spring reverb balanced > unbalanced debugging

[brndvnrdn]

Hoping someone can impart some wisdom.

I am making a spring reverb unit, and first had a working prototype that used an unbalanced in and output. After that I wanted to add some features (relay switching bypass, balanced in and out).  The bypass works great, but am having some trouble with the unbalanced balanced part of the circuit.

I used a part of the ssl mixbus schematic for the balanced to unbalanced conversion and vice versa. Something seems to be going wrong, because I am getting a lot of distortion/high output level from the output of the spring reverb.

When I bypass the spring section of the schematic I get a high boost in volume as well.

 

[RuudNL]

I think there is a series resistor missing at the inverting input of  U2.1.
I would start with 15 K.

 

[brndvnrdn]

Thanks, good suggestion. I tried it, but unfortunately still crackling/distorted output. I'm going to try a new pair of 5532/5534's, see if there's a problem with them.

 

[brndvnrdn]

Nope, same problem with different ic's unfortunately. Any other ideas ?

edit : hmm, the tl074 now seems to be getting hot as well (didn't happen before or i didn't notice it). maybe it's oscillating in a high frequency or it has a big load on the output?