[Patrick Turner]

I am probably a voice in the wilderness about global warming. Northern
hemisphere dudes shiver in the cold so of course they see Copenhagen
as a giant load of bull****. But soon ships will regularly travel the
Northwest Passage thus not having to use Suez, because the ice has
melted.

Meanwhile Oz has recorded near record high temps again and 100+ bush
fires burn across NSW.

So I take no notice of northern ppl wishing the temperature would
rise.

I have just got a headphone amp to work acceptably. It has its PSU on
the same compact chassis as the two amp channels which use 12AT7
paralleled for an input tube and a 6BQ5 in triode for the output tube.
There is a 23.2:1 OPT, giving an 8k6:16 ohm load match. There is a
necessary 10dB global NFB from 6BQ5 anode to the 12AT7 cathode Rk =
680 ohms. Not including the OPT secondary in the NFB loop made the amp
much easier to stabilize.
There are 2 pairs of L&R outputs; one is from the OPT but with 22 ohms
series R at the output and voltage gain of about 5. This allows the
amp to be used as a preamp with useful gain.

The other outputs from the OPT sec have 15 ohms and 8 ohms to make a
loading divider resistance with Rout = 5.2 ohms which gives a low
enough Rout for most headphones of 32 ohms, and fine for the 330 ohm
Sennheiser phones of my customer.

So the 6BQ5 with Ea 280V and Ia = 32 mA is always loaded with a high
RL value regardless of whatever is the phone load.

Without the 15r and 8r divider or anyNFB, I found the hum level was
about 0.2 mV and was audible in my test headphones. This would be OK
if I was driving speakers, but headphones need far lower levels of
noise from any source.
The hum is generated somehow in the output stage and probably by stray
magnetic induction, despite the potting of all transformers in steel
pots and setting them apart on a steel chassis.
If the signal is 200mV average, the SNR is only -60dB. 200mV is loud.
But with 50mV of signal the SNR is only -48dB.
So the first requirement for any amp system is that the noise at idle
without any signal present be inaudible no matter what.

With the 15r&8r divider, the amp noise is reduced about 12dB. The
signal must be 12dB higher at the OPT sec. I finally got levels of hum
below audibility, or below 20uV at the headphones. The NFB helped
achieve this.
Relative to 100mV, the amp noise of 20uV is -74dB. In many headphne
amps I have worked on the noise is higher and the cure is quite
difficult; the Da-ming headphone is an example where noise is audible
without any signal.

My amp can make up to about 1.6Vrms output from the R divider and the
Sennheisers need an average 0.2Vrms level for a near deafening sound.
So the amp has enough headroom. With a low level source up to 0.3Vrms
peak the gain must be turned up a fair way, but with CD which has a
much higher output the gain will be lower without being too low.

I didn't want to use a remote PSU. Had I done so it would have been
much easier to achieve low hum levels.

The amp sure sounds well. Bandwidth is 10Hz to 55kHz at normal levels.
Its slightly less at idiotically high levels because of the OPT
saturation.
OPT are from a 1960 Trio receiver where EL84 were used in 5W SE
outputs.

Patrick Turner.

[Peter Wieck]

On Dec 10, 4:24*am, Patrick Turner wrote:

So I take no notice of northern ppl wishing the temperature would
rise.

Yeah. Let it be. Those birds are busy ****ting in their nest and those
of others making several venues nearly useless for their intended
purpose. Pick one: any individual who calls himself "Lord" and an
American all at once has no idea whatsoever of how or why the United
States came to be. Certainly a clear indication of their understanding
of both history and logic.

I have just got a headphone amp to work acceptably. It has its PSU on
the same compact chassis as the two amp channels which use 12AT7
paralleled for an input tube and a 6BQ5 in triode for the output tube.
There is a 23.2:1 OPT, giving an 8k6:16 ohm load match. *
The other outputs from the OPT sec have 15 ohms and 8 ohms to make a
loading divider resistance with Rout = 5.2 ohms which gives a low
enough Rout for most headphones of 32 ohms, and fine for the 330 ohm
Sennheiser phones of my customer.
Snips
The amp sure sounds well. Bandwidth is 10Hz to 55kHz at normal levels.
Its slightly less at idiotically high levels because of the OPT
saturation.
OPT are from a 1960 Trio receiver where EL84 were used in 5W SE
outputs.

After all that, I am glad to see you are using salvaged/recycled iron
- there is a lot of very good small-power stuff out there made back in
the day when manufacturers really didn't know enough to make crap. The
stuff is certainly thick on the ground around here as the Philadelphia
region had over a dozen significant manufacturers in the radio/audio/
tube industries through the 80s, even into the 90s. Some are hanging
on after a fashion but not as originally incarnated.

Neat trick supressing the hum while driving headphones - I have found
that to be the toughest aspect of working with tube equipment - it was
no accident that many if not most tube amps and pre-amps did not have
phone outputs from the factory - even back in the day of fully-
enclosed headphones weighing about as much as a Volkswagen.

Glad to read that someone still retains a passing interest in tubes
and their care-and-feeding.

Peter Wieck
Melrose Park, PA

[Ian Bell[_2_]]

Patrick Turner wrote:
snip

I have just got a headphone amp to work acceptably. It has its PSU on
the same compact chassis as the two amp channels which use 12AT7
paralleled for an input tube and a 6BQ5 in triode for the output tube.
There is a 23.2:1 OPT, giving an 8k6:16 ohm load match. There is a
necessary 10dB global NFB from 6BQ5 anode to the 12AT7 cathode Rk =
680 ohms. Not including the OPT secondary in the NFB loop made the amp
much easier to stabilize.
There are 2 pairs of L&R outputs; one is from the OPT but with 22 ohms
series R at the output and voltage gain of about 5. This allows the
amp to be used as a preamp with useful gain.

The other outputs from the OPT sec have 15 ohms and 8 ohms to make a
loading divider resistance with Rout = 5.2 ohms which gives a low
enough Rout for most headphones of 32 ohms, and fine for the 330 ohm
Sennheiser phones of my customer.

So the 6BQ5 with Ea 280V and Ia = 32 mA is always loaded with a high
RL value regardless of whatever is the phone load.

Without the 15r and 8r divider or anyNFB, I found the hum level was
about 0.2 mV and was audible in my test headphones. This would be OK
if I was driving speakers, but headphones need far lower levels of
noise from any source.
The hum is generated somehow in the output stage and probably by stray
magnetic induction, despite the potting of all transformers in steel
pots and setting them apart on a steel chassis.
If the signal is 200mV average, the SNR is only -60dB. 200mV is loud.
But with 50mV of signal the SNR is only -48dB.
So the first requirement for any amp system is that the noise at idle
without any signal present be inaudible no matter what.

