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ADC Sound Shaper SS-115X Graphic Equalizer

pioneer07

pioneer07

Member
I recently spotted one of these vintage graphic equalizers for free on Facebook Marketplace and I grabbed it. It powers on and all of the lights work. It has a button called "EQ" which turns the equalizer function on and off. When it's off the signal just passes through, but you can still watch the lines dance. When the EQ button is on, I only get the left channel and no right channel, and no lights on the right side. I have been searching for a schematic or service manual but I haven't been able to find one. Anyone know where I might locate one?

Yes, I am going to dig in to this and check for dry solder joints (seemingly a common problem on similar ADC equalizers in other forums I read). I'll also clean all the switches, but a schematic or something would sure be nice. I do plan to re-cap it. I am pretty confident I'll be able to restore the right channel but if anyone has run into a similar issue and one of these routine services didn't fix it, I'd be curious what it was. I have a scope if we need to go there but, again, that's where that schematic sure would be handy.

Last thing - a page I found about a similar ADC mentioned upgrading the op amps. The op amps in this one are 2 of the JRC4558D. I searched for replacements for this JRC4458D and the ones being mentioned elsewhere were the NE5532 and the TL072. The applications in those discussions were different than this though. I'm kind of clueless about these things other than the little bit I read. I'm curious if upgrading these op amps is worth the trouble or risk. The other pages I read said the JRC4458D was OK in its time but has been far surpassed since then.
 
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Contact cleaning the switches does seem to have brought back the right channel. I want to test it some more to make sure volume levels are equal.

So I'm mainly curious now about how or whether to upgrade the op amps.
 
A good test of a vintage eq is to set everything to flat..no boost or cut...then play a good recording that you are familar with , while the eq set to (ON) on your ampliier's tape loop. Then switch between listening to the source with the tape loop out of circuit..then in circuit ( good headphones help).
If there's no perceptible increase in background noise and no drop in the sound quality when played through the eq's circuitry... maybe it's working fine ?
 
I did that and with EQ on it seems just a shade quieter. I can't tell a difference in background noise. It might be "fine" but I was just curious about the op amp upgrade. I think it's possible that I'd get a little different flavor of sound out of it with different ones. I might install a socket so I could change them out and compare. People in these other forums who did this were pretty adamant it was a nice upgrade.
 
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