Modifying Ebay TDA2822M BTL to amplify guitar signal

Discussion in 'The Projects Forum' started by FranciscoB, Feb 8, 2014.

  1. FranciscoB

    Thread Starter New Member

    Feb 8, 2014
    14
    1
    Bought this little amp from ebay and it works great amplifying my portable mp3 player.

    (circuit diagram inside)

    TDA2822M Amplifier Board DIY Parts | eBay

    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)
     
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Sorry but the link to the schematic GIF is broken and we can't see it.
    :)
     
  3. Metalmann

    Active Member

    Dec 8, 2012
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    Or, you could buy one of these:

    http://www.ebay.com/itm/Mini-Guitar...Joyo-JA-03-Battery-USA-Shipping-/121271585953

    Unbelievable tone and volume for any style guitar playing.
    It's as powerful, with enough gain, as some of my more expensive pedals.
    Now, when you mix the two together.......;):cool:
     
  4. Rolf Zetterberg

    Member

    Sep 20, 2008
    14
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    I suppose it's this schematic.
     
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  5. donpetru

    Active Member

    Nov 14, 2008
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    1. Those electronic components limits the frequency range of the input of the amplifier. They have a very important role especially in assemblies with IC TDA where the probability of occurrence of oscillations is very high.

    2. First, I don't recommend use that TDA for sound of the guitar. The power of that TDA2822M is very small. For example, which is acoustic enclosures we will use the output of that TDA? Can you show me? After that, I'll recommend a more suitable amp even if you have already purchased that electronic kit.
     
  6. Rolf Zetterberg

    Member

    Sep 20, 2008
    14
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    R1 is needed because the first transistor in the chip is a PNP and the base needs to be connected through a resistance of some sort to ground.This can be a resistor or a pot-doesn't really matter which.
     
  7. FranciscoB

    Thread Starter New Member

    Feb 8, 2014
    14
    1
    My main goal is to keep learning electronics, not acquiring guitar gear.

    TDA2822M can provide 1W of power and this sort of chip amps are actually popular between the guitar community to be used with headphones or very small speakers, when sound fidelity is not very important. However, LM386 and TDA7052 are more popular and there are plenty of projects out there, I chose TDA2822 because they are less popular but have potencial to be used similarly.

    As far as i have been told:

    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?). Maybe use a 0.33uF (330nF) film capacitor.
     
  8. floomdoggle

    Senior Member

    Sep 1, 2008
    217
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    That amp should be good to go as is, except you might want to play around with c1. The amplifier stage of a guitar amp doesn't give the "guitar" sound, the pre-amp does that. Any pedal should work fine as a pre-amp. I've used tda's before. Have you checked out the Little Ruby, yet?
     
  9. FranciscoB

    Thread Starter New Member

    Feb 8, 2014
    14
    1
    Yep, I've breadboarded a couple of LM386 and TDA7052 mini amps but now I'm interested in experimenting with this chip. One of the main reasons is that it's common to find them in cheap 3v portable radios and PC speakers, so I'd like to understand how difficult it is to convert these circuits and turn them into portable pratice guitar amps with speaker and heaphone already included.
     
  10. floomdoggle

    Senior Member

    Sep 1, 2008
    217
    2
    From the PC speakers, probably no modification, except c1. The radios, on the other hand, problem. Unless you disassemble the circuit board, you will have a hard time getting the signal to the amp.
     
  11. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    That's not so hard. All that would be required is cut a couple of tracks on the PCB, to ground one of the pins 6 or 7, and use a capacitor to couple the guitar audio signal into the other pin (6 or 7).

    The radio may even have one pin already grounded (which is easy to identify) so it's just a matter of cutting one PCB track to the other pin, and soldering a cap to that pin. :)
     
  12. FranciscoB

    Thread Starter New Member

    Feb 8, 2014
    14
    1
    Yep, that will be the next step, as I finally was able to test the original circuits it with a guitar pedal as "preamp" and it works properly.
     
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