With the 15r&8r divider, the amp noise is reduced about 12dB. The
signal must be 12dB higher at the OPT sec. I finally got levels of hum
below audibility, or below 20uV at the headphones. The NFB helped
achieve this.
Relative to 100mV, the amp noise of 20uV is -74dB. In many headphne
amps I have worked on the noise is higher and the cure is quite
difficult; the Da-ming headphone is an example where noise is audible
without any signal.

My amp can make up to about 1.6Vrms output from the R divider and the
Sennheisers need an average 0.2Vrms level for a near deafening sound.
So the amp has enough headroom. With a low level source up to 0.3Vrms
peak the gain must be turned up a fair way, but with CD which has a
much higher output the gain will be lower without being too low.

I didn't want to use a remote PSU. Had I done so it would have been
much easier to achieve low hum levels.

The amp sure sounds well. Bandwidth is 10Hz to 55kHz at normal levels.
Its slightly less at idiotically high levels because of the OPT
saturation.
OPT are from a 1960 Trio receiver where EL84 were used in 5W SE
outputs.

Patrick Turner.


I am interested in headphone amps and I have always been curious as to
why many designs look like small scale speaker amps when in practice the
requirements are far more modest.

As you say, 200mV is loud in the 330R Sennheiser phones. 0.2Vrms into
330R is a mere 13.3mW which confirms my finding that present day
headphones only need 10 to 20mW to drive them to deafening levels. Most
current headphones provide a sound level of 110dB SPL or more with just
1mW of input, so 10mW gives 120dB SPL which is getting really loud.

Consider a straightforward CF with a quiescent current of say 10mA. This
will easily drive 10V rms into a 10K load with minimal distortion and
10V rms into 10K is 1mA and 10mW which is ample for most phones. You
also get the added benefit of the natural PSRR of a CF. Typical CF
output noise level is no more than 100uV which is 100dB below 10V rms so
any ouput noise/hum above this is going to be induced.

The only problem now is impedance matching. Fortunately, Sowter do a
rather nice headphones transformer type 8665 designed to be driven by a
CF and presenting it with a 10K load. It has various secondaries that
can be arranged to match it to almost any headphone impedance.

Cheers

Ian

[Cosmo]

Patrick Turner wrote:
I have just got a headphone amp to work acceptably. It has its PSU on
the same compact chassis as the two amp channels which use 12AT7
paralleled for an input tube and a 6BQ5 in triode for the output tube.
There is a 23.2:1 OPT, giving an 8k6:16 ohm load match. There is a
necessary 10dB global NFB from 6BQ5 anode to the 12AT7 cathode Rk =
680 ohms. Not including the OPT secondary in the NFB loop made the amp
much easier to stabilize.
There are 2 pairs of L&R outputs; one is from the OPT but with 22 ohms
series R at the output and voltage gain of about 5. This allows the
amp to be used as a preamp with useful gain.

I have to confess that the finer technical details of the above are a
little lost on me but I am looking for a tube headphone amp so this post
is more than welcome.

I have some soldering skills and would like to build it myself but I
don't want to start from scratch. Can anyone recommend a kit to build a
good quality headphone amp, preferably that is available in the UK? Or,
if not a specific make/model, what I should look out for in the
technical description? It will be connected to a Conrad Johnson PF-1
pre-amp and, until I get something better, a pair of old Nakamichi SP-7
headphones if that makes any difference.




Cosmo

[Phil Allison[_3_]]

"Ian Bell"

( snip Turneroid drivel)
I am interested in headphone amps and I have always been curious as to why
many designs look like small scale speaker amps when in practice the
requirements are far more modest.

As you say, 200mV is loud in the 330R Sennheiser phones.

** Massive fallacy.


0.2Vrms into 330R is a mere 13.3mW

** Try the math again - pal.

The real figure is 121 * MICRO * watts !!!!

Translates to only about 88 dB with Sennheiser high quality phones.


Most current headphones provide a sound level of 110dB SPL or more with
just 1mW of input,

** Some may, most do not.

The average figure for high quality phones ( like Sennheisers) is more like
97 dB / mW


so 10mW gives 120dB SPL which is getting really loud.


** The real figure is more like 107 dB which is not that loud.

A good headphone amp needs to deliver 200mW, at low distortion, at any
impedance from 32 ohms to 600 ohms.

A simple, low power, CF will not do.



...... Phil

[Ian Bell[_2_]]

Phil Allison wrote:
"Ian Bell"

( snip Turneroid drivel)
I am interested in headphone amps and I have always been curious as to why
many designs look like small scale speaker amps when in practice the
requirements are far more modest.

As you say, 200mV is loud in the 330R Sennheiser phones.

** Massive fallacy.


0.2Vrms into 330R is a mere 13.3mW

** Try the math again - pal.

The real figure is 121 * MICRO * watts !!!!

Whoops my bad!


Translates to only about 88 dB with Sennheiser high quality phones.


Most current headphones provide a sound level of 110dB SPL or more with
just 1mW of input,

** Some may, most do not.

I disagree. I just checked out the Sennheiser web site and nearly all
their phones use Neodymium magnets and quote sensitivities above 110dB.


The average figure for high quality phones ( like Sennheisers) is more like
97 dB / mW


I disagree. See above.


Cheers

Ian

so 10mW gives 120dB SPL which is getting really loud.


** The real figure is more like 107 dB which is not that loud.

A good headphone amp needs to deliver 200mW, at low distortion, at any
impedance from 32 ohms to 600 ohms.

A simple, low power, CF will not do.



..... Phil

[Ian Bell[_2_]]

Phil Allison wrote:
"Ian Bell"

( snip Turneroid drivel)
I am interested in headphone amps and I have always been curious as to why
many designs look like small scale speaker amps when in practice the
requirements are far more modest.

As you say, 200mV is loud in the 330R Sennheiser phones.

** Massive fallacy.


0.2Vrms into 330R is a mere 13.3mW

** Try the math again - pal.

The real figure is 121 * MICRO * watts !!!!

Translates to only about 88 dB with Sennheiser high quality phones.


Most current headphones provide a sound level of 110dB SPL or more with
just 1mW of input,

** Some may, most do not.

The average figure for high quality phones ( like Sennheisers) is more like
97 dB / mW


so 10mW gives 120dB SPL which is getting really loud.


** The real figure is more like 107 dB which is not that loud.

A good headphone amp needs to deliver 200mW, at low distortion, at any
impedance from 32 ohms to 600 ohms.

A simple, low power, CF will not do.



..... Phil




Patrick, I just looked at all the professional phones on the Sennheiser
web site and not one is listed as 330 ohms. Which precise model does
your client use?

