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Old 2nd March 2012, 09:18 AM   #1
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Default measuring dc offset in OTL headphone amp

I've not managed to find a consensus on this, perhaps someone can chime in: is it more relevant (as in: will the amp damage my headphones longterm) to measure the dc offset with or without a headphone load connected?

Example: my OTL tube amp measures around a meandering few +/- mV unloaded, sometimes hitting 10-30mV and, with my DMM set to record min/max/avg over ten minutes or so, a peak of -300mV, although this was definitely a spike, it didn't slowly climb to, or fall from this value.

With a 600ohm headphone load connected, it's typically <1mV, peak of 5mV, per channel.

All measurements taken after the amp has warmed up for over a minute or two.

Which is the figure to be more confident with??
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Old 2nd March 2012, 09:47 AM   #2
Doz is offline Doz  United Kingdom
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Do you not have an output coupling cap?
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Old 2nd March 2012, 09:50 AM   #3
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yep - 91uF film caps
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Old 2nd March 2012, 07:49 PM   #4
Doz is offline Doz  United Kingdom
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Then you shouldn't have a DC offset, unless your cap is goosed.


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Old 2nd March 2012, 08:10 PM   #5
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thanks
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