[chillysalsa]

OK, could someone please explain to me the general relationship between the ratings of headphones & amps?

When selecting heaphones to work with the jack on your amp, what is the 'minimum' impedance you can run based on the specs? How do you calculate it?

I'm not interested in any specific headphone/amp combination, but the rule of thumb to follow...

For example, if the specs for headphone jack are:
Rated output - 0.3V @ 8 ohms
Impedance - 680 ohms

A min impedance for the headphone should be ____?

ohm my gosh I can't figure it out...

THANKS!

 

[aeberbach]

It is essentially meaningless. Good headphones come in high and low impedances. All that really matters is that it is a reasonably close match with your amplifier, or if mismatched, that the amplifier is sufficiently powered to overcome the difficulty.

When you have a high impedance connected to a low impedance amp, the amp has to work harder to produce the same sound level. Double and half to estimate the effect - often you will see ratings saying "2W into 4 ohms, 1W into 8 ohms, 1/2W into 16 ohms" etc - so just keep doubling and halving until you get to 600 ohms and you'll see that maybe that amp isn't the best HD600 driver.

When you go the other way, well I don't know - probably it places great stress on the amplifier, be careful not to exceed current rating on output devices. Unless you're doing DIY tube stuff with output transformers and multiple taps on those transformers you will rarely have the problem of an amp expecting too much speaker/phone impedance. In P. Millett's (Wheatfield Audio) ECC99 amplifier schematic he shows optional resistors in series with the headphone output to overcome this problem, as he designed it for use with 120 ohm AKG K1000 phones.

Just use the quoted figures as a guide, it is no indication of performance unless you have both sets of figures to compare.

Amplifier output impedance is another thing entirely

Bruce explains it pretty well:
http://www.transcendentsound.com/amp..._impedance.htm

 

[elrod-tom]

Thanks to aeberbach for this post...very helpful for those of us who are electronically challenged.

 

[Budgie]

We recently had a thread about this:

http://www.head-fi.org/forums/showth...ight=efficency

I think it would be worth looking at.