Cheers

Ian

[Don Pearce[_3_]]

On Sat, 12 Dec 2009 11:00:50 +0000, Ian Bell
wrote:


I disagree. I just checked out the Sennheiser web site and nearly all
their phones use Neodymium magnets and quote sensitivities above 110dB.


The average figure for high quality phones ( like Sennheisers) is more like
97 dB / mW


I disagree. See above.

Taking the HD515 as an example. It produces a SPL of 108dB at 1 volt.
This is a 50 ohm phone, so that makes a power level of 20mW. That is
13dBm, so to get the SPL at 1mW, subtract 13 from 108, which is 95dB /
mW.

The HD595 is 99dB / mW

The HD600 is 97dB / mW

The HD800 is 97dB / mW


So that all comes out about a 97dB average.

d

[Ian Bell[_2_]]

Don Pearce wrote:
On Sat, 12 Dec 2009 11:00:50 +0000, Ian Bell
wrote:

I disagree. I just checked out the Sennheiser web site and nearly all
their phones use Neodymium magnets and quote sensitivities above 110dB.

The average figure for high quality phones ( like Sennheisers) is more like
97 dB / mW

I disagree. See above.

Taking the HD515 as an example. It produces a SPL of 108dB at 1 volt.

Are you sure? Their web site makes no such statement that I can see,
Sensitivity is usually specified as dB (SPL) for 1mW input. That equates
to about 200mW into 50 ohms.

Cheers

Ian

This is a 50 ohm phone, so that makes a power level of 20mW. That is
13dBm, so to get the SPL at 1mW, subtract 13 from 108, which is 95dB /
mW.

The HD595 is 99dB / mW

The HD600 is 97dB / mW

The HD800 is 97dB / mW


So that all comes out about a 97dB average.

d

[Don Pearce[_3_]]

On Sat, 12 Dec 2009 12:18:57 +0000, Ian Bell
wrote:

Are you sure? Their web site makes no such statement that I can see,
Sensitivity is usually specified as dB (SPL) for 1mW input. That equates
to about 200mW into 50 ohms.

Cheers

Ian


Here's a copy and paste from their web site:

Nominal impedance 50 Ohm
Contact pressure 3,5 N
Weight w/o cable 255 g
Jack plug 6,3 mm stereo (3,5 mm Adapter)
Transducer principle (Headphones) open, dynamic
Ear coupling circumaural
Cable length 3 m detachable single-sided OFC copper cable
Frequency response (headphones) 14.....26000 Hz
Sound pressure level (SPL) 108 dB (1 kHz and 1 Veff)
THD, total harmonic distortion 0,2 %


From he

http://www.sennheiser.co.uk/uk/home_...341?Open&row=3

d

[Don Pearce[_3_]]

On Sat, 12 Dec 2009 12:21:30 GMT, (Don Pearce) wrote:

On Sat, 12 Dec 2009 12:18:57 +0000, Ian Bell
wrote:

Are you sure? Their web site makes no such statement that I can see,
Sensitivity is usually specified as dB (SPL) for 1mW input. That equates
to about 200mW into 50 ohms.

Cheers

Ian


Here's a copy and paste from their web site:

Nominal impedance 50 Ohm
Contact pressure 3,5 N
Weight w/o cable 255 g
Jack plug 6,3 mm stereo (3,5 mm Adapter)
Transducer principle (Headphones) open, dynamic
Ear coupling circumaural
Cable length 3 m detachable single-sided OFC copper cable
Frequency response (headphones) 14.....26000 Hz
Sound pressure level (SPL) 108 dB (1 kHz and 1 Veff)
THD, total harmonic distortion 0,2 %


From he

http://www.sennheiser.co.uk/uk/home_...341?Open&row=3

d

Just wondering what on earth a single-sided cable is.

d

[Ian Bell[_2_]]

Cosmo wrote:
Patrick Turner wrote:
I have just got a headphone amp to work acceptably. It has its PSU on
the same compact chassis as the two amp channels which use 12AT7
paralleled for an input tube and a 6BQ5 in triode for the output tube.
There is a 23.2:1 OPT, giving an 8k6:16 ohm load match. There is a
necessary 10dB global NFB from 6BQ5 anode to the 12AT7 cathode Rk =
680 ohms. Not including the OPT secondary in the NFB loop made the amp
much easier to stabilize.
There are 2 pairs of L&R outputs; one is from the OPT but with 22 ohms
series R at the output and voltage gain of about 5. This allows the
amp to be used as a preamp with useful gain.

I have to confess that the finer technical details of the above are a
little lost on me but I am looking for a tube headphone amp so this post
is more than welcome.

I have some soldering skills and would like to build it myself but I
don't want to start from scratch. Can anyone recommend a kit to build a
good quality headphone amp, preferably that is available in the UK? Or,
if not a specific make/model, what I should look out for in the
technical description? It will be connected to a Conrad Johnson PF-1
pre-amp and, until I get something better, a pair of old Nakamichi SP-7
headphones if that makes any difference.




Cosmo


You could try this one:

http://wduk.worldomain.net/acatalog/info_HD83.html

It is a bit expensive but most of the cost is in the iron. I suspect it
uses another of the Sowter headphone transformers, probably the model
8968 at 150 quid a pop.

Cheers

Ian

[Patrick Turner]

On Dec 11, 12:04*am, Peter Wieck wrote:
On Dec 10, 4:24*am, Patrick Turner wrote:

So I take no notice of northern ppl wishing the temperature would
rise.

Yeah. Let it be. Those birds are busy ****ting in their nest and those
of others making several venues nearly useless for their intended
purpose. Pick one: any individual who calls himself "Lord" and an
American all at once has no idea whatsoever of how or why the United
States came to be. Certainly a clear indication of their understanding
of both history and logic.

Things are not going to well in Copenhagen. Its doubtful anyone will
make any worthwhile sacrifices to end carbon based energies.

Blind Freddy could see that the West should give China and India all
the free nuke power stations they want. Then these countries can
continue with making billions of bucks worth of imports every
westerner buys at prices -20dB below the price of US manufacturing.
And the CO2 would be reduced. If we all live in the world together and
if we believe in everyone having equal rights and duty of care about
each other, then the responsibility for being your brother's keeper
applies to all.

Pigs will fly before such idealism flies methinks.

The only trouble with turning to nuclear or any other form of
alternative to fossils is that when you establish a service, the
demand exceeds the the supply because when ppl get more they want more
because there is more to be had and wanted and the demand is always
way in excess of supply.

If the world had cheap green electricity for all energy, then ppl
would still want so much more of everything that all the resources of
the world will be plundered and dissipated. Polititians are talking
about conditions in 50 years but what about 1,000 years from now?

Anyway, back to the bottles..........



