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Old 15th February 2012, 08:50 PM   #1
champ04 is offline champ04  United States
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Join Date: May 2009
Default perplexing problem.......

This morning I found my DAC with a nasty 60Hz hum coming from the right channel and little to no signal. I assumed it's the power supply so I start probing the regulators in the power supply. Nothing seems too out of of whack. None of the caps seem disturbed. I unplug briefly to turn unit over and check regs that are located on each pcb. Nothing out of the ordinary. I plug back in to give another listen. Everything seems fine. Then, about 10 minutes later the right channel starts getting really distorted and finally ends up with that same 60Hz hum.

So I unplug unit. Rewire so that the I/V (passive resistor) section from each channel feeds the opposite channel output buffer. Idea is to see if the problem comes before or after this point in the chain. Ie. if the distortion/hum moves to opposite channel, problem is located at the DAC conversion stage. If not, it's in the output buffer.

Plug back in and no more hum. It's been playing non stop for almost 5 hours now with no issues.

Anyone have ideas as to what may have been going on??

Thanks!!

Note: after the first few hours I returned the I/V outputs to their respective output buffers. Still playing with no problems at all.

Last edited by champ04; 15th February 2012 at 08:58 PM.
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Old 15th February 2012, 09:54 PM   #2
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Join Date: Mar 2009
Location: Groningen
Hi champ04,

Seems to me that something didn`t make connection to the I/V-stage anymore, looking from the output inwards that is (not from the dac to the preamp or what you have there, but from preamp to dac).

Look for bad connections in ground:
Do both output cables connect well to ground/no loose contacts?
Both passive resistors soldered well? etc.

It helps if you get the problem back again. In that case:
check signal cables and verify grounding everywhere.

If it persists, it`d help to know what schematic you use.

Goodluck!
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