Hello Everyone!

As part of a bigger project I'm working on, I need a decent audio amplifier. I've tried out a couple of ICs such as lm241, lm386N, etc.. and found tda2822m works best for me. I've built a bridge circuit shown in the datasheet for the TDA2822M and it works fine, giving little distortion. I also need volume control for this, but I'm not sure where to put the pot. I've tried putting a 50k pot just before the speaker, and this works, but if the resistance is increased, one of the 10uF caps blows up. (did this twice before I figured out what was happening). So basically, my question is where is the best place to place a pot for volume control?

Thanks in advance.
-Igor

 

Put the pot in the input. Replacing the 10K ohm input resistor with a 10K ohm pot should work.

Connect the ends of the pot between your input signal and ground. Connect the wiper of the pot to the amp input. (See Figures 17 & 21 in the data sheet).

 

I'm not meaning to have a go but this is why it's important to fully understand things before you build them.

Adding a 10k pot to the output isn't any good because it a very high resistance compared to the 8/4hm: speaker.

I can't understand how it would have caused a capacitor to blow though. Are you sure that all the capacitors have an adequate ripple and voltage rating?

I agree with crutschow, put the potentiometer on the input.

Please post a schematic.

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Hello,

Thanks for the answers. I replaced the 10k resistor with a 10k pot at the input, and now volume control works nicely. The schematic of the circuit I have built can be found in TDA2822M datasheet, page 4, figure 7 (Test circuit bridge), with only difference that I have replaced a 10k resistor with a 10k pot at the input, as noted above.

However, the pot I am using is type A (logarithmic?), and has only one turn. I would like to have a more gradual volume control. Does this mean I should get a pot with more turns, and should it be linear or logarithmic?

Thanks for help,
-Igor

 

Logarithmic is fine for audio as it matches the response of the human ear.

If you want a more gradual control, use a pot with more turns or, if possible gear it.

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A linear volume control pot will reduce the level (-6dB) a little when it is turned down from max to half.
Then is also reduced a little when it is turned down from half to 1/4.
Then the level is reduced a little when it is turned down from 1/4 to 1/8.
At 1/8 it is still pretty loud and if you turn it down more it will just turn off.

You can see (hear?) that the range is stretched out at full volume and the range is crowded together at the low volume end.

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Uncle $crooge

 

On a side note, I bought a cheap multiband receiver from London Drugs, mostly just for listening to pay-per-view hockey games. AM works fine, FM works fine, SW I get nothing (no surprises there).

The fun thing is that the volume knob is linear instead of log. All the action happens in the first 1/8 of the knob's turning radius, like audioguru said. Very annoying. Not annoying enough for me to have opened it up and replaced the pot with a proper log pot yet, though.

Note to self: Coby brand radios are junk.


Torben

 

You can convert a linear pot to give a sort of quasi-log output if you connect a resistor load from the pot wiper to ground, for example 1k ohm with a 10k ohm pot. The 1k provides a relatively low impedance as compared to the pot impedance at low volume (1k to 10k) but becomes relatively less as the pot is turned louder (1k compared to 5k at midpoint for example). Thus the pot output changes less for a given pot movement a low levels then at higher levels, which is what you want. At the half point the level is now reduced by -16.9dB from the maximum as compared to -6db without the resistor. This is equivalent to the 1/7 point of the plain pot.