Thanks for the clarification John. That makes their sensitivity about 95 dB at 1 mW. They ought to update their published specifications. I'm still surprised 6V was needed... hope you ears are OK Demian!
Two important points;
With headphones peak levels can be 30 db or more than listening levels.
It is not quite so simple to measure what a headphone delivers to the listeners ears. There is standardized equipment to do this which gives reasonably nice repeatable results, however although it corresponds to what is delivered to humans it is not the same.
I was asked to review the test data in a hearing loss claim. The plaintiff's expert used a cavity that was half the volume of the standard so that all his numbers were 6 db higher. A small note mention that the results were comparable to the standard. But then the hearing loss was the same in both ears and the exposure was only to the left ear.
Because of music dynamics, the peak is 30 dB over the average level. And the same signals ought to produce approximately the same dynamics with a speaker system.
Regardless, a time averaged 90 dB to the ears with headphones or speakers is the same, right? (Lets say for one 4 minutes songs so that we are not trying to damage ears.)
Actually with loudspeakers and the room masking caused by even the limited reverberation in the listening space 20db is more the norm. That is why some use headphones for more critical listening. In doing live symphony work outdoors I found I could hear clipping when the system had less than 30db of headroom. Indoors that drops to 20db. So for headphones the minimum should be at least 30db maybe even more.
An average level of 90 is louder than I prefer, however Osha allows 8 hours per day to 90db. The WHO allows 11 minutes for 91db! Testing if hearing damage is the same from headphones or loudspeakers would be an interesting research project, any volunteers?
But I suspect that with the large volume of the headphone's coupling space that the measured sensitivity is really delivering about 80db to the listener. That is allowed for several hours by the WHO.
The other factor not stated is power compression or that at the loudest levels the increase in volume is not the same as at lower power levels.
So these reasonably efficient headphones used 40db below clipping for really critical listening could possibly be used all day and meet everyones hearing preservation standard.
But that is my OPINION as to the possibility, I have not measured them or seen the test setup used by others or even how big someone else's ear cavities are!
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The LCD-2's have a large internal volume. They are too large for my NBS9a coupler- they overhang the edge and have a huge leak. The sensitivity numbers sound about right. I don't listen at such high levels. However the extra drive or some aspect related seems to have a significant impact on the perceived bass impact and depth.
Measuring SPL inside a headphone is an exercise in standards vs reality. Academics have been going around and around over this for years. You can use a probe microphone and measure the spl inside even an in ear headphone. However the relationship between that and perceived level or response is, shall we say, not established. The headphone manufacturers just ask for a target curve since there is no accepted "right" curve.
This is drifting pretty far from Blowtorch stuff, except perhaps the drive issue.
Measuring SPL inside a headphone is an exercise in standards vs reality. Academics have been going around and around over this for years. You can use a probe microphone and measure the spl inside even an in ear headphone. However the relationship between that and perceived level or response is, shall we say, not established. The headphone manufacturers just ask for a target curve since there is no accepted "right" curve.
This is drifting pretty far from Blowtorch stuff, except perhaps the drive issue.
Mr Curl does talk a lot about the low (noise) end of dynamic range - maybe he also has thoughts on the other end?
I certainly advocate for "audiophile grade" headphone amps to at least be able to drive the desired headphones to 120 dB SPL without clipping
for low feedback circuits, operating at a small fraction of the bias point is another tool for distortion reduction - again pointing to huge "headroom" being desirable
I certainly advocate for "audiophile grade" headphone amps to at least be able to drive the desired headphones to 120 dB SPL without clipping
for low feedback circuits, operating at a small fraction of the bias point is another tool for distortion reduction - again pointing to huge "headroom" being desirable
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It seems like my previous post was deleted.
So I'm trying again.
John could you please email me the info from Kirkwood?
Cheers
Stein
I got a reply from Linear Systems. They are about to release the LSK74 in limmited quantity.
Concerning headphones i had trouble to drive my AKG701. The Headamp shown drives virtually everything. I raised the output bias later to 70mA and made an improvement to the buffer. The output transistors have to be cooled.
I drives the AKG to 5V Class A and that was needed for best results.
Concerning headphones i had trouble to drive my AKG701. The Headamp shown drives virtually everything. I raised the output bias later to 70mA and made an improvement to the buffer. The output transistors have to be cooled.
I drives the AKG to 5V Class A and that was needed for best results.
