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Do I need a Headphone Amp?
YellowOnion
post May 4 2012, 02:52
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I have a Xonar DS, and a pair of PC-151 Sennheisers They're perfectly fine volume.

but I'm looking at replacing the headset with headphones and a modmic attachment, I'm currently looking at the AKG Q701 since all reports seem to say they are $500 headphones but amazon has them for $250 and anything of comparison is in the $400 range.

My worry is that they'll be too quiet, I've been calculating the peak SPL via some equations on NwAvGuy's blog and the peak will be somewhere around 10dB less than my current ones, setting windows volume to -10.5dB (50%) the volume is probably getting far too low (replay gain seems to apply about -9.50dB on the reference song to begin with)

for reference,

the PC-151's are 118dB/V and 32ohm, or 103dB/mW via the equations

and the Q701's are 105dB/V and 62ohm or 93dB/mW

I'm pretty sure that this is a different measurement to the typical Volume on your computer.

Also my Soundcard's docs say that it outputs 1Vrms with Peak to peak 3V no indication of ohms

I live in NZ so I would rather not have to do two shipments so testing by ear I would rather leave as a last resort

Any help would be great
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skamp
post May 4 2012, 09:59
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My only reference is my laptop's integrated audio and my FiiO E7. With my relatively sensitive headphones (100-106dB/mW), the former is too quiet, and with replaygain on, the latter is set at 2/3 the maximum volume already. The E7 measured at 113mW into 15 ohms (no idea how much it outputs into my 25-32 ohm loads).

So my gut feeling is that you will need an amp for the Q701 indeed, preferably with an output impedance of less than 8 ohms. Xonar soundcards are known to have relatively high output impedance. The FiiO E9 would deliver enough power to drive the Q701, though the 1/4" jack has an output impedance of 10 ohms, which is close enough I guess, but not strictly ideal. NwAvGuy's own Objective 2 amp would be more than adequate and would give you piece of mind, though it costs a bit more than the E9. There are many other amps out there, but none that I know of that were measured.

If it were me buying such (somewhat expensive) headphones, I'd make sure they were driven properly. I'd go for the O2 and be done with it.


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See my profile for measurements, tools and recommendations.
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probedb
post May 4 2012, 14:37
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I also have an E7 but I have rather sensitive IEMs (Westone UM3x) and the main difference for me is that the E7 output is silent, whereas there is low level noise on the PCs internal card. This goes away with a much cheaper and less sensitive set of IEMs.
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DVDdoug
post May 4 2012, 18:28
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QUOTE
I live in NZ so I would rather not have to do two shipments so testing by ear I would rather leave as a last resort
It's a good idea to make some calculations/estimations before making a decision. But either way, you are taking a gamble... You can only hope to maximize the odds of making a good bet. wink.gif

QUOTE
setting windows volume to -10.5dB (50%) the volume
Are you sure that's -10.5dB? (When I adjust Windows volume I don't see a dB reading...)

How loud do you normally listen? With your current headphones, do you have the volume at or near the maximum? Or when you crank it up to maximum, is it "way to loud" or "just a little too loud?"

If you like to listen loud and you're worried about the new headphones not being loud-enough, it seems like the best "bet" is to order the amp.

If you like to listen loud once in awhile, another option is to use the Sennheisers when you're in the mood for loud music.


QUOTE
...the PC-151's are 118dB/V...

...and the Q701's are 105dB/V ...
Solid state amplifiers (and soundcards) are essentially "constant-voltage" devices (until you load them with too-low of an impedance). So, I'd say you're looking at a 13dB difference! The difference could be a little less if you're current 32 Ohm headphones are "loading" the output, but I wouldn't count on that.

3V P-P is about 1V RMS, so you should be able to get 105dB SPL (peak) when ReplayGain is not limiting the volume.

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YellowOnion
post Jun 10 2012, 14:56
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First off I would like to apologise for taking so long to reply, been busy and I'm never good at remember things.

QUOTE (DVDdoug @ May 5 2012, 05:28) *
Are you sure that's -10.5dB? (When I adjust Windows volume I don't see a dB reading...)


if you right click on the percentage meter, you get an option to change to dB.



QUOTE
How loud do you normally listen? With your current headphones, do you have the volume at or near the maximum? Or when you crank it up to maximum, is it "way to loud" or "just a little too loud?"


