HP amp out impedance vs. HP impedance

[ginetto61]

Hi !

sorry if the issue has already been discussed
But in an old review of the Grace m901 headphone amp I read the following statement

... The 901 uses a high-current output amplifier with an output impedance of 1 ohm and is capable of driving 8 ohm loads.
Perhaps because of its low output impedance, the 901 has the best low-frequency control of any headphone amp I have heard.

Is this statement correct ? I would like to get a nice low-frequency control on my low Z headphones so I would like to know if an amp with a very low Z out is mandatory.
Thanks a lot for any kind advice
Kind regards,
gino

 

[Rubin]

The short answer is "yes": Low output impedance is essential for bass control on low impedance headphones.

A wonderful article on this topic recently appeared on Inner Fidelity:
Meridian Explorer: A Case Study of the Effects of Output Impedance on Headphone Listening | InnerFidelity

 

[ginetto61]

Thank you very much indeed for your kind and valuable reply
What i do not understand is why low Z out amp are not very common while a lot of HPs around are indeed low Z
For instance I am listening to a HP of 55 ohm with an amp with a Z out of 10 ohm
The bass is very unsatisfactory in terms of control
The very same amp drives much better a 250 ohm HP by the way
Is it so difficult to build low Z out amp ?
This is extremely strange to me
Thanks for the very interesting article and regards,
gino

 

[sandyK]

Some headphones are designed to comply with the old IEC61938 specification, that headphones should be driven from a 120 ohms source impedance irrespective of their impedance. The AKG 701 is one example. It sounds far more tonally balanced when driven from a 120 ohm source impedance, (although a few prefer 100 ohms.) You then need an amplifier with higher voltage drive capabilities for best results . Those using + and -15V ( or even + and - 20V) supply rails are a good choice.
SandyK

 

[ginetto61]

Ok but i would very much liked a comment on the quoted statement
If the low frequencies are not controlled I am quite sure that they will blurred all the other frequencies
A low damping of the driver will cause the driver to have some kind of ringing
For me this is extremely clear
Nevertheless I would like to get a confirmation from experts
I think this is a fundamental issue
And sorry but to say

The AKG 701 is one example. It sounds far more tonally balanced when driven from a 120 ohm source impedance,

is a little generic
Kind regards,
gino

 

[sandyK]

Ok but i would very much liked a comment on the quoted statement
If the low frequencies are not controlled I am quite sure that they will blurred all the other frequencies
A low damping of the driver will cause the driver to have some kind of ringing
For me this is extremely clear
Nevertheless I would like to get a confirmation from experts
I think this is a fundamental issue
And sorry but to say
is a little generic
Kind regards,
gino

Gino
There are quite a few members of a U.K. based forum that own K701s, and that is their general consensus. The K701s when driven from a much lower impedance source are far too detailed and fatiguing for long listening sessions. The same applies to the Audio Technica W1000 that I own.

Regards
Alex

 

[ginetto61]

It would be nice to have more info
For instance a list of amps that make those HPs sound good
Saying that an amp with 120 ohm of Z out is needed for the best sound from that AKG is a little vague
And it would be useful also to know which low Z out amps are not good for the AKG
I say this because a friend of mine had a Melos Sha Gold HP amp, a vey low Z out unit but a very high quality one
It was just splendid with both Grado 32 ohm than Beyerdynamic 250 ohm
Fatiguing for me means usually distorting
Kind regards,
gino

 

[sandyK]

Gino
Check out the impedance graph for the K701
Regards
Alex`

http://www.soundstagemagazine.com/measurements/headphones/akg_k701/impedance2.gif

 

[ginetto61]

Thank you
But so do you exclude that a low Z out amp can make the K701 sound very good ?
I am quite obsessed about the danger of muddy bass that over imposes itself on the rest of the band
And actually i have found usually better the bass of high Z HPs, like 250 ohm HPs
Kind regards,
gino

 

[jackinnj]

Might want to consult Richard Marsh's article in Linear Audio Volume 3 -- an HP amplifier and equalization scheme.

 

[ginetto61]

Might want to consult Richard Marsh's article in Linear Audio Volume 3 -- an HP amplifier and equalization scheme.

Actually my knowledge and ability to understand is very limited
I just wanted to get opinions about the statement quoted at the beginning
For instance, i sincerely do not know if a comparison with loudspeakers and HPs can be done
We tried a same speaker with a tube power amp (high Z out) and then with a solid state power amp (very low Z out)
The performance in the bass was completely different with the SS am much much better
The SS amp had a grip on the woofers that the tube amp did not match at all.
As to find low Z out amp is very very difficult I think that i will solve with a 250 ohm HP and a normal amp
Thanks and regards,
gino