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scanfiend

Headphone Amps - some random musings

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Hi fellow forumers! I know there is a keen interest amongst many of us on headphone amps. Below is a cut and paste from various threads in different forums on the matter. I've saved the posts that I feel that is most relevant, and they don't necessarily come from the same thread, so it may read a little disjointed. :P

 

I do think it's informative, and if nothing else, should generate some great discussion in Sgheadphones (I hope) :D

 

Happy reading!

 

----------------------------------------

[Tomb-headfi]

Your conjecture is somewhat close, but you don't get a cigar, yet.

 

You are confusing a volume control with amplification. Even the lowliest portable can drive many heaphones to ear splitting volumes. However, most of that volume will be produced by the peak power capability of the amplifier circuit at a very limited set of frequencies, and the rest will be distortion.

 

As a for instance, one of the first introductions to hi-fidelity sound is that you notice that higher quality equipment can produce higher volume without as much irritation. Most easily see this comparison with speakers; it is very little different with headphones.

 

Music consists almost entirely of transients on top of a baseline of more-or-less constant tone, depending on the music. Quality amplification (translated: separate headphone amp) will have plenty of power to produce the constant tone for an overall acceptable volume level, but will also have plenty of power in reserve for any transients. Besides transients, there is also the problem of differing power levels needed for different frequencies. Bass frequencies require more energy and require more power. There again, another reason for a huge amount of power over and above the simple rating of a headphone's Sound Pressure Level (SPL) efficiency.

 

All of this is pretty much an afterthought in basic component players, including iPods, etc. There are many more design considerations to deal with that have a greater influence on affecting overall product design. That's one of the reasons you see only earbuds or very efficient headphones with portables. They simply do not have the necessary design for a better power supply. Simple Physics dictates that more power is possible with much less effort if the voltage is higher (Power is dependent on the current squared). Unfortunately, batteries are probably more limited in voltage than current, but pretty much limited in both.

 

That's why you a see a culture of headphone amplifiers with power supplies up to 24V, and many with batteries up to 18V. It simply isn't possible for mfrs to include this stuff in portables meant for the masses. So, the extra headphone amp is all to ensure that every frequency, every transient gets all the power a quality pair of headphones want. The result is not necessarily an ability to turn the volume up, but a crispness, airiness, and prescence that never existed before in your headphone listening.

 

[Mulveling-headfi]

First of all, forget the misconception that the purpose of hifi headphones amps is just to go louder - it's about higher quality at comparable volumes.

 

Anytime you listen to headphones, you're using an amplifier to drive them. The amplifier could be the built-in amp from an ipod, a dedicated headphone amp, or sometimes people even use the output stage of their source as the amp. When you plug your headphones into a receiver or integrated sepaker amp, a numer of things could be happening:

 

1) the headphone jack is driven by a headphone amp stage built into the receiver; usually of exceeedingly poor quality

 

2) the jack is powered by the preamp stage of the receiver

 

3) the jack is powered by the power amp stage with resistors added to bring the level down

 

It is true that amplifiers cannot mitigate distortions from a source. However, amplifiers always add distortion of their own, and this is often what audiophiles seek to minimize by replacing the low quality "stock" headphone amps with a higher quality one. Note that this point is sort of debatable though - some types of distortion are considered euphonic in moderate amounts, while other kinds of distortion sound awful even in small amounts.

 

Anyways, the point is that amplifiers sound different because they add different types and amounts of distortion to the signal. Cheap amps (usually the kind that are built in) often add judicious quantities of the bad, non-euphonic kind of distortion. Also of importance is that an amplifier will often output increased distortion when driving a load it wasn't designed (or not properly designed) to drive. Here's where we get into the need for a powerful dedicated headphone amp - low impedance headphones need an amp with high current capabilities, else the amp will be strained (and distort more). High impedance headphones require a higher voltage swing (again, else distortion). High quality amps will typically be capable of large current and voltage swings, keeping distortion low over a wide rage of headphone impedances. The output impedance of the amp also affects distortion. High output impedance will cause distortion, but the quick fix (global negative feedback) itself is considered to cause very non-euphonic distortion. There are many design considerations to an amp that all affect the sound.

 

A single transistor or opamp can't come close to doing the job right, which is why high end amp design is complicated and why the cheap built-in amps sound like crap.

