Weird idea of creating audio feedback pedal

[gasmask]

First of all, I thought about modifying boss df-2. But it
would be too difficult to me. So I've checked theory
of audio feedback on 'magic source of knowledge'.
(en.m.wikipedia.org/wiki/Audio_feedback)

And my idea is:
1. Build pedal with input and output for guitar + input for microphone
2. Signal from microphone is amplified (for example by simple lm386n-1) and
  connected to guitar signal in parrallel.
3. Pedal is the first pedal in pedalboard.
4. Microphone is placed nearby speaker of amp.


It's only idea. I will breadboard it in May/June because of lots of work.
What do you think about this idea?

Gasmask

[amptramp]

This has the potential for a lot of uncontrolled feedback and phase reversal.  For example, if you have an A440 playing and the microphone is 15 inches from the speaker, you have a phase reversal because the speed of sound is 1100 feet/second and the phase of a 440 Hz signal is reversed 15 inches from the speaker.  (The A440 wavelength is 30 inches long.)  You could get some of the effect of a phaser or delay, but you are also amplifying ambient noise and you have even less control of the feedback level than you do with an all-electronic feedback chain.  Now if you could move the microphone back and forth, you could get the shimmer of a phaser or the vibrato of a delay, depending on how you do it.

It may be fun, but don't expect consistent results and it may not be that usable in a high-noise environment.  Expect oscillation if the gain from microphone to amp goes equal or greater than unity.

[gasmask]

Well, I thought about adding 3 pots:
1. Between microphone and input of amplifier (sensitivity)
2. Gain of amplifier
3. Output volume of amplified signal

[PRR]

Does your amplifier have two inputs? Plug a mike in the second input and turn-up *carefully*.

While an all-purpose mike input needs a preamp, a mike "close" to a stage speaker has a HIGH output, more than is needed to excite a guitar amp input.

Use SM58 and one of those XLR-to-1/4" adapters.

I propose this method because I think it will do essentially what your plan does, and after a fun-filled hour of howling you will tire of the effect, can sell the mike to your singer. (SM58 is the classic rock-vocal mike, SM57 is the classic amp-mike; they are the same except the pop-filter.)