Why is this a "bad" headphone circuit?
Mar 19, 2006 at 4:53 PM Thread Starter Post #1 of 8

redchiro

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I posted an inquiry on a Sony website about the technical aspects of the headphone circuit in my Sony STR DA-7ES multichannel receiver.
(I use this for a modest home theater and it actually sounds pretty good playing CD's, SACD's, DVD-A through it).
It has one of those headphone circuits where you plug in the 'phones and the speakers automatically mute. The answer I got was, that this receiver, has no separate headphone amp/circuit built in. It simply uses a voltage divider with a 680 ohm resistor across the L/R speaker outputs.
In theory this sounds good-like I would be getting the same pure signal that is fed to the speakers. Instead, it is just shunted to the headphone jack. There are no cheap op-amps in the signal path. I notice that there is certainly tons of power (volume).
In contrast, the headphone output in my Sony XA-777ES CD/SACD player doesn't get much louder as you turn the pot past 12-o-clock (driving HD-650's). It is loud enough for me, but barely gets there-no guts at all. It apparently uses an "afterthought" op-amp based circuit.
My Perreaux SXH1 has plenty of power but even it can't play as loud as the receiver headphone out. Not that I would ever need anything near that kind of volume.
So in terms of quality, is there anything inherently wrong with this inexpensive, resistor across the speaker outputs approach to a headphone amp? Is it about impedance matching, damping, and things like that that make a dedicated headphone amp better at it's sole function?
The rcvr's headphone circuit sounds good to my ears. I have not done an extensive comparison btw. it and the Perreaux but there is no obvious difference in tonal shift upon a quick comparison. No added harshness, or loss of detail, etc.
Thanks for any quick "electronics 101" lessons.
 
Mar 21, 2006 at 11:20 PM Post #3 of 8

fewtch

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It's workable with some cans, but with others (like Senn HD6x0) the higher impedance causes bloated/flabby and uncontrolled bass, and too much midrange warmth.
 
Mar 22, 2006 at 5:24 PM Post #4 of 8

sgrossklass

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Quote:

Originally Posted by fewtch
It's workable with some cans, but with others (like Senn HD6x0) the higher impedance causes bloated/flabby and uncontrolled bass, and too much midrange warmth.


Exactly. (I guess it works with the K1000 since this is fairly bright to begin with. Maybe it was even intended to be driven that way.) An easy (but volume-reducing) fix is placing a resistor (a good bit smaller than the nominal impedance of the headphone, e.g. something like 100 ohms for 300 ohm cans, metal film) in parallel to each headphone driver. This is probably best done with some kind of external adapter.
 
Mar 22, 2006 at 5:46 PM Post #5 of 8

rickcr42

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Quote:

It's workable with some cans, but with others (like Senn HD6x0) the higher impedance causes bloated/flabby and uncontrolled bass, and too much midrange warmth.


improper load or the "new" voicing to please the puppy brigade who want BASS DAMMIT.

ALL headphones were once designed to be driven from power amps which presented a 120 ohm load so the end sound was exactly what the manufacturer meant for it to be when driven by this standard and made measurements way easier for direct 1:1 testing.

Portables screwed that up and now we have a guessing game going on where it is up to the consumer to try and weasle out just what the cans were designed to be driven by.

It is so bad the consumers have driven away all the studio headphones meant to be used in "strings" of parallel 600 om cans directly from monitor amps to single cans driven by wimp headphone amps and all called progress
rolleyes.gif
 
Mar 22, 2006 at 6:01 PM Post #6 of 8

wang228

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redchiro,
It's a fairly well known fact that output impedance of an amp has an effect on sound. The voltage divider (resistor you put across), 'devides' the output voltage of an amplifier differently at different frequencies, as the impedance of the phone varies as a function of frequency. Some search would help. I used to wonder the same thing some time ago too.
 
Mar 22, 2006 at 6:07 PM Post #7 of 8

rsaavedra

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Quote:

Originally Posted by wang228
as the impedance of the phone varies as a function of frequency.


Not all headphones though. Most if not all Grado's have basically ruler flat impedances.

graphCompare.php
 
Mar 22, 2006 at 6:49 PM Post #8 of 8

wang228

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Quote:

Originally Posted by rsaavedra
Not all headphones though. Most if not all Grado's have basically ruler flat impedances.

graphCompare.php



agree. i knew somebody is going to catch me on this : )
 

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