I have just got a headphone amp to work acceptably. It has its PSU on
the same compact chassis as the two amp channels which use 12AT7
paralleled for an input tube and a 6BQ5 in triode for the output tube.
There is a 23.2:1 OPT, giving an 8k6:16 ohm load match. *
The other outputs from the OPT sec have 15 ohms and 8 ohms to make a
loading divider resistance with Rout = 5.2 ohms which gives a low
enough Rout for most headphones of 32 ohms, and fine for the 330 ohm
Sennheiser phones of my customer.
* *Snips
The amp sure sounds well. Bandwidth is 10Hz to 55kHz at normal levels.
Its slightly less at idiotically high levels because of the OPT
saturation.
OPT are from a 1960 Trio receiver where EL84 were used in 5W SE
outputs.

After all that, I am glad to see you are using salvaged/recycled iron
- there is a lot of very good small-power stuff out there made back in
the day when manufacturers really didn't know enough to make crap.

Oh yes they all knew how to make crap alright, and most of it most
surely was crap.

The SE OPTs I salvaged were used for a 4k4:8&16 load ratio.

This load is OK for EL84 in pentode. In triode mode which I am using
the load should be about 7k+ for the Ea and Ia conditions. I havbe a
divider off the 8 ohm tap with 15 ohms plus 8 ohms so the load is at
least 23 ohms always so the anode load is quite high. There are twin
phone jacks so two ppl can listen regardless of what their phone
impedance is.
But the two phone sets would have to be about equal sensitivty.
The inductance was a bit low despite the primary being 330 ohms dcr
which indicates many P turns on a core with Afe = 25mm x 25mm. The
onset of core saturation at 120Vrms at the anode is at 35Hz, nearly
twice what a good SE OPT should have, but it does not matter at all
because the levels for phones are so low and then Fsat at -12dB is
about 8Hz.

The 6BQ5 amp in triode can put 2W into an 8 ohms speaker. I have a
pair of RCA outputs at the amp rear direct from the 8 ohm tap. This
would suit beroom operation of background speakers; the sound is good
despite the slightly high Fsat.

At normal listening levels with phones the THD rarely rises above
0.05%.

I have seen a lot worse OPTs in radios and old amps from the 1950s and
60s.

stuff is certainly thick on the ground around here as the Philadelphia
region had over a dozen significant manufacturers in the radio/audio/
tube industries through the 80s, even into the 90s. Some are hanging
on after a fashion but not as originally incarnated.


Neat trick supressing the hum while driving headphones - I have found
that to be the toughest aspect of working with tube equipment - it was
no accident that many if not most tube amps and pre-amps did not have
phone outputs from the factory - even back in the day of fully-
enclosed headphones weighing about as much as a Volkswagen.

The hum is most easily suppressed by making the PSU remote and with
all heaters fed with dc.
But I wanted to avoid the hassle of two chassis and a cable.

So I went for potted power tranny. The OPT already have encasement
with close fitting sheet metal. I thought hum was nice and low
straight off the 8 ohm OPT tap , less than 250uV, but that was clearly
audible. Turning up the gain didn't increase the hum and I found that
it must be induced hum between PT and OPT despite the optimum
locations of trannies and potting. 250uV is quite OK for an amp for
speaker use. If the speaker signal was 2.5V, then 2.5mV of hum is
-60dB SNR, and 250uV is -80dB and not bad.
Now average speakers fed with 100mV of signal at 1M are a lot louder
than most headphones at 1M with the same signal level. But the phones
worn close to ears makes them much more sensitive, and then the 100mV
signal is quite loud.
250uV of noise is quite annoyingly audible. So with 10dB of NFB the
noise dropped to about 80uV, just audible, and with a 15R & 8R
resistor network between 8 ohms tap and 0V the noise level then
becomes about 27uV max, and finally acceptable.
I can see a maximum of about 0.5mV on my CRO. If I run the phone
output signal to a little preamp I have with 26dB gain, I see the same
0.5mV reading 10mV on the CRO. So when the hum is less than 30uV, it
becomes almost invisible. The amount of RF noise is much greater than
the harmonics of hum harmonics related to the rectifier. So I place a
1uF cap with short leads across the output and you can then see the
hum in all of its horribility.


Many 30W stereo amps have headphone jacks where there is a an R
divider using say 56ohms plus 8 ohms which improves the SNR by a
factor of 8. Most crap made in the early tube era would never allow
connection of phones on speaker terminals - they were far too noisy.
Hence the resistance divider. One could do the job with a special OPT
tap for heaphones. Where there are taps for speakers between the
common and 8 or 16 taps, one could use the phones across the 8 to 16,
where the turns are 0.3 times the turns for 16, ( and a match for 1.44
ohms ) but the voltage drop and noise drop isn't enough. With the R
divider the load seen by the tubes ( or transistors ) becomes very
high so most of the operation if not all of it is pure class A so THD
is much reduced.
The best way to check power amps for hum levels at idle is to use a
pair of phones off the speaker terminals. Then if you have 1mV of hum
you really hear it loud and clear.

Its probably a lot easier to make a phone amp using a single class A
mosfet driven by a j-fet with some FB.

Patrick Turner.


Glad to read that someone still retains a passing interest in tubes
and their care-and-feeding.

Peter Wieck
Melrose Park, PA

[Patrick Turner]

On Dec 12, 6:43*am, Ian Bell wrote:
Patrick Turner wrote:

snip







I have just got a headphone amp to work acceptably. It has its PSU on
the same compact chassis as the two amp channels which use 12AT7
paralleled for an input tube and a 6BQ5 in triode for the output tube.
There is a 23.2:1 OPT, giving an 8k6:16 ohm load match. *There is a
necessary 10dB global NFB from 6BQ5 anode to the 12AT7 cathode Rk =
680 ohms. Not including the OPT secondary in the NFB loop made the amp
much easier to stabilize.
There are 2 pairs of L&R outputs; one is from the OPT but with 22 ohms
series R at the output and voltage gain of about 5. This allows the
amp to be used as a preamp with useful gain.

The other outputs from the OPT sec have 15 ohms and 8 ohms to make a
loading divider resistance with Rout = 5.2 ohms which gives a low
enough Rout for most headphones of 32 ohms, and fine for the 330 ohm
Sennheiser phones of my customer.

So the 6BQ5 with Ea 280V and Ia = 32 mA is always loaded with a high
RL value regardless of whatever is the phone load.

Without the 15r and 8r divider or anyNFB, I found the hum level was
about 0.2 mV and was audible in my test headphones. This would be OK
if I was driving speakers, but headphones need far lower levels of
noise from any source.
The hum is generated somehow in the output stage and probably by stray
magnetic induction, despite the potting of all transformers in steel
pots and setting them apart on a steel chassis.
If the signal is 200mV average, the SNR is only -60dB. 200mV is loud.
But with 50mV of signal the SNR is only -48dB.
So the first requirement for any amp system is that the noise at idle
without any signal present be inaudible no matter what.