I have been hearing that from Linear Systems for the last 3 years, so I shall believe when I can actually buy any !!
As to AK701 (sorry for being off topic), my DAO follower using LU1014s in triode mode will drive them with ease. People have tried phones with 25 ohms also and reported more than satisfactory results. Not the most energy efficient I admit. And you might need a gain stage if you wish to use high it with impedance phones. But then a Blowtorch would be perfect for that.
http://www.diyaudio.com/forums/head...llower-headphone-amplifier-2.html#post2133200
Patrick
As to AK701 (sorry for being off topic), my DAO follower using LU1014s in triode mode will drive them with ease. People have tried phones with 25 ohms also and reported more than satisfactory results. Not the most energy efficient I admit. And you might need a gain stage if you wish to use high it with impedance phones. But then a Blowtorch would be perfect for that.
http://www.diyaudio.com/forums/head...llower-headphone-amplifier-2.html#post2133200
Patrick
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I care about energy efficiency of cars, ships and aircraft, not headphone amplifiers!
I tried your DAO design that has been built by a friend... it really is very good. Nice work Patrick.
Your amp looks interesting. However it does bring up a real question- the discrete portion can be replaced by this: LME49600 - High Performance, High Fidelity, High Current Audio Buffer to do the same with a few less parts. probably a little more expensive but the transistor matching comes with it. There is a drawing of the same application on the web page. I have heard the part and it seems OK. I don't know if its better than the discrete parts. The question being where do you transit from discrete to integrated circuit solutions?
I think the answer probably depends on perspective...
If doing it professionally, such as yourself, then BOM cost and marketing requirements must surely be significant factors.
However if designing at home, such as myself and a thousand lurkers, then we must decide if we feel the added effort of going discrete brings a sonic benefit. Then comes the inevitable questions of PP or SE, open loop or gNFB, etc., etc. !
How do you guys choose?
Build and listen to find out what works for you.
That is the only way.
I have built balanced discrete Class A's.
I have also build various chip amps, including Nelson's X'ed design.
Many of them are very nice sounding.
In the end, for serious, long listening, I always go back to Class A balanced.
So that is what works for me -- balanced Class A, minimum no of gain stages, no global loop feedback.
Like the DAO -- utterly simple, sounds fantastic, way beyond my own expectation.
Patrick
That is the only way.
I have built balanced discrete Class A's.
I have also build various chip amps, including Nelson's X'ed design.
Many of them are very nice sounding.
In the end, for serious, long listening, I always go back to Class A balanced.
So that is what works for me -- balanced Class A, minimum no of gain stages, no global loop feedback.
Like the DAO -- utterly simple, sounds fantastic, way beyond my own expectation.
Patrick
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Patrick, many thanks for your reply. Do you have a link to your amp, so that I may learn?
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You are being too modest.
No, I have not published, but you can imagine a high output voltage (say +/- 20V) blowtorch or Ayre frontend with a gain of 20, followed by a MOSFET Circlotron follower (unity gain). As simple as that.
I will eventually want to replace the UHC MOSFETs (2SK3163 cascoded) by some high transconductance power JFETs. I guess for a quick start, you could use 4x LU1014 in parallel (see Zen Version 9) per leg of circlotron if your speaker is not low impedance.
Patrick
No, I have not published, but you can imagine a high output voltage (say +/- 20V) blowtorch or Ayre frontend with a gain of 20, followed by a MOSFET Circlotron follower (unity gain). As simple as that.
I will eventually want to replace the UHC MOSFETs (2SK3163 cascoded) by some high transconductance power JFETs. I guess for a quick start, you could use 4x LU1014 in parallel (see Zen Version 9) per leg of circlotron if your speaker is not low impedance.
Patrick
i build versions with the LME49600 and also with the BUF634. The BUF worked without trouble but i got offset with the LME. I whould recommend a servo in the Opamp stage then.
All of this versions can be made to sound well but for DIY the discrete is maybe more interesting because people may have most parts aready in stock.
The Diamond Buffer can be made much simpler without sounding much worse. I was more concerned about PSU rejection and in fact my version is dead quiet.
All of this versions can be made to sound well but for DIY the discrete is maybe more interesting because people may have most parts aready in stock.
The Diamond Buffer can be made much simpler without sounding much worse. I was more concerned about PSU rejection and in fact my version is dead quiet.
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