ADC Sound Shaper Two and Three Inductor EQ help

Hello Everyone,

I know this is a long shot but I was seeing if anyone could help me with improving this eq for use in the studio.  They are loaded with high quality inductors and I did test them out in my studio and I got some interesting results.  The Eq has a cool vibe to it but I can't help but feel that the amp section feels a bit "anemic". It appears to be a -10 dbv box so perhaps my signals were a bit hot going in but lowering the signal level didn't change the sound character too much until there was obvious distortion.  I would be interested in ideas for modifying the circuit to improve this unit whether that is just part swapping, beefing up the power suppply, or cutting some traces to isolate the amplifier section and drop in some new boards and reconnect.  There are tantalum capactitors all over this thing so perhaps it would help to swap those.  The service manual has a detailed description on how the circuit operates but it is a bit above my pay grade at the moment so I'm hoping that some of the brilliant folks here can help translate some of that into more practical terms . 

https://www.hifiengine.com/manual_library/adc/sound-shaper-three.shtml

Try doing a frequency  sweep measurement. If you are loosing low end,it may be time for a recap.

Thank you, replace the lyric caps is in the plan and increasing values where appropriate. I will have to do more research to understand the amplifier circuit and whether this is limiting the Sonics in any way.

rjb5191 said:

The Eq has a cool vibe to it but I can't help but feel that the amp section feels a bit "anemic". It appears to be a -10 dbv box so perhaps my signals were a bit hot going in but lowering the signal level didn't change the sound character too much until there was obvious distortion. I would be interested in ideas for modifying the circuit to improve this unit

Click to expand...

Attaching the schematic in case it can generate some more input.. Balanced option could be cool....?

Start with the basics. Frequency response with faders at 0db. Anaemic implies loss of bass / low mids ? Comparison with Bypassed signal ?

What would make them change these resistors to lower values in the Mark ll version from the original? They also omitted a resistor in the lower frequency...

They did add leds to the sliders in the Mark ll... and used some different chip for the led meters but I think that's all so far.

?? Maybe I should ask, would anyone here change those values and why?lol
Surplus of resistors?

Perhaps they changed the values to affect the 'Q' of the circuit.
The BEST mod you could do to that unit is to replace the anemic 4558 opamps to something better---a LM4562 would be a good choice; an OPA1656 maybe even better.

Steven Paris said:

Perhaps they changed the values to affect the 'Q' of the circuit.
The BEST mod you could do to that unit is to replace the anemic 4558 opamps to something better---a LM4562 would be a good choice; an OPA1656 maybe even better.

Click to expand...

Thanks. Yeah I was figuring it was to adjust the Q, but wasn't sure. Even so, I wonder if it was an improvement .
All the chips in these are just for metering. There is an ic version however......