The Objective2 (O2) Headphone Amp DIY Project

[merlin2069er]

wow, very nice.

Actually I do have a pair of cheap ipod headphones. I'll have to recharge my SLA battery and plug it into my dac to get an output for the O2 amp.

[regal]

I am still impressed with this little $50 unit , more power than my spud SET amp, but they share more similiarities than differences driving grados. Its just that the O2 has a more power, better bass extension, better mid bass, better lower mids, but not as realistic with sharp transients (at least with grados.) At these power levels the differences in the sonics and probably measurements aren't that big as you would think comparing the tube amp to the opamp, a tube amp with every harmonic below -80dB isn't something one can say is adding color. You have no idea how long it took to get the SET amp to the point where it had a complete silent background with Grados, the O2 was there in a few hours.

The one thing I keep asking is shouldn't the C11 and C12 be silver mica, isn't there microphonic issues with ceramic capacitors in the signal path, maybe that is why transients are not sounding accurate? Just a question.

One thing for certain the more I listen the more realize the key design features of ultra low noise floor, minimal constant (non increasing) distortion with power, and moderate bandwidth for low rfi susceptibility make this a world class headphone amplifier.

[FloridaBear]

I have to question the comment about "sharp transients." If the O2 is flat to 40KHz, how could there be any audible transient that would be "less accurate?" The slew rate should be more than adequate for any audible wave form.

[sgrossklass]

C11/12 are C0G (NP0) caps, which are beautifully linear.

Not like it would matter much, they're essentially opens at audio frequencies anyway.

[regal]

Originally Posted by FloridaBear

I have to question the comment about "sharp transients." If the O2 is flat to 40KHz, how could there be any audible transient that would be "less accurate?" The slew rate should be more than adequate for any audible wave form.

I have no idea maybe my tube amp covers up a flaw in my DAC? Or possibly there is a little overshoot? Hell maybe its the magnum grado headphones, I don't believe any amp does a perfect job with sharp transients. I think the amp is very nice, its not a big deal, just something I noticed over the last month of listening to it. With headphones being right against your ear a big transient isn't going to be realistic following design, there is some art left in this.

So ceramic NPO caps are not microphonic like the old ceramics? I did not know that, good one less thing to worry about

[FloridaBear]

I was toying with the idea of building an ABX box using a serial-port controlled relay box I have laying around so I could do some of my own ABX testing, but then I'd need gear to test. I'm afraid that would be a long, expensive road (even though I could write the ABX software myself). It would sure be interesting to see if I could hear subtle differences between gear--and that's the only way I could "practice what I preach."

[merlin2069er]

Yes! Got it running successfully.

How do you go about checking the power level in the unit? How many hours roughly can you get out of playing with the 2x 9v batteries.

[ethanolson]

Here's a cool little measurement that was conducted on capacitors: The "Sound" of Capacitors

[sgrossklass]

Originally Posted by regal

So ceramic NPO caps are not microphonic like the old ceramics? I did not know that, good one less thing to worry about

That's a "low-K" dielectric, while the nasty types have high to very high permittivity and may have severe voltage and temperature coefficients. Low-K ceramics actually were very handy when first produced in the 1930s, as they can be made with various temperature coefficients and as such allowed for very accurate temperature compensation and hence good frequency stability in LC oscillator circuits. (You can find more on this in the discussion of the Telefunken E52 "Köln" receiver.)

Originally Posted by merlin2069er

How do you go about checking the power level in the unit? How many hours roughly can you get out of playing with the 2x 9v batteries.

That should be mentioned in one of the O2 articles. The only power indication is power management turning the amp off when batteries run low.

Originally Posted by ethanolson

Here's a cool little measurement that was conducted on capacitors: The "Sound" of Capacitors

Unfortunately this doesn't say all that much about distortion. Some of the best research on the topic can be found in a series of articles by Cyril Bateman that you'll find archived here and here.

[merlin2069er]

Here's my O2.