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My stereo amplifiers produce mono output with stereo source!
My stereo amplifiers produce mono output with stereo source!
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Old 3rd November 2013, 03:01 AM   #1
tsiros is offline tsiros  Greece
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Send a message via MSN to tsiros My stereo amplifiers produce mono output with stereo source!
Default My stereo amplifiers produce mono output with stereo source!

toroidal 2x20 Vrms, 200 VA into a full wave rectifier into smoothing caps. the positive rail of the power supply powers two amplifiers. Each amplifier is the "Single supply, high power amplifier" in the TDA2030(A) datasheet.

i am using the headphone out from my external usb soundcard. oscilloscope verifies that the signal reaching each amp is the correct signal.
when only one amp is connected to the power supply, it plays the correct sound. The other amplifier is physically completely unconnected. Power, signal, output, all disconnected completely.

when both amplifiers are connected and powered, then, both amplifiers will play both channels. L plays L+R, R plays L+R. Oscilloscope verifies that the L+R signal appears at both amplifiers' signal inputs, even when the two amplifiers are connected but unpowered.

The sound is heard loud and clear no distortion no clipping no hiss (except for slight buzz when i connect the laptop to its power supply. No, the downmix problem perists even with the laptop on battery)

I tried with two 9 V NiMH batteries in series as a power supply, still the same result (also plays very loud!)

Any ideas?

Schematic of amplifier: in page 7 of this pdf

I omit the supply schematic because i am using only batteries.

i have a DSO nano, a multimeter, and an iwatsu 5711c quadchannel 100MHz oscilloscope.
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Old 3rd November 2013, 04:36 AM   #2
DUG is offline DUG  Canada
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Check the ground of the supplied signals.

You may have lost the connection.

Just a thought.

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Old 3rd November 2013, 07:17 AM   #3
tsiros is offline tsiros  Greece
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Send a message via MSN to tsiros My stereo amplifiers produce mono output with stereo source!
well i found out what was wrong

the directions and the pcb indicated that pins 1,2 are ground and signal, respectively

if one takes a good look at the pcb, though, it turns out that pins 1,2 are signal and ground, respectively.

as an added bonus, 9 V are enough for that amplifier!
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