Problem with STA-540 audio amp

Kits
1

Hi,

I’ve followed the manual including the testing at the end and everything came up correctly. I’ve posted a video that shows the problem: https://youtu.be/owkn94P_45U

Supply voltage is 12V. Music source is the Papa Soundie. I’m doing ok with digital, but analog and amplifiers are a bit of a mystery for me. Any guidance is appreciated. As you can see I have a scope, so anything I can measure to assist… just tell me where to probe… Thanks!

2

  • - What are you using as a power supply?

  • - Can you supply a schematic diagram showing your connections?
    • 3

    The power supply is a commercial 12V supply:

    amp_power_supply.jpg800×600 102 KB
    http://powersoft.ca/files/amp_power_supply.jpg

    Between it and the amp is the this circuit

    amp_power.png873×299 4.3 KB
    http://powersoft.ca/files/amp_power.png

    audio input is L and R from papa soundie, with common ground. Speakers are 4 ohm. The scope shows the supply voltage in 2V / div, when amp is on standby the voltage is clean.

    4

    don’t know why the images don’t show. First link is http://powersoft.ca/files/amp_power_supply.jpg

    Second link is http://powersoft.ca/files/amp_power.png

    5

    Couple of things you can try:

  • - Reducing the volume on the amp kit, get your sounds playing and then increase the volume.

  • - Cleaning the bottom of the amp kit board with an old toothbrush and some 70% rubbing alcohol. Flux residue left over from soldering can cause these to oscillate as well.
    • 6

    Volume was already at minimum, so that’s not it. Scrubbed the board with a toothbrush and Isopropyl Alcohol, but no change. What else can I do?

    7

    Might give a different power source a try, something like a 12 volt SLA battery or a charged car battery would be ideal for testing.

    Can you send a clear photo showing the bottom of the amp board?

    8

    with a deep-cycle Marine battery, the popping noise does not occur, but the right side of amp is not working. Confirmed that popping noise only occurs on right channel when using my power supply. Left side amplifies fine. Current consumption when using battery is about 110mA with no sound being input. With sound goes up to roughly 140mA. Photo of back of board is at http://www.powersoft.ca/files/20210408_182425.jpg

    http://www.powersoft.ca/files/20210408_182425.jpg(image larger than 4 MB)
    http://www.powersoft.ca/files/20210408_182425.jpg

    9

    with a deep-cycle Marine battery, the popping noise does not occur

    OK, that confirms your power supply isn’t quite up to the task of running the amp, I know it says 5A on the label but I suspect it’s not able to deliver that much.

    It’s hard to tell from your photo, but I do see one suspect connection that’s in the right channels audio path through the board, you might want to try touching that up and see if things work on the right channel then.

    20210408_182425.jpg
    20210408_182425.jpg3024×4032 1.83 MB

    Another thing you might want to check is disconnecting the right channel input from your audio source and connecting it to the left channels input, that way your sending the same known working audio to both channels. If that does the trick, you know the issue is with the audio source and not the amp.

    Last thing to check is your right channel speaker. Try swapping the speakers and see if the non working channel switches from the right to left side.