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Today I got my O2 + ODAC combo and with the low gain setting I'm very impressed but not with the high gain setting.
The music sounds a litte bit scratchy and distorted while using the high gain settings compared to the low gain setting by listening to the same volume level.
Low gain and maximum level (potentiometer at max level) -> no distortion
High gain and half level (potentiometer at half level) -> little bit of distortion
Do you picked up the same experiences by comparing the low and high gain settings ?
Headphone was my Beyer 880 (600 Ohm) and the O2 was driven by a power supply.
The Beyer at 600 ohm would cause any inherent gain issues with the O2 to manifest themselves most easily. From what little I know about it, the design took a departure from accepted headphone amplifier design and placed the volume pot inbetween the gain stage and output buffer. That means that any input signal beyond a certain voltage will be clipped. A high-impedance load such as the 600 ohm Beyers will require much more gain than other headphones. When that gain is dialed-in, if the source is not below a certain voltage, the O2 will clip.
AMB made these same arguments to the designer. It reduces the applicability of the design in the real world, perhaps in favor of better testing results. The volume pot after the gain stage may be less noisy than otherwise. Plus, 600 ohm headphones are not everyday, run-of-the-mill headphones. So it may have been a design risk worth taking.
Personally, I find it interesting that some are commenting that lower gain settings are in favor of better sound, but this is exactly what one might expect with that kind of design decision (locating the volume pot in-between amplifier stages). Clipping is not an immediate, "OMG - it sounds bad!" result in every case. Instead, you may have peaks and highs that somehow seem stilted, reduced, distorted, per se, or a sense that something is not quite right with the settings.
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The ODAC's lineout is too high for the high gain setting (which is really for low-voltage sources such as ipods) and will clip, which is probably what you're hearing.the ODACi s pumping out plenty of voltage, so you shouldn't need the O2 on anything more than 2.5x unless you bypass the ODAC to play off your ipod.
There's no reason an amp can't handle a strong source, unless the attenuation was placed after the gain stage. Just my personal opinion again, but it seems somewhat ironic to find that a source from a designer may exceed an amp's gain capability that comes from the same designer.
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Thanks
And yes the low gain setting deliver more than enough power. It was only question whether my O2 is defect or not.
Power is not the question. This is often misunderstood when looking at gain. A high-gain setting on an amp, or a strong source may seem like there's a lot of power present - simply because things get loud at very low volume-knob-travel settings. It doesn't mean there's a lot of power at all - things may start clipping at just a little bit further up on the volume knob. You could easily have ear-splitting volumes at 9 o'clock, but clipping could occur at 9:30 or 10.
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The behavior you describe is how the design works. Some people might call the design defective (I would say: misconfigured), but your particular sample seems to be working to spec, as it should.
With the default gain levels set on the O2 (configurable by swapping a resistor for each of the L and R channels), the high gain will clip any input of greater than roughly 7V / 6.5 = 1.08V (rms sine wave), where 6.5 is the default high gain, no matter what the O2's volume knob is set to. ODAC line output is around 2V. If you set full volume in software, you could well surpass 1.08V all the time with the right music. Solution is to reduce the output level of the DAC or reduce the gain on the O2.
If low gain is good enough for you, then you can just keep using that and ignore the other setting.
I wouldn't call the design "defective," either.
The volume pot was designed to be put in the place in the circuit where it resides. It was a conscious decision, perhaps interesting in its deviation from accepted practice. However, there are consequences for that decision. An advantage is that there is generally less noise when placing the volume in the interstage instead of at the signal input. The disadvantage has already been mentioned. One can design to meet measurements to the exclusion of all else, or one can design a product for the best usability. The two goals may not have the same results. In this case, if a source is a bit stronger or a pair of headphones needs higher gain, the O2 may have trouble without attenuating the signal at some point in the circuit other than the volume pot.
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Yep, the same over here.
As I mentioned above in this thread, I am using the unity gain (1x) on the ODAC
with the Beyerdynamic Beyer 880 (250 Ohm; 2005 Edition).
(Last week the standalone ODAC and standalone O2 arrrived from JDS Labs.)
If it's quiet around me, the volume on the O2 is set at 9 o'clock.
If my surrondings are not very quiet I set the volume at 10 o'clock.
There's no need for higher gain in my situation. - In my opinion the O2 is a very powerful amp indeed.
I've tried higher gain but the sound was not in the same league as when using the unity gain.
Also, I am lucky and happy that my new laptop does not cause any USB-related problems. -
I am knocking on wood and touching wood right now!
There's no whining, etc as some of you whined (ha, ha, ...) about.
So, I don't need a powered hub, but I am gonna get it
just for sake of experimentation/comparison.
Again, gain does not mean power. Just because 10 o'clock on the volume knob is ear-splitting, doesn't mean the amp is not clipping at 10:30 - or even somewhat clipping at 10 o'clock. You may simply not notice the increased distortion. Your acknowledgement that unity gain is superior in sound quality may be a confirmation of this.
As for the USB related connections with the ODAC, I was surprised to see the schematic when it was finally released. There is no power capacitor anywhere on the PCB. A typical DIY DAC might have 1000uf to 1500uf onboard the PCB somewhere. There is only a single SMD 22uf capacitor on the 5V USB buss in the ODAC. It's no wonder it's super-sensitive to USB power fluctuations, laptops, etc., and that a powered-USB hub works wonders. Yes, I would consider this
a design-flaw.
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This is an uncharted but very interesting territory for me.
Just out of curiosity, how can one
I guess that one needs to be a DIYer or an engineer who knows how to open the ODAC and to swap some resistors?
Obviously, in my case I am applying the second solution, namely using the O2's unity (1x) gain and it works fabulously.
Same-same as above. The lower gain perhaps sounds better because of the minute distortions occurring from clipping at higher gain settings.
Just some guesses and observations - I'm not claiming to be an absolute expert. It just seemed as if you guys needed some possible explanations or elaborations.
