[leadbythemelody]

Oh okay. But wouldn't the sound of a 300 ohm headphone be different when using different gains high/low even though a low gain can produce enough volume? (sorry don't have much experience with amps).

 

[wolfetan44]

Quote:

Oh okay. But wouldn't the sound of a 300 ohm headphone be different when using different gains high/low even though a low gain can produce enough volume? (sorry don't have much experience with amps).

It produces more bass right now as I'm testing it. I don't like that.

 

[leadbythemelody]

Plus, what are the proper reasons for using which gain other than impedance which is not a proper criterion?

 

[HamilcarBarca]

Quote:

Plus, what are the proper reasons for using which gain other than impedance which is not a proper criterion?

 
What I wrote wasn't especially meaningful. The O2 can drive most headphones (other than the most demanding.) Most amplifiers (Class A amps being a notable exception) tend to have a higher level of distortion with (a) higher gain; or (b) their lowest and maybe highest volume settings.
 
The most important criterion is efficiency (the ratio of "sound output" for a given "power input".) Less efficient headphones, such as 600-Ohm Beyers, the Q701 and its cousins, and isodynamic headphones, need more power. To get very loud, the HiFiMan HE-500 probably requires the high-gain setting. All of my headphones would work fine with a gain lower the the lowest default setting, 2x, to suit my taste.
 
All this is more or less theoretical. I find the theory interesting. But there are probably other considerations which I've missed.
 
The "bottom line" is not to worry about it. Use the low-gain or high-gain setting. Use low or high volume levels. Choose the ones which suit you. The audible difference, if there is any, should be extremely small. If you like the sound, listen to it.

 

[leadbythemelody]

Okay thank you for clearing that up for me, I think I understand now

 

[leadbythemelody]

I was considering buying an ODAC but I'm not sure...did using an ODAC paired with the O2 amp give any huge improvement to sound quality when using 128-320kpbs mp3's?

 

[leadbythemelody]

Or maybe even minute improvements?

 

[HamilcarBarca]

Quote:

I was considering buying an ODAC but I'm not sure...did using an ODAC paired with the O2 amp give any huge improvement to sound quality when using 128-320kpbs mp3's?

 
DAC's and amps can't exactly improve anything. A neutral DAC and amp will produce audio signals which are exactly as good or bad as the original material. (Plus, good 320kbps MP3 files are almost always indistinguishable from the original material.)
 
Some listeners prefer a certain sound signature. They perceive electronics which color their output as improving the sound quality. If they like it, it's an improvement. Some listeners, such as myself, aren't interested in this kind of equipment. If we don't like it, it's not an improvement.

 

[adamlr]

to the guy asking about using an O2 with 32 ohm headphones:
 
sorry, but i forgot to quote so i used big letters to attract your attention...
 
anyway, im currently using the O2 with a pair of m-100s, who have an impedance of 32 ohm and sensitivity of 103 dB @ 1kHz 1mW. using an amp for these is just overkill. my laptops sound gear is terrible, so i use an odac+o2, but let me tell you - its WAY too powerful for them, even when using unity gain. 
what you can do is lower digital volume, or get an impedance adapter like this one, which i got as an experiment and am happy to report that it works just fine, with no major alterations to the sound that my untrained ears can detect.

 

[xnor]

It depends on your headphone but these adapters with resistors will effectively raise the output impedance and can certainly change the sound signature. The ER4P to S adapter probably adds about 70 ohm (since it will turn a ~30 ohm P into a 100 ohm S model).

 

[leadbythemelody]

Hmm... that is interesting. Thank you for educating me haha. 

 

[xnor]

Ime, output impedance is the main reason for people hearing differences between amps. With less than 1/8th or 1/10th, or to be on the safe side close to zero ohms, the frequency response will remain "unchanged".
With increasing output impedance there will be peaks in the FR similar to what you see in the impedance plot of the headphone.
 
A 30 ohm headphone with a 60 ohm impedance peak at 100 Hz would result in a +2.5 dB peak with a 30 ohm output impedance. With 60 ohm output you'll get about +3.5 dB. Basically it works like a peak filter in a parametric EQ. Increase the output impedance and you'll increase the boost.
Some IEMs have a very weird impedance curve due to multiple crossovers, drivers .. so you could get a peak in the treble or even mids.
 
Everyone using a headphone amp should know that but sadly many don't (from what I can tell anyway).
 
---
 
As you wrote you could use digital attenuation if 1x gain is still too much. But you can also use an attenuator between your source and amp.

 

[adamlr]

Quote:

It depends on your headphone but these adapters with resistors will effectively raise the output impedance and can certainly change the sound signature. The ER4P to S adapter probably adds about 70 ohm (since it will turn a ~30 ohm P into a 100 ohm S model).

 
Quote:

Ime, output impedance is the main reason for people hearing differences between amps. With less than 1/8th or 1/10th, or to be on the safe side close to zero ohms, the frequency response will remain "unchanged".
With increasing output impedance there will be peaks in the FR similar to what you see in the impedance plot of the headphone.
 
