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I think I have found the End Game Amp

For the past couple of years I have been searching for a power amp that plays well with the highly resolving nature of the Esoteric K-01XDSE source and the Rockport Atria II speakers.

How do I get a mid-range to captivate without losing the sense of air and space?

The K-01 and the Atrias deserved something great in between but I could not bring myself to spend $25k - $50k if I went all out on both pre and power.  Building an amp is surely easier than building transducers?

The closest I came was with a Cary SLP-98 pre - with NOS RCA 6SN7s and the Elekit 8900 running Black Plate 2A3s.  There was not quite enough power, slight sounds of strain at fff and not quite the warmth in the mids.

I was enamored of the 2A3 sound and wondered if there exists a PP or PSET 2A3 amp, so I discovered and contacted Frank Ng at Triode Labs.  He had recently found a pair of Tamura OPTs and Tango chokes and had built a pair of the PP 2A3 GT-C amps that I could have immediately!  Working with Frank was an absolute joy, getting a story of his constant search for the Tamura OPTs, and seeing his views on various tubes.

He gave me great price (he supplied only the 6SQ7s) and I was able to pay through PayPal - I rounded up (dividing by .96) to cover the fees.  I got him to autograph the base plates!

The shipping boxes were superbly protective but easy to unpack.

Even cold out of the box I could hear something special; there is just a natural quality to the sound.  The amps now have about 30 hours and Frank expects break in to be about 200.

Everything I play sounds - I am not sure of the word - but "right" seems to fit.  I have played everything, from Angela Hewitt's Goldbergs - you can clearly her management of tone from her Fazioli piano - to Simon Rattle's Mahler 7 (Bavarian Rundfunk).  Also the Borodin recording of Shostakovitch quartet 9, the Beethoven op.132, the Sveshnikov Rachmaninov Vespers with Klara Korkan's haunting mezzo, Hilary Hahn playing Bach.  AMAZING!

There will be some tube rolling to fine tune (!) everything but at this time the SLP 98 has coin base a 6SN7 gain stage, Tung Sol buffers.  The GT-C has Motorola branded 6SQ7s, Smoked glass RCA 6SN7s, JAN Black Plate 2A3s and Sophia 274B rectifiers in the main amp..

 

 

 

retiredaudioguy
retiredaudioguy OP
330 posts
 

@posbwp55 Thanks for the article.  I read it through and it seems to (just) validate what I hear on theoretical grounds.

I mentioned that I measured the SPL at my listening position at 84dB with 2 watts (2.83v).  14 watts yields an additional 8.45 watts (theory) and in practice 92 dB is about my comfortable peak for orchestral stuff.

At the bottom end pp passages are at 65db, do a dynamic range of 27dB - in line with the article's 26 dB range.

So, yes, the power is marginal at the upper limit but the SQ in the middle is sublime.

@mclinnguy No, I cannot shake the walls at 92 dB, but I live in a log home and it would take a bulldozer to move them anyway!

Most of the time I am listening in the mid 70dB range - .5 watts.

Regarding "wooly bass" and 300B amps, for many years I had a VAC Ren 70/70, driving Audio Physic Virgo IIIs.  Than could do excellent bass!

 

 

larryi
4,642 posts
 

As long as you don't require head banging volume, a pushpull 2a3 amp can be used with somewhat inefficient speakers.  I think most people greatly overestimate how much power they need or put too much emphasis on the ability to play at extremely high volume even though such demand requires a lot of compromise in the ability to play beautifully for the vast majority of the time.  I am a big fan of low-powered tube amps.  I own a parallel SET 2a3 amp and a pushpull 349 amp (5 watts per channel).

posbwp55
24 posts
 

Retired audio guy,

It seems you value a beautiful midrange presentation as your highest priority. Let me recommend the 6SN7 that is the king of beautiful midrange presentation, that tube is the Brimar black glass 1988 labeled tube. They are expensive but they are special in midrange presentation. If you primarily listen to choral and string quartets type classical, you may value their presentation.

retiredaudioguy OP
330 posts
 

@posbwp55 yes, a beautiful midrange, but also a sense of space & air.  This seems to be what 2A3s do better than any other tube.  300Bs don't quite get the air of the 2A3s.  I'll keep an eye out for the Brimars, currently I am using the smoked glass RCAs in the critical preamp gain stage.

In my analog setup the cartridge is the Koetsu Rosewood Signature Platinum with a mid range unsurpassed, and the Dos Locos brings out its best.

@larryi The Rockports are really average sensitivity, there are many much lower than 87.5, and they really do show what everything else in the system is doing, utterly transparent; I think that you cannot get that with "high efficiency" speakers - I'm probably going to get taken apart for saying that.

posbwp55
24 posts
 

I thought about addressing that comment regarding high efficiency speakers. I currently own high efficiency speakers and I hear no degradation in sound from the numerous pairs of speakers I have owned that were lower efficiency. That includes the Avalon’s I owned with almost identical specs to your Rockports. I think my current speakers are the best I have owned and will be my last speakers. The other thing is that I can use a 60W parallel SET amp that uses two 845’s per channel (parallel), a 300B driver, a single 6SN7GT and two 6SN7GTB input tubes. This combination of four different tube types of the best sounding tubes ever made for audio gives massive ability to fine tune. That said, even the 60W’s on very efficient speakers, I feel us slightly outperformed by a 300W SS muscle amp capable if driving any speakers on the planet. I am guessing the massive difference in headroom cor the amps contributes to this to some degree. None of the presence, transparency and life like presentation are lost when I switch to the SS monos.

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