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Merging two circuits questions

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adown

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Hello, I found a simple VU meter using a 3915, but it only had one input. I found another with a more complicated power circuit that I don't want to use. I am wondering if I merge them as shown, if it will work. I am posting both circuits, with a merged photo also. Can I get some feedback please.

Wouldn't I need diodes on the inputs to keep them separated?

Thanks, adown
 
The "more complicated power circuit" is used to provide a negative voltage for the LM358 opamp.
Without a negative supply the peak detector will not work correctly.
Just thinking out aloud, it may work correctly from a single supply if you use a TL072 instead of the LM358.

As for needing diodes on the inputs, I assume that you mean the L and R inputs.
You will not need diodes, infact diodes would be a bad thing to put on the input.
The 51k resistors should give enough isolation between channels for most practical purposes (depending on the impedance of the signal sources, if they are low impedance there will be no problem).

JimB
 
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Thanks Jim, could I use right and left inputs with the 51k resistors on the first circuit. Instead of the input connection to the LM358, connect that to the input pin 5 of the 3915. I think the peak detector is for accuracy? I don't need any kind of accuracy, just lights that follow the music in my car. Thanks again, adown
 
I think the peak detector is for accuracy?
No. It provides persistence of the display. Without it the LEDs may light too briefly to be noticeable. Recommend you use it.
 
Thanks to everyone taking the time to offer your input. I learn a lot from these posts. Cheers to Electro-Tech and the electronic wizards that help.

adown
 
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