Satisfied with my O2 and ODAC setup, that drives my Philips SHP9500s.
An externally hosted image should be here but it was not working when we last tested it.
Just a word of caution, if using NwAvGuy's original O2 gerbers. The power jack he used (Kobiconn 163-7620-E) was Mouser's own brand and was discontinued by them. All the replacement jacks have rear terminals that are wider and won't fit the rear PCB hole. The folks selling O2 boards have modified the original gerber files so the current power jacks (165-7620E-E, or RAPC722X) will fit.
Interesting story there. A couple of years ago I asked Mouser if they could re-start production of those original power jacks, explaining about the O2 boards and the missing NwAvGuy. The rep came back with "the manufacturer says the tool die has broken and therefore they can't make anymore." LOL. The real reason, I believe, is the Mouser "Kobiconn" jack was intended to be the house-brand knock-off of the brand name Switchcraft RAPC722X, but they screwed up originally and made the rear terminal too big. The new Kobiconn jack is an exact copy of the Switchcraft now.
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Hi all, I made an O2/ODAC using some information here and on RocketScientist's website.
Using JDS Labs for the board and enclosure (and ODAC), Mouser for the parts, JameCo for a 16VAC wall adapter, and Digi-Key for some supplies I forgot, it costed about $186.
I have yet to drill in the holes for the front and back, or make a ground connection from J2. Because I taped the bottom of the ODAC to the enclosure, and it uses up all the space there, the amp isn't sliding in and out. The Tenergy 9V NiMh rechargeable batteries are on the way, so I haven't been able to test them yet. The "hum" with the O2 not grounded might be more noticeable from battery power, I'm just hesitant to try to fix a problem I don't seem to have. Originally, I was only going to run it through AC power, as the ODAC would take up the space, but then I found out through this thread you can just put it underneath.
This is the first time I've noticed an audible improvement using a DAC/AMP instead of on-board PC audio. The O2 running through an auxiliary cable from the laptop output got pretty loud, but it's nowhere near as full sounding as through USB. Since I connected it so that the J2 input jack still functions, I can do an A-B comparison, and the ODAC audio has way more bass on my 300 ohm 6XX. I only really expected a subtle difference, because I had gotten used to the basis that all hype about audio products is snake oil, but it's like night and day. Half the reason I bought this was just to have some fun working on a project, and it definitely was worth the cost and time. I'm considering making the "O2 Booster Board," but I'm not so sure about paying $60 for an improvement that might not have an audible benefit with my current headphones.
Also, I can confirm the $6 PCB by JDS Labs works with the 165-7620E-E, I believe there is a version made specifically for the PJ-002A as well.
Using JDS Labs for the board and enclosure (and ODAC), Mouser for the parts, JameCo for a 16VAC wall adapter, and Digi-Key for some supplies I forgot, it costed about $186.
I have yet to drill in the holes for the front and back, or make a ground connection from J2. Because I taped the bottom of the ODAC to the enclosure, and it uses up all the space there, the amp isn't sliding in and out. The Tenergy 9V NiMh rechargeable batteries are on the way, so I haven't been able to test them yet. The "hum" with the O2 not grounded might be more noticeable from battery power, I'm just hesitant to try to fix a problem I don't seem to have. Originally, I was only going to run it through AC power, as the ODAC would take up the space, but then I found out through this thread you can just put it underneath.
This is the first time I've noticed an audible improvement using a DAC/AMP instead of on-board PC audio. The O2 running through an auxiliary cable from the laptop output got pretty loud, but it's nowhere near as full sounding as through USB. Since I connected it so that the J2 input jack still functions, I can do an A-B comparison, and the ODAC audio has way more bass on my 300 ohm 6XX. I only really expected a subtle difference, because I had gotten used to the basis that all hype about audio products is snake oil, but it's like night and day. Half the reason I bought this was just to have some fun working on a project, and it definitely was worth the cost and time. I'm considering making the "O2 Booster Board," but I'm not so sure about paying $60 for an improvement that might not have an audible benefit with my current headphones.