Along the lines of "a little too loud" sometimes I'll max them out but can't stand it for longer than a hour or so (this is with replay gain though).

I usually throttle back the volume on the headset by about maybe 90% via the inline adjustment for most things.


The other thing is I'm somewhat intrigued by wiring up my own Headphone Amp I haven't done electronics since High-school so I will be extremely rusty and have no equipment.
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stephan_g
post Jun 10 2012, 16:30
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QUOTE (YellowOnion @ Jun 10 2012, 14:56) *
if you right click on the percentage meter, you get an option to change to dB.
[image]

Cool, I didn't know this existed. You live and learn. Seems to be for that particular dialog only, but hey, better than nothing. With an ALC262 the adjustment range is -46.5 dB over ~-10 dB at center position to 0 dB. That sort of response was inspired by fader pots, I guess, but I'd prefer something a little closer to a pure log response.

QUOTE (YellowOnion @ Jun 10 2012, 14:56) *
QUOTE
How loud do you normally listen? With your current headphones, do you have the volume at or near the maximum? Or when you crank it up to maximum, is it "way to loud" or "just a little too loud?"

Along the lines of "a little too loud" sometimes I'll max them out but can't stand it for longer than a hour or so (this is with replay gain though).

I usually throttle back the volume on the headset by about maybe 90% via the inline adjustment for most things.

Haven't you noticed the sound change when doing so? Most inline volume adjustments are simple pots wired in series with the drivers, and headphone drivers generally have a non-constant impedance. I'd expect things to become noticeably more bassy.

Speaking of which, the headphone out is likely to have non-zero output impedance to begin with. For a cap-coupled output on the usual Realtek chips, for example, the manufacturer recommends 75 ohms. This gives a nominal 10.5 dB level reduction on nominal 32 ohm headphones, reduced to about 7 dB with 60..64 ohm cans like K/Q70x. So you'd still end up with about 6 dB less than now.

That seems plausible. These sound chips usually output a hair over 1 Vrms maximum, which in real life should be good for a little over 100 dB SPL. However, you lose 7 dB in the output resistor, so you end up in "usually OK, but not generous" territory.

QUOTE (YellowOnion @ Jun 10 2012, 14:56) *
The other thing is I'm somewhat intrigued by wiring up my own Headphone Amp I haven't done electronics since High-school so I will be extremely rusty and have no equipment.

Now that sounds like fun. Unfortunately, these AKGs are in the slightly more demanding camp. You'd probably get passable results with a 4556-based cMoy (split voltage supply preferred), though I would prefer a buffered concept ( la Apheared-47, but again using the 4556).

In terms of finished products, you'd have to be looking at a FiiO E9 (mains-powered) or E11 (portable) minimum. While not terribly expensive for what they do, they still cost a good bit more than a plain cMoy or similar DIY amp in an Altoids tin.

This post has been edited by db1989: Jun 10 2012, 21:15
Reason for edit: removing unnecessary repeated image
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Happy Camper
post Jun 10 2012, 21:12
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The 701s are a 62 ohm impedance can and AKG states a maximum input of 200 mw. By experience, I'd say that is continuous. They do need to be given some power to sound like they're are capable of. Trying to power them off a sound card will usually sound dull with terrible bass response. Find yourself a .5 watt amp to handle the peaks and you will find a very good headphone. Not as bass heavy as others but the soundstage is special and if your source isn't bright, I think they are pretty darned good.
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YellowOnion
post Jun 10 2012, 23:43
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QUOTE (stephan_g @ Jun 11 2012, 03:30) *
QUOTE (YellowOnion @ Jun 10 2012, 14:56) *
if you right click on the percentage meter, you get an option to change to dB.
[image]

Cool, I didn't know this existed. You live and learn.



I'm a bit of a perfectionist, and so I usually explore things in-side out for optimal performance and found this.

QUOTE
I'd expect things to become noticeably more bassy.

Actually if anything, it is less bassy, but not very noticeable without testing.

QUOTE
Realtek chips


How much different would the Xonar be? I haven't found much information on it, and I don't usually use my Realtek unless I'm on voice chat and use it as a separate out.

QUOTE
Now that sounds like fun. Unfortunately, these AKGs are in the slightly more demanding camp. You'd probably get passable results with a 4556-based cMoy (split voltage supply preferred), though I would prefer a buffered concept ( la Apheared-47, but again using the 4556).

