[MrKazador]

   
The spec page is useless does not give any clue about the output voltage.
 
I'm guessing the D3 has fix output level which is greater than 1V. At 6.5x gain, O2 easily clips. That's why you have to turn down the volume control in Windows to avoid O2 from clipping. Not an ideal match to get the maximum power output from O2.
 
If other Fiio products is any indication I think the output voltage of D3 is 1.5V. Too much for O2 at 6.5X. Did you try it at 2.5X? 

 
2.5x doesn't clip at all with full Windows volume which is why I'm using 6.5x to get the most that I can from the amp. I could adjust the gain but I don't really feel like it...

 

[Jony27]

Received my combo today, just wondering which gain is set when the gain button is pressed down?
For the standard gain which is 2.5x/6.5x, would it be the higher or lower gain?
Also, whats a good Windows volume for the amp on low and high gain?

 

[MrKazador]

Pushed in is 6.5x. Volume depends on your source output voltage and gain setting (2.5 or 6.5).

 

[jellofund]

  Received my combo today, just wondering which gain is set when the gain button is pressed down?
For the standard gain which is 2.5x/6.5x, would it be the higher or lower gain?
Also, whats a good Windows volume for the amp on low and high gain?

 
This might be useful for setting up the ODAC
 
http://www.jdslabs.com/pdf/Instructions_ODAC_Standalone.pdf 
 
In case it's of interest the reasons for setting Windows / digital volume just below 100% are discussed on this page: http://www.head-fi.org/t/616331/o2-amp-odac/3720

 

[headwhacker]

   
2.5x doesn't clip at all with full Windows volume which is why I'm using 6.5x to get the most that I can from the amp. I could adjust the gain but I don't really feel like it...

 
I'm afraid 6.5x in your case doesn't get the most out of O2 but rather cripples it. That is why you are only getting 110 dB out of your Mad Dogs. I bet you'll measure greater SPL at 2.5x.
 
6.5x is only meant for sources that can only deliver 1V of signal or less. It's important to get the proper match between your source and the gain settings in O2 so you have the 7Vrms available to drive headphones and avoiding clipping.

 

[vertical]

Doesn't using the higher gain also increase the noise floor?

 

[MrKazador]

   
I'm afraid 6.5x in your case doesn't get the most out of O2 but rather cripples it. That is why you are only getting 110 dB out of your Mad Dogs. I bet you'll measure greater SPL at 2.5x.
 
6.5x is only meant for sources that can only deliver 1V of signal or less. It's important to get the proper match between your source and the gain settings in O2 so you have the 7Vrms available to drive headphones and avoiding clipping.

I measured 112db with 6.5x (Windows volume at 38) and 108db with 2.5x (Windows volume maxed) playing Metallica - No Leaf Clover. The volume was maxed out on the o2. Wouldn't adjusting the Windows volume decrease the voltage so it matches perfectly with the 6.5x gain setting?

 

[jseaber]

  I measured 112db with 6.5x (Windows volume at 38) and 108db with 2.5x (Windows volume maxed) playing Metallica - No Leaf Clover. The volume was maxed out on the o2. Wouldn't adjusting the Windows volume decrease the voltage so it matches perfectly with the 6.5x gain setting?

 
Yes, this is a valid way to achieve peak output power from O2+ODAC a 6.5x gain.

 

[adydula]

and what might lowering the volume to 38 do??? good? bad?
 
Alex

 

[JacobLee89]

Doesn't using the higher gain also increase the noise floor?

 
If there's an audible noise floor to begin with, then yes.
 
If you have a noise floor that is incredibly difficult to locate even at high volumes in a low-gain setting, you'll most likely not notice it in high-gain settings either.

 

[vertical]

Okay. Yeah, makes sense...Thx

So, ideally, one should just use the lowest gain setting that achieves their target volume level.

 

[raoultrifan]

O2 with original opamps clips after 7V, so for 2V sources max. gain would be 3.5X. If you upgrade gain opamp to 5532 or to 4562 you might be able to increase the gain up to 4X at most, but at 4X the max. output should be 8V which is quite too much for the 2x4556 buffers. If you'll increase the voltage to 15V, then max. output might get up to 10V, but on 12V will most likely clips after 7.5-8V, so changing gain opamp will probably give you only 0.5V more (4X instead of 3.5X) if not incrrasing voltage too.

 

[diamondears]

Can someone compute the mW and Vrms requirement of the HE-6 based on its sensitivity of 83.5 dB/mW and impedance of 50 ohms?

 

[headwhacker]

Can someone compute the mW and Vrms requirement of the HE-6 based on its sensitivity of 83.5 dB/mW and impedance of 50 ohms?

 
115dB = 1413mW / 8.4Vrms
 
110dB = 447mW / 4.72Vrms
 
105dB = 141mW / 2.66Vrms

 

[jseaber]

Can someone compute the mW and Vrms requirement of the HE-6 based on its sensitivity of 83.5 dB/mW and impedance of 50 ohms?

 
45 mW --> 100 dB
141 mW --> 105 dB
447 mW --> 110 dB
794 mW --> 112.5 dB
1413 mW --> 115 dB
 
P = [(VRMS)^2 / Z]
VRMS = (P*Z)^0.5
Where: Z = headphone impedance in ohms, P = output power in mW
 
 
See also:
https://docs.google.com/a/jdslabs.com/spreadsheets/d/1****TwWffXKld7PgHt5wZOP7KnBVO6SyvG9yZEJ-smI/edit#gid=1006269980