The joy of "digital" amplifier modules!

Discussion in 'The Projects Forum' started by THE_RB, Dec 16, 2013.

  1. THE_RB

    Thread Starter AAC Fanatic!

    Feb 11, 2008
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    I had a trusty old piece of equipment blow up recently. It is a modified Akai cassette radio, that for 20 years has been a faithful stereo amplifier with two RCA input jacks that I added, tapped into the existing audio amp on the cassette radio PCB.

    The old audio amp blew the right channel, from old age and static probably. The amp gets used a lot for TV applications as it gets plugged into the stereo AV connectors on set top boxes and DVD players etc.

    Instead of trying to source a new linear amp IC to replace the ancient 1980's IC, I just scrapped the entire radio cassette PCB and was left with an empty speaker box apart from the mains transformer, original diode PCB, speakers etc.

    The new digital stereo audio amp module is a TINY little PCB that I got from ebay, I got a few, for about $4 each, fully assembled.

    It is a class-D digital amp based on the PAM8403 IC, that acts like a SMPS driver with high efficiency (typically 80-90%) so the tiny chip can make 3W x2 into 4 ohm speakers (which the unit has).

    The digital amp requires a power supply of 2.5v to 5.0v DC. Since the transformer and diode bridge made about 12v DC I added a chunk of 20mm aluminium angle, and a 7805 regulator IC to provide a fixed 5.0v DC. Also a couple of 680uF caps on the 7805, and a large 2200uF cap was added on the bottom of the digital amp PCB. I aslo added a 1W 2.2ohm resistor in series between the diode bridge and the 7805 input, to reduce cap surge current at turn on.

    The result is awesome! From such a tiny amp module the sound is great, being very flat frequency response from about 100Hz to about 14kHz. Plenty fine for TV audio use and testing appliances. The sound is loud and clear, easily loud enough to fill the room with sound for watching a movie etc.

    The only thing I can fault is that it does not have huge gain, it's not quite getting to its 3W max from the max audio level available on TV AV outs. So for some applications you would need a preamp.

    Anyway, if you need a replacement small stereo amp, that is very energy efficient, very small and very cheap than these little beauties will do fine. Especially for people making battery powered apps!

    For a $4 solution it's a definite thumbs up! :)
     
    Last edited: Dec 16, 2013
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  2. Sensacell

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    Jun 19, 2012
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    Cool idea!
     
  3. wayneh

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    Sep 9, 2010
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    This might make a nice way to upgrade the typical cheap computer speaker system. Most I've seen use a little transformer/rectifier power supply and use the LM386.

    Now if we could just as easily upgrade to "digital speakers"! :)
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I see one of the Chinese sellers must have misplaced a decimal point.
    He's selling them for $488.00 ea, but free postage!:rolleyes:
    Max.
     
  5. tracecom

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  6. THE_RB

    Thread Starter AAC Fanatic!

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  7. wayneh

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    Incredible.
     
  8. iimagine

    Active Member

    Dec 20, 2010
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    I just bought 5 of these for 5.00! :)
    Gotta wait 3 weeks for them thought :/
     
  9. wayneh

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    Just curious - did you see any issue with low gain as RB reported?

    I ask because I've always wanted a way to mix my guitar in with my iPod, for an easy and self-contained practice setup. I'm sure I'd need a pre-amp for the guitar with one of these modules. But now that the price is right (i.e. almost free :D) maybe I'll finally do this project.
     
  10. tracecom

    AAC Fanatic!

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    No, there is plenty of gain with the amp that I used. http://www.ebay.com/itm/12V-Mini-Hi...310?pt=LH_DefaultDomain_0&hash=item2eccc69666

    Generally, I run my MP3 player at close to maximum any time I am using it with an external amp; I set the PAM8610 amp volume for midpoint or below for quiet room listening.
     
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  11. THE_RB

    Thread Starter AAC Fanatic!

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    Definitely!

    A complete high efficiency stereo amplifier for under a buck. :)

    Re the low gain, the datasheet says the gain is set by the two Ri input resistors. I checked mine and it has 10k input resistors, some others on ebay look to have 1k input resistors so they are set up for higher gain.

    I'll fiddle with mine later to see if I can easily bump the gain.

    Re using one for guitar, it might not have the gain for direct input of a guitar pickup, but it should be fine if you use any guitar effects unit as they put out a good strong signal, equal or louder than AV audio signal.
     
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