[sdiy] ADSR output oscillation

[Tim Parkhurst]

On 1/9/07, Charles Bisaillon <sdiy at oveloe.com> wrote:
> Hi list,
>
> I would really appreciate some help on this one. In my opinion, this is
> basic stuff, but some of us are still just getting there.
>
> We have built the ADSR from this circuit.
> http://www.oveloe.com/concordia/IMG.jpg
>
> We spent all day troubleshooting this circuit because it has an AC output
> frequency of 9Mhz and 20Vpp. The odd thing about it is that this AC
> frequency is only present at the ENV out which is also connected to + of A2
> and - of A5. Nowhere else in the circuit can we find that oscillation.
>
> Other than that, the ADSR is working well, we see that the DC component
> follows all of the ADSR stages even though there is that oscillation through
> it, so it is working fine underneath. Any help is appreciated.
>
> Thanks
>
> Charles
>
>
> http://www.oveloe.com
> Voltage-Controlled Brain Waves
>

Hey Charles,

This looks like a circuit from Barry Klein's book. If so, you might
want to check Barry's site
http://members.cox.net/barryklein/em.htm
and see if there are any corrections for that particular schematic.

Other than that, it sounds like you've got some oscillation going on
around one of the op amp sections you mentioned. I'd try putting a
10pF cap between the Env Out and the A5- input.


Tim (got some oscillation goin' on) Servo
-- 
"Imagination is more important than knowledge." - Albert Einstein