Moog Music Forum

Iv seen all this hoopla about "OLD oscillator board" on ebay.
What is it?

Officially there are 3 versions of the oscillators board. The very early one, using only discrete transistors and extremely unstable, and then the "old" one that most Minimoog D have, and finally the "new" one that was installed in late models just before the end of the production run back in 1981, and retrofitted in some earlier models.

At one time I knew all the details about which serial numbers had which, but it's been a while... That info is easily available around the net though...

im so happy to be in this club!
to think it only cost $3,000, my transmission in my car and several hundred in ebay parts!

To expand this discussion for some of the newer members of this board (including Jaythejunkie) the Minimoog Model D had a long production run from around 1970 to 1981 during which several small design changes were made in the circuitry. Because of the coveted sound that the Minimoog is known for, the differences in sound imparted by these circuit design changes is often discussed and debated. The first 2 oscillator board versions are considered by many to sound more organic or richer than the later 3rd design. MC on these forums has meticulously modified his early production RA Minimoog to stablize its version 1 oscillators. However, he has stated more than once that he believes that the Minimoog filter version is more important to the sound than the oscillator boards. (Please step in here MC; hopefully I am stating your view accutately). My experience between 3 Minimoogs is that my 1973 Minimoog with the 2nd oscillator board sounds better than the later 1975 and 1978 Minimoogs (that I used to have) which both had the 3rd version of the oscillator board. Of course several other things inpart the unique sound of the Minimoog that we enjoy so much - many of which have been discussed at length in these forums.

This site has some info about when the osc board revisions were introduced:
http://minimoog.monsite-orange.fr/page1/index.html

You are accurate about the filter, torinkrell (thanks). EricK's link not only discussed the osc boards but also the filter.

Yeah I did modify my 3046 VCO board to stay in tune better. They need more than better opamps. I had to correct some circuit errors, change the pitch wheel, and improve the power distribution. But none of my modifications were in the audio chain, only in the control domain. Frankly none of the oscillator boards will perform better without these corrections.

I did get a discrete VCO board from Kevin Lightner years ago (RIP) but haven't had time to monkey with it.

The only mod done on mine (old vco board) was to move the Tempco resistors on top of the CA3046 for better thermal feedback. But all the op amps are the original 741. And my Mini is remarkably stable since.

Thermal coupling of the tempco's was one of the first things I did, but it wasn't a sole solution. The rest were incremental improvements. Wonder if your 741s were later generation which were better? Mine may have been early ones, back then there were not many alternate sources.

The date codes on my 741s are from 1973 to 1974, some from Raytheon Corp and some from Texas Instruments. All original from the years my Mini was made (early 1975).
Mind you, the oscillators still do drift a little, but it's very light and very manageable.

Emu, in the day, preferred using the no longer available 556 opamp as it was superior to the 741. They used 741's only in non critical areas. Their 1200 vco sub module ( I have 3) is fully potted in epoxy. Dave Rossum's vco design, which many felt was superior to Moog, did not require a heater.

I used a minimoog a lot when I was composer in residence, of sorts ( it paid money!) during undergrad at their planetarium. The planetarium purchased it in 73 for my use. I always loved it.

We had an arp 2600 and sequencer for the small electronic music studio I designed for the school of music along with a couple of nice 10 1/2 " Revox reel to reels and a small mixer.

I miss those days.

On the "old oscillator board" of the Mini, the 741 op amps are not in the audio path. Only in the CV section of the VCO board. So the 741 slew rate and other characteristics (and limitations) are not so critical.