[sdiy] Op Amp Question

[Harry Bissell]

In effect, the low impedance stops crosstalk. I'm assuming each has
a feedback resistor, the feedback would remove any residual signal.
Just keep the resistors high enough in value to avoid loading the opamp.

I didn't quite follow the ascii-matic... I think you don't need the additional
22K resistor, you can send the junction of the 22Ks direct to the inverting
input of the opamp (through the analog switch)

H^) harry



----- Original Message -----
From: Stewart Pye <stewpye at optusnet.com.au>
To: Synth DIY <synth-diy at dropmix.xs4all.nl>
Sent: Tue, 14 Dec 2010 16:06:19 -0500 (EST)
Subject: [sdiy] Op Amp Question

I have a circuit where I want to switch two additional inputs to an op 
amp summing circuit using an analog switch. So that I can get away with 
using just one analog switch I had the idea of joining the summing end 
of the resistors together and have an analog switch between there and 
the summing node.

It would look something like this.

                              |---------////22k////---------|
                              |                                          |
OP amp 1 Output --- ////22k//// |                       |
                                               analog switch --- Op Amp 
inverting input
OP amp 2 Output --- ////22k//// |


My question is when the switch is in the off position we are left with a 
44k resistor between the two op amp outputs. Would this cause any bleed 
from one output to the other, or does the low output impedance of the op 
amps eliminate this?
When the switch is off I want only the op amp 1 output ( with half the 
gain of when the switch is on) but don't want any bleed from op amp 2 
output...

Cheers,
Stew.



_______________________________________________
Synth-diy mailing list
Synth-diy at dropmix.xs4all.nl
http://dropmix.xs4all.nl/mailman/listinfo/synth-diy

-- 
Harry Bissell & Nora Abdullah 4eva