 

Sometimes you'll see people chain a higher quality amp after a lower quality amp stage, ie: using a dedicated headphone amp from the ipod headphone jack. At first such an arragnement seems counterproductive - why would you want to add the distortion from two amps into the signal chain - however it's not necessarily as bad as it seems. By feeding the ipod amp into another amp, you're presenting the ipod a different load than that of a headphone. Typically, the input impedance of an amp is very high (10,000 - 100,000 ohms, compared to 32 - 300 for headphones), which is easier to drive (meaning lower distortion) for many preamp and headamp stages. Same with people who are using their sources (ie: soundcard) to directly drive headphones. By adding a dedicated amp, they take the burden off the source's output stage so that the overall distortion goes down (or becomes more euphonic ).

 

[Tomb-headfi]

Yep, you are correct - IMHO. Personally, I prefer 1/2 to 3/4 of the volume control, but it depends on quality of the source. You are correct to suspect that you can start clipping with the source prior to an amp if the volume is too high (assuming no line out, of course).

 

Turn the volume too low, and your amp may be amplifying more noise than signal. I truly believe that without a line out, it's an experimental process.

 

----------------------------------------

 

[NotJeffBuckley-Hydrogenaudio]

Huh. I didn't know you post here, MirrorSaw. Yeah, you need a headphone amplifier to adequately power high- and low- impedance headphones; low impedance headphones require more current to accurately reproduce bass frequencies (and thus benefit more from large coupled capacitors, such as the 2200 microfarads found in the PA2V2 or the 1800 microfarads in the Go-Vibe), while high impedance headphones require more voltage to excurse the drivers and avoid op-amp clipping.

 

The current provided by a typical portable audio player is usually less than 15ma per channel, which can lead to notable distortion with low impedance headphones that require more current draw - I'm not sure to which headphones you refer when you say "overwhelming majority;" I'm sure many of the exceptionally sensitive cheap headphones designed specifically for volume headroom and tuned for bass resonance are more than adequately driven by a portable player's voltage swing of less than 2v at less than 30ma total output current, but I wouldn't want to use less sensitive 32ohm headphones with any less than 50ma per channel available. Further, the capacitors are there primarily for dynamic headroom;

 

they supply current for particularly taxing excursions where an op-amp's steady output would be insufficient. That's the "real purpose" of coupled output capacitors, nothing nefarious there (although I agree that 2200microfarad is rather in excess of what is necessary, especially with a low voltage op-amp, but it extends the flat response considerably beyond the audible spectrum and into sub/hypersonics).

 

[steve999-Hydrogen Audio]

 

May I add..... buyer beware!!!

 

Headphone amplifier channel balance for low-level listening can be a major issue too, IMHO. Noise can be an issue both in terms of noise floor due to too high gain or just poor s/n ratio, and in terms of ground hum noise. Noise tends to be more of an issue with very sensitive low impedence phones like the MDR-V6s, especially if the gain is too high. An amp's ability to work around difficult ground-loop hum issues can be quite important, IMHO. These issues are what separate the good stuff from the just okay stuff, in my experience. A near-0 ohm impedance headphone amp will usually have the least impact on frequency response, though some phones are designed to be driven from an industry-standard 120-ohm jack. Some smaller battery-powered amps will have trouble driving very low-impedence phones without some small amount of bass rolloff (the ipod photo headphone out had this problem, as I understand it).

 

The biggest problem with high-impedence, low sensitivty phones like the HD600 and HD650 is usually not noise or channel balance at low levels but just getting them loud enough without pushing the amp's performance limits too far (resulting in clipping or distortion), and this is usually only an issue with battery-powered portable equipment. Most things that you plug in a wall will drive them very comfortably.

 

I use a Behringer UB802 mixer. The input gain is adjustable on two channels if you are a perfectionist. Or you can just use other channels with fixed gain. It drives my Senn HD580s and Beyer DT880s very easily, and my Sony MDR-V6s very quietly. My confidence in my UB802 increased when a friend took measurements on its big brother, the UB1202, and it did quite well for noise, frequency response, and distortion. Though I am not the expert on this stuff. The UB802 mixer also has bass, mid, and treble controls, and multiple inputs and outputs. And panning controls that you can use as a primitive (but continuously variable) crossfeed for old recordings with excessive or tacky stereo separation. And pretty flashing lights. Price: $60.