With the 15r&8r divider, the amp noise is reduced about 12dB. The
signal must be 12dB higher at the OPT sec. I finally got levels of hum
below audibility, or below 20uV at the headphones. The NFB helped
achieve this.
Relative to 100mV, the amp noise of 20uV is -74dB. In many headphne
amps I have worked on the noise is higher and the cure is quite
difficult; the Da-ming headphone is an example where noise is audible
without any signal.

My amp can make up to about 1.6Vrms output from the R divider and the
Sennheisers need an average 0.2Vrms level for a near deafening sound.
So the amp has enough headroom. With a low level source up to 0.3Vrms
peak the gain must be turned up a fair way, but with CD which has a
much higher output the gain will be lower without being too low.

I didn't want to use a remote PSU. Had I done so it would have been
much easier to achieve low hum levels.

The amp sure sounds well. Bandwidth is 10Hz to 55kHz at normal levels.
Its slightly less at idiotically high levels because of the OPT
saturation.
OPT are from a 1960 Trio receiver where EL84 were used in 5W SE
outputs.

Patrick Turner.

I am interested in headphone amps and I have always been curious as to
why many designs look like small scale speaker amps when in practice the
requirements are far more modest.

Indeed the requirements look modest. But in fact getting the damn amp
to have low hum is much more difficult for headphones than for speaker
use. So one may as well make a downsized speaker amp with maybe 2W
speaker capability, then avoid loading it down, and have a resistance
divider or very high OPT ratio.

As you say, 200mV is loud in the 330R Sennheiser phones. 0.2Vrms into
330R is a mere 13.3mW which confirms my finding that present day
headphones only need 10 to 20mW to drive them to deafening levels. Most
current headphones provide a sound level of 110dB SPL or more with just
1mW of input, so 10mW gives 120dB SPL which is getting really loud.

So one needs to have low amplifier hum levels. Headphones can be quite
insensitive. Some are, some are not.

Consider a straightforward CF with a quiescent current of say 10mA. This
will easily drive 10V rms into a 10K load with minimal distortion and
10V rms into 10K is 1mA and 10mW which is ample for most phones. You
also get the added benefit of the natural PSRR of a CF. Typical CF
output noise level is no more than 100uV which is 100dB below 10V rms so
any ouput noise/hum above this is going to be induced.

In fact I found 100uV of noise to be clearly audible with phones I
bought to check the amp performance

200mV gave loud levels into Sennheisers and the cheapo test phones.
Low level stuff would be 30mV, and if my amp hum/noise was 30uV then
the SNR = -60dB, and barely good enough. So forget SNR, the noise
without a signal must be made to be just plain LOW. My distortion
tests showed noise didn't change at high levels.


The only problem now is impedance matching. Fortunately, Sowter do a
rather nice headphones transformer type 8665 designed to be driven by a
CF and presenting it with a 10K load. It has various secondaries that
can be arranged to match it to almost any headphone impedance.

The 4k4:8 OPT I have used gives a TR = 23.2, and ZR = 537:1. With the
approximate 20 ohm load on the 8 ohm tap the anode load becomes
10.74k, and at clipping there is 125Vrms at the anode, and a bit
asymetrical which does not matter because the phone use rarely has
anode levels going above 31V, or 1.33V at the 8 ohm tap.
With 15R&8R divider, levels at the phones is then 0.46Vrms. If phones
average levels are 100mV, and peaks go to 1V, then there must be 2.6V
at the 8 ohm tap and about 62V at the anode. Its better to have a lot
of dynamic headroom than barely enough.

I prefer using a normal plate loaded triode with high RL value to give
very listenable results with zero gobal NFB.
But hum was a bit high to I used a 12AT7 driver and some loop FB from
6BQ5 anode to unbypassed 12AT7 cathode.
The network was 120k with series 0.47uF to block anode dc flow to AT7
cathode and Rk = 820 ohms for the 12AT7 two halves paralleled. I
needed 10k plus 270pF HF stabilising network from AT7 anode to 0V, and
33pF across the 120k.
Any value of capacitor load could be connected across the 8 ohm outlet
without HF oscillations. The low level output with R divder have the
tubes seeing ONLY a resistive load.

So, with the two tubes set up like a miature power amp, the closed
loop gain from input to 8 ohm tap is about 5.6x, and about 1.5x to the
phone jacks. This means that with old fashioned sources with average
levels of 200mV the phones can have sufficient levels with gain set at
about -10dB, and with CD play gain set is at about -26dB.

The volume attenuator is a nice quiet DACT 20k log switch, 24
positions. It is placed before all the tubes which I have set up to
run quietly. The other way to do all this is to allow the full DC
levels to be amplified up by at least stage 1 and then have the
attenuator after stage one or after the power stage OPT and using a
switched transformer from Billington, but that's all very expensive,
and allowing signals to be so high before cutting them down for the
phones seems like madness.
Maybe SNR is good, but THD will be far greater.

Patrick Turner.


Cheers

Ian- Hide quoted text -

- Show quoted text -

[Ian Bell[_2_]]

Don Pearce wrote:
On Sat, 12 Dec 2009 12:18:57 +0000, Ian Bell
wrote:

Are you sure? Their web site makes no such statement that I can see,
Sensitivity is usually specified as dB (SPL) for 1mW input. That equates
to about 200mW into 50 ohms.

Cheers

Ian


Here's a copy and paste from their web site:

Nominal impedance 50 Ohm
Contact pressure 3,5 N
Weight w/o cable 255 g
Jack plug 6,3 mm stereo (3,5 mm Adapter)
Transducer principle (Headphones) open, dynamic
Ear coupling circumaural
Cable length 3 m detachable single-sided OFC copper cable
Frequency response (headphones) 14.....26000 Hz
Sound pressure level (SPL) 108 dB (1 kHz and 1 Veff)
THD, total harmonic distortion 0,2 %


From he

http://www.sennheiser.co.uk/uk/home_...341?Open&row=3

d


Amazing, I looked at the same site but the page for the G4ME version
which says:

Jack plug 3.5 mm stereo jack
Nominal impedance 50 Ω
Weight w/o cable 255 g
Transducer principle Dynamic, open
Cable length 3 m single-sided OFC copper cable, detachable
Frequency response (headphones) 14.....26000 Hz
Sound pressure level (SPL) 108 dB (SPL)
THD, total harmonic distortion 0.2 %
Ear coupling circumaural

No mention of voltage.

