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Clip+ DC offset

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jdc:
Hi, I've been hearing little squeaks when I pause my Clip+ and occasionally when playing so I decided to measure the DC offset. While playing it appears to be about 5mV but when I pause it it settles on anything from 0 to 60mV offset. I booted the original firmware and it seems to be 0.1mV while playing then 0mV when paused. Is this a problem? I imagine it is especially when amplified you could have upwards of 600mV. I'm not sure if it's related but a pair of IEMs I used almost exclusively with rockbox on this Clip+ have one channel partially broken (way quieter then the otherside).

Sansa Clip+ 8GB with rockbox 3.7

I apologize if this isn't hardware issue because I wasn't sure.

Cheers,
James

saratoga:

--- Quote from: jdc on November 27, 2010, 05:22:41 PM ---Hi, I've been hearing little squeaks when I pause my Clip+ and occasionally when playing so I decided to measure the DC offset. While playing it appears to be about 5mV but when I pause it it settles on anything from 0 to 60mV offset.

--- End quote ---

How are you measuring this?  With or without headphones connected?


--- Quote from: jdc on November 27, 2010, 05:22:41 PM ---I booted the original firmware and it seems to be 0.1mV while playing then 0mV when paused. Is this a problem?

--- End quote ---

Hard to say without knowing what you measured, but 60mV into 16 ohms is 225 microwatts, not exactly a huge amount of power.  Might be worth looking into how the OF does it though.

jdc:
I'm just measuring between ground and each channel with my multimeter. I brought it up because from what I've read making headphone amps you want the DC offset to be less than 20mV otherwise you can damage your headphones. It seems strange that it happens with rockbox and not the OF. I'll double check it tonight to makes sure i haven't made any errors.

saratoga:
If you measure like that the output is basically floating.  Try putting a pair of headphones in there and see if theres still a DC offset when the output isn't floating.

jdc:
ah yes you're quite correct I'll tie each channel to ground with a 1k resistor and see what I measure.

edit: tried that, no change. would it be possible that rockbox stays at the current sample when paused rather going to zero?

edit 2: turns out I had OF volume turned down compared to Rockbox so I turned it up and it measured the same 5mV approx while playing but went to zero when paused. I am thinking it could be the above because it varies every time it is paused and once paused it goes up and down as I change the volume. The worst I measured was 240mV with rockbox turned up to max.

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