Power amp for headphones

[kvik]

Hi Frans

This is possibly an odd question, but.. If you have a very good source and preamp (which many people do) why are there no power amps for headphones available on the market?

Someone asked this on a different fourm, and no-one there seemed to be able to come up with an answer.

Is it perhaps that this power amp would need to be specifically matched to each set of headphones? Or are there other limitations making this power amp concept not viable?

I am talking about a power amp connected to the variable output of a preamp, where this power amp is meant to drive headphones only. A second variable output would connect to the speaker power amp, and the output selector on the preamp would be used to choose headphones or speakers.

[Solderdude]

Usually dedicated headphone amps have a volume control as well.
This is so you can adjust the speaker and headphone volume independently.

Of course there are many headphone amps with line-outs that 'double' as pre-amp (without input selector)

You can use any headphone amp (with volume control) as a headphone amp controlled by a pre-amp by simply setting it's volume control at maximum setting.
Almost all headphone amps basically have the volpot on the input and a 'dedicated headphone power-amp' behind it.
By passing the volume control (setting it to max.) basically is what you asked about.

I don't know of any headphone amp without volume control though.

[kvik]

Will the headphone amp volume pot have a detrimental effect on sound if set at maximum?

[kvik]

Also, if a headphone power amp was to be constructed, would it need to be specifically matched to the headhpones used?

[Solderdude]

Will the headphone amp volume pot have a detrimental effect on sound if set at maximum?

It basically is completely out of the signal path.
On the maximum setting the wiper makes direct contact with the 'input'.

[Solderdude]

Also, if a headphone power amp was to be constructed, would it need to be specifically matched to the headhpones used?

Not particularly. It should be able to provide enough current to drive low impedance headphones and enough output voltage to drive high impedance headphones.
This is really easy to make.
Basically a low noise speaker power amp.

[kvik]

Will the headphone amp volume pot have a detrimental effect on sound if set at maximum?

It basically is completely out of the signal path.
On the maximum setting the wiper makes direct contact with the 'input'.

Does this depend on pot quality and/or type, or is it a universal truth?

[Solderdude]

All potmeters I have seen work this way.

[kvik]

Thank you, Frans.

[Solderdude]

http://www.geofex.com/article_folders/p ... s/pot5.JPG

That's a typical volpot track.
You can see where the wiper tracks are and that near both ends the track no longer makes contact with the resistance (black) material but with metal surface.

[Kolind]

Interesting question in fact. I have a very fancy DIY preamp lying around but have newer seen any pointe in using it since i moved away from that setup. I have always assumed that it would make no sense to attempt hooking it up when there is a vol. control on the amp itself. I mean - two times volume control would never improve anyhing. However, if a maxed regular pot is in fact just passing the signal along, it could make sense attempting to use my old preamp instead.
I do suspect though that the benefit of my better pot on my preamp is neglible when adding two more connection points of cabling etc instead of 'just' doing the job in the headphone amp instead. What are your thoughts on that?

Edit: My amplifyer in question here is an old Darkvoice 336i which i assume has a somewhat mediocre potmeter

[Solderdude]

the output resistance is kind of high (78 ohm)
It is suited for high impedance headphones though.