PT2399 in a Cave Dweller

[VanDerchuck]

Currently building my second Cave Dweller. The first was on vero board, this one is with a MadBean PCB. I get the same results in both pedals. I get this fuzzy/bad repeat. No matter how many PT2399's I use. These being the only chips I have and the only ones I have to go from, I'm not sure if there is an issue with the chips or the build or this is how it's supposed to sound. I've tried eleven of them.

All the voltages are really close to the ones in the instructions.

Should I expect a nice clean repeat? Or is that just the chip?

[matmosphere]

The 2399 isn't the cleanest chip by any means, and the Cave Dweller is sort of lofi compared to some other 2399 projects. That said you should be able to get it to sound pretty nice (i always thought it sounded great).

Are all your ICs from the same place? Try to pick up some from several different shops if you can. I know that recently people were having a lot of issues with the ones Tayda sells, so if that's where yours are from that might be the issue.

[jimilee]

I saw in diygp where someone ran like a 220p or similar from pin 2 to ground for this issue. I was going to give it a try on a cave dweller project I'm working on.

[VanDerchuck]

Thanks guys. That cap from pin 2 to ground didn't do anything. I might have to try some different chips. I hate to buy more of them. It's cutting into my project fund. I just need one good one to base the rest of them on.

Anyone have good luck with Mklec chips?

[madbean]

The PT2399 is pretty clean up to around 250-300ms, which is the max delay it is spec'd for. Most delay projects push that into the 600ms territory including the CD. So, at that point you have to filter it pretty heavily to get rid of the noise it introduces. But, you can't go too far because then it ends up darkening the delay in the "good" range, too.

I'm not sure which version of the CD you are building. The 2015 version has a pretty significant LP filter at the delay output (at around 1.6kHz). So, if you are building that one and still getting a significant amount of noise, it could be the batch of chips you have but I can't say for sure. What I can tell you is that it is best to avoid buying the cheapest you can find of the PT2399 (cough, Tayda) because they may well be out of spec. I have chips from a few different places but I keep one or two of the Smallbear ones on hand as reference chips (I mark them with a Sharpie). That way I can compare performance of other chips to some kind of benchmark.

Anyway, on the 2015 version you could try changing that filter a bit if you want to experiment (instead of just running out and buying more chips). Here are two suggestions (one or the other but not both):
Change R9 from 1k to 2k.
Change C11 from 47n to 100n.

[VanDerchuck]

Thanks Brian. I'm building the 2015 version. I'll try that mod. I just ordered from Small Bear. Maybe they will let me change it since it hasn't shipped yet.