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Old 9th January 2013, 07:06 PM   #1
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Default Loud noise from AMP6-Basic

Hi!
Last summer I built a portable boombox using an AMP-6, the assembly went great and I was really pleased with what this little amplifier had to offer!

Anyway, after a while of usage, maybe a couple of hours in total, the amplifier started to output a loud noise from both channels. I turned the amplifier off and then back on again, the noise was gone. A couple of minutes later, the noise came back. Now the noise is constant, ie it doesn't help turning the amp off and then back on again to get rid of the noise.
I've mapped the problem down to a level where the noise only appears if a sound-source is connected, in my case a Logitech Bluetooth receiver. So, if the amplifer is on and I disconnect the receiver the noise disappears, one channel at a time (I'm using RCA-plugs to connect to the bluetooth receiver).
I've also tried connecting my phone directly to the amplifier; same problem!


I've tried since to become a member on 41hz since the problem first appeared, but something seems to be wrong with their forum!

So now I'm wondering if someone here could help me with the problem!

Thanks in advance!
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Old 9th January 2013, 08:42 PM   #2
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Sounds like a ground loop problem. Is the amp and source connected to the same power source when you experience the problem? And does it go away if both run on their own power source?
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Old 9th January 2013, 09:20 PM   #3
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I did have a ground-loop problem until I realized that the bluetooth reciever had to run on a separate power source to not interfere with the amplifier because of the radio communication. Therefore, the bluetooth reciever is now running on it's own little battery!

Plus, the ground-loop sounded really odd with varying sound, the noise right now is a constant sound, like when you turn the volume up to the max on an amplifier without any sound going into it, you can hear a low noise through the speakers. It's like that only louder!

I did try to put a variable resistor on the sound going into the amplifier, and the volume of the noise varied as a turned the potentiometer, maybe this means something?
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Old 9th January 2013, 09:46 PM   #4
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Quote:
Originally Posted by jacobastrom View Post
I did try to put a variable resistor on the sound going into the amplifier, and the volume of the noise varied as a turned the potentiometer, maybe this means something?
Try bypassing that. Could be a bad solder or stray wire.
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Old 9th January 2013, 10:00 PM   #5
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Quote:
Originally Posted by Saturnus View Post
Try bypassing that. Could be a bad solder or stray wire.
Maybe I was unclear, I was only checking if the noise varied with a potentiometer if there was one between the sound source and the amplifier, and indeed it did, I then removed the potentiometer so it's not there anymore!
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Old 11th January 2013, 02:16 PM   #6
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Never mind, I fixed the problem!
The problem was that one of the yellow capacitors on the bottom side of the amplifier wasn't connected to the mainboard properly!
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