Re: [Elecraft] headphone impedance

[Joe Subich, W4TV]

> Headphone efficiency clearly has other dependencies than
> impedance.

Yes, there are other dependencies like the weight and "stiffness"
of the diaphragm, the strength of the magnet, the coil geometry,
etc.  However, there is still a strong correlation of efficiency
with impedance in well built headphones.

73,

   ... Joe, W4TV


On 12/29/2015 4:55 AM, Barry N1EU wrote:

Jim, I think it would be great if you would clarify your comment to
Steve.  I've looked at the data sheet and everything Steve said seems
correct to me???

And I'm not sure I'm willing to totally buy (per Joe) that there's
necessarily a proportional relationship between headphone impedance
and efficiency that makes up for the inverse relationship between
output power and load impedance.  I just don't observe this efficiency
rule consistently in my collection of headphones with varying
impedance.  Headphone efficiency clearly has other dependencies than
impedance.

73,
Barry N1EU



On Tue, Dec 29, 2015 at 6:46 AM, Jim Brown  wrote:


You clearly don't understand what you're reading on that data sheet, nor the
design of audio output stages. I refer you to my earlier posts, and to those
by W4TV, W2RU, and W3FPR.

Those numbers you quote are NOT the output impedance, they are the minimum
LOAD impedance that the output device is designed to work into. Modern
output stages are essentially constant voltage sources. That's what Bud is
telling you with his discussion about damping factor -- the output Z (source
Z) is typically 50-100 times the load Z.

With headphone amplifiers, a good designer will add some small value of
resistance in series with the output to prevent the output stage from
failing if a short is connected to its output (which could occur when a plug
is being inserted, or with an improperly wired plug). Line level outputs use
a series output resistor to prevent the output stage from seeing the
CAPACITANCE of a long cable, which could, by interaction with the feedback
network, cause the output stage to oscillate.

Executive summary -- simply buy good quality headphones, and don't worry
about impedance.

73, Jim K9YC
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Re: [Elecraft] headphone impedance

[Barry N1EU]

Jim, I think it would be great if you would clarify your comment to
Steve.  I've looked at the data sheet and everything Steve said seems
correct to me???

And I'm not sure I'm willing to totally buy (per Joe) that there's
necessarily a proportional relationship between headphone impedance
and efficiency that makes up for the inverse relationship between
output power and load impedance.  I just don't observe this efficiency
rule consistently in my collection of headphones with varying
impedance.  Headphone efficiency clearly has other dependencies than
impedance.

73,
Barry N1EU



On Tue, Dec 29, 2015 at 6:46 AM, Jim Brown  wrote:

> You clearly don't understand what you're reading on that data sheet, nor the
> design of audio output stages. I refer you to my earlier posts, and to those
> by W4TV, W2RU, and W3FPR.
>
> Those numbers you quote are NOT the output impedance, they are the minimum
> LOAD impedance that the output device is designed to work into. Modern
> output stages are essentially constant voltage sources. That's what Bud is
> telling you with his discussion about damping factor -- the output Z (source
> Z) is typically 50-100 times the load Z.
>
> With headphone amplifiers, a good designer will add some small value of
> resistance in series with the output to prevent the output stage from
> failing if a short is connected to its output (which could occur when a plug
> is being inserted, or with an improperly wired plug). Line level outputs use
> a series output resistor to prevent the output stage from seeing the
> CAPACITANCE of a long cable, which could, by interaction with the feedback
> network, cause the output stage to oscillate.
>
> Executive summary -- simply buy good quality headphones, and don't worry
> about impedance.
>
> 73, Jim K9YC
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Re: [Elecraft] headphone impedance

[Steve Ellington]

I have a pair too. They are indeed loud and are 8 ohm impedance . I like
them for cw however they get uncomfortable after a while. I prefer "around
the ear" types vs. "on the ear".
Steve N4LQ

