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On Friday, May 12, 2017 at 9:25:22 AM UTC-4, Scott Dorsey wrote:
Ralph Barone wrote:
Like any other feedback circuit, you just have to ensure that the loop gain
is less than one at all frequencies where the phase shift through the loop
is 0°. So just keep the loop gain less than one (ie: feedback is lower
level than the original signal) and it should all come out in the wash.

Right, and a lot of depends on how long the delay of the reverb is. The
Accutronics one out of the Hammond has a 33ms delay between input and output.
So if you put it into a positive feedback loop, it would howl at about 30 Hz.
And it's easy to just highpass the system so that is out of band.

It's not really all that unusual for people to use spring tanks in a feedback
loop in order to get a longer reverberation times. With some guitar amps,
you can in fact make them self-sustaining so with the gain up they just ring
at one note forever, and that note gets increasingly distorted as they go on.

Not to say that I've seen this, but it shouldn't be difficult to achieve
with a spring reverb.

The king of this technique was the LT Sound Microplate Reverb which managed
a very smooth and not-clangy reverb with a very long reverb time using
fairly inexpensive spring tanks.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

I agree that I have never SEEN a guitar amp with the springs driven by the power amp, but if it was done, it could work.

It would have the same limitations that any other reverb system with feedback has..... and that is as the other poster said, the gain around the loop has to be 1.

The tape loop or bucket brigade or any other reverb system has same limitation. With a tape loop, if the feedback is 1 the tape loop will create an ever increasing echo that becomes a continuous feedback sound.

A spring reverb with feedback could work as long as the feedback gain is 1 which is the same limitation all the other revers have.

To avoid a flame war...I agree that I have never seen it done in practice.

m