PT2399 headache

Protip: Buy more than you need

terribly hard to find a quality source for these

I ventured into building delay effects, and had a string of 3 consecutive failures. First one was the Earthquaker Space Spiral, followed by Smalltime, then my version of the Clari(not). I threw the spiral and smalltime aside to troubleshoot for another day but finally realised on the clari(not) build that all my PT2399 chips were faulty.

I noticed that the blend pot was giving me the “dry” signal no problems but the wet signal from the PT2399 was either pure noise or absent; depending on the chip inserted. I went through all 10 of my chips until one of them worked perfectly then stopped working. I think it locked up, this is a well known thing with PT2399s.
Anyway, I ordered another set of 10 from another seller and got a batch where only 2 were working. Frustrating but better than nothing.

The string of bad luck continued in this build, I got a dead LDR and a potentiometer with intermittent wiper contact. Just glad to have finally completed my first delay pedal build. I will have to revisit the Space Spiral and Smalltime another day, wish that I socketed the PT2399 on the other 2 builds because I’m pretty sure those chips were the main issue.

Final PT2399 body count: 3/20

For this build, I etched my own single side pcb, it took the third try to get it right too!😅

Reason for failures:

1) Tried to laser engrave the board directly, impossible to cut through the copper cleanly.
2) Left too little space between traces and earth plane, continuity leaks.

Attempt #2 was just being overly conservative and trying to leave as much copper on the board as possible.

Attempt #1 was an interesting failure.
The copper was very hard to etch through especially when the laser beam was engaging with the copper at more perpendicular angles. Meaning that the copper directly under the laser was more resistant to being ablated compared to the parts further out from the center of the lens. This is visible in the image above actually.

There are many interesting articles online regarding the difficulties of laser engraving copper.

I learnt a lot from this small failure.

I went further and eventually seemed to take off the copper where I needed but the bakelite was all charred and there were still continuity leaks.

My etchant of choice was hydrochloric acid and hydrogen peroxide, but it seems I got sulphuric acid instead as the copper solution turned blue instead of green. It still works but the copper sulphate solution is not a regeneratable etchant unlike copper chloride. If I end up with enough spent copper sulphate, I might try to electroplate 3D printed parts in copper one day.

I’ll skip the rest of the details as I’m not too familiar with the PT2399 chip yet. Other than it truly is a pain the arse finding working ones. Below is a video of the pedal being tested.

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