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Old 21st December 2012, 10:35 AM   #21
Tajzmaj is offline Tajzmaj  Slovenia
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This might help. I think the author knows what to listen and how to describe it.
Cheers
Battle Of The Flagships (50+ Headphones Compared)
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Old 21st December 2012, 10:46 AM   #22
EUVL is offline EUVL  Europe
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To quote a sentence from the above linked review :

" ..However, my findings over time were that the K701 is an extremely difficult headphone to drive. Its low-sensitivity design requires the amplifier to put out a substantial amount of current......"


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Old 21st December 2012, 10:53 AM   #23
qusp is offline qusp  Australia
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yeah except he's incorrectly called it low sensitivity..... i'd hate to see what he calls efficient

aha I thought there was something odd about that number, seems AKG like to rate in dB/V rather than dB/mW @1kHz. so they arent that efficient, they still dont call for that much power by the numbers.

i'll still try them out again, but my current amps have output impedance measured in fractions of a mOhm and output 200mA +/-15v balanced, cant see how they could need more than that but i'll give it a try

Last edited by qusp; 21st December 2012 at 11:06 AM.
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Old 21st December 2012, 11:25 AM   #24
EUVL is offline EUVL  Europe
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Or try them with a gain clone.


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Old 21st December 2012, 11:46 AM   #25
qusp is offline qusp  Australia
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oh no its easier for me to try with the DAO as setting up the amp again is less trouble than building a gainclone, just have to wait till the next set passes through here for recabling, shouldnt be too long.
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Old 21st December 2012, 11:51 AM   #26
EUVL is offline EUVL  Europe
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No everyone has a DAO lying around.
If you use the DAO, try the 65R 0.1 Zobel in parallel.


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Old 21st December 2012, 12:00 PM   #27
qusp is offline qusp  Australia
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true that, maybe more soon

interesting about the zobel, I noticed the AKG K1000 appeared to have some sort of Zobel on the little PCB internal to the headphones. crappy components though, I often wondered about trying with different values and higher quality parts.
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Old 21st December 2012, 07:05 PM   #28
Blues is offline Blues  United States
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Questions 1-4 are considered if we are driving multi-driver loudspeakers with their larger moving surface areas, complex/multi-freq crossovers, longer run cables, etc. Just compare the impedance/phase plots of most headphones and see they're not as crazy as loudspeakers. 98dB SPLs are very, very loud but my ears are 10 feet away and I'm in a large room.

5. For digital sources and dacs I can recommend 200 ohms or less Zo which modern designs now are typically lower. In some cases even 600 ohms is acceptable depending on recorded material levels.

6. Of course always design a headamp for the greatest flea watt if not the greatest 1st watt...I don't even bother to use one these days. Choose a superbly spec'd, great sounding source/dac, an effective volume control, connect your favorite headphones then blissfully listen.

7. Much better?

Have a peaceful Christmas!
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Old 21st December 2012, 11:16 PM   #29
Blues is offline Blues  United States
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Quote:
Originally Posted by qusp View Post
yeah except he's incorrectly called it low sensitivity..... i'd hate to see what he calls efficient

aha I thought there was something odd about that number, seems AKG like to rate in dB/V rather than dB/mW @1kHz. so they arent that efficient, they still dont call for that much power by the numbers.

i'll still try them out again, but my current amps have output impedance measured in fractions of a mOhm and output 200mA +/-15v balanced, cant see how they could need more than that but i'll give it a try
I don't know if you're surprised to know that 105 dB/V of the K701 is actually 117 dB/mW...
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Old 22nd December 2012, 05:47 AM   #30
EUVL is offline EUVL  Europe
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According to the website of AKG :
K 701 - AKG
the K701 is specified at 200mW, 62 ohm, 105dBSPL/V.

It is not specified whether the V is rms or absolute.
Let's assume best case, that 1V means +/-1V sine wave. I think it is not an unreasonable assumption.
+/-1V sine into 62 ohm = 1*1/62/2 = 8.06mW.

So 105 dB/V => 105dB/8.06mW = 105-20*log(8.06) dB/mW
= 86.9 dBSPL/mW_rms

If one wants to use peak power instead of RMS then it will be 6dB less.
i.e. 80.9 dBSPL/mW_pk

Assuming max. power rating of 200mW, constant impedance, and sinusoidal signals,
v_pk = sqrt (200mW x 2 x 62) = 4.98V
i_pk = 4.98/62 = 80.3mA

Allow a factor of 1.5~2 for transient current in case of unfavorable back emf phase.
It would not be unreasonable, IMHO, to specify a maximum output current of 150mA for the headphone amplifier.
The amplifier would then in any case not be the limiting factor in this audio chain.


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Last edited by EUVL; 22nd December 2012 at 05:55 AM.
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