FOTM: 5-pin Headphone Jack

[nikongod]

Dusty:

Yeah, that's right. So far. So, you're asking the same question on the amp side. The L/R- is unterminated. I definitely don't want a switch there.

If the output phases are at ground, just figure out a way to get ground up to the outputs.

So, in summary the problem is with a 4-pin jack, or even two 3-pin jacks, that are used on the output of a four channel design, you cannot "convert" this using any combination of adapters, custom or otherwise, for use by a single ended terminated headphone. You need a ground reference.

The problem is not really that it cant be done with adapters & dongles. The problem is that these dongles need to be built for one type of amp and once you have built this adapter and set it loose in the wild who knows what people will do with it.

Will whoever has this dongle take the 4-pin --> 1/4" adapter which grounds to the shell/chassis and plug it into the second example amp I gave, blowing everything up? Will they take an adapter you built for a specific amp that behaves well when the negative phases are tied together and mount it on an amp that dosnt appreciate that treatment? Who knows.

On that note: if you have room for 2*3 pin you have enough panel space for the "dual" 3-pin/1/4"TRS jacks or 1*4pin & 1*1/4"TRS. Every connection on them is separate from the others so you can easily control what goes where and how.

If the amp is designed to have the outputs at ground potential just use the ground reference as the return from the SE headphone jack. Depending on what you think about active ground it wont work as well as that, or certainly balanced. Thats OK, if there are XLR's on a single ended amp people will re-terminate their headphones to use them... Its a no-brainer on an amp which is actually balanced.

If you built a 4-channel amplifier whose output is not at ground potential (both outputs at say +12.000V to facilitate DC coupling without voltage shifters) and have separate outputs for SE and balanced just cap couple the SE outputs.

Edited February 1, 2010 by nikongod

[luvdunhill]

If the amp is designed to have the outputs at ground potential just use the ground reference as the return from the SE headphone jack. Depending on what you think about active ground it wont work as well as that, or certainly balanced. Thats OK, if there are XLR's on a single ended amp people will re-terminate their headphones to use them... Its a no-brainer on an amp which is actually balanced.

Thanks Ari. If the amp has outputs at ground potential there is one snag, if I'd like to avoid some sort of of "balanced" / "single-ended" input selector switch. Thus, all four outputs would be active.

With regard to adapters, there was almost fail at the DFW meet due to one of these, I believe the LD mk6 has one of these custom adapters. I still cannot figure out how it worked...

Edited February 1, 2010 by luvdunhill

[nikongod]

Thanks Ari. If the amp has outputs at ground potential there is one snag, if I'd like to avoid some sort of of "balanced" / "single-ended" input selector switch. Thus, all four outputs would be active.

Its really easy to get balanced outs from either input if you have a phase splitter/diff pair integrated into the amp Input transformers are always nice.

If feedback loops cross-couple the 2 phases converting to SE may not be so simple. I could not think of a good way to do this on the silver ghost (SE & balanced in, SE&balanced out with global feedback) so I just left it open loop.

Assuming the output impedance of the amp is reasonably low:

Without something to split phase that accepts SE and balanced inputs I think the easiest thing would be to ground the inputs to the "negative phase amplifiers" when SE inputs are used and make them work as channel specific active grounds to the XLR's and do the TRS output the same way regardless of what input is used. This could all be done easily with a single source selector switch.

If the output impedance of the amp is on the OTL tube high side things look bleak without a phase splitter. Using the "negative amp" as an active ground shoots the amp in the foot. Most of the SP amps I have seen fail big time for this when using XLR outs & RCA ins. A couple SP amps used input transformers and avoid this. RSA gets around this on the B52 (and I think the Apache, although why he didnt do the thing above, IDK) with some relays to ground the -pin on the XLR when an RCA input is used. I guess Ray deserves credit for only making the end user touch 1 knob rather than mucking about with switches on the back panel like others, although why none of the OTL tube designers integrate a phase splitter into their amps is beyond me. its still only 1 knob for source selector on the RSA, it just controls a more complicated relay network.

[Currawong]

Forgive me if I missed someone else suggest it, but why not make a break-out dongle with a 1/4" and 4-pin XLR jack coming which plugs in using something infrequently used, like a 5 or more pin XLR? At least then it can't be plugged into the wrong amp easily.

[luvdunhill]

yeah, that was pretty much my suggestion. As long as they don't think those 5-pin XLR jacks near the baseboards in the fancy hotel conference rooms aren't headphone outs, you're probably good.

[spritzer]

What about a Lemo connector? They are available in 5 pin and short of somebody believing they were a HE90 socket it's easy to see what it does. Not cheap though but pretty well made.

[luvdunhill]

it's not really a question of which 5-pin connector, IMHO, but yeah, they are rather nice.

[spritzer]

The only issue for me is that the Jade has a 5 pin XLR and some idiot might think those two are compatible.

[cetoole]

I guess it is time to point out that pretty much all good headphones are already terminated to 5 pin plugs.

[swt61]

Just when I was starting to like you.

[cetoole]

I said pretty much. K1000 are one of the exceptions.