AMB stuff: 95% assembled b22 w/s22 power and e22 backplane, 0% assembled M3 kit

Backstory:
So a bajillion years ago when 3-channel headphone amps were still a popular thing, I fiddled around with my own designs and came up with a variation of Jan Meier's 3-channel ground driven topology (link) with a bit of opamp chicanery. But why use opamps when I could go bonkers with discrete? Except I'm not good enough to design my own discrete, thus enters the M3 and B22. The crazy plan was then to build an M3->B22 contraption, wherein I would hack the M3 to take the input 2 channel and produce my desired 3 channels by modifying and crosslinking the feedback architecture of each channel, then using those to feed into the B22. So basically the M3 was going to be my preamp and "processor" for lack of a better word. As many grandiose projects go though, I got partway through and life took a turn in some wonky direction and the project has been sitting on a shelf ever since.

I got as far as working on the b22 boards and power supplies. I did not hack any of the circuits so everything is stock.

Sadly, my DIY time these days is spent more on fixing crap around the house than building amps, and I really need to try and clean up the workspace a little.

This is what's available: (preference to sell the amps & related power supplies together, but willing to separate I guess)

B22 boards- 3 populated boards (maybe 99% complete?), I *think* they were all x5 gain, never tested.
E22 backplane - I think this is mostly populated, never tested.
S22 power supply - complete and I think tested once upon a time, comes w/toroidal transformer

M3 - full kit 0% assembled, nothing hacked or modified
s11 power supply - I'm sure I have this somewhere; it must be hiding in another box, it's either 0% or 100% built


Also available:
A20 - 3 populated boards, 2 tested working, 1 maybe (it's been too long, I vaguely remember having a voltage offset drift)
S22 power supply - tested working once upon a time, comes w/non-toroidal transformer


Prices:
Honestly I have no idea. Make me an offer? trade me something cool or random? donate to a good cause? give Marv a purple nurple and post the video?
Everything sold as-is. it's been too long, I can't guarantee anything at this point and all my tools are packed away.
No weird hackjobs on any of the circuits; I never made it that far.

 

Are these cased??

 

No case... once upon a time my original plan was to build this whole thing into a suitcase for "transportable" use

 

Ugh, I can't drill a hole to save my life much less FPE anything! Finish these up??

 

What's the 3rd channel for? A sub?

 

Virtual ground design: https://tangentsoft.net/elec/vgrounds.html

 

Was just trying to edit and say I should probably check this out first.
Thanks

 

Honestly, I just don't have the drive to work on these any more. It's like... project momentum y'know? Give me a new one and I can plunk away. But re-start one I dropped years ago? eh, the motivation just isn't there. Plus, my casework skills are no better (which is partially why I was going to build them them into a suitcase lol). I don't even have a drill press (been wanting to get one though) and do hack jobs with a hand drill or dremel or sometimes even hand ream things out.

 

This brings back memories .. dB

 

Those are circuits that get you a dual voltage output from a single voltage power supply.
The Meier active balanced ground lets you use a balanced signal on a headphone with shared grounds (cable goes to one side only so ground for both drivers is common). Y cable headphones don't have this problem and are easy to use balanced.
Although that Meier explanation is, ummm, something. Dielectric has as much effect in balanced circuits as single-ended, among other things.

 

Thanks. I gust grabbed what I could. It does kind of explain the floating ground concept. I just did not want to post a link to the nwavguy article, but it is out there for anyone to Google.

 

An active ground is not balanced. It is merely an active buffer stage between the input ground and output signal ground. The idea is to isolate the output signal ground and reduce any ground level noise. The concept is good but it is expensive to implement commercially (essentially adding a 3rd channel with all the "stuff" needed to support it) while adding one extra channel (4th) offers all the benefits of balanced signal handling and you can charge for it.

The goods offered up for sale here are worthy products but I would build them as separate amps. Both the B22 and M3 are highly regarded.

.. dB

 

I think both headphone amps are favorites of renowned mastering engineer Bob Katz.

 

I can't find my notes anymore, but I think my planned design was something like: (the * denotes the new output)
L* = 2L-R
R* = 2R-L
G* = -L-R
So if you summed the voltages in all three wires in the cable, you'd get net zero. And then at the transducer you'd have something like:
L* - G* = 3L
R* - G* = 3R

I had two working prototypes. Man that feels like a lifetime ago.

 

You're right, my bad.

 

It's been a couple weeks, I'll give this a bump.

 

Interested, PM'd.