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Topic: How to tell if an AMP/DAC/Soundcard is able to drive the headphones ? (Read 9754 times) previous topic - next topic
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How to tell if an AMP/DAC/Soundcard is able to drive the headphones ?

Let's use the AKG K701/702/712 (same specs) in this example.


AKG specs
-------------

Sensitivity headphones   105 dB SPL/V
Max. Input Power   200 mW
Rated Impedance   62 Ohms


Asus Xonar Essence STX
------------------------------

Code: [Select]
Output Signal-to-Noise Ratio (A-Weighted) (Front-out) : 124 dB
Output Signal-to-Noise Ratio (A-Weighted) (Headphone-out) : 117 dB
Input Signal-to-Noise Ratio (A-Weighted) : 118 dB
Output THD+N at 1kHz (Front-out) : >0.0003 %(-110 dB)
Output THD+N at 1kHz (Headphone-out) : >0.001 %(-100 dB)
Frequency Response (-3dB, 16bit/44.1KHz input) : 10 Hz to 90 KHz
Output/Input Full-Scale Voltage : Line output (RCA, 3.5) : 2 Vrms (5.65 Vp-p)
Output impedance: ~11 Ohms


O2+ODAC
-------------

Code: [Select]
DAC PERFORMANCE

Frequency Response    +/- 0.1 dB (10 hz – 19 Khz 24/44)
THD+N 100 hz 0 dBFS    0.0029%
THD+N 20 hz –1 dBFS    0.003%
THD+N 10 Khz –1 dBFS    0.003%
IMD CCIF 19/20 Khz –3 dBFS    0.0011%
IMD SMPTE –1 dBFS    0.0004%
Noise A-Weighted dBu 24/44    -102.8 dBu
Dynamic Range    > 110 dB A-Weighted
Linearity Error -90 dBFS 24/44    0.0 dB
Crosstalk 0 dBFS Line Out 100K    -93.5 dB
USB Jitter 11025 hz J-test 24/44    Excellent
Maximum Output Line Out 100K    2.0 VRMS
Distortion    < 0.005%

DATA SUPPORT

Audio Formats    16/44, 16/48, 16/96, 24/44, 24/48, 24/96
Interface    USB, Audio Class 1
Native Driver OS Support    Windows XP & Later, OS X x86, Linux
DIMENSIONS

Case Dimensions (mm)    108.50 x 80.00 x 29.50
Case Dimensions (in)    4.27 x 3.15 x 1.16
Weight    11oz

AMPLIFIER PERFORMANCE

Frequency Response    +/-0.1 dB (20Hz-20kHz)
THD 1 Khz 150 Ohms    0.0016%
IMD CCIF 15 Ohms    0.001%
IMD SMPTE    0.002%
Noise (ref 400 mV)    -105 dB
Max Output (33 Ohms)    613 mW
Max Output (150 Ohms)    355 mW
Max Output (600 Ohms)    88 mW
Output Impedance    0.54 ohms
Crosstalk (15 ohms)    -65 dB
Channel Balance (50% volume)    0.6 dB

CONFIGURATION

Gain    2.5x and 6.5x*
Volume Potentiometer Taper    Alps 15A or 3B

CONNECTIVITY

Analog Output    3.5mm or 6.35mm*
Analog Input    3.5mm
Digital Input    Mini-USB
DAC Line Output    3.5mm or RCA**
Power Input    14-20VAC
* Denotes Customization Option


For this question, which specs are important to look at ?

I just need some examples with this headphone, so I'll be able to do the same with my other headphones.

Another question: I'm using the SoX Resampler DSP set to 24/48 in foobar with the O2+ODAC, and in the sound control panel, in the preference for the O2+ODAC, it's set to 24/48. Is it redundant to have 2 resampler ? I mean, can I remove the resampler DSP from foobar and let the O2+ODAC do the resampling, or will it be DirectSound that will do it ? I'm using Wasapi Event mode.

Thanks HA

Alan

How to tell if an AMP/DAC/Soundcard is able to drive the headphones ?

Reply #1 –
Usually you would look at the impedance.

AFAIK normal generic headphones have 32 ohm impedance. The volume might be slightly lower than expected.

How to tell if an AMP/DAC/Soundcard is able to drive the headphones ?

Reply #2 –
Quote from: Makaki on
Usually you would look at the impedance.


There's a "magic" number, isn't there? Output impedance should be less than 1/n headphone impedance, and if I remember rightly (I have a problem with numbers, even single-digit ones) it is 8.

But does this mean that low-output-impedance is, simply, good for anything and everything, ie always good, or should those with higher-impedance 'phones use and amplifier with a higher output impedance?

I just changed from using 32-ohm ATH-AD900 to 300-ohm Sennheiser HD600. I had to turn the volume a long way up, until I remembered that the amplifier has a gain switch. It still worked at low gain, though, but lacked the potential for deafening volumes. I think that the O2 has  adjustable gain too. 

Can I bring volume/gain into this at the novice level, please?

