Class D power amps as headphone amplifiers

CSMR · « **on:** 2 Feb 2005, 05:47 am »

We all know about the how good budget class-D amplifiers are with speakers. This technology hasn't infiltrated headphone amplification.
There seem to be two ways of using speaker amplifiers with headphones:
1. Use a headphone designed for use with a power amp: AKG K1000, some Stax I think
2. Use an adapter
Headphone inputs are two channels and a common ground, so the speaker amplifier needs to have outputs with a common ground on both channels. (OR the headphone cable has to be cut up to give four separate wires.)
Adapters are either an in-line resistor or something more complicated involving impedence matching.

Am I the only person interested in this possiblity?

I tried the Teac with an adapter and it didn't work. Some of what I have said is taken from rickr42 here:
http://www6.head-fi.org/forums/showthread.php?t=104175.

Rob Babcock · « **Reply #1 on:** 2 Feb 2005, 06:33 am »

My Griffin Pwave is supposed to be a good 'phone amp, but I don't have a decent pair of cans to try it out.

Occam · « **Reply #2 on:** 2 Feb 2005, 03:52 pm »

A quick caveat-
Many of the class D amps people are using are BTL (bridge tied load) achitectures, where none of the output leads are sitting at ground potential. Both output leads of these amps are sitting at about half the voltage of the output stage's powersupply. Signal is derived by both leads of the amp sitting at that voltage swinging in opposite phase.
All this means is that the common practive of using a common ground connection in headphone cables (or the cans themselves) is going to cause a "misfunction". You need to be very careful as to how the wiring chain from the amp to the phones is constructed.

You also need to consider the specific amp and which specific chip is being used. The Powerwave and Teac are BTL amps, while the BelCanto and CarverZRs are not. All of those amps are using chips from Tripath.

Long story short - make sure the wiring to your phones share no common ground, for both the cable and phones themselves.

CSMR · « **Reply #3 on:** 2 Feb 2005, 07:00 pm »

That's interesting Occam.

Do you happen to know whether the Panasonic, JVC or Sharp amps are Bridged Tied Load?

Occam · « **Reply #4 on:** 2 Feb 2005, 08:21 pm »

CSMR,

I'm not sure, though I think??? these amps ouputs have conventional grounds, but I'm not gonna buy you a new pair of phones

Nor did I mean to dissuade you from using the Powerwave as a headphone amp, just that you should be careful that when you wire the outputs to the headphones that they do not share a common ground connection, as that 'ground' is not sitting at ground potential and actually carries signal. The Powerwave,, like the Teac, is really a balanced output amp.

CSMR · « **Reply #5 on:** 2 Feb 2005, 09:46 pm »

Thanks; I'll try to get in touch with Panasonic or Sharp directly to check.

Occam · « **Reply #6 on:** 2 Feb 2005, 10:26 pm »

CMSR,

I feel like Emily LaTella from the old 'Saturday Night Live', nevermind!
I was totally wrong as I was confusing the Sonic Impact amp with the Powerwave. As the front to the PowerWave has a standard 'phones' input I can only assume it addresses the issue, which you specifically referred to in your first post of this thread.
What I said previously does apply to the SonicImpact and Teac, but assume is not true for the Powerwave.

Sincere apologies,
Paul

kaxixi · « **Reply #7 on:** 6 Feb 2005, 10:05 pm »

Panny has a series of CD players with digital headphone amplifiers. They presumably use them to increase battery life--but they also sound really good.