I notice many of their professional phones quote IEC 268-7 for the SPL
spec which gives different and generally lower figures. I have not yet
managed to find a copy of IEC 268-7 so I am not sure what meathod is
specifies.

Cheers

Ian

[Ian Bell[_2_]]

Patrick Turner wrote:
On Dec 12, 6:43 am, Ian Bell wrote:
Patrick Turner wrote:

snip







I have just got a headphone amp to work acceptably. It has its PSU on
the same compact chassis as the two amp channels which use 12AT7
paralleled for an input tube and a 6BQ5 in triode for the output tube.
There is a 23.2:1 OPT, giving an 8k6:16 ohm load match. There is a
necessary 10dB global NFB from 6BQ5 anode to the 12AT7 cathode Rk =
680 ohms. Not including the OPT secondary in the NFB loop made the amp
much easier to stabilize.
There are 2 pairs of L&R outputs; one is from the OPT but with 22 ohms
series R at the output and voltage gain of about 5. This allows the
amp to be used as a preamp with useful gain.
The other outputs from the OPT sec have 15 ohms and 8 ohms to make a
loading divider resistance with Rout = 5.2 ohms which gives a low
enough Rout for most headphones of 32 ohms, and fine for the 330 ohm
Sennheiser phones of my customer.
So the 6BQ5 with Ea 280V and Ia = 32 mA is always loaded with a high
RL value regardless of whatever is the phone load.
Without the 15r and 8r divider or anyNFB, I found the hum level was
about 0.2 mV and was audible in my test headphones. This would be OK
if I was driving speakers, but headphones need far lower levels of
noise from any source.
The hum is generated somehow in the output stage and probably by stray
magnetic induction, despite the potting of all transformers in steel
pots and setting them apart on a steel chassis.
If the signal is 200mV average, the SNR is only -60dB. 200mV is loud.
But with 50mV of signal the SNR is only -48dB.
So the first requirement for any amp system is that the noise at idle
without any signal present be inaudible no matter what.
With the 15r&8r divider, the amp noise is reduced about 12dB. The
signal must be 12dB higher at the OPT sec. I finally got levels of hum
below audibility, or below 20uV at the headphones. The NFB helped
achieve this.
Relative to 100mV, the amp noise of 20uV is -74dB. In many headphne
amps I have worked on the noise is higher and the cure is quite
difficult; the Da-ming headphone is an example where noise is audible
without any signal.
My amp can make up to about 1.6Vrms output from the R divider and the
Sennheisers need an average 0.2Vrms level for a near deafening sound.
So the amp has enough headroom. With a low level source up to 0.3Vrms
peak the gain must be turned up a fair way, but with CD which has a
much higher output the gain will be lower without being too low.
I didn't want to use a remote PSU. Had I done so it would have been
much easier to achieve low hum levels.
The amp sure sounds well. Bandwidth is 10Hz to 55kHz at normal levels.
Its slightly less at idiotically high levels because of the OPT
saturation.
OPT are from a 1960 Trio receiver where EL84 were used in 5W SE
outputs.
Patrick Turner.
I am interested in headphone amps and I have always been curious as to
why many designs look like small scale speaker amps when in practice the
requirements are far more modest.

Indeed the requirements look modest. But in fact getting the damn amp
to have low hum is much more difficult for headphones than for speaker
use. So one may as well make a downsized speaker amp with maybe 2W
speaker capability, then avoid loading it down, and have a resistance
divider or very high OPT ratio.
As you say, 200mV is loud in the 330R Sennheiser phones. 0.2Vrms into
330R is a mere 13.3mW which confirms my finding that present day
headphones only need 10 to 20mW to drive them to deafening levels. Most
current headphones provide a sound level of 110dB SPL or more with just
1mW of input, so 10mW gives 120dB SPL which is getting really loud.

So one needs to have low amplifier hum levels. Headphones can be quite
insensitive. Some are, some are not.
Consider a straightforward CF with a quiescent current of say 10mA. This
will easily drive 10V rms into a 10K load with minimal distortion and
10V rms into 10K is 1mA and 10mW which is ample for most phones. You
also get the added benefit of the natural PSRR of a CF. Typical CF
output noise level is no more than 100uV which is 100dB below 10V rms so
any ouput noise/hum above this is going to be induced.

In fact I found 100uV of noise to be clearly audible with phones I
bought to check the amp performance


At the headphones themselves quite probably but 100uV should be
achievable at the transformer primary (with a preamp type of tube
anyway) whether you use an SE of CF so at the secondary it should be
much lower. Nor sure what the typical anode noise level in a power tube is.

200mV gave loud levels into Sennheisers and the cheapo test phones.
Low level stuff would be 30mV, and if my amp hum/noise was 30uV then
the SNR = -60dB, and barely good enough. So forget SNR, the noise
without a signal must be made to be just plain LOW. My distortion
tests showed noise didn't change at high levels.

The only problem now is impedance matching. Fortunately, Sowter do a
rather nice headphones transformer type 8665 designed to be driven by a
CF and presenting it with a 10K load. It has various secondaries that
can be arranged to match it to almost any headphone impedance.

The 4k4:8 OPT I have used gives a TR = 23.2, and ZR = 537:1. With the
approximate 20 ohm load on the 8 ohm tap the anode load becomes
10.74k, and at clipping there is 125Vrms at the anode, and a bit
asymetrical which does not matter because the phone use rarely has
anode levels going above 31V, or 1.33V at the 8 ohm tap.
With 15R&8R divider, levels at the phones is then 0.46Vrms. If phones
average levels are 100mV, and peaks go to 1V, then there must be 2.6V
at the 8 ohm tap and about 62V at the anode. Its better to have a lot
of dynamic headroom than barely enough.

I prefer using a normal plate loaded triode with high RL value to give
very listenable results with zero gobal NFB.
But hum was a bit high to I used a 12AT7 driver and some loop FB from
6BQ5 anode to unbypassed 12AT7 cathode.
The network was 120k with series 0.47uF to block anode dc flow to AT7
cathode and Rk = 820 ohms for the 12AT7 two halves paralleled. I
needed 10k plus 270pF HF stabilising network from AT7 anode to 0V, and
33pF across the 120k.
Any value of capacitor load could be connected across the 8 ohm outlet
without HF oscillations. The low level output with R divder have the
tubes seeing ONLY a resistive load.

So, with the two tubes set up like a miature power amp, the closed
loop gain from input to 8 ohm tap is about 5.6x, and about 1.5x to the
phone jacks. This means that with old fashioned sources with average
levels of 200mV the phones can have sufficient levels with gain set at
about -10dB, and with CD play gain set is at about -26dB.

