measuring dc offset in OTL headphone amp

gh0st · 2nd March 2012, 09:18 AM

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??

Doz · 2nd March 2012, 09:47 AM

Do you not have an output coupling cap?

gh0st · 2nd March 2012, 09:50 AM

yep - 91uF film caps

Doz · 2nd March 2012, 07:49 PM

Then you shouldn't have a DC offset, unless your cap is goosed.

Sent from my iPad using Tapatalk

gh0st · 2nd March 2012, 08:10 PM

thanks

2nd March 2012, 09:18 AM	#1
gh0st diyAudio Member Join Date: Aug 2011	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??

2nd March 2012, 09:47 AM	#2
Doz diyAudio Member Join Date: Jul 2010 Location: Sat Down	Do you not have an output coupling cap? __________________ "To err is human.. to make a real balls-up requires a computer"

2nd March 2012, 07:49 PM	#4
Doz diyAudio Member Join Date: Jul 2010 Location: Sat Down	Then you shouldn't have a DC offset, unless your cap is goosed. Sent from my iPad using Tapatalk __________________ "To err is human.. to make a real balls-up requires a computer"

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2nd March 2012, 09:50 AM	#3
gh0st diyAudio Member Join Date: Aug 2011	yep - 91uF film caps

2nd March 2012, 08:10 PM	#5
gh0st diyAudio Member Join Date: Aug 2011	thanks

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