[Shaggy_J]

Just curious what the DC offset was for other imods.  I am looking at building the PIMETA and then the PPC so I am just trying to figure out what I need to do for an input cap and the DC offset that I measured seemed to be extremely high (according to tangent's website).  http://www.tangentsoft.net/audio/input-cap.html

Thanks,
Jad

[Vinnie R.]

Just curious what the DC offset was for other imods.  I am looking at building the PIMETA and then the PPC so I am just trying to figure out what I need to do for an input cap and the DC offset that I measured seemed to be extremely high (according to tangent's website).  http://www.tangentsoft.net/audio/input-cap.html

Thanks,
Jad

Hi Jad,

Welcome to audiocircle!

Just curious what the DC offset was for other imods.

What do you mean when you say "for other imods?"

For all the iPods that I mod, there is no dc offset on the output.  

Best regards,

[Shaggy_J]

Here is what I am seeing on my multimeter...   So I am probably just a moron but from what I read on tangent's website that is considered DC offset.  I am probably wrong so could someone explain what I am looking at?  (One photo for left channel and one photo for right channel)  Also, it usually measures a fairly solid ~.8 and ~.7 VDC but for some reason it seems to be measuring a bit lower in the photos.

Thanks,
Jad

[Vinnie R.]

Hi Jad,

When you are playing music, there is definitely voltage (a signal) on the output and your voltmeter set to measure DC volts is going to see it, but what you are reading is NOT dc offset.

What happens when you pause the music but keep your iPod ON?  Use the millivolt setting....it should be very, very close to 0mV.  

With coupling caps on the output of your iPod, dc offset will be blocked so I wouldn't worry about it...

Best regards,

[Shaggy_J]

Vinnie,

Ya it registers about the same .47 or .31 VDC when paused.   That is in both Rockbox and the ipod firmware.

Thanks,
Jad

[Vinnie R.]

Vinnie,

Ya it registers about the same .47 or .31 VDC when paused.   That is in both Rockbox and the ipod firmware.

Thanks,
Jad

Hi Jad,

Hmmmm, this doesn't sound right.  

Out of curiosity, what voltage are you reading when you connect the two meter leads together?  Is your Fluke in calibration?

Thanks,

[Shaggy_J]

Vinnie,

When I hold the leads together the meter reads 0.0000 or at times 0.0001 or -0.0001  VDC.  I have tried measuring other sources and the DC offset is .0005 or up to .001 VDC.  So I think I am measuring things correctly...  One other thing that I stumbled on is that the right channel when off measures -.55, and when on .85 VDC.  The left channel while off measures .-13 and on measures 1.25 VDC.  The difference between on and off states for each channel is: right 1.4 VDC, left 1.38.  These measurements were taken with a full battery charge so I think that is why they are higher than some of the previous information.  So the mystery continues...

Thanks for the help,
Jad

[Vinnie R.]

Jad,

These voltages are very high.  Something is not right.  If you send it over to me I will check it out once I receive it and let you know what I find.  I don't want to jump to conclusions now, but it almost seems like the coupling caps have been blown  

Whatever it is, I'll take care of it ASAP once I receive it.

Thanks for your patience,

Vinnie

[Shaggy_J]

Vinnie,

The imod is on its way...  Should be there by Thursday.

Thanks for the help,
Jad

[eico1]

A headphone-type load might help discharge the output cap faster than the dvm.

steve

[Vinnie R.]

Hi Jad,

I received and carefully tested your modded iPod and found no dc offset problem.  I measured 0.02mV dc offset on both channels...essentially 0V.

I suspect what Steve mentioned above (thanks, Steve!) about discharging the cap is probably what is throwing off your reading.  

The important thing to note is that the dc coupling caps on the output are working fine and doing there job.  

I will ship it back to you today.

Best regards,