PT2399 Problem

[fosimoor]

Hi all,

I've built a PT2399-based delay using a design by rené schmitz: https://www.schmitzbits.de/pt2399.html. I'm having a weird issue that I didn't see mentioned anywhere online: instead of a delayed input signal, I only get these evenly spaced clicking noises from the IC. The tempo of the clicks changes if I twist the 47k pot that's supposed to set the tempo for the internal VCO of the PT2399, but it's not like one direction is fast and the other is slow.

I have made sure that all the other parts of my circuit work: the two op-amps conditioning the input signal before the PT2399 are doing their job (I've listened to their output, seems fine), and the one sending out the output signal is working as well (the dry signal's coming through no problem). The clicking noise is present at pin 14 of the PT2399, so I'm assuming the fourth op-amp is also not the problem. The clicking is audible even without an input signal, by the way.

I've listened to the output at pin 15 and it just sounds like a downsampled version of my input signal. Very strange. I've already switched out the PT2399 for another one, but I get the exact same behaviour. Also, I've reheated all the joints and triple-checked my stripboard layout. Seems fine to me.

Here are some measurements I took from all the pins of the IC. I also documented the ICs behaviour when the probe connected to the respective pin.

Pin1: 4,89V
Pin2: 2,42V
Pin3: 0V
Pin4: 0V
Pin5: 1,7V (clicking accelerates a lot)
Pin6: 2,4V (clicking accelerated a bit)
Pin7: 4,47V
Pin8: 4,48V
Pin9: 4,69V (clicking accelerates slightly)
Pin10: 0,46V (clicking accelerates slightly)
Pin11: 0,45V
Pin12: 4,67V
Pin13: 2,43V (noise on the output)
Pin14: 0,13V
Pin15: 4,84V (momentary hiccup in the clicking)
Pin16: 2,36V (irregular clicking)

Any idea what could be wrong? Thanks!

[JovianPyx]

When touching a pin with a meter or scope probe causes changes in the circuit's behavior - this is often caused by a grounding problem.

Check all connections, re-solder those that look bad (like cold solder, cracked etc).

[fosimoor]

Thanks for the reply! I got it to work in the meantime – René schematic seems to be faulty, there needs to be a DC blocking capacitor before the "in" of the Delta t block! I put a 1 uF cap there and now it's working like a charm.