 

Expensive headamps edge on over into snake-oil-ville as price increases, IMHO. In many circumstances, a home receiver or home CD deck (with headphone jack) or computer sound card will provide solid amplification even with the HD600s or HD650s, IMHO. As to whether one could hear a difference versus an expensive headphone amp in an ABX test, I make no claims. I can tell you based on experience that any difference is not worth it to me, though. A $100 portable amp could be genuinely useful if you are going to use such hard-to-drive headphones as the HD600 or HD650 portably. Thing is, you could get a second pair of really nice and more practical headphones for portable use for the price of that portable amp.

 

If someone is thinking of paying $200 or $300 or more for the meager amount of amplification needed to drive a pair of headphones, I suggest taking the time to come to a better understanding of what you are paying for. :P If someone at hydrogen audio asserts you need to pay that much for transparent headphone amplification, I say prove it. What is it -- T.O.S. 8? :blink:

 

 

[niktheblak-Hydrogen audio]

 

I do notice that you used the phrase "get the proper sound out of them..." ... if "proper" means loud, then yes, you'll need a headphone amp to drive them to loud levels. If "proper" means a pleasant sound at decent normal listening levels, then a special headphone amp is not required.

 

Unfortunately just 'loud' doesn't quite cut it. The problem with computer/other line-outs is that they generally have high-impedance output and expect a very high-impedance load, such as 30,000Ω amplifier input. When someone plugs a 60Ω headphone into a line-out expecting 30,000Ω load, the frequency response characteristics of the line-out may change considerably. Probably the single most common phenomenon is attenuation of lower frequencies since they usually have the lowest impedance in most headphones. So you can achieve a sound that is 'loud' but still lacks a major proportion of the spectrum. Also when volume (load) is yet increased with such an underpowered source, pretty much anything can happen to the frequency response curve, but it almost certainly won't be flat. And at this point we've drifted a long way away from 'hi-fi'.

 

So basically a headphone amp's most useful purpose is to perform impedance matching between line-out and a pair of headphones. If you already have a low-impedance output expecting a low-impedance load (such as high quality headphone output of a mixer table), then you shouldn't have major problems driving headphones and don't need a headphone amp.

 

----------------------------------------

 

[Wikipedia]

On the other hand, the final power amplifier stage of a typical audio device often introduces distortion. But "line out" is derived from some point before that final amplification takes place. So "line out" signals tend to be of higher quality than those from a speaker (or headphone) connector.

 

"Line in" expects the kind of signal "line out" provides. So you can typically connect the "line out" connector of one device with the "line in" of another. However, if you do this with a straight cable, and both devices are AC powered, you may run into ground - loop - hum.

 

A typical "Line in" inputs is actually a high impedance input with an impedance of around 10,000 ohms. When a "Line out" signal output, with its impedance of around 100 ohms, is connected to a high impedance "Line in" input like this one, the result is that most of the voltage (over 99%) appears across the input resistance, and almost none of the voltage is dropped across the output impedance. This is the desired effect. Since the impedances are far from matched, very little power is transferred, but the goal is not power transfer, it is voltage transfer. These are voltage signals (as opposed to current signals*) and it is the signal information that is desired, not power to drive a transducer (e.g. speaker) or (transmitting) antenna.

 

[Cnet Audio Glossary]

An audio jack on a sound card or other media device that outputs line-level (0.5- to 2-volt) analog signals. Suitable for sending signals to stereos, tape decks, and so on. By contrast, a headphone output can produce signals 10 or more times that strength.

 

Edited by scanfiend

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Guest joi-ful

:thumbup:

Two thumbs up for you! That's really really useful for newbies like me. Make it a STICKY!! :grin:

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Great information reads you got for us, Scanfiend. Thanks. I second joi-ful's suggestion to make it a Sticky... as now only understand bits of it, and they are certainly useful to be re-visited when more experiences gained thro more audio equipments tried and more listening sessions. Looking forward to Top-Gun's contributions. Cheers.

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A lot of this is true, but it should not be taken as absolute or always true. For example running many headphones from an iPod Touch (Shure 940, Phiaton MS400, Beyer DT48E, Philips Stretch, B&W P5, Senn PX series etc.), at average to semi-loud volumes there are no problems at all even with demanding music except for the inherent inferiority of the iPod Touch's amps compared to a good headphone amp. Then there is also the bad news about headphone amps. If you have a headphone that's borderline bright which might be irritating on some tracks, it can actually get worse with many headphone amps, even thought it's technically "better". Now some people might say it's still better to go for the better fidelity, but the bottom line is your listening enjoyment. If your listening enjoyment is compromised by being chained to a non-portable amp, or by having to lug around a "portable" amp that's not pocketable and inconvenient to carry, then you defeat your purpose. And since different amps sound different, you need to evaluate one that works best with your headphone(s), in a very quiet place where you can hear the tiny differences that justify the amp. Good luck on that.

