I recently purchased the 02+ODAC headphone amp to accompany my Beyerdynamic DT 880s (600ohm). But I'm a bit confused as to what some of the dials and inputs on the front of the amp indicate and how they can best be used to achieve desirable results.
 
As I don't have permission to post a picture, here is an image of the inputs and button in question.
 
Thanks, your help is much appreciated!

The dial is the volume control. The jack on the right is the line-level input from your source (if you are not using the DAC), the button is a high/low gain switch.

Thanks @billybob_jcv! Ok, just read up on gain a little.
 
Yet I'm surprised my cans, with an impedance of 600 ohms, give me decent volume control at the lowest gain setting. I usually hover between 25-55% on the volume dial. Beyerdynamic also makes this model with a 250 ohm impedance, am I correct in reasoning that pair would place me even lower on that volume dial (like 10-35% for example). IE, what would happen to my usage if I were to use lower impedance headphones?
 
Also, couldn't find anything useful on "line-level input". Do you mind explaining that a bit more?

I assume you are connecting the O2+ODAC to your PC using a USB cable, correct? If so, then that means you are feeding a digital audio signal into the ODAC, where it is converted into an analog signal prior to being fed into the O2 amp.

The line level input is for connecting to analog sources. So, for example, if you wanted to use your phone with the O2, you would connect a cable from the headphone jack on your phone to the analog line input on the O2. This would bypass the ODAC and feed an analog signal directly into the O2 amp.

The volume level actually depends more on the sensitivity of the headphones. A lower impedance headphone that is also lower sensitivity may require a higher percentage of your volume dial.

Ah I see, that's a very clear explanation. I see, didn't realize sensitivity is another variable to account for, i'll start reading up on that. 
 
Would the amp then also be powered by my phone's power source? Could I make this device portable? Interesting, so a regular 3.5mm -> 3.5mm would accomplish this?

explorak said:

  Thanks @billybob_jcv! Ok, just read up on gain a little.
 
Yet I'm surprised my cans, with an impedance of 600 ohms, give me decent volume control at the lowest gain setting. I usually hover between 25-55% on the volume dial. Beyerdynamic also makes this model with a 250 ohm impedance, am I correct in reasoning that pair would place me even lower on that volume dial (like 10-35% for example). IE, what would happen to my usage if I were to use lower impedance headphones?
 
Also, couldn't find anything useful on "line-level input". Do you mind explaining that a bit more?

Click to expand...

In the case of your Beyers, the 250 ohm version will be about 30% (4 dB) louder than the 600 ohm version, if sensitivity is the same.
 
Amps adjust the voltage of a signal, so the position of your volume knob corresponds to a certain voltage. The impedance of the headphone determines how much power is delivered to the headphones from that voltage. Sensitivity in dB/mW is how loud a headphone gets from 1 mW of power. Higher impedance means less power, and as a result less volume if sensitivity is the same. You can do 600/250 to find how much more power the 250 ohm version is getting, 2.4 times as much here. Skip the math and it comes out to nearly 4 dB more volume, 30% louder.
 
It's hard to say what that means for the position of the volume knob, except it will be lower. The levels you're using right now are fine, so it doesn't really matter.
 
I also suggest you check out ReplayGain if it's compatible with your audio player. I never touch my volume knob

explorak said:

  Ah I see, that's a very clear explanation. I see, didn't realize sensitivity is another variable to account for, i'll start reading up on that. 
 
Would the amp then also be powered by my phone's power source? Could I make this device portable? Interesting, so a regular 3.5mm -> 3.5mm would accomplish this?

Click to expand...

The all-in-one unit is not portable. The standalone O2 has batteries that can be charged and used on the go, but in the all-in-one unit the batteries have to be removed to make room for the ODAC. The O2 needs to be powered by an AC outlet or batteries, a phone's not enough.

No - the amp cannot be powered by your phone. Some versions of the O2 amp have 2 x 9V batteries that can be installed, but I think you lose that capability on the O2+ODAC. It requires the AC adapter.

Yes, you can connect a 3.5 mm male-male cable between your phone and the O2.

Ah I see, thanks dude. But I could presumably find a usb battery power source with a high enough voltage correct?