I've been reading most of the AMB audio site, and reading up on old threads from this forum that have addressed balanced builds people have done.  I'm really considering an M^3 balanced build, but I'd really like to get the form factor down to a smaller size (and yes, I plan to put all the power supply components in the same enclosure). In particular, THINNER would be desireable.
 
I know that imposes problems with cooling, because all the heat sources (mainly the power MOSFETS, right?) will be in close proximity, and there will be less space for buoyancy-driven convective cooling.  So, instead, I was thinking of using the 
alpha 20 amp circuit (x4) instead of two M^3 boards.  They are smaller, and could be mounted vertically to enhance cooling performance (of course, with some intelligent rearrangement of some of the heat sinks).  I guess the Sigma11 power configuration could be used, in much the same way as a balanced M^3 build.  
 
Has this been addressed before?  If it has, I apologize for my ignorance...I DID look on this forum for old posts on this topic.  Can anyone make some suggestions or specific recommendations who has had experience with either an M^3 or 
alpha 20 build?  I have experience with analog instrumentation, soldering, circuit design, etc...but I've never done an audio project before.  
 
I have some additional questions as well:
 
1) Does putting the power supply components in the same enclosure as the amp circuit introduce so much noise/interference that the benefits of the balanced build become pointless?
 
2) Am I crazy to attempt to reduce the size of the completed amp build, in particular because I'm making a balanced amp that will produce more heat and have more components?  Most of the builds I have seen in photos show pretty large enclosures...maybe they're like that for a reason!?
 
3) Is the 
alpha 20 circuit comparable in Sound Quality to the M^3?  I know the M^3 is generally quite well regarded, but I haven't really heard much talk of the alpha 20.  AMB's website describes both as so-called "high-performance"...which is great, but doesn't help me compare the two.  I only I knew more about electronics...

Thanks in advance for any insight into this.
 
Mike
 
<edit: changed all instances of "epsilon 24" to "alpha 20">
 

You do realize the e24 is a power switch driver and has no amplification function what so ever, right?
 
Do you mean the mini3?

yeah ermmm, its actually quite difficult to even guess what you are getting at here. as my compatriot above has mentioned, the e24 is a protection circuit and provides nothing at all for audio amplification and the mini^3 its hard to think you could be talking about that, because it has no heatsinking at all, as only opamps are used and they sink their minimal heat to the pcb and b24 is a large class A/B power amp for speakers, or inefficient headphones.

This is probably what you want http://www.amb.org/audio/alpha20/

Why not just a single ended M3?

Oh god...yes, I meant alpha20, not epsilon24.  Stupid error.

Quote:

nattonrice said:

You do realize the e24 is a power switch driver and has no amplification function what so ever, right?
 
Do you mean the mini3?

Click to expand...

Thanks for pointing this out...you're right I just typed something other than what I intended to.
 

Quote:

nikongod said:

Why not just a single ended M3?

Click to expand...

Well, I already have a decent single ended amp.  I thought it would be cool to build my own.  I also thought it would be really cool to try out a balanced setup some day.  So why not do both at the same time?  I have heard other balanced setups, and I like what I heard.  As for the balanced source...probly have to buy that part.  Building an amp will be a big enough challenge for now.

You would be better off with a single ended m3.
The whole point of the m3 is that it has an "active ground" (among other things) and a discrete mosfet ouput.
To add to that it also has a bass boost function if you want it.
 
The a20 otoh is based on the jisbos and is has a jfet input stage with a bjt output.
Which one you prefer will depend on... well you.
 
If you are tricky with some asymmetric angle extrusion then you could easily (hehe) get the m3 in a 1u case with a side heatsink.

Just a thought, there is a new updated version of KG's Dynahi which is now super-symmetric.
Sinking requirements would most likely preclude a thin form factor.
 
There is a matching psu that should be quite familiar to you if you've been around amb's pages  =)

Quote:

nattonrice said:

Which one you prefer will depend on... well you.
 

Click to expand...

Thanks for this response, nattonrice.  But why would I necessarily prefer the bjt output over the MOSFET output of the M3, or vice versa? Simply because of sound?  If they're comparable quality, I'll probably go for the alpha 20's, purely based on size.

Quote:

nattonrice said:

Just a thought, there is a new updated version of KG's Dynahi which is now super-symmetric.
Sinking requirements would most likely preclude a thin form factor.
 
There is a matching psu that should be quite familiar to you if you've been around amb's pages  =)

Click to expand...

This is also quite thoughtful.  I'd never heard of this amp design until now.  Indeed the organization of the board in this design is perfect for side-heat-sinking
 

Quote:

mikeg88 said:

Thanks for this response, nattonrice.  But why would I necessarily prefer the bjt output over the MOSFET output of the M3, or vice versa? Simply because of sound?  If they're comparable quality, I'll probably go for the alpha 20's, purely based on size.

Click to expand...

Because to a lot of people they sound, well, different (there are technical reasons for this).
But there should be more to your desicion then that.
There is a (big) question of what you intend to drive with the amp too
 
I will admit that I've only heard an m3 once but having built a b22 (jfet input, bjt vas, mosfet output, all three stages cascoded) and a jisbos (I mocked two pcbs for something I never got around to finishing), I prefered the sound of the b22 (there's some humour here).
I'm not the worlds best wordy audiophile so I can't describe it really any better than that hehe.
 
Disclaimer: the b22 is balanced the jisbos wasn't.

Well, thank you nattonrice.  Any help is good at this stage.  
 
I was planning to drive 880's (with balanced XLR terminations, of course).  Although, I think I might use it with 650's in the future as well.  Haven't decided that yet.  
I'm also hoping someone can estimate for me how much it costs to build one complete M3 board, just so I can get a ballpark figure.  I'm sure that's come up somewhere before.
 
Honestly though, if I end up with a half-decent sounding amp, a tidy build, and I have fun in the process of making it...I'll be more than satisfied  
 
I guess that's why we're on the DIY forum.

Since I have one of those headphones and have listened extensively to more or less the other I can say go for the m3 at least.
Especially the 880, they really need a good push to sound their best.
Neither phone needs a bridged amp to sound sublime so I say go unbalanced, especially if this is your first journey into the abyss.
Power it with a s11 and use an encapsulated/potted traffo if you're going to throw it all in one case (though with those two phones it prob won't matter).
That being said simply moving the iec inlet, switch, and traffo to their own case / box under your desk will do wonders if you ever use more sensitive phones with it.
 
No idea on the cost as it is up to if you have the tools already or not, how much case work you want to diy, etc.