Author Topic: Effect of PT2399 anti-latchup circuit  (Read 533 times)

Pimpom

Effect of PT2399 anti-latchup circuit
« on: July 01, 2020, 11:37:16 AM »
I'm not exactly new to electronics but this is my first foray into echo/reverb.  As a first experiment, I built a simple reverb unit based on the PT2399 and it works as expected - except that, when the unit is switched off while the amplifier is still on, there's a whooshing decaying squeal as the unit powers down (I used a separate regulated supply to test the reverb unit). This doesn't happen if the unit and the amp are turned off at the same time.

The delay control pot has a fixed 2.2k resistor in series to avoid latch-up, but then the minimum delay is around 55 msec. This was also expected. Further reduction of the delay time would need an anti-latchup circuit and I've designed one using a MOSFET.

I could just go ahead and build another unit that includes the anti-latchup circuit but I was wondering if I could save time by making use of other people's experience. Does the PT2399 produce some extraneous sound when it comes on with the anti-latchup circuit?

Pimpom

Re: Effect of PT2399 anti-latchup circuit
« Reply #1 on: July 01, 2020, 12:24:16 PM »
Somehow I failed to notice that there's a "Building your own stompbox" section (but saw the Digital & DSP section just below it). Could the mods please move this thread there or is it OK if I just repost it?

nejir

Re: Effect of PT2399 anti-latchup circuit
« Reply #2 on: Yesterday at 10:02:57 PM »
During the power-on of the circuit, if the delay resistance from pin 6 to ground is less than 2kΩ then the PT2399 may latch-up, which will make the chip to crash and stop. ... After the first 400ms, the pin6 resistance to ground can go as low as needed.
Hi team, thanks for creating such an active forum.