As I understand it, an amplifier volume control attenuates the input level. The amplifier just amplifies that greater or lesser signal by the same amount: result, volume change. But what does a gain control do? Is it changing the actual amount of amplification? Or is this implementation specific?


 
The most important audio cables are the ones in the brain

How to tell if an AMP/DAC/Soundcard is able to drive the headphones ?

Reply #3 –
Quote from: Thad E Ginathom on
There's a "magic" number, isn't there? Output impedance should be less than 1/n headphone impedance, and if I remember rightly (I have a problem with numbers, even single-digit ones) it is 8.


1/8 or 1/10 are good rules of thumb. That ensures that frequency response is affected less than half a dB by any impedance irregularities.

Quote
But does this mean that low-output-impedance is, simply, good for anything and everything, ie always good


Pretty much, yes.

Quote
I just changed from using 32-ohm ATH-AD900 to 300-ohm Sennheiser HD600. I had to turn the volume a long way up


At the same voltage, 32-ohm headphones get much more power from the amp compared to 300-ohm ones, so you usually need a higher voltage / more volume using higher-impedance headphones. Lowering the impedance is a common trick to make loudspeakers more sensitive.

Quote
As I understand it, an amplifier volume control attenuates the input level. The amplifier just amplifies that greater or lesser signal by the same amount: result, volume change. But what does a gain control do? Is it changing the actual amount of amplification? Or is this implementation specific?


If it really is gain control, then it changes the amplification, but not all "gain controls" actually control gain - some are just additional volume controls.

How to tell if an AMP/DAC/Soundcard is able to drive the headphones ?

Reply #4 –
[quote name='Aldem' date='Nov 4 2014, 01:03' post='879462']
Let's use the AKG K701/702/712 (same specs) in this example.


AKG specs
-------------

Sensitivity headphones   105 dB SPL/V
Max. Input Power   200 mW
Rated Impedance   62 Ohms


Asus Xonar Essence STX
------------------------------

Code: [Select]
Output Signal-to-Noise Ratio (A-Weighted) (Front-out) : 124 dB
Output Signal-to-Noise Ratio (A-Weighted) (Headphone-out) : 117 dB
Input Signal-to-Noise Ratio (A-Weighted) : 118 dB
Output THD+N at 1kHz (Front-out) : >0.0003 %(-110 dB)
Output THD+N at 1kHz (Headphone-out) : >0.001 %(-100 dB)
Frequency Response (-3dB, 16bit/44.1KHz input) : 10 Hz to 90 KHz
Output/Input Full-Scale Voltage : Line output (RCA, 3.5) : 2 Vrms (5.65 Vp-p)
Output impedance: ~11 Ohms


O2+ODAC
-------------

Code: [Select]
DAC PERFORMANCE

Frequency Response    +/- 0.1 dB (10 hz – 19 Khz 24/44)
THD+N 100 hz 0 dBFS    0.0029%
THD+N 20 hz –1 dBFS    0.003%
THD+N 10 Khz –1 dBFS    0.003%
IMD CCIF 19/20 Khz –3 dBFS    0.0011%
IMD SMPTE –1 dBFS    0.0004%
Noise A-Weighted dBu 24/44    -102.8 dBu
Dynamic Range    > 110 dB A-Weighted
Linearity Error -90 dBFS 24/44    0.0 dB
Crosstalk 0 dBFS Line Out 100K    -93.5 dB
USB Jitter 11025 hz J-test 24/44    Excellent
Maximum Output Line Out 100K    2.0 VRMS
Distortion    < 0.005%

DATA SUPPORT

Audio Formats    16/44, 16/48, 16/96, 24/44, 24/48, 24/96
Interface    USB, Audio Class 1
Native Driver OS Support    Windows XP & Later, OS X x86, Linux
DIMENSIONS

Case Dimensions (mm)    108.50 x 80.00 x 29.50
Case Dimensions (in)    4.27 x 3.15 x 1.16
Weight    11oz

AMPLIFIER PERFORMANCE

Frequency Response    +/-0.1 dB (20Hz-20kHz)
THD 1 Khz 150 Ohms    0.0016%
IMD CCIF 15 Ohms    0.001%
IMD SMPTE    0.002%
Noise (ref 400 mV)    -105 dB
Max Output (33 Ohms)    613 mW
Max Output (150 Ohms)    355 mW
Max Output (600 Ohms)    88 mW
Output Impedance    0.54 ohms
Crosstalk (15 ohms)    -65 dB
Channel Balance (50% volume)    0.6 dB

CONFIGURATION

Gain    2.5x and 6.5x*
Volume Potentiometer Taper    Alps 15A or 3B

CONNECTIVITY

Analog Output    3.5mm or 6.35mm*
Analog Input    3.5mm
Digital Input    Mini-USB
DAC Line Output    3.5mm or RCA**
Power Input    14-20VAC
* Denotes Customization Option


For this question, which specs are important to look at ?

From the Xonar:

Output/Input Full-Scale Voltage : Line output (RCA, 3.5) : 2 Vrms (5.65 Vp-p)
Output impedance: ~11 Ohms

From the O2:

Code: [Select]
Max Output (33 Ohms)    613 mW
Max Output (150 Ohms)    355 mW
Max Output (600 Ohms)    88 mW
Output Impedance    0.54 ohms
[code]

But the Max output numbers are  not in terms of voltage.

