Building new system starting with power amp. What would you choose ?

D-Sonic, D-Sonic, D-Sonic.
https://www.d-sonic.com/amplifiers/

I just built a new system a little over a year ago. I went with a mcintosh mc462 and am very happy with it.

I agree with 'unsound'.....you've got it backwards. Choose the speakers that fit your taste and then find amplification that is compatible with the speakers

Because just starting out you have no idea what you really like. It will prob take years to grow, learn as evolve as you better understand what you like and what products offer what. 
Amp- I would start my buying used because if you don’t like you can resell for close to what you paid as you learn. Stick with top notch brands that hold their value. 

If you are a Tube kind of guy, then try the TriangleArt M100's just for the heck of it. I believe you will be amazed at what you will get from them.
Call and talk to Tom, he will set you up.

Odyssey Audio Stratos Exstream mono blocks, Symphonic Line Kraft 300 dual mono Amp.

Once again, the tail wants to wag the dog.

Engineering is all about achieving an optimal result within the constraints you have to work with.   Constraints are more than just budget, though that is the most obvious.  How big is your room?  What kind of music do you listen to?  How loud?  Decoration is an issue and of course, there's WAF to consider for many.

So starting with the power amp and going from there is a useless question.

That being said, with $15k to play with, I'd get a pair of VTA M125 monoblock tube amps at 120 watts each and look for a used pair of Avalon Eidolon loudspeakers.  With care you could do all of that for $15k.

Coda full class A amps are hard to beat.  

Again, depends on your speaker choice.

Respectfully,
Jose

Depends on the speakers. I could suggest if I knew which speakers  you are using 

"Within that budget, I would be looking at a pair of Coincident 211PP Dragon MK II monoblocks"

I would do what @nordicnorm says.  In fact, I did.

Andrew

Pass Labs INT250.  It is integrated at 250 W/channel RMS and nothing else will come close.

Wavac EC300b

I have Pass xa30.8 Wilson Sabrina and a Nagra 300i with some B&w both really nice

What is also really nice is the Devialet amps a mix between A and D class

CODA Continuum or Ts. 
Pass Labs

My latest video on the DIY HiFi Life Channel covers the VTV Purifi Amplifier. Stay tuned for my next video where I show how to upgrade this amp as well. Like and Subscribe is always appreciated.
https://youtu.be/mBj8EjHXBJE

Within that budget, I would be looking at a pair of Coincident 211PP Dragon MK II monoblocks:
http://www.coincidentspeaker.com/211PP-Dragon-MkII-Mono-Amp.html

Crazy that No one mentions the excellent Sugden A21se. They started it all when it comes to SS class A well over 50 years ago. At $3250, a bargain in my eyes. Pair it with some nice Tannoys and a tubed phono stage and I'm certain you will be very well pleased.

Pass Labs INT250. Nothing else will even come close. Add a phono preamp and a DAC and you are set.

I have always built my systems around the PS Audio power port or Cryoed Hubble outlet.😁

I have several vintage class A amps but I’m always looking for others. I have been looking for Levinson ML-2s. Not easy to find. I’m betting they are very expensive to update. Good luck finding a pair of the Classe DR3s. I’ve seen one for sale in 6 months. If those above are on your list then look for Krell KSA units too. 

IMHO speakers have the most influence in the overall sound and character of a system. If you’re already set on your source (RTR) then speakers logically would be the next step. Pick your "sound" and THEN get the requisite electronics. Bookshelf or floor standers? Traditional box speakers or planar? All of those will likely require different electronics to sound their best. With regards to no preamp, I’d reconsider that. For one thing you’ve completely forgone any flexibility with regards to any other sources, not to mention any convenience features like a remote. (Unless your R2R has one) In any case, enjoy the hunt!
Happy listening...

Boulder.

@andrewkelley 

the Magtech is amazing!
will drive any speaker you hook up!
  One of the best kept,secrets in audio. 
 Enjoy one of the best amplifiers made!
im glad I could help.

 Enjoy the Magtech! A lifetime of perfection!

 

I'll add another brand to the list - VAC.

If my room changed and it required changing speakers, I’d probably change amps to match my new speakers.

The only amp I “simply must have” is the one that works best with the speakers I love.  My audio DNA just don’t work the other way ‘round.  A couple that might get me thinking a little though would be the Valvet A4e mono blocks or maybe a Raven tube amp.   

Purifi by VTV at <$1500 or spend a little more and get the NAD  version, giant killers

That might be another reason to start with the amp. Room might change, speakers might have to be replaced, but your favorite amp will stay.
In my case, I will never have very big room and I listen at moderate levels.

