Moog Music Forum

Hi, I am new to the Moog community. I recently bought a Minimoog model D, manufactured in June 1973.
Everything works except for a crackling sound that comes up after playing for some minutes.
I hear the noise on the line output and the headphones output. All functions are working perfectly ( filter, controllers, VCO and so on ) but when I am playing for some 15 minutes there is a loud crackling noise that comes over the sound of the synth and it keeps crackling. You can hear it even if you turn all sources in the Mixer to zero ( the 3 oscillators and the noise generator )
When I turn off the synth and wait for maybe 20 minutes and then switch on the minimoog again, the crackling sound is gone but after some 15 minutes it starts crackling again continously , so it must be something that generates this noise when becoming warm. I am an electronics engineer so I could repair it myself. Does anyone have an idea where to search? Any questions for more details are very welcome. thanks in advance

Sounds like it's time for a can of freeze spray; definitely heat related. Possible sources are VCA, final stage amplifiers; for either audio out, or headphones depending on where you here the noise. Maybe a dirty gain POT. Sounds like an easy fix for your skills.

It must be before the filter because the timbre of the crackling noise changes when I change the filter settings. It is both in the line out and the phones output. Maybe it is somewhere between the mixer output and the filter input? I will do some more troubleshooting and let you know the result. However if anyone else is reading this topic please reply if you have relevant information. thanks.

One easy fix could be the rear panel VCA jack. It is normal to a fixed voltage with nothing plugged in. These normal contact connections tend to degrade with age. They can be restored by repeatedly plugging/removing into the jack, whose scraping action can restore the contacts.

My 1973 Minimoog occasionally has some noises that stem from the rotary octave and waveform switches. Gently exercising these especially if there are some that you do not change often may help. The rocker switches on my current Minimoog are not problematic but they were an issue on a 1975 Minimoog I had several years ago. Exercising all the rotary knobs and gently cleaning the key contacts may also help. The plugs connecting the keyboard and mod wheels (located under the modulation panel) are also sometimes problematic and are vulnerable to corrosion. Gently plugging and unplugging these may clear out some corrosion and rectify the issue. Heat can effect several marginal components in an analog synth including mechanical switches, connections, and pots which is why there is sometimes a delay before a problem occurs (or a problem subsides). So I check simple issues like these out before I send my equipment to a pro for repair. Beyond this point I will defer to the techs on this forum.

Just an update from me : I succeeded in fixing the problem. I found out that it wasn't related to "warming up".
It was some dust in the trimpots on the VCF board. I cleaned them all with contact spray and now my mini works as it should.
Best regards, Johan ( Belgium )

Glad you're running trouble free now!

Yes you are right that the dust causes the crackling sound. I also have this problem because of my windy room where dust is a common thing.