On Mon, Dec 28, 2015 at 4:19 PM, Vic Rosenthal 4X6GP/K2VCO <
k2vco@gmail.com> wrote:

> I recently started using an old set of Kenwood HS-5 phones (8 ohm) after
> my cat chewed through the cord on my nice hi-fi phones. I noticed that the
> audio was much louder, I presume a result of the lower impedance. I'm even
> thinking about adding some resistance in series, because the audio gain is
> never past 9 o'clock, even with CONFIG AFG set to LOW.
>
> The Kenwood phones also seem to have a much narrower frequency response
> than 'good' ones. Personally I like this.
>
> 73,
> Vic, 4X6GP/K2VCO
> Rehovot, Israel
> http://www.qsl.net/k2vco/
>
>
> On 28 Dec 2015 22:36, W2RU - Bud Hippisley wrote:
>
>> Perhaps this will help:
>>
>> Look up the specs on a good home audio amplifier — say, QSC or Crown.
>> You’ll find something called “damping factor”, and it’s often 50 or
>> more.  Roughly speaking, it’s the ratio of the (loudspeaker) load
>> impedance to the internal (source) impedance of the audio amplifier.
>> So modern semi-pro and stereophile audio amplifiers are “grossly out
>> of specs”, as you put it.
>>
>> I have a legacy, hernia-inducing McIntosh power amplifier,
>> circa-1960s, with output transformers and three taps — for 4-, 8-,
>> and 16-ohm loudspeaker loads.  Nothing I’ve owned since then uses
>> output transformers or matched loads.  Most audio amplifier designs
>> these days are voltage followers.  Most manufacturers don’t attempt
>> to match source impedance to load impedance.  Highly damped output
>> stages are “good” things to have.
>>
>> Yes, it’s true that voltage-follower amplifiers deliver more power to
>> low-impedance loads than to high-impedance loads.  But if I were to
>> follow your line of reasoning to its logical conclusion in the home
>> audio arena, I would conclude that 4-ohm speaker systems are
>> sonically superior to 16-ohm speaker systems simply because they
>> require more output power from the audio amplifier to play my music
>> collection.
>>
>> Does that seem like a reasonable way to choose your stereo system
>> loudspeakers?  Or headphones for your K3?
>>
>> If your 100-ohm (or higher) headphones can’t provide reasonable
>> levels of undistorted sound pressure at your ears when your K3 or K3S
>> audio gain control is at, say, 9 or 10 o’clock, perhaps it’s time to
>> buy a new pair of “cans”.  That’s certainly gotta be cheaper than
>> reverting to a 75A-4 with its audio output transformer and 500-ohm
>> tap.
>>
>> Bud, W2RU
>>
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Re: [Elecraft] headphone impedance

[Vic Rosenthal 4X6GP/K2VCO]

I recently started using an old set of Kenwood HS-5 phones (8 ohm) after 
my cat chewed through the cord on my nice hi-fi phones. I noticed that 
the audio was much louder, I presume a result of the lower impedance. 
I'm even thinking about adding some resistance in series, because the 
audio gain is never past 9 o'clock, even with CONFIG AFG set to LOW.


The Kenwood phones also seem to have a much narrower frequency response 
than 'good' ones. Personally I like this.


73,
Vic, 4X6GP/K2VCO
Rehovot, Israel
http://www.qsl.net/k2vco/


On 28 Dec 2015 22:36, W2RU - Bud Hippisley wrote:

Perhaps this will help:

Look up the specs on a good home audio amplifier — say, QSC or Crown.
You’ll find something called “damping factor”, and it’s often 50 or
more.  Roughly speaking, it’s the ratio of the (loudspeaker) load
impedance to the internal (source) impedance of the audio amplifier.
So modern semi-pro and stereophile audio amplifiers are “grossly out
of specs”, as you put it.