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Hi fellow forumers! I know there is a keen interest amongst many of us on headphone amps. Below is a cut and paste from various threads in different forums on the matter. I've saved the posts that I feel that is most relevant, and they don't necessarily come from the same thread, so it may read a little disjointed. tongue.gif

 

I do think it's informative, and if nothing else, should generate some great discussion in Sgheadphones (I hope) laugh.gif

 

Happy reading!

 

----------------------------------------

[Tomb-headfi]

Your conjecture is somewhat close, but you don't get a cigar, yet.

 

You are confusing a volume control with amplification. Even the lowliest portable can drive many heaphones to ear splitting volumes. However, most of that volume will be produced by the peak power capability of the amplifier circuit at a very limited set of frequencies, and the rest will be distortion.

 

As a for instance, one of the first introductions to hi-fidelity sound is that you notice that higher quality equipment can produce higher volume without as much irritation. Most easily see this comparison with speakers; it is very little different with headphones.

 

Music consists almost entirely of transients on top of a baseline of more-or-less constant tone, depending on the music. Quality amplification (translated: separate headphone amp) will have plenty of power to produce the constant tone for an overall acceptable volume level, but will also have plenty of power in reserve for any transients. Besides transients, there is also the problem of differing power levels needed for different frequencies. Bass frequencies require more energy and require more power. There again, another reason for a huge amount of power over and above the simple rating of a headphone's Sound Pressure Level (SPL) efficiency.

 

All of this is pretty much an afterthought in basic component players, including iPods, etc. There are many more design considerations to deal with that have a greater influence on affecting overall product design. That's one of the reasons you see only earbuds or very efficient headphones with portables. They simply do not have the necessary design for a better power supply. Simple Physics dictates that more power is possible with much less effort if the voltage is higher (Power is dependent on the current squared). Unfortunately, batteries are probably more limited in voltage than current, but pretty much limited in both.

 

That's why you a see a culture of headphone amplifiers with power supplies up to 24V, and many with batteries up to 18V. It simply isn't possible for mfrs to include this stuff in portables meant for the masses. So, the extra headphone amp is all to ensure that every frequency, every transient gets all the power a quality pair of headphones want. The result is not necessarily an ability to turn the volume up, but a crispness, airiness, and prescence that never existed before in your headphone listening.

 

[Mulveling-headfi]

First of all, forget the misconception that the purpose of hifi headphones amps is just to go louder - it's about higher quality at comparable volumes.

 

Anytime you listen to headphones, you're using an amplifier to drive them. The amplifier could be the built-in amp from an ipod, a dedicated headphone amp, or sometimes people even use the output stage of their source as the amp. When you plug your headphones into a receiver or integrated sepaker amp, a numer of things could be happening:

 

1) the headphone jack is driven by a headphone amp stage built into the receiver; usually of exceeedingly poor quality

 

2) the jack is powered by the preamp stage of the receiver

 

3) the jack is powered by the power amp stage with resistors added to bring the level down

 

It is true that amplifiers cannot mitigate distortions from a source. However, amplifiers always add distortion of their own, and this is often what audiophiles seek to minimize by replacing the low quality "stock" headphone amps with a higher quality one. Note that this point is sort of debatable though - some types of distortion are considered euphonic in moderate amounts, while other kinds of distortion sound awful even in small amounts.

 

Anyways, the point is that amplifiers sound different because they add different types and amounts of distortion to the signal. Cheap amps (usually the kind that are built in) often add judicious quantities of the bad, non-euphonic kind of distortion. Also of importance is that an amplifier will often output increased distortion when driving a load it wasn't designed (or not properly designed) to drive. Here's where we get into the need for a powerful dedicated headphone amp - low impedance headphones need an amp with high current capabilities, else the amp will be strained (and distort more). High impedance headphones require a higher voltage swing (again, else distortion). High quality amps will typically be capable of large current and voltage swings, keeping distortion low over a wide rage of headphone impedances. The output impedance of the amp also affects distortion. High output impedance will cause distortion, but the quick fix (global negative feedback) itself is considered to cause very non-euphonic distortion. There are many design considerations to an amp that all affect the sound.

