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Old 17th July 2013, 01:46 AM   #1
diyAudio Member
Join Date: Jul 2013
Default Please help me diagnose a Hypex problem

I have an older Hypex UCD400 amplifier and I hear a click on my speakers whenever I turn it on. Also, when I turn off the amplifier, there is a low volume whining noise that can be heard as the capacitors are discharging. This behavior has been present since I have had the amplifier, but the noises are not loud enough where I am afraid of damage to the speakers. My guess is that there is a DC offset, but I figured I would see what people more knowledgeable than myself think and what the best solution would be. I have attached some pics of the amp. Any help would be appreciated!
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Old 17th July 2013, 05:00 PM   #2
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Join Date: Sep 2008
My UcD180HG have a square/triangle wave sound that lowers in frequency as the capacitors discharge.
As there are no relays disconnecting the speakers the click is probably the oscillation starting creating a small bump before it gets going. The whining noise is probably the oscillation breaking down as rail voltage collapse. I have not seen any DC offset push the cone ether way though.
I figured it to be normal.

If it isn't I'm sure someone will step in and yell "turn it off before you break something".
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Old 19th July 2013, 03:00 AM   #3
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Thanks, glad to hear that I'm not the only one seeing this behavior. Do you have a soft start module on your amp? I was wondering if that would make any difference.
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Old 20th July 2013, 09:28 PM   #4
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Join Date: Sep 2008
Yes I have a soft start, simple timed relay that bypasses a resistor after a few seconds.
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