A 30 ohm headphone with a 60 ohm impedance peak at 100 Hz would result in a +2.5 dB peak with a 30 ohm output impedance. With 60 ohm output you'll get about +3.5 dB. Basically it works like a peak filter in a parametric EQ. Increase the output impedance and you'll increase the boost.
Some IEMs have a very weird impedance curve due to multiple crossovers, drivers .. so you could get a peak in the treble or even mids.
 
Everyone using a headphone amp should know that but sadly many don't (from what I can tell anyway).
 
---
 
As you wrote you could use digital attenuation if 1x gain is still too much. But you can also use an attenuator between your source and amp.

i actually got a 200 ohm one. i was under the impression that it "adds" to the headphones impedance, making my 32 ohm cans into 232 ohm cans, i guess i was wrong? i must say i really dont notice a very big difference, but the way i test for changes is i listen to something new for a while until i feel used to it, then i go back to what i had before. i find differences are more apparent to me this way than plugging something new in and seeing whats up. in a week or so ill try again without the adapter. 
 
are you saying that bad impedance matching causes the peaks and nulls in the frequency response to become more extreme?
 
and how would one position an attenuator between source and amp? put the same plug on the cable going from odac into o2? or is it a different kind of plug?
 
again, this was only an experiment, im very comfortable using digital volume, i just wanted to see what would happen... 

 

[xnor]

Yeah, the resistance of the adapter adds to the load impedance so for the amp it's an easier load, after all it has to provide less current. Of course the headphone will only receive a fraction of the voltage that the amp outputs and that's the crux. 1 V will split at 0.5 V if the resistor and the impedance of the headphone are 30 ohm each. But if the headphone impedance rises at 100 Hz, which it usually does with dynamic headphones, let's say to 60 ohm the 1 V will now split at 0.333 V. The headphone now gets 0.666 V instead of 0.5 V causing the peak in the FR mentioned above.
 
From the drivers' point of view: If the diaphragm moves the driver generates voltage. If you short the driver (by having a close to zero output impedance) you will stop the diaphragm from vibrating more quickly. For the headphone it doesn't matter if the output impedance comes from resistance inside the amp, the cable, or resistors in adapters.
 
Yes, impedance matching is usually a bad idea with headphones and speakers though there are exceptions. Normally you want the output impedance to be a lot smaller than the load impedance.
 
I guess the attenuator would ideally be 1/8" to 1/8". I'm not sure such in-line attenuators are available, it would be a nice beginner DIY project though.

 

[adamlr]

Quote:

Yeah, the resistance of the adapter adds to the load impedance so for the amp it's an easier load, after all it has to provide less current. Of course the headphone will only receive a fraction of the voltage that the amp outputs and that's the crux. 1 V will split at 0.5 V if the resistor and the impedance of the headphone are 30 ohm each. But if the headphone impedance rises at 100 Hz, which it usually does with dynamic headphones, let's say to 60 ohm the 1 V will now split at 0.333 V. The headphone now gets 0.666 V instead of 0.5 V causing the peak in the FR mentioned above.
 
From the drivers' point of view: If the diaphragm moves the driver generates voltage. If you short the driver (by having a close to zero output impedance) you will stop the diaphragm from vibrating more quickly. For the headphone it doesn't matter if the output impedance comes from resistance inside the amp, the cable, or resistors in adapters.
 
Yes, impedance matching is usually a bad idea with headphones and speakers though there are exceptions. Normally you want the output impedance to be a lot smaller than the load impedance.
 
I guess the attenuator would ideally be 1/8" to 1/8". I'm not sure such in-line attenuators are available, it would be a nice beginner DIY project though.

that was a bit over my head im afraid = \
 
what was the bottom line? load impedance = headphone impedance (in this case ofcourse) right? when using the adapter like this:
 

do my 32 ohm headphones "become" 232 ohm headphones (assuming were measuring the same sine wave at the same set voltage and all that), or is my O2's output impedance of ~0.5 ohm "becoming" 200.5 ohm? or does it make no difference and the end result the same? i really dont notice alot of difference to the sound at all btw. again, im still getting used to it as it were, its only been a few days, and my ears arent exactly trained, but you say its usually noticeable at ~ 100 hz? if theres one thing id notice changing - its the bass. i gave a few tries with and without the adapter while listening to some bass heavy tracks and detected nothing. ok, no volume matching, but still. then again, perhaps there werent any frequencies of ~100hz recorded... meh...
 
and is this what you meant about attenuating the input stage? would this work? im afraid to try in case i kill something electronical 

(i recall reading the input jack has quite a high impedance anyway, but im still afraid of trying without consulting someone about it first.....)
 

 
thanks for all the explanations. this is like the #20 time you have explained things to me since i signed up to head-fi, much appreciated =]