Minimoog Oscillators DIY

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1

Following my complete build of most of the Modular items for my DIY
Modular synth and..

  1. Becoming frustrated about tuning drift of the 901a/901bs osc’s (although they sound brilliant)..and

  2. desperatly trying to overcome a feeling of anticlimax whilst holding an
    “empty” soldering iron…

I decided to attempt the pre 10175 Minimoog Oscillator. Not the full three, just one with opportunity to add more if it works.

Ive just made the PCBs and start to populate them today. My biggest worry is that the heart of the osc is the LS3954 Dual JFET which is now unobtainable so I have substituted a 2N5911 which again is obsolete although I managed to get just 2 of these.

I expect two more days should see the “big bang” or “silent dud”

I’ll post the results.

2

Wow.
Good luck. :slight_smile:

Just as some FYI’s…

If the FETs you’re using work, but don’t track perfectly, make sure you’re using a good polystyrene (or equiv) cap.
You’ll need them rated with a low dissipation factor for proper tracking at the high freqs.

Triangle symmetry can be off depending on transistors used.
Easier to change the resistors than match the trannys tho.

I’m assuming you’re using 741’s all around?
You can put high end (LT1006, for ex) opamps elsewhere, but IC3, IC5 and IC10 really need to be 741’s.

I don’t know of any major errors on the service manual for the VCOs, but there are several on the other board schematics.

Where’d you get the tempcos? I’m running low myself… :slight_smile:

Good luck again. :slight_smile:

3

Thanks Kevin…Think the Tempcos should be available from Farnells or Rapid here in UK but Oakley have some. £5 each. 1K

First attempt on power up is a deafening zero !

I suspect the Dual JFet but have others to try but alas they are surface mount packages although I may have a standard 8 pin IC that could work.

I need to get some signal from the SAW before I can progress any further. At the moment theres sod all.

4

That’s a lot for tempcos, but perhaps the price has gone up since I last bought some. I think I paid about a dollar each last time I stocked up, but it was years ago.

Is the whole thing being done via surface mount?

Sorry if your first go at it didn’t make any sound.
I’ve been there myself on other projects, so I understand.
But you sound confident and that’s good.

So here’s wishing you luck on attempt #2. :slight_smile:

5

Yeah don’t be discouraged on the first try. That happens to everyone.