Reverb driver design?

[Kevin Kuehn]

I tried driving my Super Reverb spring from the speaker last night. Feeds back really easy. Finally got up to a 1k resistor in series and then it would work ok at low reverb levels, but it was still a very peaky sounding reverb.

What happens is that the positive feedback finds the springs natural resonate frequency, and it then turns into an oscillator at that frequency. Maybe a bandstop filter at that frequency would help. But then you're getting back to more complex circuitry.

Kevin

[Enzo]

Try adding a series cap to limit low freqs getting into the pan drive.

[Kevin Kuehn]

With a 22 ohm resistor and .1uf cap in series with the pan input I can get some usfull reverb at low return levels, but its very shrill and bright sounding with little sustain.

This is with an Accutronics three spring medium delay pan. These springs can pass positive feedback better than you'd think. This one will easily squeal at 5k and above.

This is really easy to try with any Fender reverb amp. You don't even need to get inside the chassis to make any of the connections. The organs with the separate reverb amps are an all together thing. No direct feedback issues with that setup.

Kevin

[Steve Conner]

I can't imagine the computer power it would take to calculate the phase relation of the output of the spring unit to the input. It isn't a straight wire, so to speak.

Have you ever tried connecting the output of a digital reverb box back to the input, and slowly turning up the levels until it starts to freak out? That's one way of having a computer find the answer for you.

[Enzo]

But that is not the same as electrical feedback.

When a reverb pan feeds back it is a mechanical issue, not one of electrical phase.

Exception being poor lead dress, and again that is not the pan's fault.