Quote from: 2000impreza on January 03, 2013, 03:08:33 PM

I believe the output voltage for the PWD2 is 2.8v RCA(unbalanced) and 5.6V XLR(balanced). Never got a chance to measure the voltages to confirm.

Digital output from iRiver was normalized (replay gain) from track to track. The adjustments were on average about -10db to -15db for pop tracks with a peak level of 0dbFS. The Cello Suite hit 55% at peak.  In addition, the PWD2 output was set to 95 of 100. In other words, we took into consideration the OBJ2's peculiarities.

+/- 0.1 was about as good we could get with the quality of the pots and size of volume knobs. There's always slight drift anyways after it's set. I agree 0.2db is audible. It's one reason I hate steppers.

That knocks clipping right out of the park, leaving only volume matching, both in the way previously referred to and in terms of channel balance. The pot, IMHO, is easily the worst part of the O2, and channel balance can differ quite significantly between samples at low volume settings. This is unlikely to be audible as channel balance differences (unless the volume is extremely low), but similar to slight differences in volume matching could produce unpredictable results. Likewise, I don't know how the pot in the Magni performs.

Again, I'm acutely aware that doing these tests does nothing for you, but what might be interesting is to turn the pots on both amplifiers to max and change the O2's high gain setting to 5 (same as the Magni). You can then use the PWD2 at a low volume (to avoid the O2 clipping) with test tones to check that the amps are both providing the same amount of amplification, then add lots of in-line attenuation so you can turn the volume on the PWD2 pretty high, then control the volume entirely with said DAC...hey, it's just a thought!

On the point of the Magni's general measurable neutrality, you seem to have had some discussion with Jason Stoddard/relevant people: any idea what loads were used for the specs on their site? It seems strange to make a big deal out of how they're using an audio analyser on the product page (can't imagine why they'd do that ) but then to omit the information that allows the specs produced to have any real meaning. The skeptic in me is inclined to believe that omitting such details means they probably tested with very easy loads (600 ohms, 1Kohms, 2Kohms?).

Anyway, despite NwAvGuy's apparent disappearance, at least one of the major O2 builders has been in recent contact with him, so if you want to make him give $500 to charity, the option's still open!

The K701/Q701/DT880 like to be driven from higher Ohmic amplifiers (100 - 120Ohm output R) and will sound fuller and less edgy. a simple matter of voltage division, no magic there. some call it 'synergy'.

Believe it or not, that's the first time I've heard this! At least about the Q701. People always would cry about the Q701 being driven from the E9 because of it's 10ohm output impedance. When I use the Q701 with that amp, it doesn't change it's sound at all due to being 10ohm. Strangely enough, not even my 38ohm DJ100 does. It annoys me that people always assume it will destroy it's sound or something.

I tried my Q701 with my old Technics receiver from 93 and it sounds perfectly fine and quite full sounding. It has a 330ohm output impedance! The DJ100 doesn't change too much either for some strange reason. It's mids are nice and full, but no bloated bass or anything. Ruins my KRK KNS-8400 though.

Some headphones react positively to higher output resistances, others react in a negative way or hardly.
It all depends on the impedance peak (high or low in percentage, peak frequency(ies and width of the peak(s)) and if the headphone in question is already bass heavy on low output resistance amplifiers.
Another factor that comes into play is taste/musical genre and experience.

Most but certainly not all headphones prefer to be driven from low Ohmic sources.
I have seen little to no evidence that 0.001 Ohm is that different from 10 Ohm when driving headphones between 60 and 600 Ohm although some claim the damping factor is important.

To understand damping factor you have to realise the BIGGEST current limiter is the headphone itself.
See a headphone as a generator with an internal resistance of, in this case, say 120 Ohm.
Let's assume after it received a small pulse it swings out and generates a voltage of 1V (argumentative value)
Now if the headphone is damped it is because of the current that starts to flow.
Similar to switching on something that draws a lot of power in a car that runs stationary, you can hear the engine's revs go down because the generator is acting like a small brake.
That damping current is highest at 0 Ohm and becomes lower at higher resistances.
This is where the damping (factor) comes from.
Going from 0.1 Ohm to 10 Ohm is a factor 100 worse it seems... but is it ?
Nope not at all.. why ? because the resistance of the generator (driver) is in series with that low value and the current is thus determined by the driver and not the amp.
So damping factor of 10,000 or just 10 (speaking about headphones) ... highly debatable/controversial.

example: 1V and 0.1 Ohm output R... 120Ohm driver.. thus the current that will 'damp' the unwanted motion = 1V/120.1 Ohm = 8.32mA !
1V and 10Ohm ...120 Ohm driver ... current = 7.69mA.
difference in damping current: just 6% (0.5dB) almost no difference in electrical damping, yet difference in Rout 100 x !.
With output R of say 0.001 Ohm the current values are the same yet the difference in R out = 10,000 times.
The higher the impedance of the headphone the less the damping is 'compromised'.
Often people blame damping factor for the bass getting bloated... but it's the voltage division that changes the FR not the damping factor.
The smaller the headphone impedance the higher the effect of R out becomes though.
For 16 Ohm drivers the difference between 0.1 and 10 Ohm is substantial as the current is almost 40% lower with a 10 Ohm out.
So for LOW impedance headphones, which are intended to be driven from a low voltage, a low output resistance is important.

The bumpier the impedance plot of the headphone the bumpier the FR becomes by voltage division.
If this happens in critical areas (multi armature drivers) the grosser/appalling the audible effects.

I don't know of anyone here that would ever claim we don't know anything about audio design, that's a different site.  Just that there are some patterns and observations that have yet to be fully explained.

How much of a difference is the bass rolloff of the Magni and O2 compared to higher end amps?  Graphs show the HE-400 to be flat to 20-30hz, but I sure as hell can't hear it as that.  Mine begins to rolloff slowly at 40hz on all the setups I've tried.

O2 having a slightly, and I mean slightly, more extended bass than Magni was one of the things I heard with it-- it was slightly stronger at 30hz, but not enough to matter.  Overall it's also more smooth and polite sounding, while the Magni sounds a tad-bit harder, and I don't mean harder in a bad way.  Maybe solid is the word.