In terms of finished products, you'd have to be looking at a FiiO E9 (mains-powered) or E11 (portable) minimum. While not terribly expensive for what they do, they still cost a good bit more than a plain cMoy or similar DIY amp in an Altoids tin.


I'm actually thinking of the O2 Amp, NwAvGuy the guy who designed it said it's been independently verified as transparent on the DAC1 Pre, I just have to wire it to specification. and it's not badly priced either, maybe $100 if I assemble one myself.
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YellowOnion
post Jun 10 2012, 23:56
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QUOTE (Happy Camper @ Jun 11 2012, 08:12) *
The 701s are a 62 ohm impedance can and AKG states a maximum input of 200 mw. By experience, I'd say that is continuous. They do need to be given some power to sound like they're are capable of. Trying to power them off a sound card will usually sound dull with terrible bass response. Find yourself a .5 watt amp to handle the peaks and you will find a very good headphone. Not as bass heavy as others but the soundstage is special and if your source isn't bright, I think they are pretty darned good.


I had a look a some measured frequency response graphs on Inner Fidelity, and the the AKG's are comparible in price to the HD 558's but have far flatter bass-reponse, and the HD 558's drop off earlier, not so flat phase-response, and larger difference between the left and right drivers which is I assume the major reasons for the AKGs great sound-stage, but they're also far more efficient and may not need an Amp to get volume, but the low output impedance on the O2 will give me a better sound on both headphones, anyway.

Also, what do you mean by Continuous?
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Happy Camper
post Jun 11 2012, 02:21
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An amp that can provide 200mw continuous power to the headphone. I can tell you the 701/2 is one of the more difficult hps to drive. A portable amp won't typically do it. Go to Head Fi and type in K701 in the Full Sized Amps section. You will find many of us that liked the 701 sound had a difficult time finding quality power until we got into decent sized amps with stout power supplies. Many still believe a SS amp is needed but a quality tube amp can also push them.

This post has been edited by db1989: Jun 11 2012, 11:49
Reason for edit: deleting unnecessary full quote of above post
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stephan_g
post Jun 11 2012, 10:58
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InnerFidelity measurements of various specimen are showing around 300 mVrms for 90 dB SPL at 1 kHz, at impedances of 60..65 ohms. So they need levels comparable to 250 ohm Beyers or higher than 300 ohm Sennheisers, but are obviously a good deal more power-hungry and more of a load on the output stage. Much like ye olde HD570 back in the day (which had a heavy "bathtub type" response and accordingly lost sensitivity in the mids).

An O2 is another amp that should be fine for them.
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Arnold B. Kruege...
post Jun 12 2012, 13:11
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QUOTE (stephan_g @ Jun 11 2012, 05:58) *
InnerFidelity measurements of various specimen are showing around 300 mVrms for 90 dB SPL at 1 kHz, at impedances of 60..65 ohms. So they need levels comparable to 250 ohm Beyers or higher than 300 ohm Sennheisers, but are obviously a good deal more power-hungry and more of a load on the output stage. Much like ye olde HD570 back in the day (which had a heavy "bathtub type" response and accordingly lost sensitivity in the mids).

An O2 is another amp that should be fine for them.


A resaonable person would obtain the headphones, plug them into the best of what they have, and see what they think.

If that doesn't do it for them, then they should spend the chump change on a Boosteroo or a Fiio E5.

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stephan_g
post Jun 12 2012, 15:47
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Oops, looks like there's a question I missed earlier...
QUOTE (YellowOnion @ Jun 10 2012, 23:43) *
QUOTE
Realtek chips


How much different would the Xonar be? I haven't found much information on it, and I don't usually use my Realtek unless I'm on voice chat and use it as a separate out.

Good question. People have indeed complained about low headphone volume on the DS, and if this thread is any indication, this may be related to substantial output impedance. I'd be tempted to poke around on such a card with a multimeter...

I was mistakenly assuming you were using the onboard sound earlier. How does that one compare to the Xonar in terms of volume?
QUOTE (Arnold B. Krueger @ Jun 12 2012, 13:11) *
A resaonable person would obtain the headphones, plug them into the best of what they have, and see what they think.

*looks up definition of 'reasonable person'*
Hmm... Can you eat that?

All kidding aside, that can be a little risky these days. What if the best is an iPod Classic, Euro firmware (barely sufficient for 90 dB at 0 dBFS)?