The room you have; might not be suitable for the speakers you're considering.  The room might very well be the reason to reconsider a specific speaker for one that will work within it.

stibi, I agree with you, I would consider Lamm first. Question is which one.
Diablo 300 is a very fine choice if you want transistor amp, and it can easily be found used, there are couple here right now. 

What if someone special gave you your favorite amp as a gift ? You would want to start building the new system from this, right ?
Another thought. Many speakers are actually better than they might seem but they do not perform their best because the amplification is not good enough.
Lamm, Gryphon, Nagra, D'Agostino would work very well with a wide range of speakers. Not sure about Levinson ML-2, besides try to find it, I guess.

The room we have, is the room we have for most people.

You are right...

I am lucky because i could acoustically transformed my room for my audio system... At no cost at all.... Esthetic dont matter in my audio room ....

But if your audio room is the living room, it is nearly impossible to install at low cost treatament and controls of the room that are cheap.... Esthetic means often costly... i imagine that it is possible anyway in a living room in some case of positive geometry, positive topology, and positive acoustical content materials...

The room we have, is the room we have for most people.  It can be treated in many was, but realistically, unless you are moving, most people are locked into their room.

If you choose your power amp first, you clearly are limiting your speaker choices, and vice versa.  I own Maggies, thus eliminating many amplifier choices and I am good with that.  My amps are McIntosh MC501s and the combination has pleased me for the last 15 years.

Good luck with your selections as building a system is a great joy.

I'll take the Gryphon Diablo 300.

You must chose the room first, not the amplifier, not the speakers....

No educated listenings ears give a dam about the gear, give me anything, or almost, and i will make it sound good...

It is called embeddings controls and treatment of the working dimensions of the audio system...

Any fixation on a piece of gear is an obsession, call it a taste if you want, but acoustic, mechanic and electricity are the 3 playing ground....

Read me right, i love my Sansui Au 7700, but the room/ears/brain is the main component....

(Odyssey Audio)

Solid State: Ampzilla Monoblocks or PassLabs amps.  I have both.  Have the 250.5 PL amp- great sounding, presents solid state in a most pleasurable way.  Only problem is it weighs 100 pounds.  Just picked up a 150.5 PL amp.

Tube: Canary Monoblocks.  I have a pair of 140 wpc that were good stock and are outstanding after modification by Asi Teknology.  Decware Anniversary Mystery Amp.  If you have moderately sensitive speakers this 40 wpc amp sounds fantastic. I drove to Peoria, IL to listen to them.  

My experience is limited to what I have owned or heard elsewhere.  I know there are many other fine amps out there.

A pair of Classe DR3 VHC amplifiers used in monoblock configuration gives 100 watts
of Class A power per channel.  These were designed to drive the notoriously inefficient
Apogee Scintilla at its 1 ohm setting.  A used pair of DR3 VHC's should cost you
about $4000.  New in 1987 they were about $4300 each.  

 Personally I would never start with an amp. If already knowing the budget and room: I'd start with speakers.
 That aside, and playing along, if I were to start with an amp already knowing the lone source and without a preamp, i.e. RTR deck,: I would seek out an an amp with an input impedance, and sensitivity for maximum output that would suitably match the output impedance and voltage output of said lone source (RTR deck) with as much power as I might need. 

Both your initial choices are great, although I would look for the Lamm first before moving to Gryphon.

Nagra. Excellent choice indeed.

My fantasy amp brand is NAGRA. If I win the lottery, I want to have all-Nagra electronics. 

Anyway, I do have speakers in my mind that I would consider first, if I could find them used - Kharma.

Yeah, around power cords.

misguided concept from the start

why not build a system around cables you love?  🤔

When tape deck with volume control is your source you don’t need a preamp. Electrically must be matched, though.

It don't work that way. You have to decide what speakers you can live with. Then get an amp that feeds them what they want. And why oh why do you think that you don't want a preamp?

@arcticdeth 
i love my Magtech. Fyi, your suggestion is the reason i looked into sanders. Im not sure how any other amp could be better. Nothing ive heard at least.

I'd like the Sim audio amps myself very neutral warm sounding. The w8 was phenomenal.

I have a Krell KSA-80B which sounds even better than an ML-2.  It puts 640 watts into my One Ohm Apogee Scintillas.  It never strains.  Its very musical.  I had it factory recapped a couple of years ago.  Its my amp for life.

Go to your favorite audio dealer(s) and listen.  Learn.  Observe.  Make a judgement.

Just keep in mind that tube amps require care and feeding that solid state amps do not.  Depending of the rest of your system, a very good solid state amp will give you as much satisfaction as a tube amp without the tube amp hassle.