[Arm3nian]

I got my hd650s a couple of days ago off Amazon for $313, cheapest they've been for years. They only sound slightly better than my hd555s, but I'm using onboard on my $70 motherboard lol. Looking for a big upgrade with o2+odac.

 

[TeddyK]

But as some said , 1X/3.5X some the most versatile setting (even if i choose 1X/2.5x , anyway as said i listen at moderate volume so

) .

2.5X;3.5X : Is there a reason not to choose 3X gain with O2 ?

 

[jseaber]

  2.5X;3.5X : Is there a reason not to choose 3X gain with O2 ?

 
Dig into the underlying mathematical requirements of O2+ODAC and you'll find that 3.5x is the optimal high gain position. Gain of 3.0x would waste a few decibels of headroom.

 

[Arm3nian]

2.5X;3.5X : Is there a reason not to choose 3X gain with O2 ?

Potential channel balance problems as the blog mentions. More noise and distortion is always something that comes with more gain. Now if the noise and distortion are actually audible is another story, but theres no point to higher gain if a lower setting does everything you need. The difference is only 3db between 2.5 and 3.5, not that huge of a difference anyway. If headphones don't get loud enough with 2.5x then 3.5x is barely going to help.

 

[TeddyK]

Thanks for your responses.

 

[diamondears]

Dig into the underlying mathematical requirements of O2+ODAC and you'll find that 3.5x is the optimal high gain position. Gain of 3.0x would waste a few decibels of headroom.

Hello John. Can you elaborate on this? Is 3.5x gain still the optimal high gain position as compared to unity gain even when the HP can get loud enough at unity gain? Say HP is 91 db /mW and 50 ohms impedance.

Also, what do you mean by losing/wasting few decibels of headroom if 3.0x gain? You mean unity gain?

Cheers.

 

[Solrighal]

I thought it was a case of the least gain required the better. Or am I wrong?

 

[headwhacker]

Hello John. Can you elaborate on this? Is 3.5x gain still the optimal high gain position as compared to unity gain even when the HP can get loud enough at unity gain? Say HP is 91 db /mW and 50 ohms impedance.

Also, what do you mean by losing/wasting few decibels of headroom if 3.0x gain? You mean unity gain?

Cheers.

 
By optimal it just mean you have the maximum output of O2 available to use. O2 has a maximum output of around 7Vrms.
 
If ODAC is your source (2Vrms output), 7 / 2 = 3.5
 
if O2 is set to 3.5x gain you have as much as 7Vrms of headroom. Above 3.5x O2 will clip. Below that you won't reach 7Vrms. Hence, you are losing a few dBs of headroom.
 
But if you have a source other than ODAC, which most probably have a different output voltage then the optimal gain value will change. ( 7Vrms / source voltage).
 
If your HP gets loud enough at 1x gain then it is the optimal gain.  

 

[jseaber]

Hello John. Can you elaborate on this? Is 3.5x gain still the optimal high gain position as compared to unity gain even when the HP can get loud enough at unity gain? Say HP is 91 db /mW and 50 ohms impedance.

Also, what do you mean by losing/wasting few decibels of headroom if 3.0x gain? You mean unity gain?

Cheers.

 
X = Objective2's maximum VRMS input signal before clipping = 7/A
A = Gain (Vout/Vin)
 
ODAC output = 2.0VRMS = X
 
2.0 = 7/A
A = 7/2 = 3.5
 
Setting high gain to 3.5 gives maximum amplification of 2*3.5 = 7.0VRMS. This is slightly below O2's maximum capability of ~7.5VRMS, but ensures no clipping will occur.
 
Most listening with dynamic headphones is (or rather, should be) conducted at low gain, since the noise floor is superior. Assuming a 1.0/3.5x gain configuration for O2+ODAC, unity gain of 1.0 gives output ranging from 0.0 to 2.0VRMS, and high gain gives a range of 0.0 to 7.0VRMS.
 
At a proposed high gain of 3.0, output would be limited: 0.0 to 6.0VRMS. This is a loss of 1VRMS compared to 3.5x. Why unnecessarily limit the amplifier?

 

[diamondears]

X = Objective2's maximum VRMS input signal before clipping = 7/A
A = Gain (Vout/Vin)

ODAC output = 2.0VRMS = X

2.0 = 7/A
A = 7/2 = 3.5

Setting high gain to 3.5 gives maximum amplification of 2*3.5 = 7.0VRMS. This is slightly below O2's maximum capability of ~7.5VRMS, but ensures no clipping will occur.

