Q701 with O2 Question
Jan 3, 2013 at 9:36 PM Thread Starter Post #1 of 30

Shazb0t

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I recently bought an O2 amplifier and a set of Q701's to use with my Titanium HD.  I am a competitive fps player so having the x-fi chip is important to me.  
 
I have hooked up the the O2 to the Titanium HD using RCA out from the card to 3.5mm input jack on the O2.  I then am plugging the Q701 into the 3.5mm output jack on the O2.  With the system volume for the Titanium HD set to 100% volume and the card set to headphones I have to turn the O2 volume adjustment knob to between 1.5-2.5 o'clock depending on the song to attain normal listening volumes.  Is this normal?  I was under the impression that the O2 would deliver a lot of power and that I wouldn't come close to maxing out the volume adjustment.  I want to make sure I haven't messed anything up with the installation.  Any information would be greatly appreciated.
 
Jan 3, 2013 at 10:06 PM Post #2 of 30

shadow419

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Sounds normal, especially if it's using an A taper alps volume pot.  The A taper forces you to use more of the pot travel, but this helps with channel imbalance that pots may have in the 7-9 o'clock area.  You can still blast your eardrums though if you wish.  It will get plenty loud.
 
Jan 3, 2013 at 11:33 PM Post #4 of 30

MrMateoHead

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Quote:
So I am new to the whole head-Fi scene.  I recently bought an O2 amplifier and a set of Q701's to use with my Titanium HD.  I am a competitive fps player so having the x-fi chip is important to me.  
 
I have hooked up the the O2 to the Titanium HD using RCA out from the card to 3.5mm input jack on the O2.  I then am plugging the Q701 into the 3.5mm output jack on the O2.  With the system volume for the Titanium HD set to 100% volume and the card set to headphones I have to turn the O2 volume adjustment knob to between 1.5-2.5 o'clock depending on the song to attain normal listening volumes.  Is this normal?  I was under the impression that the O2 would deliver a lot of power and that I wouldn't come close to maxing out the volume adjustment.  I want to make sure I haven't messed anything up with the installation.  Any information would be greatly appreciated.

Did you opt for the stock gain settings on the O2? Those are 2.5x/6.5x switchable.
 
Your card puts out 2V from the RCA, so actually your volume level seems very high compared to my 2V source (ODAC). Under most conditions, I am between 9 O'Clock and 12 O'Clock on a much less efficient pair of phones.
 
Even with a 1V onboard soundcard, I didn't typically need to wander much past 12 O'Clock to experience loud volume.
 
I would double check your windows settings, and card settings. Maybe the output mode is switchable? Are you sure that you have chosen the correct output? Can you try using one of your 3.5mm line-outs into the O2 instead, to verify that they are less loud or louder? Additionally, plug the phones straight into the X-fi. Is the increase or decrease in volume significant?
 
Check your cables also. I have had issues in the past where a seemingly properly inserted cable actually wasn't making good contact. Gently wiggle /re-connect your connections or swap cables entirely to be sure (if you can).
 
Finally, plug in a different pair of headphones to see if they respond in a similar way.
 
Jan 4, 2013 at 6:45 AM Post #8 of 30

jimmers

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Quote:
It's the JDS Labs version.  Stock gain with switch out.


with switch out (low gain) on HeadnHiFi O2 source from ODAC, I have volume pot around 1 or 2 o'clock, but that's with foobar at -15dB, with foobar at max it's around the 11 - 12 o'clock (I don't listen real loud).
I agree with MrMateoHead about trying out variations. Bear in mind re: muad that on testing the Q701 needs about 50% more voltage (13 times the power!) for the same SPL, despite what the official specs say; when I replace mt HD650 with the Q701 I need to add more than 1 hour to the "o'clock" position on the O2 to get a similar sound level.
 
Jan 4, 2013 at 2:24 PM Post #9 of 30

MrMateoHead

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Quote:
with switch out (low gain) on HeadnHiFi O2 source from ODAC, I have volume pot around 1 or 2 o'clock, but that's with foobar at -15dB, with foobar at max it's around the 11 - 12 o'clock (I don't listen real loud).
I agree with MrMateoHead about trying out variations. Bear in mind re: muad that on testing the Q701 needs about 50% more voltage (13 times the power!) for the same SPL, despite what the official specs say; when I replace mt HD650 with the Q701 I need to add more than 1 hour to the "o'clock" position on the O2 to get a similar sound level.

That is a crazy dB cut!
 
Also, regarding the apparent fudging of the AKG 701 specs. Innerfidelity claims about 65 Ohm impedance for the 701s, and 1.57 mW for 90 dB. HD 650 is 330 Ohm impedance, requiring only .13 mW for 90 dB. So, while the Senns have about 5 times the resistance, they also require 12 times less power. So, without doubt, they are more efficient than the 701s.
 
The HE-400s that I use are rated 51 Ohms, and .33 mW for 90 dB. Even with similar impedance, apparently the AKG 701 require 5 times more power than my planars!
 
Bottom line, those are some inefficient headphones. Chances are, they are going to soak up most of the power the O2 can pump out. The good news is that, despite that, the O2's output is very low distortion until max rated power is reached - which is about a half a watt or a little more. You could always try the new Schiit amp if you thought more power would help - but honestly, I can't see it adding much SPL to the AKGs (is is twice or less than twice the output of the O2).
 
Jan 4, 2013 at 3:38 PM Post #10 of 30

Shazb0t

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I'm very happy with the sound and it gets loud enough that it would cause damage if I tried to listen at full volume so I'm pleased with the O2 as is. I just wanted to confirm that the amount of power was normal for these headphones.
 
