"mike" wrote in message ...
Norm Dresner wrote:


Just to be clear, I recommended you use the lm317 to power the new 741.
The sine distortion is gonna be critically dependent on the stability
of this reference voltage. I never used a 317 anywhere I cared about
voltage stability and have no direct experience. May be just fine.
Also, if you use it to replace the supply, you also need to worry about
voltage differential when you short the 20V supply. Don't remember what
the max differential for a lm317 might be.

While you're at it, put some resistance in
pin 3 of U410 so C406 won't blast the input on power down.

mike

My point in checking for oscillations was that sometimes an oscillating
Op
Amp can give some very strange readings on a simply DMM.

Norm


Aha! I understand -- use the IC regulator to drop the voltage to the Op Amp
to a level where I could use a commercial grade safely. Good point.
Regarding max voltage inputs, I think I can safely use an LM7824 to drop
whatever the input is down to 24 volts to drive a jellybean 741 and I've got
one or two in some drawer somewhere around here.

As for C406, my circuit diagram shows a diode CR410 whose anode is connected
to the + side of the capacitor and the cathode to the V+ input to the Op Amp
to keep its input voltage no more than a diode drop above the supply
voltage. I couldn't find the diode on the circuit board anywhere or in the
parts location diagram but it's clearly on the schematic. If I can't find
it, I'll put a 1N4148 in as a "jumper"

Thanks
Norm