It's A Mystery: Bad Compander?

[heyniceguy]

Another installment from my "not-yet-hopeless" pile of broken effects:

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UNIT: DOD 670 Flanger Pedal (circa 1980)
UNIT TOPOLOGY: Uses SAD512 for delay generation, NE571 for compander, LM354 for quad op-amp, JRC4558 for signal/mixing, CD4001 for clock buffer. 4 knobs: speed/depth/manual/regeneration. +15v/0v powered. Indicator flashes to speed of flange. Big orange box.
PROBLEM: In effect mode, flange works, but volume is increased GREATLY, to the point of signal breakup.
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I bought this off Ebay with the old "only dry signal in effect mode". I thought it had an SAD1024 in it, so i thought, sweet i can fix that. But it had an SAD512. SHIT! Anyway, after probing, i saw no clock signal to the SAD512. Turns out the CD4001 was bad and the SAD512 was good. Hoo-rah!! So i had really sweet flanging, much akin to a Ross Flanger. But, when engaged, the volume increase was so much greater than the bypassed signal. And if i played hard, the signal began to distort.

I've read all i can about flangers, and it seems to me that there is something screwy with the expander stage. Does anyone have any insight to this? I plan on making an order to small bear and i plan on including a new NE571 with that order. But could i be off track?

[R.G.]

It's likely that something is screwy, and it's a reasonable guess that it's part of the compander.

I would first replace all of the electrolytic caps. See my polemic on resuscitating old effects at GEO (http://www.geofex.com) in the guitar effects debugging page.