Hi-Fi Stereo Amplifier gain regulation with potentiometer

[kendall]

I have built a stereo hi-fi (end) amplifier 2x10W based on a IC

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Zaloguj się, aby zobaczyć treść (możliwe logowanie za pomocą ) . I have bought it as a construction (learning) kit ready to solder.

Schematic:

(the pictures are from the manual that came with the kit, please don't mind the Czech headers)

Parameters for the circuit (from the manual) are:

 

Us power supply voltage: 8-28V (I use 9V power supply)

Peak output current Io (freq. >= 20Hz): 3.5A

...and more but IMHO (now) not important values

Now, everything worked great (although I had to replace the C8 capacitor, no idea why it was broken), so I decided I want to replace the R1 and R3 resistors with a potentiometer for variable gain (gain control). I bought stereo potentiometer, linear, 1kOhm, wired it up to R1s and R3s place (first pin ground, second and third pin to the PCB). When I turned the circuit on, the pot started smoking and burned.

If I get it right, I understand that the potentiometer couldn't handle the load when set to little resistance. I didn't really had a choice when selecting the pot as the one I used was the only stereo 1kOhm pot they had in the shop.

So I need to know:

 

Is my approach correct here? Can I replace the two resistors with a stereo pot?

Am I right thinking that the pot couldn't handle the current/load, or was it just a bad piece?

How do I calculate the power that can be on the resistance R1/R3?

Thank you for help!

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[S4Home]

You should ask on elektroda webside. More practitioners are there.

[micwoj]

You should ask in DIY forum, not HIFI. There are also practitioners :)

But anyway.

I could not understand where you did put the potentiometer, can't see R1s etc., but it shoud be between INL INP and ground. The R1/R2 and R3/R4 voltage dividers set up the negative feedback loop. For those, use values as in TDA datasheet.

The potentiometer should be logharytmic, min. 10kohm (50k usually).

See drawing as it should be connected:

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And consider adding more voltage power. 9V is an absolute minimum. You should go for 15-24V instead. This is a car amplifier and will work best with car voltages.

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