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dayton APA 150 question

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  • dayton APA 150 question

    Hi guys, i have a Dayton APA 150 amp powering a pair of speakers(dayton BR-1's i assembled myself) for my PC. Worked fine for many many years but a few weeks ago it started making a humming/buzzing sound. Its off warranty so im on my own to fix it if possible.

    I have a electronics background and have alot of test equipment including a load tester and a scope available at home to use. But my background is not in audio circuits, its in mostly DC circuits from PC's (motherboard, GPU, etc) and LED/Laser driving circuits, so im lost with audio equipment unfortunately.

    Im looking for some direction as to exactly what component failed and where to focus my search when i crack it open this weekend, im thinking transformer related but thats just a gut instinct based on little real experience with audio equipment.

    Lets start with the sound, its fairly loud, louder than my PC's fans. It happens all the time even when its unplugged from all speaker and RCA connections so i know its not from the source or from a short in the speakers(speakers also work fine hooked up to my Harmon Kardon amp in my living room). Also tried various outlets and running it off a generator and sound is the exact same for all except the generator, when running off the generator sound is louder. So its not the power source causing it either. It also stays the same when playing music through it, I have to crank up sound to overpower it but sound remains at all volume levels.

    So any ideas on where to start?

  • #2
    I don't know if this will help. I have a B&K st140 that developed a hum. If it was on,,,,, it hummed. I traced it to the transformer. It had a 1/4in bolt holding it to the chassis with a rubber gasket between. I first tightened the bolt. That didn't work. I unbolted it, changed the orientation of the gasket and bolted it back up. It still hummed. I sent it back to B&K. They said they could not reproduce the hum. I told them to change the transformer anyway.

    When I got it back,,,,, no more hum.

    Hopefully some of the amp guys here will chime in as to why something like this happens.

    Good luck! Mark