I have a legacy, hernia-inducing McIntosh power amplifier,
circa-1960s, with output transformers and three taps — for 4-, 8-,
and 16-ohm loudspeaker loads.  Nothing I’ve owned since then uses
output transformers or matched loads.  Most audio amplifier designs
these days are voltage followers.  Most manufacturers don’t attempt
to match source impedance to load impedance.  Highly damped output
stages are “good” things to have.

Yes, it’s true that voltage-follower amplifiers deliver more power to
low-impedance loads than to high-impedance loads.  But if I were to
follow your line of reasoning to its logical conclusion in the home
audio arena, I would conclude that 4-ohm speaker systems are
sonically superior to 16-ohm speaker systems simply because they
require more output power from the audio amplifier to play my music
collection.

Does that seem like a reasonable way to choose your stereo system
loudspeakers?  Or headphones for your K3?

If your 100-ohm (or higher) headphones can’t provide reasonable
levels of undistorted sound pressure at your ears when your K3 or K3S
audio gain control is at, say, 9 or 10 o’clock, perhaps it’s time to
buy a new pair of “cans”.  That’s certainly gotta be cheaper than
reverting to a 75A-4 with its audio output transformer and 500-ohm
tap.

Bud, W2RU

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Re: [Elecraft] headphone impedance

[Kevin Stover]

I love my  HS-5's.

On 12/28/2015 3:19 PM, Vic Rosenthal 4X6GP/K2VCO wrote:
I recently started using an old set of Kenwood HS-5 phones (8 ohm) 
after my cat chewed through the cord on my nice hi-fi phones. I 
noticed that the audio was much louder, I presume a result of the 
lower impedance. I'm even thinking about adding some resistance in 
series, because the audio gain is never past 9 o'clock, even with 
CONFIG AFG set to LOW.


The Kenwood phones also seem to have a much narrower frequency 
response than 'good' ones. Personally I like this.


73,
Vic, 4X6GP/K2VCO
Rehovot, Israel
http://www.qsl.net/k2vco/




--
R. Kevin Stover
AC0H
ARRL
FISTS #11993
SKCC #215
NAQCC #3441


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Re: [Elecraft] headphone impedance

[Don Wilhelm]

Barry,

Normally for audio, the impedance is not a problem.  It is the voltage 
that matters.  The output of the headphone amplifier is a low impedance 
source which will drive loads of varying impedance.
Compare with plugging an appliance into a household AC receptacle - The 
power company provides a low impedance source, and the power transferred 
depends on the impedance of the appliance that you plug into the receptacle.


73,
Don W3FPR

On 12/28/2015 8:10 AM, Barry N1EU wrote:

Is there an acceptable range of headphone impedance for the K3/K3s?

I've got some 300-ohm headphones and wondering if the impedance alone
makes them a poor choice for my K3s?




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Re: [Elecraft] headphone impedance

[W2RU - Bud Hippisley]

The headphones I have used for over a decade are 600-ohm high-end stereo 
high-fidelity phones.  I obtain “comfortable” audio with my audio gain control 
set at about 9 o’clock.  I am 99% CW, and they are my preferred-by-far 
headphones for both the K3 and the K3S, although I use something else when I 
need an integrated headset for phone contests.

Bud, W2RU

> On Dec 28, 2015, at 8:10 55AM, Barry N1EU  wrote:
> 
> Is there an acceptable range of headphone impedance for the K3/K3s?
> 
> I've got some 300-ohm headphones and wondering if the impedance alone
> makes them a poor choice for my K3s?
> 
> Thanks & 73,
> Barry N1EU
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Re: [Elecraft] headphone impedance

[Barry N1EU]

Thanks for all the public and private responses!  My 300-ohm
headphones should not be a problem for the K3s.

