I am connecting the input of a TDA2040 audio amp to the line out of my laptop computer. I would like a volume control (voltage divider) on the TDA2040 PCB itself, instead of adjusting it on the laptop. What value pot should I use, assuming the laptop is set to maximum possible output level.
This is the amp circuit I intend to use:
Should it be log or linear?
Ben Hartley
"Ben Hartley"
** 10kohms, audio type or log.Labelled " 10KA " or maybe " 10KC " .
Piece of cake.
.... Phil
Use a log unit about 100k.
"Rheilly Phoull"
** With a load of 22kohms ?That is not ideal.
... Phil
I think the polarity of C7 is backwards.
A line output on a soundcard these days is pretty beefy since they often drive earbuds. The impedance should be about 100 ohms. Your load is 22K at audio frequencies. I'd make the pot 1k to maybe a 4.7K. Log.
Depending on what you are trying to achieve, I'd consider an amplifier with a bridged output. That would get rid of the electrolytic in the output between the chip and the speaker. TI/National makes the for flat panel TVs. The chips are a bit more modern than the old car stereo stuff.
Those designs with large coupling caps in the output often "thunk" on power up.
On a sunny day (Thu, 14 Mar 2013 10:45:37 +0800) it happened Rheilly Phoull wrote in :
No that would not be such a good idea, did not want to get involved, but the 100k will be largely shorted for AC by R6 (22k). Personally I use a 10 k LIN in a similar application, If t is just for audio (mine drives other things) use a log perhaps. Make sure you do not run any sort of DC in the pot, so replacing R6 with a 22k pot with wiper on IC input is bad, it will start cracking, and / or worse. When adding a pot, add an other input cap BIPOLAR if possible
bipolar o---||--- | C7 [ ]
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