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Old 16th December 2011, 11:39 PM   #1481
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I've just finished soldering every thing, and the first test fails. I'm only geting 7.5v across the batteries. I tried switching it on to see if the LED works and it came on. I switched it off right away but it took around 10 seconds for it to go dim again. I'm guessing one of the capacitors are keeping the charge? Any ideas?
Do I follow the power input with the DIMM and see where it starts to drop?
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Old 16th December 2011, 11:41 PM   #1482
Turbon is offline Turbon  Sweden
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At last I took the time to test the new values of R9 and R25 and I can confirm that with Tenergy 250mA Ni-MH there has now been silence for 7 minutes after the O2 shut down. Well chosen values RS - perfect.

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Old 16th December 2011, 11:51 PM   #1483
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Hi, I barely got started on testing before running into problems...
Installed U2 and measured voltage across C8 and C9 and got 5.82. I measured them individually and got 5.66 and .23.
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Old 17th December 2011, 12:11 AM   #1484
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Here's what I posted at Head-Fi for a starter subjective review of my O2.

OK here is a quick subjective comparison. O2 vs mildly modded Crack with Speedball.

Source = PC-> Foobar-> Wasapi-> AMB Gamma 2

Cans= HD595

Tunes+ Vince Guaraldi , A Charlie Brown Christmas, Fur Elise, The Christmas Song, Greensleeves

Had the wife help out. She would change the amps while my back was turned and start the song. I could tell the difference clearly, the Crack was smoother with more seeming detail, wider sound. The sound was kinda towards the rear and spread beyond the outside sides of the headphones. The instruments seemed to be a bit more clearly defined in the space. Bass was full and clear, mids good and cymbals and brushes were smooth and crisp. O2 did really well though, crisp sound, a bit forward and closed in, the sound was confined to my head. Definition was very good bass was deep and well defined but not as rich, mids good, cymbals and brushes were not as lush(?) and brighter.

Overall the O2 did a remarkably good job, it was fun to build, a great price and sounds very good. I mean the 6NS7 chrome top cost more than two boards and all the parts for two O2s... not to shabby!

Pardon my lack of description, my very first review of this type.
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Old 17th December 2011, 12:23 AM   #1485
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@billyk,

I'm not surprised by your findings. I was playing around with my DAW (Adobe Audition, in this case) a few months back and found that if I introduce very small amounts of delay or overlay delay at different frequencies that I could push the sound outside my headphones. It was fantastic and I think it's the kind of trick I'd like to employ for some recordings.

What I'm telling you is that your tube amp has very likely introduced distortion so that there is a fractional time delay on one channel. It may also be something else, but my experience tells me that time delays are the way to make things 3D. I hope you enjoy it. I'm mature enough to think it's cool and it's welcome when I want it and know clearly what it is I'm getting. A few years ago I would've been heartbroken. I'm more man now to accept reality and also to accept the reality of musical fun through distortion, but a foundation of clarity such as the O2 gives is necessary to me. Could you imagine what would happen if I spun a track from my DAW with distorted or uncorrectable equipment?
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Old 17th December 2011, 12:28 AM   #1486
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Quote:
Originally Posted by kmc52087 View Post
Hi, I barely got started on testing before running into problems...
Installed U2 and measured voltage across C8 and C9 and got 5.82. I measured them individually and got 5.66 and .23.
And to be more specific C9 has the larger charge.

EDIT: Even more information. I installed all the amps and I now get .68 over C9. -1.24 over C8 and -5.4 total. Tried with batteries and got 1:2 ratio again. Did I fry a MOSFET? Is there a way to check the MOSFETS?

Last edited by kmc52087; 17th December 2011 at 12:50 AM.
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Old 17th December 2011, 12:33 AM   #1487
billyk is offline billyk  United States
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@ethanolson No doubt! I have been in love with my tubes for many years. I have owned top of the line conrad johnson gear, and lots in between. I agree that there is something "else" going on. I don't care... I just know what sounds good to my ears!

Edit: And the O2 is definitely one of the good sounding ones!