The volume attenuator is a nice quiet DACT 20k log switch, 24
positions. It is placed before all the tubes which I have set up to
run quietly. The other way to do all this is to allow the full DC
levels to be amplified up by at least stage 1 and then have the
attenuator after stage one or after the power stage OPT and using a
switched transformer from Billington, but that's all very expensive,
and allowing signals to be so high before cutting them down for the
phones seems like madness.
Maybe SNR is good, but THD will be far greater.


So did you actually manage to sort out the source of the hum?

Cheers

Ian


Patrick Turner.

Cheers

Ian- Hide quoted text -

- Show quoted text -

[Don Pearce[_3_]]

On Sat, 12 Dec 2009 14:41:58 +0000, Ian Bell
wrote:

Don Pearce wrote:
On Sat, 12 Dec 2009 12:18:57 +0000, Ian Bell
wrote:

Are you sure? Their web site makes no such statement that I can see,
Sensitivity is usually specified as dB (SPL) for 1mW input. That equates
to about 200mW into 50 ohms.

Cheers

Ian


Here's a copy and paste from their web site:

Nominal impedance 50 Ohm
Contact pressure 3,5 N
Weight w/o cable 255 g
Jack plug 6,3 mm stereo (3,5 mm Adapter)
Transducer principle (Headphones) open, dynamic
Ear coupling circumaural
Cable length 3 m detachable single-sided OFC copper cable
Frequency response (headphones) 14.....26000 Hz
Sound pressure level (SPL) 108 dB (1 kHz and 1 Veff)
THD, total harmonic distortion 0,2 %


From he

http://www.sennheiser.co.uk/uk/home_...341?Open&row=3

d


Amazing, I looked at the same site but the page for the G4ME version
which says:

Jack plug 3.5 mm stereo jack
Nominal impedance 50 Ω
Weight w/o cable 255 g
Transducer principle Dynamic, open
Cable length 3 m single-sided OFC copper cable, detachable
Frequency response (headphones) 14.....26000 Hz
Sound pressure level (SPL) 108 dB (SPL)
THD, total harmonic distortion 0.2 %
Ear coupling circumaural

No mention of voltage.

I notice many of their professional phones quote IEC 268-7 for the SPL
spec which gives different and generally lower figures. I have not yet
managed to find a copy of IEC 268-7 so I am not sure what meathod is
specifies.

Odd, they have forgotten to state the signal level that produces that
amount of sound. I guess a web designer missed it.

d

[John Byrns]

In article ,
(Don Pearce) wrote:

On Sat, 12 Dec 2009 12:21:30 GMT, (Don Pearce) wrote:

On Sat, 12 Dec 2009 12:18:57 +0000, Ian Bell
wrote:

Are you sure? Their web site makes no such statement that I can see,
Sensitivity is usually specified as dB (SPL) for 1mW input. That equates
to about 200mW into 50 ohms.

Cheers

Ian


Here's a copy and paste from their web site:

Nominal impedance 50 Ohm
Contact pressure 3,5 N
Weight w/o cable 255 g
Jack plug 6,3 mm stereo (3,5 mm Adapter)
Transducer principle (Headphones) open, dynamic
Ear coupling circumaural
Cable length 3 m detachable single-sided OFC copper cable
Frequency response (headphones) 14.....26000 Hz
Sound pressure level (SPL) 108 dB (1 kHz and 1 Veff)
THD, total harmonic distortion 0,2 %


From he

http://www.sennheiser.co.uk/uk/home_...nes_audiophile
-headphones_005341?Open&row=3

d

Just wondering what on earth a single-sided cable is.

Perhaps one that connects directly to only one driver with the other
feed through the headband, without a "Y" cable underneath your chin?

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[mick]

On Fri, 11 Dec 2009 23:28:40 +0000, Cosmo wrote:

snip

I have some soldering skills and would like to build it myself but I
don't want to start from scratch. Can anyone recommend a kit to build a
good quality headphone amp, preferably that is available in the UK? Or,
if not a specific make/model, what I should look out for in the
technical description? It will be connected to a Conrad Johnson PF-1
pre-amp and, until I get something better, a pair of old Nakamichi SP-7
headphones if that makes any difference.




Have a look he
http://gilmore2.chem.northwestern.ed.../showfile.php?
file=cmoy5_prj.htm

or same site with a shorter url: http://alturl.com/swwq

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

[Phil Allison[_3_]]

"Ian Bell = ****ing IDIOT "


0.2Vrms into 330R is a mere 13.3mW

** Try the math again - pal.

The real figure is 121 * MICRO * watts !!!!

Whoops my bad!


Translates to only about 88 dB with Sennheiser high quality phones.


Most current headphones provide a sound level of 110dB SPL or more with
just 1mW of input,

** Some may, most do not.

I disagree.

** Shame you are a ****ing moron.


I just checked out the Sennheiser web site and nearly all their phones use
Neodymium magnets and quote sensitivities above 110dB.

** But not the HIGH quality ( ie audiophile) models.


The average figure for high quality phones ( like Sennheisers) is more
like
97 dB / mW


I disagree.

** Shame you are still a ****ing moron.



...... Phil

[Ian Bell[_2_]]

Phil Allison wrote:
"Ian Bell = ****ing IDIOT "

0.2Vrms into 330R is a mere 13.3mW
** Try the math again - pal.

The real figure is 121 * MICRO * watts !!!!
Whoops my bad!

Translates to only about 88 dB with Sennheiser high quality phones.


Most current headphones provide a sound level of 110dB SPL or more with
just 1mW of input,
** Some may, most do not.
I disagree.

** Shame you are a ****ing moron.


I just checked out the Sennheiser web site and nearly all their phones use
Neodymium magnets and quote sensitivities above 110dB.

** But not the HIGH quality ( ie audiophile) models.

The high quality ones would be the professional ones. The audiophile
ones would just be regular phones with added bass treble and 2H distortion.

Cheers

Ian



The average figure for high quality phones ( like Sennheisers) is more
like
97 dB / mW

I disagree.

** Shame you are still a ****ing moron.



..... Phil

[Phil Allison[_3_]]

"Ian Bell = Massive ****ing IDIOT "


0.2Vrms into 330R is a mere 13.3mW

** Try the math again - pal.

The real figure is 121 * MICRO * watts !!!!

Whoops my bad!

** ****wit.



Most current headphones provide a sound level of 110dB SPL or more with
just 1mW of input,

** Some may, most do not.

I disagree.

** Shame you are a ****ing moron.


I just checked out the Sennheiser web site and nearly all their phones use
Neodymium magnets and quote sensitivities above 110dB.

** But not any of the HIGH quality ( ie audiophile) models.

You ****ing IDIOT !!!!


The average figure for high quality phones ( like Sennheisers) is more
like 97 dB / mW


I disagree.

