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 Forum index » DIY Hardware and Software » Jürgen Haible designs
SOST Flanger troubleshoot advice
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jumunius



Joined: Apr 19, 2010
Posts: 346
Location: San Francisco, CA
Audio files: 13

PostPosted: Sun Sep 11, 2011 1:20 pm    Post subject: SOST Flanger troubleshoot advice Reply with quote  Mark this post and the followings unread

Hi, I'm really struggling to understand what is wrong with my SOST Flanger. I readily admit the problem will probably be a wrong component, bad solder, etc, but I've been over it a few times now (albeit haven't checked every resistor value). It's a big board and I'd like some advice as to where to start looking. I would like to be able to isolate out discrete areas of the Flanger and verify functionality as I go.

So, for example, I've disconnected the LFO entirely by lifting one leg of R6, so at least I know it's not messing with CVs. Should I ignore BBD2 for now and just test BBD1? Disconnect other CVs? Etc.

So, here's what is happening:

Manual knob has a minimal effect, and makes a low "pop" around 12:00
Bounce makes several of those pops during rotation, and then pops erratically as long as it stays up. For testing I leave it at minimum setting.
There is a pervasive, quiet, hum, as if from 2 or more oscillators (and maybe ground hum) tuned to different notes.
Resonance works well on "Short" (Res) setting, and inverting (Res) has pronounced effect
Resonance doesn't work on "Long"
No apparent difference between Long and Short BBD settings, and inverting BBD2 while on Long BBD setting turns entire audio signal to low frequency thumping.
2 Direct Path switches no apparent effect.
Fine Tune works cleanly
Env Mod/Rls have subtle effect

And here's what I know so far:

-All ICs appear to be getting correct voltages.
-ICs mounted correctly
-TDA1022 chips have been swapped and work
-Clock signal into TDA1022 seems to work.

Thanks in advance to anyone able to offer advice.
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