Tank reverb noise-gated

[PRR]

I have never seen this trick, yet it makes good sense. The old-old Standell "The Imperial" guitar amp has a noise-gate around the reverb tank.



Recovery amplifier Q10 is "off" at rest. When signal is shoved into the tank, it also feeds side-chain Q9 D2 D3. This charges C28 to a voltage which now biases Q10 "on". When drive signal stops, bias decays back to "off" in a couple of seconds ("tails").

Yes, don't tell me everything is upside down. Positive Ground. This was 1971 and many designers still thought in Germanium, even though this is Silicon. (There may have been a Ge version before this.)

[antonis]

I'd never seen a cap (C22) rated at 64V...!!! 
(plenty of them at 63V, of course..)

[Mark Hammer]

Hey, it was the 70's, and not far from the 60's; LSD, free love, don't trust anyone over 30, etc.  We could spec caps for whatever values we wanted.

One sees a lot of "unusual" values and specs for caps from that period.

The idea that a spring tank should only be heard when someone is playing into it - as opposed to being kicked or otherwise shaken by sources other than whomever is plugged into the amp - is a sensible one.  Of course, as with any gate, the time constants are critical to keeping things musical.

I remind folks of the same strategy, as applied to the Boss CE-1 and A/DA Flanger.  Both employed a gate sub-circuit to keep delay-path noise out of the output when the user wasn't playing.

A project that appeared in Electronics Today many years back had an optional limiter preceding the spring tank driver, to constrain the "sproing" from initial high-amplitude peaks.  Given springs' susceptibility to mechanically-generated noise, having both a limiter and gate as options makes perfect sense.

Thanks for that, Paul.

[anotherjim]

BBD and early digital delays had the gate to stop the unholy racket on power up due to the random junk in the memory. If regen was set high, that racket would go on quite a bit. Noise fans would love it. Ordinary mortals would think it's broken.

Digital with a CPU in control can clean the memory during setup, but often also clamp the audio output until setup is complete.

[vigilante397]

Hey, it was the 70's, and not far from the 60's; LSD, free love, don't trust anyone over 30, etc.  We could spec caps for whatever values we wanted.

Thank you for a most enjoyable quote.