** Shame you are still a lying, bull****ting ****ing moron.



...... Phil

[Ian Bell[_2_]]

Phil Allison wrote:
"Ian Bell = Massive ****ing IDIOT "


0.2Vrms into 330R is a mere 13.3mW
** Try the math again - pal.

The real figure is 121 * MICRO * watts !!!!
Whoops my bad!

** ****wit.
#

**Selective message snipper.


Most current headphones provide a sound level of 110dB SPL or more with
just 1mW of input,
** Some may, most do not.
I disagree.

** Shame you are a ****ing moron.


I just checked out the Sennheiser web site and nearly all their phones use
Neodymium magnets and quote sensitivities above 110dB.

** But not any of the HIGH quality ( ie audiophile) models.

You ****ing IDIOT !!!!



The high quality ones would be the professional ones. The audiophile
ones would just be regular phones with added bass treble and 2H distortion.

Cheers

Ian

The average figure for high quality phones ( like Sennheisers) is more
like 97 dB / mW
I disagree.

** Shame you are still a lying, bull****ting ****ing moron.



..... Phil

[Trevor Wilson]

Ian Bell wrote:
Phil Allison wrote:
"Ian Bell = ****ing IDIOT "

0.2Vrms into 330R is a mere 13.3mW
** Try the math again - pal.

The real figure is 121 * MICRO * watts !!!!
Whoops my bad!

Translates to only about 88 dB with Sennheiser high quality
phones.
Most current headphones provide a sound level of 110dB SPL or
more with just 1mW of input,
** Some may, most do not.
I disagree.

** Shame you are a ****ing moron.


I just checked out the Sennheiser web site and nearly all their
phones use Neodymium magnets and quote sensitivities above 110dB.

** But not the HIGH quality ( ie audiophile) models.

The high quality ones would be the professional ones. The audiophile
ones would just be regular phones with added bass treble and 2H
distortion.

**Huh? How do you figure that? Look at the HD800 (top-of-the-line audiophile
headphones):

http://www.sennheiser.com/sennheiser...dphones_500319

102dB @ 1 VRMS. (Damned near 97dB/mW)
14Hz ~ 44kHz +/- 3dB (not much added bass & treble there)
/= 0.02% THD (not much added 2H distortion there)


--
Trevor Wilson
www.rageaudio.com.au

[Ian Bell[_2_]]

Trevor Wilson wrote:
Ian Bell wrote:
Phil Allison wrote:
"Ian Bell = ****ing IDIOT "

0.2Vrms into 330R is a mere 13.3mW
** Try the math again - pal.

The real figure is 121 * MICRO * watts !!!!
Whoops my bad!

Translates to only about 88 dB with Sennheiser high quality
phones.
Most current headphones provide a sound level of 110dB SPL or
more with just 1mW of input,
** Some may, most do not.
I disagree.
** Shame you are a ****ing moron.


I just checked out the Sennheiser web site and nearly all their
phones use Neodymium magnets and quote sensitivities above 110dB.
** But not the HIGH quality ( ie audiophile) models.
The high quality ones would be the professional ones. The audiophile
ones would just be regular phones with added bass treble and 2H
distortion.

**Huh? How do you figure that? Look at the HD800 (top-of-the-line audiophile
headphones):

http://www.sennheiser.com/sennheiser...dphones_500319

102dB @ 1 VRMS. (Damned near 97dB/mW)
14Hz ~ 44kHz +/- 3dB (not much added bass & treble there)
/= 0.02% THD (not much added 2H distortion there)




No information on how the frequency response was measured at what level
etc, etc.

The distortion was measured only at 1KHz and of course they choose the
lowest level they can get away with.

Take those figures with a pinch of salt.
Cheers

Ian

[Trevor Wilson]

Ian Bell wrote:
Trevor Wilson wrote:
Ian Bell wrote:
Phil Allison wrote:
"Ian Bell = ****ing IDIOT "

0.2Vrms into 330R is a mere 13.3mW
** Try the math again - pal.

The real figure is 121 * MICRO * watts !!!!
Whoops my bad!

Translates to only about 88 dB with Sennheiser high quality
phones.
Most current headphones provide a sound level of 110dB SPL or
more with just 1mW of input,
** Some may, most do not.
I disagree.
** Shame you are a ****ing moron.


I just checked out the Sennheiser web site and nearly all their
phones use Neodymium magnets and quote sensitivities above 110dB.
** But not the HIGH quality ( ie audiophile) models.
The high quality ones would be the professional ones. The audiophile
ones would just be regular phones with added bass treble and 2H
distortion.

**Huh? How do you figure that? Look at the HD800 (top-of-the-line
audiophile headphones):

http://www.sennheiser.com/sennheiser...dphones_500319

102dB @ 1 VRMS. (Damned near 97dB/mW)
14Hz ~ 44kHz +/- 3dB (not much added bass & treble there)
/= 0.02% THD (not much added 2H distortion there)




No information on how the frequency response was measured at what
level etc, etc.

The distortion was measured only at 1KHz and of course they choose the
lowest level they can get away with.

Take those figures with a pinch of salt.
Cheers

**Now you're just grasping at straws. Take your beating like a man. Lie
down.


--
Trevor Wilson
www.rageaudio.com.au

[Ian Bell[_2_]]

Trevor Wilson wrote:
Ian Bell wrote:
Trevor Wilson wrote:
Ian Bell wrote:
Phil Allison wrote:
"Ian Bell = ****ing IDIOT "

0.2Vrms into 330R is a mere 13.3mW
** Try the math again - pal.

The real figure is 121 * MICRO * watts !!!!
Whoops my bad!

Translates to only about 88 dB with Sennheiser high quality
phones.
Most current headphones provide a sound level of 110dB SPL or
more with just 1mW of input,
** Some may, most do not.
I disagree.
** Shame you are a ****ing moron.


I just checked out the Sennheiser web site and nearly all their
phones use Neodymium magnets and quote sensitivities above 110dB.
** But not the HIGH quality ( ie audiophile) models.
The high quality ones would be the professional ones. The audiophile
ones would just be regular phones with added bass treble and 2H
distortion.
**Huh? How do you figure that? Look at the HD800 (top-of-the-line
audiophile headphones):

http://www.sennheiser.com/sennheiser...dphones_500319

102dB @ 1 VRMS. (Damned near 97dB/mW)
14Hz ~ 44kHz +/- 3dB (not much added bass & treble there)
/= 0.02% THD (not much added 2H distortion there)



No information on how the frequency response was measured at what
level etc, etc.

The distortion was measured only at 1KHz and of course they choose the
lowest level they can get away with.

Take those figures with a pinch of salt.
Cheers

**Now you're just grasping at straws. Take your beating like a man. Lie
down.




LOL, my tongue was in my cheek all along. ;-)

Cheers

Ian