The Objective2 (O2) Headphone Amp DIY Project

Here
It's a compilation of a series of small articles from 2001, that. A guy was designing an discrete headphone amplifier with goal of putting all key elements under constant dissipated power conditions so there would be no drift of DC conditions and associated shift of amp's parameters.


Here is a method which he used to measure 'memory' - integration of DC offset at amp's output after signal has been cut off.

He noticed improvements from that, though also he has found an improvement using high(~100dB) feedback and in general admitted that high feedback is an easiest method to combat it, and O2 as a chip amp, already has that, I suspect.
 
lorriman and Rullknufs: just curious - which channel has the rustling and does your O2 build use the capacitors in the BOM for C13 and C14 (the square 2.2uF caps)?

According to RocketScientist/NwAvGuy's writings rustling is DC through the wiper in the pot. There should be essentially 0Vdc across the pot since the output of U1 should stay more-or-less centered about zero unless clipping occurs. But it will drift a little with op amp input offset bias and offset caused by input bias current differentials through the input resistors.

If the rustle is there with large signal audio but not with small signal or zero signal, seems like the DC bias out of U1 is shifting slightly, which in turn charges/discharges C13 and C14 until it equalizes again. Or something like that. :) Just pondering out loud.
 
lorriman and Rullknufs: just curious - which channel has the rustling and does your O2 build use the capacitors in the BOM for C13 and C14 (the square 2.2uF caps)?

According to RocketScientist/NwAvGuy's writings rustling is DC through the wiper in the pot. There should be essentially 0Vdc across the pot since the output of U1 should stay more-or-less centered about zero unless clipping occurs. But it will drift a little with op amp input offset bias and offset caused by input bias current differentials through the input resistors.

If the rustle is there with large signal audio but not with small signal or zero signal, seems like the DC bias out of U1 is shifting slightly, which in turn charges/discharges C13 and C14 until it equalizes again. Or something like that. :) Just pondering out loud.

Yes, I'm using the square caps.
Here's a picture of my board
DSC_0549.JPG

The gain resistors are removed now though, but otherwise it's the same.
Tried it quickly and with no signal there's no rustling when turning the volume knob.

Is there any quick and easy fix for this?
 
Is there any quick and easy fix for this?

If you happen to have a LME49720 = LM4562 on hand, a really interesting test would be swapping the LME49720 for the NJM2068 and see if the problem gets better. The 49720 has about 1/3 the input offset voltage and about 1/10 the input bias current of the 2068. The AC parameters (distortion, etc) are the same or better. So if there is an improvement it would be largely due to the DC performance (DC output drift across the pot).
 
If you happen to have a LME49720 = LM4562 on hand, a really interesting test would be swapping the LME49720 for the NJM2068 and see if the problem gets better. The 49720 has about 1/3 the input offset voltage and about 1/10 the input bias current of the 2068. The AC parameters (distortion, etc) are the same or better. So if there is an improvement it would be largely due to the DC performance (DC output drift across the pot).

Unfortunately I have no components at hand :( But maybe somebody else here does?
 
Yeah, he seems to have just suddenly disappeared. Last comments on his blog were back in August. Hope he is OK! Must have either been medical or a sudden loss of interest.

Reminds me of the "Dr Xin" situation over on the H-F forum. He apparently just disappeared one day in the middle of taking orders for a headphone amp.
 
Yeah, he seems to have just suddenly disappeared. Last comments on his blog were back in August. Hope he is OK! Must have either been medical or a sudden loss of interest.

Reminds me of the "Dr Xin" situation over on the H-F forum. He apparently just disappeared one day in the middle of taking orders for a headphone amp.

I dont think RS would appreciate this comparison and you havent got the story right. he didnt just disappear, he simply stopped filling peoples orders or responding to emails. people who paid with credit card were mostly OK because it wasnt charged till the order shipped, but many people lost their money through paypal, some are still waiting years later. every now and then an amp would be shipped, at a staggeringly low frequency and amps that were sent back for updates or repairs, some were repaired and appeared out of the blue, some never returned.

he did send some refunds too, very strange situation

I think its much more likely RS just got bored and moved on, can you blame him? either that or he was paid off or snuffed out =P
 
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yeah, but a reality check may have revealed that he was essentially doing high paid work 24/7 for nothing, answering the same questions over and over again, that would do my head in and its not really challenging is it?

youre right though, its all guessing, its all there is left to do though.

luckily the O2 is the last amp you'll ever need to own right?

who's going to pick up the ball?
 
