The Objective2 (O2) Headphone Amp DIY Project

Do you populate R1 and R2 for the AC only version? In the schematic it is shown as part of battery and AC operation.

I think this is about an earlier post (#2647) about the desktop AC-only version I built? (apologies if not)

On the O2 circuit diagram there's a dotted line around BT1, BT2, D2, D6, R1, and R2, with the text 'Battery Power (omit for AC only operation)'. If there aren't any batteries, then R1, R2, D2, and D6 aren't in circuit so can be safely left out.

All of the power management section (U2, Q1, Q2 etc) is present - if it's left out there's a big switch-on transient, as described by NwAvGuy (and it's true - I tried it just out of curiosity).

One thing I did notice in my earlier post - I said that the gain switch S2 and associated resistors were left out because I was running with a gain of 1. I must have been on autopilot when I assembled the board, because although I left out the gain switch I actually put in the default gain resistors R17, 19, 21, and 23 as you can see from the picture I posted. They have no effect because the switch S2 is absent, and the O2 runs with a gain of 1.

D
 
Is anyone using the Audeze LCD-2 or HiFiman HE-500 on the O2? Is it a nice combo?



The gain resistors(R17 - R21 and R19 - R23). If i don't add any resistors there, then the gain switch wount work. But if I add:

133ohm to R19-R23 will the gain be 12x when I push in the gain button?

And if I add the 499ohm to R17-R21 will that give 4x gain with the gain button not pushed in?
 
After a quick check, it looks like he's posted in the comments of his own blog as of yesterday, so I presume he's still alive and kicking, doing alright. He's probably just busy with real life and/or finalizing ODA or ODAC-related documentation or design.

I'm kind of curious what the final O2 -> ODA changelist will be too.
 
Thanks for the quick responce Mr Slim :) . I have indeed read that article; I should have probably explained better. I was planning to build an ODAC+O2 combo for a friend of mine who intends to use it with a DT880-600 Ohm and since the 5532 seems to perform marginally better at gains >5x, I thought it was a good idea. On another note I did find a note on NWAVG/RS blog (in the comments section) that he did test the NJM and did not find any significant difference between that and the NE part.