73, Barry N1EU

On Mon, Dec 28, 2015 at 10:20 AM, W2RU - Bud Hippisley
 wrote:
> The headphones I have used for over a decade are 600-ohm high-end stereo 
> high-fidelity phones.  I obtain “comfortable” audio with my audio gain 
> control set at about 9 o’clock.  I am 99% CW, and they are my 
> preferred-by-far headphones for both the K3 and the K3S, although I use 
> something else when I need an integrated headset for phone contests.
>
> Bud, W2RU
>
>> On Dec 28, 2015, at 8:10 55AM, Barry N1EU  wrote:
>>
>> Is there an acceptable range of headphone impedance for the K3/K3s?
>>
>> I've got some 300-ohm headphones and wondering if the impedance alone
>> makes them a poor choice for my K3s?
>>
>> Thanks & 73,
>> Barry N1EU
>> __
>
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Re: [Elecraft] headphone impedance

[Jim Brown]

On Mon,12/28/2015 10:08 AM, Barry N1EU wrote:

I believe this also means that the K3 headphone output circuit will
deliver 10X power (with fixed V, P~1/R) into a 30-ohm headphone as a
300-ohm headphone, so at some point the amp might clip as you raise
the headphone impedance?


Only if you crank the headphone output too high. My 1V example is simply 
the maximum sine wave output at clip, and that value is typical. When 
you turn down the headphone gain, you reduce that voltage. I don't 
recall the spec for the K3. In your 30 ohm headphone example, you would 
probably not need to crank the gain nearly as high, so the output 
voltage would stay below clip. The exception might be if the operator 
has significant hearing loss, so was driving the headphones very hard.


73, Jim K9YC
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Re: [Elecraft] headphone impedance

[Jim Brown]

On Mon,12/28/2015 5:10 AM, Barry N1EU wrote:

I've got some 300-ohm headphones and wondering if the impedance alone makes 
them a poor choice for my K3s?


As others have told you, it's not an issue. For at least 50 years, audio 
equipment has low impedance outputs that are designed to work into 
relatively high impedances. In audio, we don't "match" impedances like 
we would in RF. Power amplifiers, of which headphone amplifiers are a 
special set, are typically designed to provide 1V or so into any Z 
greater than about 100 ohms.


Think of it this way. High Z phones are designed to require more voltage 
but less current, while low Z phones require less voltage but draw more 
current. The IR drop in the output stage will reduce the voltage to 
low-Z phones, but they don't need as much voltage to be loud enough. And 
there will be little or no IR drop to higher Z phones, so they see the 
full 1V output.


Bottom line -- nearly all modern headphones are designed to work with a 
1V source.


There's discussion of these issues in

http://k9yc.com/GroundingAndAudio.pdf

73, Jim K9YC
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Re: [Elecraft] headphone impedance

[Barry N1EU]

I believe this also means that the K3 headphone output circuit will
deliver 10X power (with fixed V, P~1/R) into a 30-ohm headphone as a
300-ohm headphone, so at some point the amp might clip as you raise
the headphone impedance?

Barry N1EU

On Mon, Dec 28, 2015 at 12:57 PM, Jim Brown  wrote:
> On Mon,12/28/2015 5:10 AM, Barry N1EU wrote:
>>
>> I've got some 300-ohm headphones and wondering if the impedance alone
>> makes them a poor choice for my K3s?
>
>
> As others have told you, it's not an issue. For at least 50 years, audio
> equipment has low impedance outputs that are designed to work into
> relatively high impedances. In audio, we don't "match" impedances like we
> would in RF. Power amplifiers, of which headphone amplifiers are a special
> set, are typically designed to provide 1V or so into any Z greater than
> about 100 ohms.
>
> Think of it this way. High Z phones are designed to require more voltage but
> less current, while low Z phones require less voltage but draw more current.
> The IR drop in the output stage will reduce the voltage to low-Z phones, but
> they don't need as much voltage to be loud enough. And there will be little
> or no IR drop to higher Z phones, so they see the full 1V output.
>
> Bottom line -- nearly all modern headphones are designed to work with a 1V
> source.
>
> There's discussion of these issues in
>
> http://k9yc.com/GroundingAndAudio.pdf
>
> 73, Jim K9YC
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Re: [Elecraft] headphone impedance

