Vintage Minimoog oscillator stability modification

[Jim Alfredson]

I have a lot of videos on my FB page concerning vintage synthesizer repair (and also tube amp repair). Here is a simple one that is a modification to vintage Minimoogs.

Like many other analog synths of the era, the vintage Minimoogs utilize tempco resistors to dynamically adjust the pitch of the oscillators as the temperature changes within the chassis. The problem is that these resistors are placed on the PCB far away from the actual transistor chips that are responsible for the oscillations.

 

The mod is simple: Move the tempco resistors to the top of the transistor arrays, securing them with thermal epoxy. Then run jumper wires from the tempcos to their respective old through-hole positions.

Here's the vid: https://www.facebook.com/jim.alfredson.3/videos/3588758281403651

 

[RABid]

Interesting. For me it was always osc 2 that went out. 1 and 3 were fine. 2 drive me crazy.

[The Real MC]

On 9/5/2023 at 3:26 AM, Jim Alfredson said:

I have a lot of videos on my FB page concerning vintage synthesizer repair (and also tube amp repair). Here is a simple one that is a modification to vintage Minimoogs.

Like many other analog synths of the era, the vintage Minimoogs utilize tempco resistors to dynamically adjust the pitch of the oscillators as the temperature changes within the chassis. The problem is that these resistors are placed on the PCB far away from the actual transistor chips that are responsible for the oscillations.

 

The mod is simple: Move the tempco resistors to the top of the transistor arrays, securing them with thermal epoxy. Then run jumper wires from the tempcos to their respective old through-hole positions.

Here's the vid: https://www.facebook.com/jim.alfredson.3/videos/3588758281403651

 

 

To clarify, this is for the 3046-based oscillator boards.

 

7 hours ago, RABid said:

Interesting. For me it was always osc 2 that went out. 1 and 3 were fine. 2 drive me crazy.

 

Very common problem on 3046-based oscillator board.  Jim's mod won't perfect it (I implemented that fix on mine), and is due to a design fault not easily fixed.