Preamp as headphone amp?

[DancingPriest]

Excuse my ignorance, but why can't a preamp be used as a headphone amp?
And yes, I have been drinking...

[Fran]

Often pre-amps are made to work into an impedance of a power amp, typically above 10K ohms. They can sound weak and anaemic into headphones with an impedance anywhere from 32 to 600 ohms. They can lack the "grunt" to drive the headphones.

Also, the output capacitor typically present on most preamps, (usually ~1-10uF) will set up an RC filter (much like that in a crossover of a speaker) with the impedance of the headphone which means you will have a bass cut in the headphone.

Typical example, my aikido headphone + preamp. Preamp output taken from the valves through a 4uF cap to the power amp. Headphone outputs go through a mosfet stage and are followed by a 1800uF cap.

Not a hard and fast rule, but usually each is engineered for different things unless deliberately designed so.


Fran

[james]

A few years ago I was looking for a headphone amp and I read the Naim Forum http://forums.naimaudio.com/eve and Pink Fish Media http://www.pinkfishmedia.net/forum/ for advice.

There were a lot of posts saying that a particular Naim pre amp [the 32.5] made a good Headphone amp ...

Of course with Naim everything is OK pricewise until you add the [optional] upgraded power supply.

In the end I bought the Naim headphone amp.

James

[DancingPriest]

Belated thanks lads!