Low heat alternative to FIRSTWATT J2 ?

Any Gainclone or Class D or battery power alternatives available? I like the crazy good micro dynamics and rhythmic cohesion of the J2. My speakers are 93db full range. Also interested in AMP/DAC combinations like the devialet or NAD D7050 that meet the J2 performance (those 2 mentioned don't)
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Since you are so happy with it, I would try to make the J2 work somehow. Its not an easy amp to beat. But if you must, see is you can demo an Ayre V5. It does sound different from your Pass, but has a lot of the qualities you are looking for. There's a good chance that you'll like it better.

"I like the crazy good micro dynamics and rhythmic cohesion of the J2."

The Ayre does that better than the J2. It also has more resolution, more power, bigger dynamic contrast and the imaging is incredible. One thing that you may, or may not like about the V5 is that its not quite as forgiving as your current amp. Its probably due to the fact that Pass uses mosfet transistors, and most other amps use bipolar. You may think that's good or bad, depending on your personal preference.

Some other good choices you may want to look at are solid state BAT, Theta and maybe Sim. They're all fully balanced, 0 feedback designs, like your J2.
I would try to adapt to the heat. Is there any way you can sit at a distance that the amp is not annoying you with its heat, or are you concerned about children touching it.
Audio Consulting Mipa. 2x30W. 2 battery. No heat. I have one for sale. It needs a preamplifier with very low output impedance or passive with transformers.
The First Watts are sick good (I have the M2)…Man, I would keep it if at all possible.
Buy one of those small refrigerators and put the amp inside that. Cut a hole in it for the cables and seal it off with a rubber grommet. Problem solved. Just make sure you run a dedicated line directly to the fridge so its isolated from your system, and don't forget to put cones under it.
Bojack I'm inclined to agree with you. I'd keep the First Watt compared to the other alternatives suggested. Not so sure they will sound better than the F.W. J2.
Just a small correction- the J2 does have negative feedback.

OP: Ayre and DarTZeel are the two A/B amps (cooler) that don't use negative feedback. The latter has a new integrated with built-in DAC which might interest you.
"01-13-15: Keithr
Just a small correction- the J2 does have negative feedback."

I didn't know that. I thought all Pass amps were 0 feedback. Thanks for the info.

Talking about Pass amps and heat, I just remembered that one of my Pass amps burst into flames right in my living room. It was actually kind of funny. But not to worry, it was an Aleph, not a Firstwatt. Most likely the problem is fixed in the newer models.
How hot does the J2 get?
I recently got myself a J2 and they don't get that hot. Less heat than a push pull tube amp. I was very concerned about heat given I live in small NYC apartment. But it's totally manageable. It doesn't heat up my room. Make sure to have the amp in an open space. I can keep my hands on the amp chassis without getting bothered by heat.
How hot does the J2 get?
According to its manual the J2 consumes 200 watts. Since it operates in class A it will draw that amount of power essentially all of the time it is being operated, regardless of the dynamics of the music. So the amount of heat injected into the room will be approximately the same as the heat produced by two 100 watt light bulbs.

-- Al

Thats not that hot imo. The way the op was looking for battery powered amps, I was thinking the J2 was burning down the house
The J2 doesn’t use any MOSFETs. It uses JFETs throughout. That’s where it gets it’s unique character from. All Pass Labs amps use feedback. That’s what Su-Sy is. First Watt amps are a mixed bag with the F7 using both negative and positive feedback.
You're not likely to find anything that sounds quite like a J2 on account of those big power JFETs. The unique thing about them is that they have conduction curves that resemble triodes whereas MOSFETs and BJTs resemble pentodes. 
The J2 and F7 are the two I am considering.
The reason the First Watt sounds like it does is its class A. Class A makes more heat; you're not going to find a cool running amp that is class A, so if you like the sound I would find a way to deal with the heat. Putting it in a refrigerator BTW will not work- the refrigerator has to get rid of the heat and will do so via its heatsink system.