Most listening with dynamic headphones is (or rather, should be) conducted at low gain, since the noise floor is superior. Assuming a 1.0/3.5x gain configuration for O2+ODAC, unity gain of 1.0 gives output ranging from 0.0 to 2.0VRMS, and high gain gives a range of 0.0 to 7.0VRMS.

At a proposed high gain of 3.0, output would be limited: 0.0 to 6.0VRMS. This is a loss of 1VRMS compared to 3.5x. Why unnecessarily limit the amplifier?

Thanks John. Very clear.

One last question for now: in terms of SQ, and assuming the HP could get loud enough on 1.0x gain, would there be any improvement or advantage in using the 3.5x gain instead?

Cheers.

 

[blse59]

Thanks John. Very clear.

One last question for now: in terms of SQ, and assuming the HP could get loud enough on 1.0x gain, would there be any improvement or advantage in using the 3.5x gain instead?

Cheers.

Nope, never. Lower gain will always have higher quality SQ in practically every scenario.

 

[diamondears]

Nope, never. Lower gain will always have higher quality SQ in practically every scenario.

Yes, that's my current understanding too, but you never know. I always hear the higher gains to have more treble, maybe the additional noise, etc. But I ask re higher gains bec they feel more powerful..

 

[Arm3nian]

   
X = Objective2's maximum VRMS input signal before clipping = 7/A
A = Gain (Vout/Vin)
 
ODAC output = 2.0VRMS = X
 
2.0 = 7/A
A = 7/2 = 3.5
 
Setting high gain to 3.5 gives maximum amplification of 2*3.5 = 7.0VRMS. This is slightly below O2's maximum capability of ~7.5VRMS, but ensures no clipping will occur.
 
Most listening with dynamic headphones is (or rather, should be) conducted at low gain, since the noise floor is superior. Assuming a 1.0/3.5x gain configuration for O2+ODAC, unity gain of 1.0 gives output ranging from 0.0 to 2.0VRMS, and high gain gives a range of 0.0 to 7.0VRMS.
 
At a proposed high gain of 3.0, output would be limited: 0.0 to 6.0VRMS. This is a loss of 1VRMS compared to 3.5x. Why unnecessarily limit the amplifier?

I don't understand this. I thought gain was the last step before sending the signal into the headphones? At 2v the o2 can output 13.3mw into 300ohm headphones, making all of my previous calculations an order of magnitude off. The maximum output power specified then is with 3.5x gain with a 2v input source such as the odac, making it 7VRMS.
 
So using this to save time for (hd650s 97.8db/mw efficiency and 300ohms impedance): http://www.headphone-amplifier.com/calculator.htm
unity gain (2000mv) would give me 109db, 2.5x gain (5000mv) would give me 117db, and 3.5x (7000mv) gain would give me 120db. Not that much of a difference between 2.5x and 3.5x, but the 8db gain from 1x to 2.5x might be useful. Question is how much distortion/noise is added with each different setting. 

 

[headwhacker]

  I don't understand this. I thought gain was the last step before sending the signal into the headphones? At 2v the o2 can output 13.3mw into 300ohm headphones, making all of my previous calculations an order of magnitude off. The maximum output power specified then is with 3.5x gain with a 2v input source such as the odac, making it 7VRMS. So with 3.5x gain the o2 could output 177mw into 300ohm headphones. 

 
That is about right. At 3.5x gain and ODAC as source, max power around that value (163mW) for 300ohm load. At unity gain (1x) O2 acts like a buffer and output is 2Vrms for max power of 13mW for 300ohm load.

 

[jseaber]

  I don't understand this. I thought gain was the last step before sending the signal into the headphones? At 2v the o2 can output 13.3mw into 300ohm headphones, making all of my previous calculations an order of magnitude off. The maximum output power specified then is with 3.5x gain with a 2v input source such as the odac, making it 7VRMS. So with 3.5x gain the o2 could output 177mw into 300ohm headphones. 

 
Voltage gain occurs in any stage of amplification (either as attenuation, unity gain, or amplification). An amplifier can have any number of stages. In O2, voltage gain occurs in the pre-amplification stage, followed by analog attenuation, then a current buffer output stage.
 
Someone posted a longer mathematical explanation in this thread a few weeks ago, so I will not repeat the exercise.