[sdiy] Topic cem3396

Tim Parkhurst tparkhurst at siliconbandwidth.com
Mon Apr 19 20:29:08 CEST 2004

Hi pHobax,

The CEM3396 needs a compensation CV at pin 2 (for oscillator 1) and pin 10
(oscillator 2) to keep the amplitude of the saw/triangle waves constant.
Also, since the variable pulse width wave is derived from the saw, the saw
level dropping will affect the pulse wave too. If the amplitude of the waves
is dropping off, I'd check whatever is feeding pins 2 and 10 of the 3396s.
It could very well be one of the 4051s (an 1 to 8 analog
switch/multiplexer). This sort of problem would not be caused by a bug in
the dividers or the high frequency oscillator. It also doesn't sound like
the 3396s are bad (I doubt that all six of them would have the same
failure), but if you do need to replace one, they can still be found at
Synthtech. Hopefully, you won't need to replace any of those, but if you do,
check whether you have the wide body (about 1" wide) or narrow body (about
1/2" wide) 3396. The wide body versions are $40 each and the narrow ones are
$15 each.


Tim (owner of many 'extinct' CEM chips) Servo

"Imagination is more important than knowledge." - Albert Einstein


> -----Original Message-----
> From: pHobax at gmx.de [mailto:pHobax at gmx.de]
> Sent: Friday, April 16, 2004 4:45 AM
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] Topic cem3396
> Hi. I own a elka ek-22 with 6 cem-3396-voices.
> A real annoying bug occured, effecting all six voices:
> The synth doesn't produce the right waveforms anymore. The saw has a much
> less amplitude on all octaves except an the 1st and 2nd.
> PW is not real ajustable anymore, it seems to depent on the note played.
> With some ajustments the PW is 0 on c3.
> Tri isn't accesable anymore etc....
> In addition the seperate voices vary in their volume (not very strong, but
> it sux) and the described bugs.
> This problem seems not to be located in the chips.
> I thoght  the divider or the digital osc could be the reason.
> Is there any possibility to replace this unit, and if not is there a good
> diy-project using the cem3396??
> nice greetings, max.
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