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Old 27th December 2006, 03:34 PM   #1
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Default 3886 oscillating?

Hi there,
I built a chipamp from BriantGT and everything was in good working order. However, i have connected it to my new rogue preamp, which is said to be 'inverting' and now the amp is (I think) oscillating. I am not sure I have inverted the inputs from the pre to the amp, but if i didn't would it cause this behaviour?
The other thing that i changed was to put the jumpers back onto my speakers to remove the bi-wiring...
Thanks,
Mantisory
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Old 27th December 2006, 04:11 PM   #2
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What makes you think the amp is oscillating? Are you hearing hum or other noise? Is the chip getting hot even with no signal applied to the input?

I_F
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Old 27th December 2006, 04:23 PM   #3
Nordic is offline Nordic  South Africa
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do you mean you are not sure if input wires are the wrong way around? yes, this would cause some noise...
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Old 27th December 2006, 04:31 PM   #4
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the chip is not overheating - i checked that early on.
there is audible periodic (1 second frequency maybe?) noise coming from the speakers even with no signal.
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Old 27th December 2006, 04:39 PM   #5
CarlosT is offline CarlosT  United States
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1 second? Hhhhmmm...sounds like a long interval for the usual 60Hz stuff from the power side.

I got a terrible loud buzzing sound (prolly like 60 Hz) when I grounded the metal mounting tab on an LM3875T the other night. Could something be grounded that shouldn't?
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Old 27th December 2006, 04:44 PM   #6
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yeah, maybe, i dunno - i am going to try some different speaker cables and also switch the inputs around.
it may be as wmuch as 2hz, but no more than that i think...i remeber that i had a similar problem in one channel when it wasn't connected to my speaker (I have read elsewhere that the chipamp doesn't like to be un-loaded), so i wonder if maybe my cabling is an issue..
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Old 27th December 2006, 05:19 PM   #7
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Default oscillating

Disconnect your pre amp and short the input to the chip amp to ground and see if you get the same result, if you do its the chip amp if not its probably the pre or a cableing issue
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Old 27th December 2006, 05:22 PM   #8
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will give 'er a go after work - thanks.
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