[Steve Ellington]

No problem...Just grossly out of specs.
Whatever happenshappens
73

Steve N4LQ

On Mon, Dec 28, 2015 at 2:53 PM, W2RU - Bud Hippisley 
wrote:

> What am I missing?
>
> I use 600-ohm stereo headphones plugged directly into the front panel jack
> of my K3S.
>
> I run the Audio Gain control at 9 o’clock — roughly a 25% rotation toward
> full volume.
>
> I have more than enough audio for my elderly ears, and when I pull the
> headphone plug out of the jack, my speaker audio is at a comparable level.
>
> What is the non-problem with high-impedance phones that you guys are
> trying to solve?
>
> Bud, W2RU
>
> > On Dec 28, 2015, at 1:59 09PM, Steve Ellington 
> wrote:
> >
> > K3  uses the.
> >
> > LM4811  Headphone Amplifier
> >
> > Texas Instruments Specs for output Z
> >
> > RL = 16Ω 105 mW
> > RL = 32Ω 70 mW
> >
> > At 60 ohms the output power drops to 20 mw. Per their graphs.
> >
> > 300 ohms is not even considered.
> >
> > Amplifier gain control is done digitally within the chip. With such a
> high
> > Z load, gain would likely need increasing.
> > The results of doing so are unknown. Consider pop, click, white noise
> etc.
> >
> > Also consider what happens when switching from headphones to speaker when
> > the AF Gain control is turned up high. Blasting?
> >
> > I suggest sticking within the 16 to 32 ohm range.
> >
> > Steve N4LQ
> >
>
>
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Re: [Elecraft] headphone impedance

[W2RU - Bud Hippisley]

What am I missing?

I use 600-ohm stereo headphones plugged directly into the front panel jack of 
my K3S.

I run the Audio Gain control at 9 o’clock — roughly a 25% rotation toward full 
volume.

I have more than enough audio for my elderly ears, and when I pull the 
headphone plug out of the jack, my speaker audio is at a comparable level.

What is the non-problem with high-impedance phones that you guys are trying to 
solve?

Bud, W2RU

> On Dec 28, 2015, at 1:59 09PM, Steve Ellington  wrote:
> 
> K3  uses the.
> 
> LM4811  Headphone Amplifier
> 
> Texas Instruments Specs for output Z
> 
> RL = 16Ω 105 mW
> RL = 32Ω 70 mW
> 
> At 60 ohms the output power drops to 20 mw. Per their graphs.
> 
> 300 ohms is not even considered.
> 
> Amplifier gain control is done digitally within the chip. With such a high
> Z load, gain would likely need increasing.
> The results of doing so are unknown. Consider pop, click, white noise etc.
> 
> Also consider what happens when switching from headphones to speaker when
> the AF Gain control is turned up high. Blasting?
> 
> I suggest sticking within the 16 to 32 ohm range.
> 
> Steve N4LQ
> 

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Re: [Elecraft] headphone impedance

[Steve Ellington]

K3  uses the.

LM4811  Headphone Amplifier

Texas Instruments Specs for output Z

RL = 16Ω 105 mW
RL = 32Ω 70 mW

At 60 ohms the output power drops to 20 mw. Per their graphs.

300 ohms is not even considered.

Amplifier gain control is done digitally within the chip. With such a high
Z load, gain would likely need increasing.
The results of doing so are unknown. Consider pop, click, white noise etc.

Also consider what happens when switching from headphones to speaker when
the AF Gain control is turned up high. Blasting?

I suggest sticking within the 16 to 32 ohm range.

