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TDA7240 distortion at low volumes

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I recently built a few amps using TDA7240 ICs. I used the circuit design from the spec sheet. They seem to work pretty well, but for some reason, when set to a very low volume, there is an audible "scratchiness" to the music. Any ideas what would cause this? I did not use shielded wires to connect the source (iPod) to the amp input. Is this the likely culprit? I'm doubting it's the volume potentiometer itself, but I'm no expert.

here's a schematic of the circuit if you'd like to take a peek:

Thanks for all the help!

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The TDA7240 was replaced by the TDA7240A. Maybe the "A" version fixed something in the obsolete original one.
It is a car radio amplifier IC, not a hi-fi amplifier. Its distortion is as high as 0.5% which is audible when its output is from 50mW to only 12W into 4 ohms with a 14.4V supply, and is built using the pcb design in its datasheet. If you used a breadboard then it probably oscillates and sounds realy bad. If your supply voltage is less than 12V then there is probably crossover distortion.

Every audio amp needs shielded audio cables for its input.

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