Moog Music Forum

Hi, i have searched all over the internet for this problem,
but i cant find any clues so here it goes.

Since one day i turned on my Minimoog Model D, a constant note is oscillating
in the background, regardless of what outputs im using, and regardless of which,
or how many of my, oscillators that's turned on. I does'nt seem to
go through the filter, or the ADS-envelope, and sounds to me as something between
a sine wave, and a triangle wave.

The sound is there independent on wether i touch the keyboard or not, and the sound is not in any way
affected by any of the knobs on the front.

So now i have decided to take it to somebody who can fix it, but
he is not a synth expert so he wants to know where he can look for the problem in the circut schemes.
If anyone has any idea on what the problem could be, or where i can look for the problem
it would help me alot!

All help is much appriciated, it would made my day!
(Perhaps my week)

-A from Norway.

Sounds like you're speaking of the A-440 tuning oscillator - did you check the panel switch?

- G

I would check that first. It's in the OUTPUTS section on the front panel. It's a blue switch labeled A 440. Just toggle that switch.

Yes. It is most probably the A-440 switch that is in the "on" position. Simply turn it off.
However, if it is already in the "off" (flipped to the left) position and you are still hearing it, that is another story. But I doubt that very much.

Have your tech scope the power rails at the oscillator cards. If he sees the offending frequency, one of the connector flags on the VCO board for the power rails may have spread apart and is no longer making contact. Common problem and the minimoog service manual gives the WRONG solution.

The power rails for the VCO cards is a kelvin force/sense system designed for rock stable levels. It's a closed loop feedback system for a power supply. If either of the F/S lines are open, it causes an audio frequency to ride the power rails and it appears in the audio circuits.

MC wrote:Have your tech scope the power rails at the oscillator cards. If he sees the offending frequency, one of the connector flags on the VCO board for the power rails may have spread apart and is no longer making contact. Common problem and the minimoog service manual gives the WRONG solution....

What would be the RIGHT solution, if it were to ever happen to someone ? And also, how sensitive is this sensing circuit to bad connections ?
Thanks for the info.

Al.

thealien666 wrote:

MC wrote:Have your tech scope the power rails at the oscillator cards. If he sees the offending frequency, one of the connector flags on the VCO board for the power rails may have spread apart and is no longer making contact. Common problem and the minimoog service manual gives the WRONG solution....

What would be the RIGHT solution, if it were to ever happen to someone ? And also, how sensitive is this sensing circuit to bad connections ?
Thanks for the info.

Al.

If the connector flags have spread apart...

Did you get a solution? I have the same problem.