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Passive summer/mixer to combine a differential speaker-level signal and a single
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kubark42:
For the input to a mono amplifier, I would like to mix together a differential signal coming from a PAM8302 (differential amplifier, 2.5W to 4 Ohm load) with a single-ended line level signal. The differential signal is a continuous series of constant-volue beeps and boops, and the the single-ended is an occasional computer voice. Audio fidelity is almost completely irrelevant, and the volume can be controlled independently for each device.

For (lack of) power reasons, the mixer needs to be passive. However, the result shouldn't be heavy (weight is more critical than audio quality).

Is there a schematic for such a beast?

Is it as easy as putting https://www.alliedcomponents.com/storage/transformers/pdfs/at4365.pdf in the circuit and hooking up the two outputs to two windings and the input to the third winding?
themadhippy:

--- Quote --- I would like to mix together a differential signal coming from a PAM8302 (differential amplifier, 2.5W to 4 Ohm load) with a single-ended line level signal
--- End quote ---
The output of the amp will more than likely be  to hot to feed into a further amp,id use a couple of resistors to bring the level down to something a bit more usable ,feed that into a transformer and the output into a simple passive mixer with the  line level source
kubark42:
Thanks for the answer. If I've understood your suggestion correctly, it's something like the attached schematic, right? If so, would the resistor be necessary, could I not accomplish the same thing with a step-down transformer?
kubark42:
Or by "couple of resistors", did you mean a voltage divider like in the below? If I have a voltage divider, do I then need the transformer if the stereo-level input is constant volume?
themadhippy:

--- Quote ---Or by "couple of resistors", did you mean a voltage divider
--- End quote ---
yep

--- Quote --- If I have a voltage divider, do I then need the transformer
--- End quote ---
yes,it avoids the differential output of the amp being grounded.
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