Hi all, hi Dieter (if you're listening :^),

I'm new to modular synthesis and got my hands on a used Doepfer A-100 base system which worked fine until this year's scorching summer, or at least I didn't notice any issues before; not sure if there's a connection with the high temperatures we've been experiencing.

I know the A-110 VCO's tuning/tracking is often discussed to death on forums, but I appear to be stuck with a pair of untunable A-110's.

The two A-110 VCOs in my kit (rev.3, > 15 years old ) have both drifted WAY out of tune. I followed the calibration procedure on Doepfer's website, but after 4 attempts, I've given up: both VCOs barely track over 1 octave, and the scaling pots on both (P7) are at their limits. But get this: they are at opposite ends of their respective limits, i.e. the tracking of these VCOs is actually divergent. I find that pretty weird.

Just to make sure, I've calibrated the A-190 MIDI-CV interface accurate to 1mV, and checked that the supply voltages are within spec too. I even checked the relative values of the critical resistors R1, R1', R2, R3, R3'; they are all within 0.1% as required.

I'm at the end of my rope. Is it time to replace the aged opamps, or should I just replace both modules outright

Many thanks,

--GT