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

[Armaegis]

RSA using a large 4-pin XLR for their full sized, and a small 4-pin square thing on their portables...
http://www.raysamuelsaudio.com/

iBasso has some sort of 6-pin connector on their portable balanced amp...
http://ibasso.com/en/products/show.asp?ID=70
and mini6 to large 4-pin adapter: http://ibasso.com/en/products/show.asp?ID=68

[Doc B.]

Well, as usual the industry has a big gun aimed at their foot when it comes to setting standards that make it easy for the consumer. I'm just gonna go with the most universal mounting holes we can offer. The D style mounting hole allows for XLR, TRS, RCA, Tuchel, Speakon, CAT-6 and probably a bunch of other styles of jacks. I'll let the cable guys make adapters for the oddball stuff.

[Spinifex]

I have a small question, after reading the page. It is a parafeed amplifier, but is it a SET or a push-pull?

[Doc B.]

It's single ended, just a single very linear triode gain stage for each channel. The other triode in each tube is the heart of the hybrid shunt regulator for the corresponding gain stage. SE is our area of expertise and IMO it sounds better than PP for these low power levels.  You might take a look at the Paramount soft start driver stage upgrade kit. It's basically the same topology on the same PC board driving an output transformer rather than a 300B. But what you will see under the tube sockets will look very similar.

Rather than making a differential circuit the balanced output is derived at the output transformer secondary, a method that allows for great isolation of the left and right signals and, IMO, better retention of subtle spatial cues in the signal.

[Jim R.]

I suppose you could always wire two 4 pin xlrs in parallel and plug in two sets of identical cans for his/her listening?  Say a pair of HD-600s?

Just sent in my pre-order by email as I'm still having problems with the shopping cart and my screen reader.

-- Jim

[Doc B.]

I think that the idea could work well as long as both sets of cans are the same sensitivity, like your two pairs of HD 600 concept. Otherwise, only let the person with the more sensitive cans set the volume! I have some 650s on the way so I can test the theory with my 600s and the 650s.

[Paul Joppa]

I'm still refining the switching matrix, but here's some complicated details:

1) The switches will be on a board that mounts below the output transformer, under the chassis - so it's not for frequent switching, but no soldering requires to change the settings.

2) there are two impedance switches, giving four possible impedances. They'll be labelled LO, ML, MH, and HI, (16, 32, 64, and 128 ohms respectively) so the same switches can be used with the SEX amps and the Stereomour - they all have OPTs with the same topology, though different impedances.

3) There will be a third switch on the board, for balanced or single-ended output.

4) Here's the messy part - there are eight possible settings, and two kinds of output, as you can see. Total 16 combinations! I'll try to summarize - please understand, I'm on my second G&T (see other posts - family distractions going on) so this may not be accurate  :^)

LO and ML impedance, balanced - the XLRs are balanced with 240 ohm resistors to ground from either balanced output; the 1/4" jack in front is IHF standard 120 ohms source impedance, like the stock SEX.

LO and ML impedance, unbalanced - the XLRs are grounded on the cold side, same as the 1/4" jack in front. The 1/4" jack sees the full voltage, same as the XLRs, with no extra series resistance.

MH and HI impedance, balanced - the XLRs are balanced with the transformer center tap to ground from either balanced output; the 1/4" jack in front is on one half of the output transformer (half the voltage of the balanced outputs).

MH and HI impedance, unbalanced - the XLRs are grounded on the cold side, same as the 1/4" jack in front. The 1/4" jack sees the full voltage, same as the XLRs

[mrarroyo]

I can say that Red Wine Audio on the new Class A headphone amp module only uses the 4-Pin version. Also Ray Samuel has included the 4-Pin besides the dual 3-Pin on his units. The new Apex Pinnacle a $10,000 unit includes both versions, the Eddie Current ZDT and Balancing Act have a 4-Pin as well. Hope this helps.

[Doc B.]

OK, our production prototype (the one we photograph for the assembly manual) chassis is on order, and after a once over of PJ's design I will be ordering some of the output switching PC boards. These boards are quite versatile in that they will also fit the S.E.X. V2.1 and the Stereomour, allowing for switchable output impedance on those amps as well.

[Doc B.]

Did a bit of listening with our prototype today, which we have set up with rotary switches to allow switching between 32, 64 and 128 ohms output impedance. This rotary switch setup is a bit of a kludge that we did before having worked out the more refined and useful slide switch scheme that will be in the production model.

We listened to a range of headphones - HD600, HD650, K701, MB Quart QP400, Skullcandy Aviator and Ultimate Ears Triple Fi 10V ranging from 32 ohms impedance to 300 ohms. The switchable settings really work well, we found that each headphone seemed to work best at the impedance setting closest to its own impedance. The high impedance cans sounded really nice and the low and medium (K701) impedance cans that we more or less came up with the Smack to work with sounded great as well. Unfortunately I don't have an assembled Crack amp handy to A/B, but I think I would still put my money on Crack as the very best bet for 200 ohm+ headphones. For someone with a good sized collection of headphones who wants a single amp to use with them Smack is a great choice, though I think it's criminal to have many headphones and just one amp, myself. Smack and Crack together could give great performance from a whole lot of headphone types.

[Armaegis]

Am I allowed to cackle maniacally in anticipation?

[Doc B.]

Certainly, please cackle away. Shawn is restoring a Crack that we attempted some genetic engineering experiments on a while ago. Soon we will have the ability to A/B the various headphones in our listening room on all three amps (S.E.X., Crack, Smack) and start to post more detailed reports.

[tdogzthmn]

I am interested in how the sound signature of the Smack compares/contrasts from the Crack.  Which of the two would be considered more neutral?  Im interested in the Smack for use with my 100 ohm ER4S and 120 ohm K400/K500 which work well with the Crack but I can easily hear the difference in amp requirements when I have my HD600 plugged in.

[ironbut]

I believe that there's a Seattle Headfi meet on the August the 27th. I assuming that Doc will have all three of his headphone amps there.
I think it's always better to get several folks opinion on an unknown amp.
You might think about posting in that Meet thread and get a few guys to agree to do amp comparisons with particular cans before the meet.
I can't tell you how many times I see folks all bummed out and posting in the meet impressions thread that they wished that someone had taken such and such headphones to do comparisons. When it gets to the impressions thread,.. it's a little late to complain about that kinda stuff.

[Doc B.]

Actually the meet is this Saturday, August 20th

http://www.bottlehead.com/smf/index.php/topic,1995.msg15372.html#msg15372

We will try to have the production prototype of the Smack finished in time for the meet and we will also have S.E.X. 2.1 and a slightly tricked out Crack.