Yes... this circuit is a real piece of work. The distortion from this
circuit must be tremendous.

Professor
www.telstar-electronics.com



Frank Gilliland wrote:
On 14 Apr 2005 18:06:58 -0700, "Professor"
wrote in
.com:

Anyone want to comment on this circuit?
http://www.cbcintl.com/images/DSPSCHEM.GIF


DSP? Looks like an analog clipper to me.....

For starters, set the voltage of your center rail (your "6.2 VDC
bus")
with a voltage divider because the zener can make the op-amps lock up
on power-up, and any noise on the power supply is going to get
amplified like mad. For the same reason, don't isolate your inverting
inputs from DC -- tie them to the center rail with a high value
resistor (except for A2, more on that later). 1 Meg is fine and
shouldn't degrade the operation of the circuit. Add another 1 Meg to
ground on the mic side of C2 to prevent static noise when using a
crystal or ceramic mic (or any other mic that is DC isolated, such as
some power mics). Back to A2: ground the NC end of VR1 and feed A2
from the wiper (through R3) to keep the input impedance high, then
replace the electrolytic C3 with whatever you are using for C4 so you
can avoid polarity issues and prevent loading the output of A1 (which
will screw with your frequency response). You might also want to try
1N4148 diodes in the clipper because they tend to behave better than
1N914 switchers. This will also allow you to scale up the value of
the
resistors in the clipper, and thus prevent overloading A3 (1K is a
pretty heavy load for the LM324).

I probably missed a couple things. I'll look at it more closely
later.

Oh yeah -- get yourself an audio signal generator so you don't look
like an idiot by noting test voltages obtained from "loud whistling".
An old Heathkit or Eico shouldn't cost you more than $20 plus
shipping
on ebay. If you can't find one there, drop me an email and I'll sell
you one of mine.





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