Steve N4LQ



On Mon, Dec 28, 2015 at 1:16 PM, Jim Brown 
wrote:

> On Mon,12/28/2015 10:08 AM, Barry N1EU wrote:
>
>> I believe this also means that the K3 headphone output circuit will
>> deliver 10X power (with fixed V, P~1/R) into a 30-ohm headphone as a
>> 300-ohm headphone, so at some point the amp might clip as you raise
>> the headphone impedance?
>>
>
> Only if you crank the headphone output too high. My 1V example is simply
> the maximum sine wave output at clip, and that value is typical. When you
> turn down the headphone gain, you reduce that voltage. I don't recall the
> spec for the K3. In your 30 ohm headphone example, you would probably not
> need to crank the gain nearly as high, so the output voltage would stay
> below clip. The exception might be if the operator has significant hearing
> loss, so was driving the headphones very hard.
>
> 73, Jim K9YC
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Re: [Elecraft] headphone impedance

[Don Wilhelm]

Steve,

Look closely - that is the *power* that can be developed by the 
amplifier.  Certainly a higher impedance load will reduce the power 
available from the amplifier, but the output voltage will be higher and 
the current requirement is lower.
Most headphones (other than some audiophile types) do not require much 
power at all.


73,
Don W3FPR

On 12/28/2015 1:59 PM, Steve Ellington wrote:

K3  uses the.

LM4811  Headphone Amplifier

Texas Instruments Specs for output Z

RL = 16Ω 105 mW
RL = 32Ω 70 mW

At 60 ohms the output power drops to 20 mw. Per their graphs.

300 ohms is not even considered.




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Re: [Elecraft] headphone impedance

[W2RU - Bud Hippisley]

Perhaps this will help:

Look up the specs on a good home audio amplifier — say, QSC or Crown.  You’ll 
find something called “damping factor”, and it’s often 50 or more.  Roughly 
speaking, it’s the ratio of the (loudspeaker) load impedance to the internal 
(source) impedance of the audio amplifier.  So modern semi-pro and stereophile 
audio amplifiers are “grossly out of specs”, as you put it.

I have a legacy, hernia-inducing McIntosh power amplifier, circa-1960s, with 
output transformers and three taps — for 4-, 8-, and 16-ohm loudspeaker loads.  
Nothing I’ve owned since then uses output transformers or matched loads.  Most 
audio amplifier designs these days are voltage followers.  Most manufacturers 
don’t attempt to match source impedance to load impedance.  Highly damped 
output stages are “good” things to have.

Yes, it’s true that voltage-follower amplifiers deliver more power to 
low-impedance loads than to high-impedance loads.  But if I were to follow your 
line of reasoning to its logical conclusion in the home audio arena, I would 
conclude that 4-ohm speaker systems are sonically superior to 16-ohm speaker 
systems simply because they require more output power from the audio amplifier 
to play my music collection.  

Does that seem like a reasonable way to choose your stereo system loudspeakers? 
 Or headphones for your K3?

If your 100-ohm (or higher) headphones can’t provide reasonable levels of 
undistorted sound pressure at your ears when your K3 or K3S audio gain control 
is at, say, 9 or 10 o’clock, perhaps it’s time to buy a new pair of “cans”.  
That’s certainly gotta be cheaper than reverting to a 75A-4 with its audio 
output transformer and 500-ohm tap.

