Sea Urchin feedback not working...

[pgodfrin]

Greeetings! I etched this one and put it all together, and it works. Except all I get is one echo. And it's modulating without any modulation circuit wired in...
any advice, please?
...puzzled
pg

[jimilee]

I don’t know about the modulation but, the PT2399 is bad about locking up in that circuit no matter who designs it. I’ve had 3 different ones. The result is one echo. Put jumper across pins 3 and 4 of the 2399.


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[madbean]

On the OG circuit, the delay pot goes to digital ground of the PT2399. This is supposed to be connected to analog ground of the PT2399 internally via a 10R resistor. But, often people run into it just not working that way. So, jumpering the two pins together usually fixes the problem.

Now, that may have nothing to do with your repeat problem. That could be a dodgy pot or something wrong in the circuitry of the feedback path such as a short to ground, bad solder joint etc.

As far as modulation the first suggestion may fix that. It's also possible to get a delay to modulate on its own by simply handling the circuit board, believe it or not. I've seen this a few times with analog delays. If you shake it around a bit the delay pot wiggles a bit and causes the repeats to change pitch slightly like you hear in modulation.

[pgodfrin]

Wow - it's awesome to hear from folks who are so knowledgeable. I basically just follow the instructions and hope it works, lol. I'll give it a try. And yes, the modulation seems to happen when moving the board. I didnt think that was possible, but there ya go!
pg

[pgodfrin]

OK, jumped 3 & 4, no joy...

[jimilee]

OK, jumped 3 & 4, no joy...

What happens if you remove the power supply and remove the chip, wait a minute and reverse the process?


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[pgodfrin]

I think I've done that when replacing the chip (I tried two different chips). But I'll give it a whirl. Is this to let the caps discharge?
pg

[jimilee]

I think I've done that when replacing the chip (I tried two different chips). But I'll give it a whirl. Is this to let the caps discharge?
pg

It’s to unlock the the 2399.


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[pgodfrin]

well, did that no joy. Seems like the feedback pot has NO effect.

[madbean]

Post pics and voltages on the PT2399, please.

[pgodfrin]

OK, will do. First let me double check ALL the values.What should the voltages be?

[pgodfrin]

OK, I realized that the schematic called for a yellow led, I used a red one. Can't see why that would make a difference, but it did. Now I get about 3 or 4 repeats, but at a very low volume. Still working it...

[pgodfrin]

Oh yeah I had jumped the wrong pins as well, maybe that's really what did the trick...

[jimilee]

OK, I realized that the schematic called for a yellow led, I used a red one. Can't see why that would make a difference, but it did. Now I get about 3 or 4 repeats, but at a very low volume. Still working it...

The LED is to tone down the distortion on the repeats that sometimes result in PT2399 delays. The bestthing you can do is compare your etch to the template to ensure that there are no anomalies. I take pictures of my etched board before I start building just for this reason. Did you see the note about D2 in the build DOC? Post close up pictures of both sides along with voltages if you need more help. We're happy to help out.

[pgodfrin]

Roger that, I'll check out those notes. If I show a pic of the underside, I'll be extremely embarrassed, it's an awful mess...