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luckily the O2 is the last amp you'll ever need to own right?
who's going to pick up the ball?

My ideal amp would involve marrying the O2 to a ludicrously expensive stepped attenuator: channel balance at very low volume levels (which, despite unity gain and a source with a reasonable 2VRMS output, is something I get uncomfortably close to with my K702s) is the only real complaint I have.

I respect the more serious DIYers such as yourself, who continue to explore the design of hi-fi equipment for the sheer fun/interest of it (note how I'm carefully side-stepping the sound quality minefield... :D), but that approach probably isn't for me. DIY is fun, but I do it for the end result rather than for the exploration.

As for who picks up the ball, I'd like to think it'll keep rolling of its own accord. Sure, some people will dismiss the entire thing as insane zealotry (thus completely missing the point), and some people will inevitably read his blog and extrapolate too far from it (EVERY AMP EVER MADE SOUNDS THE SAME 11!!!1), but on the whole I think the poke in the eye with a sharp stick was a good thing for the hobby!
 
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Hey qusp! You are right. Although the "disappearing" part is similar, Dr. Xin was selling stuff directly and taking payments (as far as I know, was before my time on the forums). RocketScientist/NwAvGuy apparently never made any money on any of it.

I noticed that Tyll Hertsens announced that he had bought an AP and was going to start measuring headphone amps at the end of this year, with a set of protocols that NwAvGuy sent him, at about the time NwAvGuy disappeared:

InnerFidelity Headphone Amp Measurement Program Update July 2012 | InnerFidelity

I've wondered if that was part of it. Maybe NwAvGuy figured "my work here is done". His big thing at the beginning seemed to be raising awareness that RMAA was nearly useless, measuring the sound card more than the amp being tested, and that many amps never had a proper testing of their specs. BTW, in that article in the link Tyll tested the O2 with his AP and confirmed a nearly exact duplicate of RocketScientist/NwAvGuy's reported measurements. They are real!

As for who would be good to run with the ball, I vote for opc of course. :D
 
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Hey qusp! You are right. Although the "disappearing" part is similar, Dr. Xin was selling stuff directly and taking payments (as far as I know, was before my time on the forums). RocketScientist/NwAvGuy apparently never made any money on any of it.

I noticed that Tyll Hertsens announced that he had bought an AP and was going to start measuring headphone amps at the end of this year, with a set of protocols that NwAvGuy sent him, at about the time NwAvGuy disappeared:

InnerFidelity Headphone Amp Measurement Program Update July 2012 | InnerFidelity

I've wondered if that was part of it. Maybe NwAvGuy figured "my work here is done". His big thing at the beginning seemed to be raising awareness that RMAA was nearly useless, measuring the sound card more than the amp being tested, and that many amps never had a proper testing of their specs. BTW, in that article in the link Tyll tested the O2 with his AP and confirmed a nearly exact duplicate of RocketScientist/NwAvGuy's reported measurements. They are real!

As for who would be good to run with the ball, I vote for opc of course. :D

You also do a lot of 'upgrade' on the amp :D my vote in on you.
 
Hypothetical question here: How much would the raw parts cost to build a Odac/O2 combo? If I were to get someone to build one for me, how much do you think they would charge?

The ODAC is only sold assembed. By the time you paid someone labor to assemble O2 parts it would cost the same or more than just buying an assembled one. Looks like around $285 USD for a fully assembled ODAC + O2 in a case from JDS labs in the US JDS Labs - O2+ODAC Combo

Audio Poutine in Canada Audio Poutine - diyAudio Head-N-HiFi in Switzerland Audio Poutine - diyAudio and Epiphany Acoutics in the UK EHP-O2 Portable Headphone Amplifier | Epiphany Acoustics likely all offer assembled O2 and ODACs for similar prices.