Geddy Lee Minimoog

[MC]

EMEAPP.org did a forensic engineering study on the Minimoog VCAs (yes the Minimoog has two VCAs, the 2nd one was for external control from the rear panel jack). Turns out during its original manufacture 1970 to 1981, there were three circuit versions of the VCAs (Gen 1, Gen 2, Gen 3). The differences were the values of three resistors. They varied the input level and output gain of the VCAs, and their changes significantly impacted the harmonic distortion. This is independent of the distortion of the filter.

Back then, VCAs were not high fidelity or low distortion. The technology had not yet advanced where they were suitable for professional audio (IE recording consoles) but they were "good enough" for synthesizers. No one ever complained about dirty sounding VCAs in synthesizers, but the Minimoog VCAs were the "secret sauce" that eluded imitators. The VCF was often duplicated but not the VCA. Until recently, few people credited the VCAs for the "fat" sound of the Minimoog. Not only was the Minimoog VCA a "distortion processor", the signal went through TWO of them!

The VCA is also the reason why early Oberheims sound so fat.

EMEAPP published an extensive engineering writeup (Ben Luce - son of Moog Music's Dave Luce - headed the engineering study with Timothy Warneck and Moog veterans Tom Rhea and Jim Scott) but those papers are no longer on their website.

Complicating the operation is the three differential amplifiers that comprise both VCAs. It turns out that the last two stages impact the distortion of the 1st, and one circuit version (Gen 3) shows that control voltage (IE EG contour) impacts the distortion level of both VCAs. "Gen 2" was the "polite" version with the least distortion; it was a modification listed in the service manual, so it was a field modification and no one knows how many Minimoogs has the "Gen 2" VCA.

So which "Gen" is the "hot VCA" in the Geddy Lee model? It's either "Gen 1" or "Gen 3". "Gen 1" was in the first ~1000 Minimoogs and the distortion, unlike "Gen 3", is independent of control voltage from the contour generator. That means regardless of EG level, the VCAs are crunching the signal constantly. "Gen 3" has the highest distortion (even driving the transistors into saturation) but the distortion is dynamic based on EG contour level.

[stiiiiiiive]

Thanks for sharing all this, MC
Indeed, I've read somewhere the VCAs were less known than the VCF as a fatness factor.

[Analog Prophet]

I discovered this way two MIDI improvements of the 2022 reissue over the 2016 one:
- The modulation wheel transmits MIDI
- It is possible to set different MIDI channels for in and out.

There may be others.

I hope that will be possible to the 2016 ReIssue as well through updating the MODI firmware (if it works that way)

[till]

I discovered this way two MIDI improvements of the 2022 reissue over the 2016 one:
- The modulation wheel transmits MIDI
- It is possible to set different MIDI channels for in and out.

There may be others.

I hope that will be possible to the 2016 ReIssue as well through updating the MODI firmware (if it works that way)

No. The mod wheels on the 2016 Reissue are not sending MIDI due to missing software function, but due to hardware not being able to do so. This is why I got the MUSE hardware from virtual-music.at to fix this and adding additional other features. Like a way better aftertouch as Modwheel function. And adds MIDI functionality (in and out) for the glide and decay switch. And use selectable pitchbend range (0 to 12 semitones in semitone steps). And you can set different channels for the MIDI in and out. And legato glide (fingered).

[stiiiiiiive]

Indeed.
Unfortunately, the MUSE card is not made anymore. I woke up few weeks too late. Would love to trigger the mod with aftertouch!

[PaulLawler]

I got one of these today, looks lovely, but mine seems to be missing the Starman badge on the front, and there's nothing in the box. A bit weird.

[stiiiiiiive]

Might be unique!!