RA Minimoog

[VCO]

Is the RA Minimoog considered the best sounding of the vintage Minimoogs? I guess there were 6 different versions of the Minimoog over the years? Thanks

[ummagumma]

No: the best sounding minimoog is the one I own

[stiiiiiiive]

That's because you're a better sounding musician, mate

[ummagumma]

Ha!

Both of those statements are not necessarily true

[VCO]

I had read about certain things that had been changed during different versions . I had read the model D had come out
In 1970 and then I read that there were different oscillator boards and some of the circuits had been changed. I guess the oscillator board was changed due to pitch drifting of the oscillators? I also had read about the Musonics Minimoog.
I wonder which versions of the original model D are the most common . I believe the Minimoog had a production run of 11 years spanning from 1970 to 1981. Just was curious what all the different iterations were and the chronological progression of the changes during various years. It would be interesting to know how many minimoogs were produced each year and what the changes were relative to that year. I know some forum members know the details being they have vintage model Ds and some have multiple Minimoogs that are from different years with design changes. Thanks

[ummagumma]

I think "synthpro" on youtube has a video with them all lined up & he talks about them. I just looked but couldn't find it: he restores synths & has a lot of interesting videos, worth checking out.

[ProspectHillMusic]

There were a few minor changes to the Minimoog during its production run but the biggest and most significant change during production was the 3 different versions of the oscillator board that were used. R. A. Moog started the manufacture of the Minimoog while the company was still in Trumansburg, NY. R. A. Moog had been manufacturing the 901 series of Voltage Controlled Oscillators for a number of years by that point in time but the 901, which used strings of diodes for the linear voltage to exponential current conversion and a unijunction transistor for the sawtooth oscillator, had notoriously poor pitch stability and tracking. When the Minimoog was under development the first prototypes used the 901 VCO design but I'm sure that engineer Bill Hemsath and others at Moog realized that the 901 design wasn't good enough for what would become the Minimoog. Bob Moog designed a new oscillator circuit that used a matched pair of transistors and a temperature compensating resistor for the exponential conversion and a more complex but better performing sawtooth oscillator core which did away with the UJT. R. A. Moog drawing #1441 dated 12/21/1970 shows the circuitry for the Triple Oscillator board that was used in the first production run. This version of the oscillator board was designed entirely with discrete components, no monolithic ICs were used. Because the op-amps that were used in critical parts of the oscillator circuitry were comprised of discrete transistors, resistors, and capacitors and the thermal matching of the expo transistors and the tempco resistor was done with a small bar of aluminum the stability of this first VCO design wasn't all that great. I've seen statements that 200 - 300 of the R. A. Moog version were made.

The next version of the Minimoog was made by Moog Music after the company had been sold and had moved to Williamsville, NY. A new oscillator board was designed which used the CA3046 monolithic transistor array and 741 type monolithic op-amps which had better accuracy than the discrete op-amps that were used on the first oscillator board. Minimoogs with this oscillator board worked quite well and were used in production of Minimoogs up to serial number 10175.

In 1978 a third oscillator board was designed and used in Minimoogs until the end of production in 1981. This design used a ua726 thermally stabilized (heated) transistor pair for the exponential conversion and there are claims that this design had the best tracking and stability. One problem with it is that the ua726 is no longer made and as a result could be hard to find if one needed replacement. In my opinion oscillator board #2 could be made to be as stable as the ua726 based oscillator board #3 by replacing some of the 741s with the more precise op-amps that are now available such as the OP07, replacement of certain resistors with metal film resistors, and thermally coupling the tempo resistors to the transistor arrays.

Based on serial numbers here are the approximate quantities of Minimoogs that were made with each type of oscillator board:

Oscillator board #1, 200-300
Oscillator board #2, about 10,000
Oscillator board #3, about 2,000 plus an unknown additional number of boards that Norlin Music sold as retrofits for used as oscillator board replacements in Minimoogs below s/n 10175.

Someone asked in an earlier post if Minimoogs with these different oscillator boards sounded different. I really don't know the answer to that question. All 3 oscillator boards used the same basic design concept, the difference was in the implementation. All 3 designs created sawtooth waveforms and had circuitry to convert the sawtooth to triangle, square and pulse waveforms but the circuitry that derived the other waveforms differed somewhat among the 3 oscillator boards but generated the same waveforms. The waveforms might look slightly different on an oscilloscope but can someone actually hear the difference? There is a similar debate about the sound of a 901 VCO vs a 921 VCO and which one actually sounds better.

[till]

I'm an owner of a late Minimoog with the third VCO board. And I can easily hear the difference in the brightness of the sawtooth when my minimoog is next to a friends Minimoog with the second VCO board. The second does sound brigther will filter fully opened. And the bass sound more bass emphased. The third VCO does track even better then all second revisions I played. I also got two 2016 Reissues here. They are based on the second revision.

I also own the faithful Synth-Werk 901ABB and 921 VCOs. And many users of the vintage modules confess, these sound like the real vintage ones. These two versions of design do sound different too. The 901Bs triangle waveshape got a little buzz in the harmonics. The sawtooth is brighter on the earlier design.
Thr tracking of the 901s is never good enough for playing in tune over 5 octaves here. The 921 are nearly perfect.

[ummagumma]

Well those are good summaries, thanks till & ProspectHillMusic!

[VCO]

Excellent information. Very insightful. Very pensive answers. I grant you both an honorary doctorate
In minimoog history and technical studies. I call it the MMMM.=Mini Moog Masters. LOL I was wondering if Till was going to chime in on that one. Thanks