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Old 9th January 2004, 11:01 AM   #1
wrl is offline wrl  United States
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Default DC offset in Hafler DH-200

Hello, I have recently finished rebuilding a hafler DH-200. The amp sounds great on conventional speakers, but I noticed that there is a 200 mV DC offset at the output.

Is this normal for this amp?? Does anyone have any suggestions (other than matching transistors) about how to decrease this?

The only reason I ask is because I'm going to use it in conjunction with electrostatic speakers and I think that this might be a bit much.

Thanks,
Wes
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Old 9th January 2004, 11:49 AM   #2
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Do there an DC servo - it is easy and effective.
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Old 9th January 2004, 11:58 AM   #3
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Sometimes I have read any recension about any Pass amp and this author positively evaluate fact , that after switching on power was offset 150 mV and after one half of hour fall down on amazing 50 mV. All is relativ .
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Old 9th January 2004, 01:20 PM   #4
djk is offline djk
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"Is this normal for this amp??"

Probably, Hafler added a DC trim pot to the DH220.

"Does anyone have any suggestions (other than matching transistors) about how to decrease this?"

There are two constant current sources for the diff pairs. You can trim either to null the DC off-set.

You could look at the DH220 schematic and add that circuit, more complicated than trimming one CCS.

You could add a DC servo, a fair amount of work.

I usually just trim one CCS.
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