crackling noise in minimoog after 15 minutes

In a Moog Mood? Here's a forum for discussion of general Moog topics.
Post Reply
synthe_64
Posts: 4
Joined: Wed Mar 30, 2016 9:53 am

crackling noise in minimoog after 15 minutes

Post by synthe_64 » Wed Mar 30, 2016 2:38 pm

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
Moog minimoog, Roland SH2, Korg Polysix, Arturia microbrute, Doepfer darktime, Pittsburgh Modular, Korg Monotribe, Behringer 12 channel mixer, EHX small stone,

User avatar
MRNUTTY
Posts: 269
Joined: Fri May 02, 2014 2:54 pm

Re: crackling noise in minimoog after 15 minutes

Post by MRNUTTY » Thu Mar 31, 2016 8:45 am

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.
VoyagerEB, Minitaur, LittlePhattyII, 4xSlimPhatty, Sub37, MF[2x101,2x102,103,104M,105,105B,105M,2x107,108M], 3xCP251, XV351, MP201;
System 55 and Minimoog clones, personally modified to bring them closer to OG spec(s).

synthe_64
Posts: 4
Joined: Wed Mar 30, 2016 9:53 am

Re: crackling noise in minimoog after 15 minutes

Post by synthe_64 » Thu Mar 31, 2016 9:24 am

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.
Moog minimoog, Roland SH2, Korg Polysix, Arturia microbrute, Doepfer darktime, Pittsburgh Modular, Korg Monotribe, Behringer 12 channel mixer, EHX small stone,

User avatar
MC
Posts: 2893
Joined: Tue Aug 12, 2003 2:20 pm
Location: Secluded Tranquil Country

Re: crackling noise in minimoog after 15 minutes

Post by MC » Thu Mar 31, 2016 3:51 pm

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.
Gear list: '04 Saturn Ion, John Deere X300 tractor, ganged set of seven reel mowers for 3 acres of lawn, herd of sheep for backup lawn mowers, two tiger cats for mouse population control Oh you meant MUSIC gear Oops I hit the 255 character limi

torinkrell
Posts: 90
Joined: Tue Jan 26, 2010 9:48 pm
Location: New York City metro area

Re: crackling noise in minimoog after 15 minutes

Post by torinkrell » Sat Apr 02, 2016 2:36 pm

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.
Akai AX-80
Korg Polysix
Roland Juno 60
Moog The Source
Yamaha e1010 BBD
Moog Parametric EQ
Sequential Prophet Pro~One
Altec AS-1600 audio oscillator (1947)
Moog Music Minimoog Model D (1973)

synthe_64
Posts: 4
Joined: Wed Mar 30, 2016 9:53 am

Re: crackling noise in minimoog after 15 minutes

Post by synthe_64 » Sun May 01, 2016 2:30 pm

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 )
Moog minimoog, Roland SH2, Korg Polysix, Arturia microbrute, Doepfer darktime, Pittsburgh Modular, Korg Monotribe, Behringer 12 channel mixer, EHX small stone,

User avatar
MRNUTTY
Posts: 269
Joined: Fri May 02, 2014 2:54 pm

Re: crackling noise in minimoog after 15 minutes

Post by MRNUTTY » Mon May 02, 2016 11:37 am

Glad you're running trouble free now!
VoyagerEB, Minitaur, LittlePhattyII, 4xSlimPhatty, Sub37, MF[2x101,2x102,103,104M,105,105B,105M,2x107,108M], 3xCP251, XV351, MP201;
System 55 and Minimoog clones, personally modified to bring them closer to OG spec(s).

albert6720
Posts: 5
Joined: Wed May 04, 2016 2:13 am

Re: crackling noise in minimoog after 15 minutes

Post by albert6720 » Wed May 04, 2016 7:06 am

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.

Post Reply