[Rescue Toaster]

I've been fiddling with the design and I may even be able to get my tube amp back to single-ended. The problem was I return the transformer primary to the cathode of the tube, not ground. Along with the CCS feeds, this essentially makes the tubes run fixed bias, and eliminates the need for a bypass capacitor.

Since they're operating fixed bias there shouldn't be much of a problem with using a shared cathode resistor, assuming the two tubes are pretty close bias-wise (less than 10 volts difference on the anodes and I'd be happy).

Of course... eventually I want to try a real push-pull differential mosfet amp, but I can wire up this guy without chopping up my stock cable for the moment.

 

[Edwood]

5 pin XLR makes no sense in the "audiophile" over-kill sense. You would really need a 6 pin XLR. Basically having two separately grounded shields for the left and right channels. Absolutely not necessary, but that is what the dual 3 pin XLR "standard" from Headroom calls for.

But since there is one mass production headphone (the discontinued K1000) in existance that uses a 4 pin XLR, I'd prefer that method.

If you really must have a shielded headphone cable, you can have the 5 pin connection with the 4 pin XLR, by connecting the shield to the tab that connects to the shell of the XLR, which gives you the 5th "pin" in a sense.

 

[Garbz]

The added ground pin was never mentioned for shielding; at least that wasn't my intention. I suggested it for backwards compatibility. With 5 connections coming out of the amp an adapter for running unbalanced headphones can be made thanks to the ground connection.

Shielding is absolutely un-necessary in headphones. They are a high impedance load and there is no amplification to increase any noise pickup. If you hear noise in your headphones because the cable isn’t shielded I’d be more inclined to worry about personal health.

 

[nikongod]

you can run 4-pin xlr'd headphones off of a single-ended amp.

you tie the negative pins together, and ground them in your 4 pin xlr-->1/4" stereo plug.

i do agree that it is un-necessary for a "power side" cable, but others dont. if you do want the "ground shield" it can be tied as stated elsewhere to the shell of the conector. after that for single ended operation, tie that to the ground of the 1/4" adapter thingy too.

ANY amp with xlr conectors should make a point of grounding the "shells" of the conectors. if not for any "audio improvement" reason, for safety.

 

[Garbz]

Yes but you can't run single ended headphones of an amp with a 4 pin xlr on it was the point. It would short two amp channels together and most likely damage something, which would be a crying shame when your friend brings over his spunky new headphones and you want to give them a try with even half of a decent amp

.

There simply isn't any reason to restrict yourself by choice of plugs. I know I did but I have a spare dynalo with a phono jack on it, so running it through half a dynamid make no sense

.

There's no doubt that the shield should always be grounded for XLRs, it has all sorts of benefits. If you get ground loops I make it a point always to have at least one ground lift switch on each chain, not that I use any of them. The point I'm trying to make is not to use a shielded cable in the first place. The majority are bulky, inflexible and don't twist. My cable is an outright pain in the arse if I'm sitting at my desk, great in bed though. Mind you if you have a shield, yeah ground it.

 

[nikongod]

why not just put a second conector on the face of the amp?

or arguably better 2 "second" conectors.

a 4-pin, and 2 "hybrid" 3pin xlr/1/4" stereo conectors.

the layout could be kept unquestionably neat, and the requirement for adapter dongles nearly eliminated.

with a well designed input section to switch from balanced inputs vss single ended inputs the above would only "exclude" designs that were cabled with 5-pins from the aftermarket.

in reality though this whole discusion is somewhat moot, as we are all talking about an amp layout that is essentially a modifyed/built to suit (insert whatever here) for the needs of the user.