Jan 4, 2013 at 9:13 PM Post #11 of 30

Shazb0t

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I experimented by plugging the headphones into the sound card without the amp and max volume from the card is regular listening volume, so the O2 definitely delivers more power.  I reconnected the O2 and tried it with the gain switch in and then the max volume becomes very loud.  I think leaving it at around 2 o'clock at the lower gain setting (button out) is perfect.  Thank you all for your help.
 
Jan 5, 2013 at 8:21 AM Post #12 of 30

Chris J

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Quote:
So I am new to the whole head-Fi scene.  I recently bought an O2 amplifier and a set of Q701's to use with my Titanium HD.  I am a competitive fps player so having the x-fi chip is important to me.  
 
I have hooked up the the O2 to the Titanium HD using RCA out from the card to 3.5mm input jack on the O2.  I then am plugging the Q701 into the 3.5mm output jack on the O2.  With the system volume for the Titanium HD set to 100% volume and the card set to headphones I have to turn the O2 volume adjustment knob to between 1.5-2.5 o'clock depending on the song to attain normal listening volumes.  Is this normal?  I was under the impression that the O2 would deliver a lot of power and that I wouldn't come close to maxing out the volume adjustment.  I want to make sure I haven't messed anything up with the installation.  Any information would be greatly appreciated.

 
Position of volume control is directly proportional to how much Voltage the headphone amp outputs.
 
Are you sure you have ALL the volume controls on the Titanium set to 100%?
I can easily listen to Q701s using an iPod or an iPad and turn the volume up as loud as I want.
OTOH, you seem to be OK with how the O2 is working.
 
The myth of the power hungry Q701 is just that...a myth.
Q701s are approx. 1 Volt = 105 dB SPL, (well probably less!) you wouldn't listen to an average level that loud.
This works out to approx. 0.316 Volts = 95 dB SPL, the O2 can easily output this.
 
I use an amp with set to gain of 10 dB (X 3.16), and I usually have the volume set to approx. 10-11 oclock. Maybe I listen quieter than you.  My DAC outputs 2 Volts
 
For efficiency they are approx 1 milliWatt = 90 dB SPL.     (there have been a few testers who think the manufacturer's efficiency and sensitivity specs are rather optimistic).
The O2 is more that capable of outputting 10 milliWatts into a pair of Q701.
 
A more powerful amp won't fix this. Which you obviously agree with!
 
Jan 5, 2013 at 9:01 AM Post #13 of 30

jimmers

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Quote:
 
Position of volume control is proportional to how much Voltage the headphone amp outputs.
 

Only if you are using a linear pot which would mean most of variation in sound level will be in the first part of the rotation.
 
Quote:
The myth of the power hungry Q701 is just that...a myth.
Q701s are approx. 1 Volt = 105 dB SPL, (well probably less!) you wouldn't listen to an average level that loud.
This works out to approx. 0.316 Volts = 95 dB SPL, the O2 can easily output this.
 
 
 
For efficiency they are approx 1 milliWatt = 90 dB SPL.     (there have been a few testers who think the manufacturer's efficiency and sensitivity specs are rather optimistic).
The O2 is more that capable of outputting 10 milliWatts into a pair of Q701.
 
 

That's according to AKG, are you saying Tyll can't do consistent measurements?
I know they are less sensitive than HD650, even though AKG specs vs Senn specs say otherwise, I find it relative sensitivities pretty much in line with test results .
 
Jan 5, 2013 at 10:08 AM Post #14 of 30

MrMateoHead

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Quote:
 
Position of volume control is proportional to how much Voltage the headphone amp outputs.
 
Are you sure you have ALL the volume controls on the Titanium set to 100%?
I can easily listen to Q701s using an iPod or an iPad and turn the volume up as loud as I want.
OTOH, you seem to be OK with how the O2 is working.
 
The myth of the power hungry Q701 is just that...a myth.
Q701s are approx. 1 Volt = 105 dB SPL, (well probably less!) you wouldn't listen to an average level that loud.
This works out to approx. 0.316 Volts = 95 dB SPL, the O2 can easily output this.
 
I use an amp with set to gain of 10 dB (X 3.16), and I usually have the volume set to approx. 10-11 oclock.
 
For efficiency they are approx 1 milliWatt = 90 dB SPL.     (there have been a few testers who think the manufacturer's efficiency and sensitivity specs are rather optimistic).
The O2 is more that capable of outputting 10 milliWatts into a pair of Q701.
 
A more powerful amp won't fix this. Which you obviously agree with!


I don't think it is a "myth". But I do think that the O2 can do about 500-700 mWs at 60 Ohms. That should be more than enough, under most, but not all listening conditions. See my Innerfidelity specs posted above.
 
The next step would be to seek an amp of 1 watt or more, but this wouldn't add a lot of loudness given the large expense (with the exception of 2 amps I can think of).
 
Jan 5, 2013 at 12:10 PM Post #15 of 30

Chris J

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Only if you are using a linear pot which would mean most of variation in sound level will be in the first part of the rotation.
 
That's according to AKG, are you saying Tyll can't do consistent measurements?
I know they are less sensitive than HD650, even though AKG specs vs Senn specs say otherwise, I find it relative sensitivities pretty much in line with test results .

 
 
A linear or log pot has nothing to do with this.
Headphone amplifiers are voltage amplifiers.
assuming you have an input signal:
9 o'clock.....low output voltage
12 o'clock.....more output voltage, etc.
a headphone amp outputs voltage whether or not headphones are plugged in.
current draw is inversely proportional to headphone impedance, therefore low headphone impedance more power draw (assuming voltage stays the same), high impedance less power draw. 
 
I don't know who Tyll is, but you are twisting my words, I'm sure he knows how to measure efficiency, sensitivity, etc.
 

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