[fzman]

Some time ago I built a fully dual-mono headphone amp, which only shares the iec inlet.  2 volume controls, two transformers, two completely seperate power supplies, etc etc etc...  i reterminated my Denon 7000s with a Bulgin 4-pin connector (708-1093-ND and it's mate and pins from digikey), and the mate on the amp, in order to preserve the dual-mono-osity,  i just finished another amp, and it is playing now (as I type this), with a Neutrik locking trs jack alligator-clipped to the board.  i also mounted a 4 pin xlr on the front panel for the "balanced" connection, and thought to abandon the Bulgin, and reterminate the denons, and mount an xlr on the original amp as well.
 
 
long back-story, but the question becomes- is this all a waste of time, and should i just put a nice 1/4" plug back on the Denons (i really like the Furutechs, and can steal one from a cheapie pair of MB Quarts which i keep around as a sacrificial test-pair)  and be done with this.
 
so, what are the sonic advantages of doing a 4-wire connection vs. 3 wire, even when the amp has a maniacally implemented star-ground shared between both channels anyway?
 
Thanks for reading this, and answering-- this is not a troll, I am genuinely curious as to your opinions, both technical and sonic.
 

 

[deadlylover]

I could be completely wrong here, but I think the 4 pin is just used for a connection into a balanced amp without having to deal with the hassle of two plugs.
There's no ground in a balanced connection, just positive and negative for each channel. (total of four amp boards)
 
I don't think dual mono is balanced, so yeah, just put whatever plug you like ^^. (or maybe dual mono is the new term for balanced? i dunno what the hipsters call it nowadays =P)
 
edit: I think the 1/4" plug shorts the outputs for a split second as well when you plug and unplug the connector, it depends on your amp if it's happy with that or not. It's a non-issue really as you can just shut the amp of for a moment, but it's something to consider.

 

[nikongod]

 
Quote:

long back-story, but the question becomes- is this all a waste of time, and should i just put a nice 1/4" plug back on the Denons (i really like the Furutechs, and can steal one from a cheapie pair of MB Quarts which i keep around as a sacrificial test-pair)  and be done with this.
 
so, what are the sonic advantages of doing a 4-wire connection vs. 3 wire, even when the amp has a maniacally implemented star-ground shared between both channels anyway?
 

 
4-WIRE vs 3-WIRE cable has some differences (at least theoretically). Impedance in the ground wire (shared between the Y-split and the TRS plug) DOES lead to cross-talk. In a 4-wire cable with TRS the "shared portion" is only the TRS plug so crosstalk due to the wire can be reduced if not eliminated. People post SCARY good numbers for crosstalk with simple cmoyish amps that drive the load from one side with a shared ground - like 80-90db. 
 
Anyways, onto connectors. 
4-pin XLR plugs do not short the outputs when you plug/unplug. TRS plugs do. Im not sure how important it is to a headphone, but the contact "quality" on an XLR plug is better than a TRS. 
 
On that note, if the "ground channels" in your amp drift they may wind up fighting if tied directly together. you know, one is 1mV above wall ground, the other 1mV below and you have 2mV across a piece of wire with the 2 channels sourcing and sinking scary amounts of current. 
 
So there are some advantages to an XLR plug even on a single ended amplifier. 
 
IMO Dual mono is most important in SET amps with very low PSRR. With Push-pull tube amps, or SS amps with PSRR in the OMG ranges its just excessive. 
 
On that note, if its a commercial product, keep it that way! Its a major selling point, even when what you describe would work WORSE than a single power supply. "quad mono" for example which makes no use of CMRR.

 

[Yoga Flame]

 
Quote:

4-WIRE vs 3-WIRE cable has some differences (at least theoretically). Impedance in the ground wire (shared between the Y-split and the TRS plug) DOES lead to cross-talk. In a 4-wire cable with TRS the "shared portion" is only the TRS plug so crosstalk due to the wire can be reduced if not eliminated. 
 

Yup, one of the first things I did after joining Head-fi was to replace my headphone's stock 3-wire cable with a 4-wire one. Crosstalk was significantly reduced. This was my inspiration: Crosstalk on M50
 
But to put things in perspective, the crosstalk level to begin with was already very low. I could only detect the original crosstalk by playing a mono sound on the left channel, turning up the volume to dangerously loud levels, and listening on the right side. With open headphones, you will get as much crosstalk at that level just from your right ear hearing the sound leakage from the left driver on the other side of your head.
 
Nonetheless, when I modded my Fostex T50RP, I made it a point to swap out the TRS jack with a TRRS one.
 

 

[fzman]

thanks for the responses.  I may have been a little unclear in my original post.  The amp pictured is based on a +/-17v psu, with the raw dc supply outboard, and the regulators and lots of post-reg. r-c filters and local bypasses.  it is set up to run on a 3-wire output, L, R and return to star ground.
 
the earlier amp i built, using the 49713 opamps, has "2 of everything", and I needed to use a 4 wire plug to maintain the complete isolation.  it may just be massive, useless overkill to keep both supplies in it anyway.  so, i may remove one, and feed both channels from the single supply anyway (those custom Electra-print trannys are not cheap, but oh so worth it!).
 
So, the question is whether to use 1/4" trs on all headphones, and use the mating jacks on the amps (the standard for ease of compatibility)......  or 
 
use 4-pin xlr on the headphones, amps, and either add 1/4"  jacks on both amps, and make up extension cords with both 4-xlrs and trs's.....   higher PITA factor, need adaptors or extra jacks/plugs- 
 
since i am in the biz, i do have access to occasional loaner equipment (e.g., the HD800s on my ears right now) and would wonder if the extra connectors in the adaptor required to connect them to my amps would result in an unlevel playing field when comparing them to my denons (if they had the 4-xlr).   
 
too many bets to hedge, too little time.