But speaking of listening, doing that before buying is, in general, highly recommended. K701s definitely are not everyone's cup of tea, being on the lighter side of things (and I can't really imagine that a PC151 would also be, so they might come as a bit of a shock). I don't know what the options are down in NZ though.
QUOTE (Arnold B. Krueger @ Jun 12 2012, 13:11) *
If that doesn't do it for them, then they should spend the chump change on a Boosteroo or a Fiio E5.

Now there's a blast from the past - I haven't seen a Boostaroo mentioned for many a year. What's inside of them these days? Back in the day when Dan "Dan's Data" Rutter reviewed one, he found a bunch of TDA7050s. (The datasheet of which does a pretty good job at hiding their performance characteristics, except for noise which seems to be enough to be on the threshold of audibility with K701s.)

The E5 seems to be running out in favor of the E6. Which, overall, is the better choice performance wise (review), but it sure is a bit of a pity that the nice metal case had to go. 8 dB of gain is decent, and it should manage about 1.5 V into K701s. It's not too practical for stationary use, but that's common to most any kind of battery-operated device.
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Arnold B. Kruege...
post Jun 13 2012, 12:40
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QUOTE (stephan_g @ Jun 12 2012, 10:47) *
Oops, looks like there's a question I missed earlier...
QUOTE (YellowOnion @ Jun 10 2012, 23:43) *
QUOTE
Realtek chips


How much different would the Xonar be? I haven't found much information on it, and I don't usually use my Realtek unless I'm on voice chat and use it as a separate out.

Good question. People have indeed complained about low headphone volume on the DS, and if this thread is any indication, this may be related to substantial output impedance. I'd be tempted to poke around on such a card with a multimeter...

I was mistakenly assuming you were using the onboard sound earlier. How does that one compare to the Xonar in terms of volume?
QUOTE (Arnold B. Krueger @ Jun 12 2012, 13:11) *
A resaonable person would obtain the headphones, plug them into the best of what they have, and see what they think.

*looks up definition of 'reasonable person'*
Hmm... Can you eat that?

All kidding aside, that can be a little risky these days. What if the best is an iPod Classic, Euro firmware (barely sufficient for 90 dB at 0 dBFS)?


OT comment? I thought we were talking about PCs.

I think I get the motivation for some of the questions. The actual motivation may be that people have a certain target cost in mind, and want to know whether they have to budget another $500 for a suitable headphone amp in addition to the $500 or so for the headphones themselves.

QUOTE
But speaking of listening, doing that before buying is, in general, highly recommended. K701s definitely are not everyone's cup of tea, being on the lighter side of things (and I can't really imagine that a PC151 would also be, so they might come as a bit of a shock). I don't know what the options are down in NZ though.


As long as NZ has a working post office, package delivery companies, and their currency is honored internationally, they have the same options as the rest of us. I've given up on brick-and-mortar stores for audio for at least a decade.


QUOTE (Arnold B. Krueger @ Jun 12 2012, 13:11) *
If that doesn't do it for them, then they should spend the chump change on a Boosteroo or a Fiio E5.


QUOTE (stephan_g)
Now there's a blast from the past - I haven't seen a Boostaroo mentioned for many a year. What's inside of them these days? Back in the day when Dan "Dan's Data" Rutter reviewed one, he found a bunch of TDA7050s. (The datasheet of which does a pretty good job at hiding their performance characteristics, except for noise which seems to be enough to be on the threshold of audibility with K701s.)


It has been years since I bench-tested mine, but if memory serves all noise and artifacts are at least 90 dB down if you don't clip it like an idiot. You're right, the TDA7050 was not exactly designed for thrilling perfectionists. I worked a cheap, effective and low-calorie upgrade on mine. I built two dummy AA cells by cutting pieces off of a wood dowel from the hardware store, drove a brass screw into one end of each dowel, soldered on wires that ran to a 5 vdc wall wart. This added several dB of headroom and made it into a worthy desktop PC add-on.

QUOTE (stephan_g)
The E5 seems to be running out in favor of the E6. Which, overall, is the better choice performance wise (review), but it sure is a bit of a pity that the nice metal case had to go. 8 dB of gain is decent, and it should manage about 1.5 V into K701s. It's not too practical for stationary use, but that's common to most any kind of battery-operated device.


You didn't notice the USB power socket?
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