I've done the arithmetic and obtain:

[code]
Power    Impedance    Voltage
0.633    33    4.57
0.355    150    7.30
0.088    600    7.27
[/quote]

The specs of the headphones are:

[code]
Sensitivity headphones    105 dB SPL/V
Max. Input Power    200 mW
Rated Impedance    62 Ohms


and converting that into volts:

200 mw into 62 ohms = 3.52 volts

3.52 volts is about 11 dB over 1 volt, so the max SPL rating of the phones is 116 dB

The Xonar puts out 5.5 v p-p which is 2 volts.  2 volts is 6 dB over 1 volt, so it will drive the headphones to about  111 dB.

IMO either amp is more than sufficient.

How to tell if an AMP/DAC/Soundcard is able to drive the headphones ?

Reply #5 –
Quote
I just changed from using 32-ohm ATH-AD900 to 300-ohm Sennheiser HD600. I had to turn the volume a long way up...
Electrical power (watts or milliwatts) can be calculated as (voltage squared)/resistance.  With all else being equal, you'll get about ten times as much power into 32-Ohms as you'll get into 300-Ohms.

If the headphones are equally energy-efficient (or anywhere close) the 32-Ohm headphone will be louder.

If you look at power amplifier specs, you'll frequently find the amp is rated at twice the power at 4-Ohms compared to 8-Ohms.

Solid state amplifiers are "constant voltage" devices.    That means that under normal operating conditions the output voltage doesn't change when you change the load impedance. 

A theoretically ideal amplifier would have a source impedance of zero and infinite current capability, so it would put-out the same voltage no matter what the load.
 

How to tell if an AMP/DAC/Soundcard is able to drive the headphones ?

Reply #6 –
Quote from: julf on
... ... ...

If it really is gain control, then it changes the amplification, but not all "gain controls" actually control gain - some are just additional volume controls.


So gain really does (or, at least, should)  mean gain. Sometimes the simple is the last thing one expects!

Thank you for that and your other replies to my post.
The most important audio cables are the ones in the brain

How to tell if an AMP/DAC/Soundcard is able to drive the headphones ?

Reply #7 –
Quote from: Thad E Ginathom on
Quote from: julf on
... ... ...

If it really is gain control, then it changes the amplification, but not all "gain controls" actually control gain - some are just additional volume controls.


So gain really does (or, at least, should)  mean gain. Sometimes the simple is the last thing one expects!

Thank you for that and your other replies to my post.


I think in this context gain refers to boosting the output signal to higher voltage than the input, whereas volume control is usually attenuation of the amplifier output (so only reducing volume/gain).  So an amplifier that takes a 1 Vrms input and at full volume produces a 5 Vrms output would have a gain of 5.  Since most headphones are driven by no more than a volt or two, and line level is about a volt, gain is usually close to 1.

How to tell if an AMP/DAC/Soundcard is able to drive the headphones ?

Reply #8 –
Quote from: Arnold B. Krueger on
and converting that into volts:

200 mw into 62 ohms = 3.52 volts

3.52 volts is about 11 dB over 1 volt, so the max SPL rating of the phones is 116 dB

The Xonar puts out 5.5 v p-p which is 2 volts.  2 volts is 6 dB over 1 volt, so it will drive the headphones to about  111 dB.

IMO either amp is more than sufficient.


Shouldn't you also take in to account the output impedance of the Soundcard? 5.5v p-p is only with a 0ohm load right?

I have a Xonar DS (with the same p-p voltage) a O2 amp and the Q701's, once you start applying Replay gain, or watching movies the standard 2.5X (+8dB~) gain resistor is useful, though the actual headphone jack (on the front of the PC) is a bit louder than the line-out, which I haven't tried in a while.

Though I think another thing to take note of is that Op-Amps start to distort on high voltages under low impedances, NwAvGuys blog has a bunch of stuff about this.

The standard O2 amp starts to distort massively @ 5v on a 150ohm load, and 15ohm load @ 2v

http://nwavguy.blogspot.co.nz/2011/08/o2-details.html

CTRL + F "LOW POWER DISTORTION & OUTPUT:" see graph there.

How to tell if an AMP/DAC/Soundcard is able to drive the headphones ?

Reply #9 –
Quote from: YellowOnion on
Quote from: Arnold B. Krueger on
and converting that into volts:

200 mw into 62 ohms = 3.52 volts

3.52 volts is about 11 dB over 1 volt, so the max SPL rating of the phones is 116 dB

The Xonar puts out 5.5 v p-p which is 2 volts.  2 volts is 6 dB over 1 volt, so it will drive the headphones to about  111 dB.

IMO either amp is more than sufficient.


Shouldn't you also take in to account the output impedance of the Soundcard? 5.5v p-p is only with a 0ohm load right?


The manufacturer's spec of 200 mW takes the headphone amp's source impedance into account.