Hafler Iris Preamp balance issue - fixed

For posterity, here are details on a fix I recently did to my Hafler Iris Preamp. Perhaps it will help others to keep their Iris up and running.

Problem:
The balance drifted slowly towards the left speaker. Nudging the balance or volume knob (local or remote) would cause the image to jump back to center, but in a few seconds it would drift back to the left.

Fix:
With a scope I found that the Left channel amplitude was growing over time (the Right channel was stable). After much pottering, I replaced two tantalum caps in the left channel circuitry. I replaced the 4.7uF at the TL082 Error Integrator, and the 2.2 uF at the LM308 E>I converter. Problem fixed.

Probably only one of those caps was bad, but it was easiest to just do both at one time. They both measured fine with my cap meter, in circuit and out, but under load one was obviously bad.

This is the second tant replacement I've done on this unit in recent years; next time I have to open it up I'll probably go ahead and replace all the tants and electrolytics just as a precaution.

I love this preamp - even after 30 years this thing still sounds great!