 

A single transistor or opamp can't come close to doing the job right, which is why high end amp design is complicated and why the cheap built-in amps sound like crap.

 

Sometimes you'll see people chain a higher quality amp after a lower quality amp stage, ie: using a dedicated headphone amp from the ipod headphone jack. At first such an arragnement seems counterproductive - why would you want to add the distortion from two amps into the signal chain - however it's not necessarily as bad as it seems. By feeding the ipod amp into another amp, you're presenting the ipod a different load than that of a headphone. Typically, the input impedance of an amp is very high (10,000 - 100,000 ohms, compared to 32 - 300 for headphones), which is easier to drive (meaning lower distortion) for many preamp and headamp stages. Same with people who are using their sources (ie: soundcard) to directly drive headphones. By adding a dedicated amp, they take the burden off the source's output stage so that the overall distortion goes down (or becomes more euphonic ).

 

[Tomb-headfi]

Yep, you are correct - IMHO. Personally, I prefer 1/2 to 3/4 of the volume control, but it depends on quality of the source. You are correct to suspect that you can start clipping with the source prior to an amp if the volume is too high (assuming no line out, of course).

 

Turn the volume too low, and your amp may be amplifying more noise than signal. I truly believe that without a line out, it's an experimental process.

 

----------------------------------------

 

[NotJeffBuckley-Hydrogenaudio]

Huh. I didn't know you post here, MirrorSaw. Yeah, you need a headphone amplifier to adequately power high- and low- impedance headphones; low impedance headphones require more current to accurately reproduce bass frequencies (and thus benefit more from large coupled capacitors, such as the 2200 microfarads found in the PA2V2 or the 1800 microfarads in the Go-Vibe), while high impedance headphones require more voltage to excurse the drivers and avoid op-amp clipping.

 

The current provided by a typical portable audio player is usually less than 15ma per channel, which can lead to notable distortion with low impedance headphones that require more current draw - I'm not sure to which headphones you refer when you say "overwhelming majority;" I'm sure many of the exceptionally sensitive cheap headphones designed specifically for volume headroom and tuned for bass resonance are more than adequately driven by a portable player's voltage swing of less than 2v at less than 30ma total output current, but I wouldn't want to use less sensitive 32ohm headphones with any less than 50ma per channel available. Further, the capacitors are there primarily for dynamic headroom;

 

they supply current for particularly taxing excursions where an op-amp's steady output would be insufficient. That's the "real purpose" of coupled output capacitors, nothing nefarious there (although I agree that 2200microfarad is rather in excess of what is necessary, especially with a low voltage op-amp, but it extends the flat response considerably beyond the audible spectrum and into sub/hypersonics).

 

[steve999-Hydrogen Audio]

 

May I add..... buyer beware!!!

 

Headphone amplifier channel balance for low-level listening can be a major issue too, IMHO. Noise can be an issue both in terms of noise floor due to too high gain or just poor s/n ratio, and in terms of ground hum noise. Noise tends to be more of an issue with very sensitive low impedence phones like the MDR-V6s, especially if the gain is too high. An amp's ability to work around difficult ground-loop hum issues can be quite important, IMHO. These issues are what separate the good stuff from the just okay stuff, in my experience. A near-0 ohm impedance headphone amp will usually have the least impact on frequency response, though some phones are designed to be driven from an industry-standard 120-ohm jack. Some smaller battery-powered amps will have trouble driving very low-impedence phones without some small amount of bass rolloff (the ipod photo headphone out had this problem, as I understand it).

 

The biggest problem with high-impedence, low sensitivty phones like the HD600 and HD650 is usually not noise or channel balance at low levels but just getting them loud enough without pushing the amp's performance limits too far (resulting in clipping or distortion), and this is usually only an issue with battery-powered portable equipment. Most things that you plug in a wall will drive them very comfortably.

 

I use a Behringer UB802 mixer. The input gain is adjustable on two channels if you are a perfectionist. Or you can just use other channels with fixed gain. It drives my Senn HD580s and Beyer DT880s very easily, and my Sony MDR-V6s very quietly. My confidence in my UB802 increased when a friend took measurements on its big brother, the UB1202, and it did quite well for noise, frequency response, and distortion. Though I am not the expert on this stuff. The UB802 mixer also has bass, mid, and treble controls, and multiple inputs and outputs. And panning controls that you can use as a primitive (but continuously variable) crossfeed for old recordings with excessive or tacky stereo separation. And pretty flashing lights. Price: $60.

