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Crossfading between 2 audio signals / single supply opamp circuit

Electrical Engineering Asked by Zilaihong on November 16, 2021

Will this circuit work? Any comments? Thanks!

Edit :
by “work” I mean I can blend the 2 audio signals in any ratio with the pot;
it would be an OPA2132 opamp;
input would be audio signals in the range of 0-3.3v

my diagram

it seems even this circuit would work? enter image description here

3 Answers

I suggest you using such a circuit as below. first section is a inverting unity gain op-amp. then a voltage divider. and finally a voltage subtract circuit.

Vou = Input2 + (Input1/K)

which K is the constant of pot R3.

Advantages of this circuit :

  1. No Loading effect on the both input voltages.
  2. Control Gain of each Input voltage independently.

schematic

simulate this circuit – Schematic created using CircuitLab

Answered by HOPE on November 16, 2021

There are simpler circuits like this one: -

enter image description here

And I've posted it for two reasons, 1) to show the decoupling capacitors that must be fitted and 2) to explain that your circuit has certain benefits that may not be that obvious.

You circuit does not rely on the signal sources being low impedance - if the pot is totally at one end of its travel it will 100% attenuate one signal whereas the simplified circuit won't do that if the output impedances of the signal sources are not zero.

If you are expecting unity gain, then you ought to figure out the proper value of feedback resistor - with your circuit's pot at one end, the other channel will suffer a fair amount of attenuation but this can be easily remedied however you need to state what value your pot has. I'd go for your circuit over my example.

Answered by Andy aka on November 16, 2021

The basic idea is OK, but the DC biasing is messed up. The DC level of R3 should be decoupled from the opamp input.

Answered by Olin Lathrop on November 16, 2021

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