CEM Oscillator woes

[klosmon]

>Date: Sat, 02 Sep 2000 17:48:51 -0500
>Subject: Re: CEM Oscillator woes
>From: "Grant Richter" <grichter at execpc.com>
>To: klosmon <klosmon at earthlink.net>, synth-diy at node12b53.a2000.nl
>Try shorting out the resistors in series with the power rails on the Ekx
>boards. That should prevent the voltage from shifting under load. John
>always uses decoupling circuits and those can be a problem for VCOs.
>

Well, hell -- that was easy!  Tried it, & it worked -- pitch is rock solid
now.
I thank you, and my few remaining functional brain cells thank you.

>----------
>>From: klosmon <klosmon at earthlink.net>
>>To: synth-diy at node12b53.a2000.nl
>>Subject: CEM Oscillator woes
>>Date: Sat, Sep 2, 2000, 4:52 PM
>>
>
>> Decided to unearth & recommission my old Curtis CEM 3340 vcos -- have two
>> on Paia experimenter cards and one on a homemade circuit from POLYPHONY --
>> the weird thing is that they ALL have the same problem:
>> altering the pulse width has an effect on the pitch.  It is the same effect
>> on all three waveforms;  measuring the control voltage going into the chip,
>> I see a change of about .06 volts moving the pulse width control from one
>> extreme to another.  this same effect occurs using external pwm voltages.
>> I've checked all I can think of to check (on all three units);  I've
>> switched power supplies.
>>
>> This is all news to me.  I'd conclude that it's a systemic problem with the
>> CEM chips, but they work just fine in my Pro-One.
>> Anybody (who's still around, and not carousing for the three-day weekend)
>> ever encounter this?
>> 
>
>