[sdiy] CEM VCOs (was Analysis of frequency variation in analogue synths)

[Tom Wiltshire]

>>
>> Does anyone have a strong feeling as to whether the CEM VCO has  
>> this analog warmth?
>
> I've owned a Roland SH-101 (single CEM3340) and Akai AX60 (6 voice  
> CEM3394 VCO/VCF/VCA chip) and concluded the CEM oscillators were  
> not as warm as other VCOs found in the SH-3a or Andromeda, or as  
> analog (but not necessarily warm) as an Odyssey VCO.
>
> On the other hand I played a MemoryMoog+ and thought it had a  
> fantastic sound, though I never brought it home for late night for  
> comparison to other gear.
>
> I am interested in other people's opinions of CEM VCOs.

I have both a single CEM SH101 and a dual CEM Sequential Pro-One.  
Most of the SH101s character comes from the filter, which is really  
something else. The Pro-One manages to get a very big dense sound out  
of a pair of 3340s, although the filter thins it out. Definitely a  
lead synth, whereas the SH101 excels for fat squishy bass. For sonic  
comparison, I've got the completely different architecture of the  
Korg Polysix. The Polysix VCO is a fairly flat sound in my opinion  
(although I think the SSM2044 filter and analogue chorus more than  
make up for it).

I haven't compared the circuit diagrams for the two CEM synth's  
oscillator sections, but I doubt either of them differ much from the  
datasheet.

Overall, I like the CEM VCOs. I do think they have 'analogue  
character', whilst also being reasonable stable, especially after  
having warmed up. In that respect, I think they are a good  
compromise. I wouldn't want them to vary or drift any _more_ than  
they do already, let's put it like that...