Also, I can confirm the $6 PCB by JDS Labs works with the 165-7620E-E, I believe there is a version made specifically for the PJ-002A as well.
Does anybody know if pot knobs which can be screwed tight, fit on the ALPS RK09 with D-shaped axis?
(something like this: https://www.conrad.de/de/drehknopf-aluminium-x-h-15-mm-x-15-mm-mentor-56156614-1-st-183836.html)
(something like this: https://www.conrad.de/de/drehknopf-aluminium-x-h-15-mm-x-15-mm-mentor-56156614-1-st-183836.html)
If you're using RK09L12B0A3Z from here RK09L Series - Basic information then it does not fit, because washer has 6x4.5mm and Mentor 5615.6614 1 St. has only 4mm.
You can anyway check RK09L Series - Products Line and compare sizes, just in case I might be wrong or you're using a different potentiometer.
BTW, you can find on eBay a lot of knobs for your O2 in case you don't like the original knob.
You can anyway check RK09L Series - Products Line and compare sizes, just in case I might be wrong or you're using a different potentiometer.
BTW, you can find on eBay a lot of knobs for your O2 in case you don't like the original knob.
Hi, there are two different knobs, the drawing refers to the one with 4 mm bore but the item number is for a knob with 6 mm bore so it will fit on the alps pot. Now the but... There is no measurement given in the dartasheet for diameter C, so it (most likely) won't cover washer and nut of the pot.
Stefan
Thanks for the reply. I am not too sure if I can replace the LED by myself though.
Objective 2 gain resistors issues
Hello all!
First post - thanks for any help in advance.
About a year ago I build my o2 amp - worked perfectly at the time.
Now after sitting in the draw I decided to take it out again.
Anyway log story short - where I'm at now is that that I've managed to blow the one of the ops amps when I managed to short a couple of components (got two on order) - only one channel works no matter what and swapping them to the other position results in the other channel working!
However the main issue I can't resolve with my limited knowledge is that the high gain circuit doesn't output correctly. If I cut the resistors giving 1 x gain all's well however once replaced I hear crackles which very loosely sound like the source audio.
I've changed to some new resistors no joy - checked joints / reworked them no joy.
Also been through the trouble shooting guide - all checks out ok afaik!
Can any of you guys offer insight or help in diagnosing this please!
Ta!
Ps Apologies I posted my own thread on this - will get that one deleted in a mo
Hello all!
First post - thanks for any help in advance.
About a year ago I build my o2 amp - worked perfectly at the time.
Now after sitting in the draw I decided to take it out again.
Anyway log story short - where I'm at now is that that I've managed to blow the one of the ops amps when I managed to short a couple of components (got two on order) - only one channel works no matter what and swapping them to the other position results in the other channel working!
However the main issue I can't resolve with my limited knowledge is that the high gain circuit doesn't output correctly. If I cut the resistors giving 1 x gain all's well however once replaced I hear crackles which very loosely sound like the source audio.
I've changed to some new resistors no joy - checked joints / reworked them no joy.
Also been through the trouble shooting guide - all checks out ok afaik!
Can any of you guys offer insight or help in diagnosing this please!
Ta!
Ps Apologies I posted my own thread on this - will get that one deleted in a mo
I think we've covered pretty much every possible fault area in this thread 
1/ Always check the DC conditions around the opamps. You should have zero volts (or very close) on every pin of every opamp (apart from the supply pins of course).
So check that is so when the problem is apparent.
2/ The input stage is a classic text book implementation of a gain stage. The resistor in the lower arm of the feedback network sets the gain. If those resistors are being switched correctly then it should all work.
Could the gain options be unsuitable for your needs ?
You can fit any suitable value to those switched resistors to give the gain you want.
1/ Always check the DC conditions around the opamps. You should have zero volts (or very close) on every pin of every opamp (apart from the supply pins of course).
So check that is so when the problem is apparent.
2/ The input stage is a classic text book implementation of a gain stage. The resistor in the lower arm of the feedback network sets the gain. If those resistors are being switched correctly then it should all work.
Could the gain options be unsuitable for your needs ?
You can fit any suitable value to those switched resistors to give the gain you want.