especially don't like the idea of mixing active electronics with my pickups.

Maybe it could be modded for setup like I suggested - more as mic placed in front of the cab, instead in the guitar?? I'll look it over some more.

[mykey]

[QUOTE=Satamax;18864]Hi guys!

Well, i like creamy distortion, and thought, can regenerative feedback, or local positive feedback be used to increase sustain?

Thanks.

positive feedback IS used to create sustain in the first place. the sound coming from the speakers of the amp reaches your guitar and causes the strings to vibrate- this IS sustain, the root cause! the more gain your amp has, the more sustain (regenerative feedback) returns to the guitar strings.
in order to accomplish this the sound from the speaker must be IN PHASE with the motion of the guitar strings.
Also I have built amplifiers with positive feedback circuits that recirculate in phase signal from one stage backwards to the previous stages. this causes regeneration of signal (sustain) within the preamp circuit itself. so yes it is possible, and there are amps out there that have been built this way.
also very good question- someone is thinking.

[Tim Hall]

...Also I have built amplifiers with positive feedback circuits that recirculate in phase signal from one stage backwards to the previous stages.

Sounds interesting. How did you go about controlling it, or keeping the amp from running away into oscillation?

Addendum: came accross this old ampage thread:
http://www.firebottle.com/fireforum/...7647161z7ka5jU