Bud, W2RU

   
> On Dec 28, 2015, at 2:57 22PM, Steve Ellington  wrote:
> 
> No problem...Just grossly out of specs.  
> Whatever happenshappens
> 73
> 
> Steve N4LQ
> 
> On Mon, Dec 28, 2015 at 2:53 PM, W2RU - Bud Hippisley  > wrote:
> What am I missing?
> 
> I use 600-ohm stereo headphones plugged directly into the front panel jack of 
> my K3S.
> 
> I run the Audio Gain control at 9 o’clock — roughly a 25% rotation toward 
> full volume.
> 
> I have more than enough audio for my elderly ears, and when I pull the 
> headphone plug out of the jack, my speaker audio is at a comparable level.
> 
> What is the non-problem with high-impedance phones that you guys are trying 
> to solve?
> 
> Bud, W2RU
> 
> > On Dec 28, 2015, at 1:59 09PM, Steve Ellington  > > wrote:
> >
> > K3  uses the.
> >
> > LM4811  Headphone Amplifier
> >
> > Texas Instruments Specs for output Z
> >
> > RL = 16Ω 105 mW
> > RL = 32Ω 70 mW
> >
> > At 60 ohms the output power drops to 20 mw. Per their graphs.
> >
> > 300 ohms is not even considered.
> >
> > Amplifier gain control is done digitally within the chip. With such a high
> > Z load, gain would likely need increasing.
> > The results of doing so are unknown. Consider pop, click, white noise etc.
> >
> > Also consider what happens when switching from headphones to speaker when
> > the AF Gain control is turned up high. Blasting?
> >
> > I suggest sticking within the 16 to 32 ohm range.
> >
> > Steve N4LQ
> >
> 
> 

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Re: [Elecraft] headphone impedance

[Joe Subich, W4TV]

Certainly a higher impedance load will reduce the power available
from the amplifier, but the output voltage will be higher and the
current requirement is lower.


Higher impedance headphones (and speakers) have larger voice coils
(more turns) than lower impedance headphones/speakers.  The larger
number of turns produces a larger change in magnetic field for a given
change in current.  Typically the magnetic field increases as the
square of the number of turns while the current in the coil decreases
linearly with the impedance.  In simple terms, because audio is "low"
frequency, doubling the number of turns will increase the magnetic
field by a factor of four while increasing the impedance by a factor
of two.

Thus, although the audio amplifier produces less *power* with higher
impedance headphones, the high-z headphones produce more sound pressure
per unit of audio input ... the higher impedance headphones will be
more *efficient* than low impedance headphones.

Where an audio amplifier is relatively limited in power output (e.g.,
old battery powered "portable" radios) high impedance headphones were
the 'phones of choice.

73,

   ... Joe, W4TV


On 12/28/2015 3:00 PM, Don Wilhelm wrote:

Steve,

Look closely - that is the *power* that can be developed by the
amplifier.  Certainly a higher impedance load will reduce the power
available from the amplifier, but the output voltage will be higher and
the current requirement is lower.
Most headphones (other than some audiophile types) do not require much
power at all.

73,
Don W3FPR

On 12/28/2015 1:59 PM, Steve Ellington wrote:

K3  uses the.

LM4811  Headphone Amplifier

Texas Instruments Specs for output Z

RL = 16Ω 105 mW
RL = 32Ω 70 mW

At 60 ohms the output power drops to 20 mw. Per their graphs.

300 ohms is not even considered.




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Re: [Elecraft] headphone impedance

[Jim Brown]

On Mon,12/28/2015 11:57 AM, Steve Ellington wrote:
No problem...Just grossly out of specs. 


Steve,

You clearly don't understand what you're reading on that data sheet, nor 
the design of audio output stages. I refer you to my earlier posts, and 
to those by W4TV, W2RU, and W3FPR.


Those numbers you quote are NOT the output impedance, they are the 
minimum LOAD impedance that the output device is designed to work into. 
Modern output stages are essentially constant voltage sources. That's 
what Bud is telling you with his discussion about damping factor -- the 
output Z (source Z) is typically 50-100 times the load Z.


With headphone amplifiers, a good designer will add some small value of 
resistance in series with the output to prevent the output stage from 
failing if a short is connected to its output (which could occur when a 
plug is being inserted, or with an improperly wired plug). Line level 
outputs use a series output resistor to prevent the output stage from 
seeing the CAPACITANCE of a long cable, which could, by interaction with 
the feedback network, cause the output stage to oscillate.


Executive summary -- simply buy good quality headphones, and don't worry 
about impedance.


73, Jim K9YC
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