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[email protected] makolber@yahoo.com is offline
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Default Questions About the Event TR5 Schematic

On Friday, October 19, 2018 at 11:09:25 PM UTC-4, Paul wrote:
On 10/15/2018 7:03 AM, Scott Dorsey wrote:
My sig gen signal only appeared before R20, and on the output pin 1.

I recall learning about virtual ground in this topology.

** Yes, that is what you had.


Think about it this way. R20 and R24 are identical, and both are coming
from sources that have effectively infinite current available.

Pin 1 is reverse polarity from the input, so pin 2 is part of a summing
junction with equal parts of the input and inverted input summed together.
So in normal operation there's nothing there.


Correct. There is a "virtual ground" on pin 2.




Maybe confusion re pins 2/3 on the XLR vs pins 2/3 on the IC U2A

The differential input signal appears across Pin 2/3 of the XLR.

On Pins 2/3 of IC2UA there will be two "virtually" identical signals ie. virtually no voltage across pins 2 and 3 of the IC. Each will be 1/2 of the input measured to ground.

The differential input signal will be on the ICU2A pin 1 output measured relative to ground.

m