Last edited by billyk; 17th December 2011 at 12:38 AM.
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Old 17th December 2011, 12:35 AM   #1488
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Originally Posted by ethanolson View Post
@Willakan (and @RS) for the K702's you can't really go lower than 2.26kΩ gain resisters on the O2 for redbook-compliant sources (in case you're wondering, I actually do use the number 2.1V) without risking damage to the headphones if AKG's specs are to be believed. I recognize that the K701 may have been less sensitive than the K702 is, but if something's too loud for a person, then the gain needs to come down... and AKG's max specs back up the claim of lower gain values for the K702 and Q701. These are the currently-produced models as the K701 is discontinued. The good news is that on the K702, you should be pumping 115dB at that point. With an iPod, you are, in fact unable, to go higher than 103dB. That's way too loud for me.

So, my 110dB math was wrong and I can't find where I got it wrong (oops!). So... an iPod can't push a K702 past 103dB with a 2.26kΩ gain resister pair; but neither can a redbook-compliant source damage your cans... just your ears.
I didn't realize the K701 is technically gone. That's kind of sad. But it seems it's just been "re-born" as the Q701 with Quincy Jones branding and now also available in neon green!

The Q701 is rated at 200 mW at 62 ohms. That's 3.5 Vrms and I was only suggesting 3.2 Vrms. So if you use your Redbook source, at a "high" 2.1 volts, that's 3.5/2.1 = 1.7X and you're correct the gain resistor would be in the 2.1 - 2.2K range.

The big difference is the question was what gain to use with an iPod as the source. To get the same 3.2V you need 3.2X - 6.4X gain depending on if you're using the LOD or headphone output.
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Last edited by RocketScientist; 17th December 2011 at 12:56 AM.
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Old 17th December 2011, 12:53 AM   #1489
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Originally Posted by billyk View Post
A wall wart I had in my bin that stated 20VAC and read 23.2 unloaded on my meter ran fine but R1 and U6 get quite hot, cannot hold finger on R1, U6 is almost too hot to hold. This is after 20 minutes. The only problem other than the heat was the turn off/on pops were very loud, I feared for the headphones, this was true at any volume setting. I won't use this traffo again, but thought my findings would be of interest.
Something is very likely wrong with your amp if R1 is getting hotter than R2 and U6 hotter than U5. You may have a battery problem--either a bad battery that won't fully charge, or worse, a battery in backwards.


Quote:
Originally Posted by hbarradah View Post
I've just finished soldering every thing, and the first test fails. I'm only geting 7.5v across the batteries. I tried switching it on to see if the LED works and it came on. I switched it off right away but it took around 10 seconds for it to go dim again. I'm guessing one of the capacitors are keeping the charge? Any ideas?
Do I follow the power input with the DIMM and see where it starts to drop?
Measure the DC voltage across C2 and C3. They should both be the same and over 17 volts. If not, there's a problem with your meter (DMM), wall transformer, D3, D4, or most likely, U5 or U6. The regulators could have a solder bridge, be in backwards, or be in the wrong locations on the board.

If you do measure over 17 volts for both C2 and C3 but only 7.5 volts at the battery terminals (with no batteries connected), I would also check the regulators as well as D1, D5, R1 and R2.


Quote:
Originally Posted by kmc52087 View Post
And to be more specific C9 has the larger charge.
I'm not sure under what conditions we're talking about? After the amp is shut off, C8 and C9 may measure somewhat differently. But with the amp powered on they should be the same. And if you're doing the "one battery test" they should read as outlined in the testing section.
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Old 17th December 2011, 01:03 AM   #1490
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Sorry for the lack of information.

That was with AC power and only U2 install. I installed all the amps and still had the problem, getting .68 over C9. -1.24 over C8 and -5.4 total. Tried with batteries and got 1:2 ratio again.

Also checked P2 and got voltages just over 1. Same with measuring from the center pin to the outer ones of the jack.

edit: I did the other checks as well. The voltage at C2 and C3 are good (17). I checked the ground to R1 and R2 and they were good as well (almost 12). The D1, D2, D5, and D6 measure about .2 or .190 (while powered on).

D3 and D4 measure in the .560/.570s (powered off) and have continuity (Should they?) when powered on.

Last edited by kmc52087; 17th December 2011 at 01:26 AM.
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