One simple solution is to have a vent placed in the room above the amplifiers locations. The vents are then ducted to a fan that blows the air outside if needed. This system can be very effective and is cheap.
I would hire a cute girl to fan myself and the amp before I got rid of my F6 .
I would think as long as you have the amp on a simple floor amp stand you would be fine.  
It’s a simple thing to wire a small quiet fan hidden near a hot amp. Years ago I had amps in a closet space and did just that and it worked…there was a brand called Whisper Fan, now there’s lots of stuff for that. An easy solution that should help even in the smallest dwellings.
Nelson Pass designed a 40 watt push pull version of the S.I.T. using the Sony VFET for the D.I.Y. community, it is pure class A. I used this amplifier in my system for 3 weeks recently. It gets very warm but not hot. I don’t see how the First Watt J2 (lower power, 25 watt @ 8 ohms) could result in a significant heat issue unless the room is unusually small and closed in.
It was mentioned above that all Pass/F.W. amplifiers use NFB.   The F2, F4, M2  and S.I.T. do not utilize NFB.
I have a FW F5. Does it run hot? Yep! However in the summer months, I will turn on my ceiling fan,and the temp drops considerably. 
zuio  I went through this EXACT dilemma recently, my firstwatt f7 in my small non air conditioned bedroom in hawaii was not useable due to heat but it sounded so good.  The amp replacement that made me happy is the Folsom TD7297 diy amp pcb and folsom antipole psu, it's a 15 watt class AB amp.  You can have a builder make it for you, such as Radu at simpletubepleasures.  It makes no heat and sounds as good as my firstwatt, with even more dynamics
Uncola.....was it the fact that the heat became unbearable in the room or the fact you were worried about overheating the amp itself? I just can’t see how an amp can overheat the room with heat. 
No not worried about the amp overheating itself, the room became unbearably hot after a couple hours with the amp on if I had the door closed
I'll say it again... 
ALL modern Pass Labs amps use negative feedback. 
The FW amps are a mixed bag. Some have none, some use negative feedback and one uses negative and positive feedback. 
OK, I see you are making the distinction between Pass Labs and Nelson Pass's designs which would include First Watt. No problem. The F. W. are definitely a mixed bag of circuit ideas by him.
Yep. The FW amps are very unusual animals. I LOVE my F5 though, and that IS an amp that runs hot. Base of the sinks hovers just under 60C. It’s warming up right now.
I borrowed a friend's J2 for two weeks and enjoyed it the whole time.  The case gets fairly warm, but, that is, in part, a result of the whole unit being fairly small in size.  In terms of the total amount of heat being radiated by the amp, I only notices that it was slightly more than that of my low-powered pentode tube amps.  

I have also heard that same friend's DIY build of the First Watt SIT amp.  That was a really nice sounding amp too, but, I suspect it puts out even more heat than the J2. 

I don't know of any solid state amps I like over the sound of the two First Watt amps I heard (although I have not looked extensively at solid state amps).  I heard the Devialet and thought it was okay sounding, but, as with the case of solid state amps, it did not hold my interest the way good tube gear does.  The brand of conventional solid state amps that I find to be nice sounding and engaging is Ayre. 
Any suggestion on J2 vs F6 ? I am considering buying one of them for my 93db Tannoys.
I have also heard that same friend's DIY build of the First Watt SIT amp. That was a really nice sounding amp too, but, I suspect it puts out even more heat than the J2.
The J2, SIT-1, and SIT-2 all have specified power consumptions of 200 watts. (In the case of the monoblock SIT-1 that would be per monoblock). And since they are biased in class A the amount of power they will draw from the wall outlet will be essentially the same at all times, regardless of the dynamics of the music or the listening volume. And aside from a tiny fraction of that power draw which ends up being converted into sound, all of it will be converted into heat and injected into the listening room, mostly by the amplifier but to a small extent also by the speakers,

All of the other First Watt amps have specified power consumptions ranging from 150 to 200 watts, and I’m pretty certain that all are biased in class A. So all of them will inject roughly the same amount of heat into the room (per monoblock in the case of the SIT-1). How hot the chassis gets has no direct relevance to that, and as Larry alluded to in his first paragraph above chassis temperature will vary depending on the physical design of the particular amp.

-- Al

Any suggestion on J2 vs F6 ? I am considering buying one of them for my 93db Tannoys.
I meant how do they compare in performance ?
He did point out that it was a DIY effort and it's not at all uncommon to bias those things to the bare knuckle limit of what a pair of heatsinks will dissipate. That's exactly what I've done with my F5 to get 40 watts out of it, and I've seen builds where people have used absolutely gigantic sinks and biased the thing up over 2 amp. Generally FW amps sound best with as much bias as you can get away with. Nobody in their right mind would sell a build like I'm running. 

The J2 and F6 are very different creatures. The voltage gain stage in the F6 is a transformer that drives MOSFETs in push-pull. The J2 is a pure JFET single ended design with somewhat limited current delivery capability on account of it's single output device. It likes higher impedance loads. Nelson talks about both these amps in his lectures at Burning Amp and the First Watt site has a wealth of reviews. Diyaudio.com is also rife with opinions on the various designs. 
@kosst_amojan, have you heard the J2 or F6 ? I am using a Tannoy Turnberry which is 93db efficient. Not really very efficient but still happy with 20 watts SET. The question is, will the J2 sound too relaxed compared to F6 ?
Kosst, good points in your response to my post.  Thanks!

-- Al
It's not so much the efficiency that will dictate the character of how they work together. It's more the impedance and phase angle. I'm not familiar with those specs for those speakers. Stereophile did a good review of the J2 and compares it's performance with a variety of different speakers. I'd imagine the J2 would drive almost anything that does well with SETs. The F6 is known to have a tube-like sound as well. These aren't the easiest amps to find and audition so the best you can really do is read the best reviews you can and get familiar with the reviewers broader body of work to get a flavor for what they're really hearing. I've never heard either, but I'm pretty convinced the J2 won't be an amp I ever build because of how it handles very reactive loads like my Focals.