Two circuits sharing power supply, interfering

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andyfromdenver

Well-known member
Joined
Nov 13, 2012
Messages
359
Location
Athens, GA
I have an LED VU meter circuit on the output of my LA2A, and a separate LED VU meter circuit on the Peak reduction.
When they have their own battery power supplies, I can calibrate both meters to give a satisfactory visual.
However, when i power both circuits with the same battery supply, the Output level indication bleeds through and dominates the Peak reduction circuit.

How can I isolate these circuits to use a single power supply?

I plan to use a 12-0-12 PT with a fullwave rectifier. I haven't had a chance to hook that up yet, if I separate the two power nodes with a resistor and their own Elytic, will it help my problem?  Or will sharing the negative cause this issue to persist?

I'm really close to adding LED VU visuals for an LA2A and this is my last hurdle before I share it all in my thread.

Thank you!

Thank you!
 
alternatively, I can add a switch so only one is powered at a time, but I believe it is not wise to remove vcc+ from an opamp circuit with a signal still connected, I guess I can break both connections too.

Ideally, both will be present and viewable like the DBX160A
 
All signals are a + with respect to a - or 0V. If when you connect the two meters together the 0V is no longer 0V that will look like input signal.

It could be as simple as lead dress, when signals are connected, but you may need to add differential circuitry (an op amp and 4 resistors, or one for each). This will keep the audio signals relative to their respective 0V.

JR
 
JohnRoberts said:
All signals are a + with respect to a - or 0V. If when you connect the two meters together the 0V is no longer 0V that will look like input signal.

It could be as simple as lead dress, when signals are connected, but you may need to add differential circuitry (an op amp and 4 resistors, or one for each). This will keep the audio signals relative to their respective 0V.

JR
Thank you so much John, for your input! 

My experiment is getting a little tangle-y with breadboards and metering components with excessive wire lengths, Perhaps when I tidy it, it will help, but I will also employ the suggested circuitry :)

So close, I can taste it!
 
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