Simple audio mixer using FET

I want to build a simple audio mixer (adder) (from stereo line inputs) of good quality and low energy consumption. I found this simple design:

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and I also found this one that also uses a transistor:

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Q1: would the simple design work well, or is it just a theoretical example? Otherwise, why would the second design add a transistor? (Q2)

The second design's webpage says: "If two of these circuits are made in the same enclosure for stereo, then there can be a single power supply to run both of them. There should be a resistor in series with the incoming 9V+ lead so as to minimize crosstalk, and reduce the PLOP when it's powered on."

Q3: How big should this resistor be (Ohm)? Q4: So each of the two stereo's mixers circuits should have their own resistor in series with / connecting to the battery?

Q5: The second design uses a lot more power because the transistor draws a current while it's not used. Battery power wouldn't be feasible, right?

Reply to
ectoplasm
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On a sunny day (5 Mar 2007 23:01:12 -0800) it happened "ectoplasm" wrote in :

Those are not very good mixers.

Perhaps it would be simpler if you just used an opamp inverting input, use symmetric supply to make life easier. Advantages:

1) good linearity (opamp) 2) good noise (opamp) 3) few caps (freq response cost) 4) if quad opamp more available for tone control etc.

R1 should be much higher in value then the pots, or use buffers (balanced input).

------R2---- pots | | []

Reply to
Jan Panteltje

What's wrong with two resistors? Zero power consumption!

Tim

-- Deep Fryer: A very philosophical monk. Website @

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Reply to
Tim Williams

You mean a passive mixer, right?

I am doing it now... it's a solution. Input signals get a bit weaker in the mixed signal, but it's ok for me.

Reply to
ectoplasm

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