Tuning Drift & QC Glitches

[pandrhola]

Have you experienced tuning drift, QC-related bugs? Would love to hear if anyone has preventative maintenance tips, reliable brands that handle this well, or technical workarounds to mitigate drift over time. Maybe even a checklist for spotting early warning signs?

[VCO]

My MiniMoog Voyager has always drifted since I purchased it in 2015.
I tune it and play it and it stays in tune but as soon as I change it to a different preset it’s out of tune again.

[MC]

There was a component substitution during the Voyager production life that affected the tuning stability.

I am the original owner of an early Voyager, a Signature model. It has always been stable.

Years later I acquired a Voyager RME from the Moog Store. When I used it, the tuning was not stable.

I uncovered incorrect charging caps in the VCO ramp core circuits. Correct value but wrong dielectric. The dielectric is critical because the VCO exponential converter tolerance with respect to temperature has to be the same as the dielectric in the cap.

The schematic specifically specifies polystyrene caps for these components, and they are in my Signature Voyager; in the RME - and many images I have seen of the analog board - the polystyrene caps were substituted with mylar caps.

Moog probably had a supply problem with the polystyrene caps which led to the substitution. But it caused the tuning stability to go south.

After I installed the correct caps (I had to buy them in the UK), the tuning in the RME was much better.

[till]

@pandrhola

Are you talking about the Voyager or the Minimoog?

My Minimoogs (1979 and 2017) and my 2003 built Voyager is are all very stable once they warm up. But you need to adjust the global tune a bit, if the room temperature is changed by more than 5°C suddenly. I never had to retune them on stage. I had these synths on stage inside in cold 300 feet high ex gas storage tank of about 10°C. And on an open air on a hot sunny summer day. Or inside a never used atomic plant cooling dome at night with a fresh summer night with stars above and the ISS seen crossing high above.

But I also experienced catastrophic tuning problems (intervals were off) with a friends Vermona Perfourmer during an open air when the air cooled down at night. While my Voyager just needed a slight adjustment in master tune.