Ebays TDA2822M BTL to amplify guitar signal

[ShareHing]

Bought this little amp from ebay and it works great amplifying my portable mp3 player.

**broken link removed**



It's a variation of the circuit featured in the datasheet, as it includes C1, C2 and R1.

http://www.circuitdiagram.org/images...er-circuit.gif

1) What is the purpose of C1, C2 and R1, filtering?

2) How can I convert it to amplify my guitar's signal and use headphones as output? (maybe also use an fx pedal between the guitar and amp)

 

[Audioguru]

C1 with R1 cut low frequencies. C2 with the volume control cut high frequencies. Then the output sounds something like a telephone.
It can drive headphones but they will be extremely loud. Use a resistor in series with them to reduce their output level.

 

[ShareHing]

Thank you for you help. If I understood correctly:

W1 and C2 form a low-pass filter, cutting all frequencies above the critical frequency defined by their values. W1=10k and C2=100pF; F=160Hz


C1 and R1 form a high-pass filter, cutting all frequencies bellow the critical frequency defined by their values. R1=10k and C2=4.7uF; F=3.4Hz

 

[Audioguru]

If the volume control is 10k and is set at half resistance then it has 5k from the signal source and has 5k to ground so as a part in a filter its resistance is 2.5k ohms.
With 100pF to ground its lowpass cutoff frequency is 640kHz to block AM radio stations and higher radio frequencies.
But a magnetic guitar pickup usually has a load of a few megohms so that it has a peak at its resonance of about 5kHz. the 10k volume control will cut its level a lot and cut its high frequencies a lot.

C1 has a source of 2.5k ohms from the volume control set at half resistance and a load of 10k for a total resistance of 12.5k ohms. With the 4.7uf coupling capacitor the highpass cutoff frequency is 2.7Hz so it will pass earthquake frequencies (from a geetar?). I would use a 0.33uF (330nF) film capacitor.

 

[ShareHing]

Very interesting, thank you very much for your time so far.

If the guitar expects a load of few megaohms from the amp for maximum power transfer and if the capacitors need replacement, should I get rid of that input stage and add a buffer of some sort?

Something like:



Q1 - J201, MPF102, 2n3819, etc.

 

[Audioguru]

Most musicians in rock bands are deaf to high audio frequencies. Therefore they boost the heck out of high audio frequencies also maybe because their speakers have poor high frequency response.

You have a HUGE 10uF coupling capacitor to feed earthquake frequencies as low as 1.6Hz to the volume control. Use a 330nF film capacitor instead.

The little power amps you showed have a fairly high voltage gain of 100. Then your Jfet as a follower with no voltage gain is better than mine that has some gain.

Here are some explanations of high impedance and of boosting the highs: