sunking ringing and feedback mixer pot Q

[jtn191]

My sunking rings noticeably (around 6kHz IIRC) when the volume is turned up and becomes even more obvious when the tone is above halfway. Is this a power filtering issue that could be fixed with higher quality/different caps of different values?

note: I'm using my cheapy GFS 5 way power supply, but it also did this at a bit quieter level with my friends built-in pedal board supply

Second, I just finished building a TB looper with feedback mixer...sourced completely at radio shack. I used this diagram http://www.beavisaudio.com/techpages/PedalHacker/LooperWithFeedbackLoop.gif

The problem with radio shack is they don't have a very good pot selection (read: crap  ) So I used this http://www.radioshack.com/product/index.jsp?productId=2062359 instead of a 500K A. As is, it works when the pot is turned left (but squeals pretty early on) , but I was wondering if a proper 500K A would give it a more useful range. Thanks!

[gtr2]

What are you using for IC3 on the sunking?

Josh

[jtn191]

It's a Maxim brand 7660CPA1184. The ringing, ironically enough, is at 7600 Hz and an octave up at 15,200 Hz

[Haberdasher]

I think there have been quite a few documented cases of the same type of thing (ringing/squealing) happening when the wrong chip is used in IC3.

It is recommended to use one of these:

7660SCPA
MAX1044
TC1044- this can take a little higher voltage, so I usually order this one

[gtr2]

yup, if you go with a 7660 it has to be the scpa

[jtn191]

k, thanks. Any special version letters of the TC1044 to worry about? I found a TC1044SCPA and a TC1044SEPA on mouser

[Haberdasher]

Hi

I've always ordered the TC1044SCPA and haven't had a problem.  I don't know about the other one.

[gtr2]

I've got a few extra 7660scpa's.  If you pm me your address I'll ship one out for you.

[bigmufffuzzwizz]

I used a 7660SCPA and it worked great for me. None of that annoying high pitch squealing.

[Mike @ Rawkworks]

Update : Just used a SEPA in mine and it works fine. Can take up to 12 volts I think, or maybe I misread it and its supposed to see 12 volts. Either way at 9 it sounds the same as the maxim chip.