Strange TDA 7262

[Menticol]

Hello again!!

I have bought yesterday a stereo amplifier kit, that uses TDA7262. I'll make a schematic for that PCB, but I think is a copy of the suggested application found in the datasheet

**broken link removed**

Even when I didn't posted the schematic yet, I guess the fail symptoms are very recognizable for an expert:

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Either when feeding the circuit with 12V battery or PC PSU:

- Very loud hum and interfence when the input (a 3.5 mm plug) is not connected to anything, or if touched with the bare fingers

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In the following cases, the PC PSU +12V and 0V rails are used to feed the cicuit:

- Loud ground loop when connected to a PC sound card. Grounding the circuit with the soundcard ground doesn't fix the problem

- When feed with signal coming from an iPod or external player, the circuit works perfectly

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Thank you in advance!

 

[audioguru]

It is spec'd with a 28V supply (not 12V). Then its power at clipping is 14W into 4 ohms or 9.5W into 8 ohms. With your 12V supply its power is only 2.5W into 4 ohms or 1.5W into 8 ohms.

If the power supply has ripple then the amplifier will make hum.
If the input cable is not shielded then it is an antenna that picks up mains radiation.
C3 rejects power supply hum. Maybe it is bad.

 

[Menticol]

thank you so much Audiguru, I'll check that tomorrow (perhaps, today!)
Do you suggest any improvement that could be made? I know is a cheap amplifier and we can't expect too much from it. But at least, preventing the loud hum when there is no input signal, would me great