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Old 17th February 2012, 09:04 AM   #2121
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Quote:
Check the U2 pin 1 and pin 7 voltages" p1= -11.72, p7=8.5
That >3V difference doesn't seem right to me. I think that ideally they should be equal + and - voltages. I regrettably haven't kept as close attention here lately as I could have, but have you verified the "Install Only U2 Next" and "Check The Raw DC Voltages" portions of the O2 Initial Testing instructions?
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Old 17th February 2012, 10:08 AM   #2122
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Quote:
Originally Posted by jfrana View Post
"Check the U2 pin 1 and pin 7 voltages" p1= -11.72, p7=8.5
Pin 1 seems OK. Pin 7 is odd. Why should it not be able to swing almost all the way to +12? What's the voltage on pin 4?
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Old 17th February 2012, 01:59 PM   #2123
agdr is offline agdr  United States
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Quote:
Originally Posted by sgrossklass View Post
Pin 7 is odd. Why should it not be able to swing almost all the way to +12?
The R8 - R25 voltage divider. That +9.8V RocketScientist shows for pin 7 in his troubleshooting voltages never got updated - still for the old R24 = 2.4M. With 1.5M it works out to be around +8.65V.

Last edited by agdr; 17th February 2012 at 02:17 PM.
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Old 18th February 2012, 08:58 AM   #2124
Zsubbo is offline Zsubbo  Hungary
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How can I calculate the gain resistors value to have 3.3~3.4x in my O2?, I can't seem to find it anywhere on NwAvGuy's blog.
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Old 18th February 2012, 10:49 AM   #2125
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That's opamps 101:

Gv = 1 + Rf/Rg

Solve for Rg. Gv is what you want, Rf is 1k5.

Make sure you leave at least an extra 20..30%, preferably 30..40% of headroom above Gv*Vin,max when using sources like a CD player. Digital sources may have output amplitudes of up to +2dBFS with very "hot" CD material (actually the maximum I've seen was +2.0something dB). Output amplitude is normally given for 0 dBFS.
For a CD player with exactly 2.0 Vrms (outputs tend to be slightly louder nowadays, 2.2..2.3 Vrms is not uncommon) that means a maximum permissible gain of about 2.6 when running on mains supply. That's why 2.5 and 2.0 are popular low gain options. People with very sensitive in-ears would even tend to go for unity gain (Rg removed) to get the volume pot into a range with better channel tracking etc.

Last edited by sgrossklass; 18th February 2012 at 10:58 AM.
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Old 18th February 2012, 11:03 AM   #2126
Zsubbo is offline Zsubbo  Hungary
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Thanx, I'll be using a Matrix mini-i from USB as a source, it has an output of 2,1 Vrms, so I think I'll just go with the gani of 3x, that way there should be enough headroom, and I don't have to buy resistors.

As a bonus, heres a few pics of my build.
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Old 18th February 2012, 11:39 AM   #2127
regal is offline regal  United States
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Quote:
Originally Posted by sgrossklass View Post
That's opamps 101:

Gv = 1 + Rf/Rg

Solve for Rg. Gv is what you want, Rf is 1k5.

Make sure you leave at least an extra 20..30%, preferably 30..40% of headroom above Gv*Vin,max when using sources like a CD player. Digital sources may have output amplitudes of up to +2dBFS with very "hot" CD material (actually the maximum I've seen was +2.0something dB). Output amplitude is normally given for 0 dBFS.
For a CD player with exactly 2.0 Vrms (outputs tend to be slightly louder nowadays, 2.2..2.3 Vrms is not uncommon) that means a maximum permissible gain of about 2.6 when running on mains supply. That's why 2.5 and 2.0 are popular low gain options. People with very sensitive in-ears would even tend to go for unity gain (Rg removed) to get the volume pot into a range with better channel tracking etc.

If you use headphones that don't even come close to needing 2VRMS, has anyone considered bypassing the gain stage. I mean a lot of us have the gain resistor jumpered running the input at unity, if our DAC is 2Vrms 600 ohm output, is that enough to hook directly to the pot ?
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Old 18th February 2012, 07:57 PM   #2128
KGee is offline KGee  United States
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Am I supposed to do anything with the middle back row pin of the two 3.5mm jacks? The lead barely goes into the hole (you can just see it in the picture), but do I still fill the hole with solder?

Thanks.
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Old 19th February 2012, 12:59 AM   #2129
Fiola is offline Fiola  United States
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I upgraded the screws for the front panel from the ones they supply with the case to a nicer one from McMaster-Carr. I used their black hex socket head cap screw and I think it complements the black front panel really well. Thought I'd share it if anyone else is tired of the sliver screw looks

These are the ones I got
McMaster-Carr

I used thread size 6-32 since i already had the tap for it.
Click the image to open in full size.
Click the image to open in full size.
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Old 19th February 2012, 03:30 AM   #2130
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definitely looks good with those hex screws and your volume knob
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