What?! Another headphone amp kit?! Smack me!

[Doc B.]

Just an update - we got word from our winder that they will be scheduling the winding of a prototype output transformer for testing very soon. This will have, as stated below, 32/64/128 ohm taps. If all goes well we should have a production prototype happening in the next month or so.

[Forte]

Any more updates on this?

[Paul Joppa]

Good call! Doc B and I just talked today about bringing that project to the front burner. I have some personal and some medical issues to deal with currently, but I expect to have a lot of time in waiting rooms when I can work on my parts....  :^)

[InfernoSTi]

I'm sorry, Paul, and wish you and your family well soon.  Having a project or two to keep busy with is also a good thing....

John

[Doc B.]

Just a quick update -

We have tested the 16/32/64/128 ohms transformers in the first prototype and they are really nice. PJ has been puzzling out some PC boards with slide switches that will mount under each output transformer and allow one to choose 16/32/64/128 ohms, single ended output at the 1/4" TRS jack at the front, or balanced output at a pair of XLR jacks at the rear of the chassis plate. At the end of the day today I have what I think is a more or less finalized chassis layout. So we are very close to putting together the production prototype.

[Armaegis]

Very cool. Looking forward to this.

[Doc B.]

A bit more progress today - got the power supply filter strip configuration laid out. And I think we're just about ready to sign off on the chassis layout and get a prototype made up.

[Jim R.]

Dan,

Are you planning on using full size or mini xlrs at the back of the amp?  Are these outputs going to need a separate single-ended to balanced transformer?

Thanks,

Jim

[Doc B.]

From what I have seen the people that are playing with "balanced" headphone output (which seems to be more concerned with supplying separate signal cold rails for each channel rather than balancing the output signal with respect to ground) are using a full sized 3 pin XLR connector for each channel. So that is what we are using. Not sure that I grasp the second question properly, but the single ended and balanced outputs are all switched from the output transformer, so there won't be a need for any additional transformers.

[Jim R.]

Actually, you answered my second question with your first answer.  Balanced, not differential -- got it -- i.e. individual returns, not balanced with respect to ground.

A little poking around and I see that's what the headphone crowd referers to as balanced, where as the pro world has a somewhat different interpretation/execustion of that idea.

This too sounds to be another great bh product, and I suppose I'll just have to get one. :-)

-- Jim

[Doc B.]

Yeah, separate signal cold for each channel is what the emphasis is in the HP community. You can do that single ended like we do with separate Paramounts and K1000s. Of course that presumes the L and R signal cold is not common in the source or preamp ahead of the amp - not a very safe assumption. But Smack will be true balanced output with respect to ground, that is, it is transformer "decoupled" and there will be a grounded center tap.

[Armaegis]

From what I understand, the cold on each side is an inverted signal from the hot, giving an effectively doubled voltage swing. As such, balanced headphone amps have twice as much circuitry because they're essentially amping 4 channels rather than two.

If you're feeding in an unbalanced source, it could be set up such that the cold on each side is essentially amping zero and the headphone operates as normal. Some balanced amps also have dual unbalanced outputs, with output 1 giving out hot left/right, and output 2 giving out cold left/right (and in a couple examples I've seen, use this as a default then use an adapter to hook up balanced headphones).

[mrarroyo]

From what I have seen the people that are playing with "balanced" headphone output (which seems to be more concerned with supplying separate signal cold rails for each channel rather than balancing the output signal with respect to ground) are using a full sized 3 pin XLR connector for each channel. So that is what we are using. Not sure that I grasp the second question properly, but the single ended and balanced outputs are all switched from the output transformer, so there won't be a need for any additional transformers.

Actually I believe there is a shift happening to the 4-Pin instead of the dual 3-Pin connectors. Not only are they cheaper but also use less "real state" and are lighter and simpler to build. I am switching all my headphones to the 4-Pin arrangement. Thanks.

[Beefy]

From what I understand......

That is all for solid state bridged amps, and doesn't really apply here.

[Doc B.]

So are the amp manufacturers going to a single 4 pin XLR as well, or is this primarily a DIY movement? When I Google 'balanced headphone cable' images most shown have two three pin XLR plugs, though there are a couple 4 pin as well. Maybe the thing to do is sell the amp as I have designed it, with the chassis punched for a pair of XLR D type connector jack shells. That way one could use the standard pair of three pin XLRs or replace them with a single 4 pin XLR, or even a pair of TRS jacks in D style shells, depending upon what is on your headphone cable. We could make this an order option.

Looks-wise, imagine a S.E.X. amp but with no plate chokes on top and nine pin miniature 5687s rather than octal 6DN7s. And it will have the XLR sockets where the speaker binding posts are on a S.E.X. amp, at the back. We're going to see if we can cook up a special pre-order price today and let folks start queuing up, as I think we can have this ready to ship in about 4 weeks.