 

Expensive headamps edge on over into snake-oil-ville as price increases, IMHO. In many circumstances, a home receiver or home CD deck (with headphone jack) or computer sound card will provide solid amplification even with the HD600s or HD650s, IMHO. As to whether one could hear a difference versus an expensive headphone amp in an ABX test, I make no claims. I can tell you based on experience that any difference is not worth it to me, though. A $100 portable amp could be genuinely useful if you are going to use such hard-to-drive headphones as the HD600 or HD650 portably. Thing is, you could get a second pair of really nice and more practical headphones for portable use for the price of that portable amp.

 

If someone is thinking of paying $200 or $300 or more for the meager amount of amplification needed to drive a pair of headphones, I suggest taking the time to come to a better understanding of what you are paying for. tongue.gif If someone at hydrogen audio asserts you need to pay that much for transparent headphone amplification, I say prove it. What is it -- T.O.S. 8? blink.gif

 

 

[niktheblak-Hydrogen audio]

 

I do notice that you used the phrase "get the proper sound out of them..." ... if "proper" means loud, then yes, you'll need a headphone amp to drive them to loud levels. If "proper" means a pleasant sound at decent normal listening levels, then a special headphone amp is not required.

 

Unfortunately just 'loud' doesn't quite cut it. The problem with computer/other line-outs is that they generally have high-impedance output and expect a very high-impedance load, such as 30,000Ω amplifier input. When someone plugs a 60Ω headphone into a line-out expecting 30,000Ω load, the frequency response characteristics of the line-out may change considerably. Probably the single most common phenomenon is attenuation of lower frequencies since they usually have the lowest impedance in most headphones. So you can achieve a sound that is 'loud' but still lacks a major proportion of the spectrum. Also when volume (load) is yet increased with such an underpowered source, pretty much anything can happen to the frequency response curve, but it almost certainly won't be flat. And at this point we've drifted a long way away from 'hi-fi'.

 

So basically a headphone amp's most useful purpose is to perform impedance matching between line-out and a pair of headphones. If you already have a low-impedance output expecting a low-impedance load (such as high quality headphone output of a mixer table), then you shouldn't have major problems driving headphones and don't need a headphone amp.

 

----------------------------------------

 

[Wikipedia]

On the other hand, the final power amplifier stage of a typical audio device often introduces distortion. But "line out" is derived from some point before that final amplification takes place. So "line out" signals tend to be of higher quality than those from a speaker (or headphone) connector.

 

"Line in" expects the kind of signal "line out" provides. So you can typically connect the "line out" connector of one device with the "line in" of another. However, if you do this with a straight cable, and both devices are AC powered, you may run into ground - loop - hum.

 

A typical "Line in" inputs is actually a high impedance input with an impedance of around 10,000 ohms. When a "Line out" signal output, with its impedance of around 100 ohms, is connected to a high impedance "Line in" input like this one, the result is that most of the voltage (over 99%) appears across the input resistance, and almost none of the voltage is dropped across the output impedance. This is the desired effect. Since the impedances are far from matched, very little power is transferred, but the goal is not power transfer, it is voltage transfer. These are voltage signals (as opposed to current signals*) and it is the signal information that is desired, not power to drive a transducer (e.g. speaker) or (transmitting) antenna.

 

[Cnet Audio Glossary]

An audio jack on a sound card or other media device that outputs line-level (0.5- to 2-volt) analog signals. Suitable for sending signals to stereos, tape decks, and so on. By contrast, a headphone output can produce signals 10 or more times that strength.

http://www.enbetas.com/

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Most of this is excellent information, however in the area of ABX (or double-blind) testing, there are way too many subtle or subliminal factors that don't quantify in those tests. People who "really believe" in Science usually concede far too much power to science to resolve all audiophile audibility factors, when science isn't there yet. And then the tests themselves are usually very flawed - the test sites are far too noisy, needing to be as quiet as a very quiet night at home, with participants fully relaxed and not anxious about testing. Participants need full 100 percent control of the music and the switching and volume controls etc., lacking only the awareness of which system is which when they switch.

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