MOTM

To anyone out there who owns/owned/spent-time-with a Mini\u2026

I was squinting at a photo the other day and I noticed something I had never noticed before. Two of the VCO\u2019s on the Mini Model D appear to have some kind of off-beat waveform. It looks like a Triangle with the symmetry set badly, or perhaps a triangle mixed with a sawtooth or a triangle mixed with a sawtooth an octave lower.

Am I looking at this wrong, or was this a real waveform on the Mini? Any idea what it is, what it was called, how it was made?

Just idle curiosity\u2026; assuming I\u2019m not mistaken, I don\u2019t know how I\u2019ve missed it before (although I\u2019ve never actually seen a Mini up close). I thought the Mini used the modular 921 VCO boards, but I don\u2019;t remember ever having seen this particular waveform anywhere else. That\u2019s why I\u2019m thinking it\u2019;s probably a composite of two other waveforms in some way.

Thanks in advance.

Mr. T

I still have my mini. Oscillators 1 and 2 have a 
waveform that is a combination of a triangle wave 
and a sawtooth wave (situated between the 
triangle and ramp waves). It starts with the 
first half of a triangle wave (linear ramp from 
-5V to +5V in modular-speak), then ends with the 
last half of a downward sawtooth wave (linear 
ramp from 0V to -5V). Sounds just like you'd 
think it would.

>To anyone out there who owns/owned/spent-time-with a MiniŠ
>
>I was squinting at a photo the other day and I 
>noticed something I had never noticed before. 
>Two of the VCO's on the Mini Model D appear to 
>have some kind of off-beat waveform. It looks 
>like a Triangle with the symmetry set badly, or 
>perhaps a triangle mixed with a sawtooth or a 
>triangle mixed with a sawtooth an octave lower.
>
>Am I looking at this wrong, or was this a real 
>waveform on the Mini? Any idea what it is, what 
>it was called, how it was made?
>
>Just idle curiosityŠ assuming I'm not mistaken, 
>I don't know how I've missed it beforeThanks in 
>advance.
>
>
>Mr. T
>

> Two of the VCO's on the Mini Model D appear to have some kind of
off-beat waveform.

This is the second waveform from the left for VCO1 and VCO2. The third
VCO simply has an inverted sawtooth. The odd shape is created simply;
the triangle wave and sawtooth are added together with some resistors
prior to the volume pots.

> I thought the Mini used the modular 921 VCO boards..

There are three types mini VCO boards. The first is all discrete and
appears to be very rare [RA Moogs only??], the second has op-amp summing
stages but with a discrete core and waveshaping, the third is op-amp
based and uses the heated uA726 in the expo. One PCB contains all three
VCOs in each case. For each 'upgrade' the VCOs got more stable.
Considering the difference in circuitry they do sound remarkably similar
to each other.

The 921 does share some similarity to the second set of mini VCOs, in
particular the CV and expo stages. Although, it has a load more features
like variable sync and sinewave generation with a clever two stage
method.

Tony