Tubes Asylum: REVIEW: Sun Audio SV300B MKII Amplifier (Tube) by Willie The Squid

Model:	SV300B MKII
Category:	Amplifier (Tube)
Suggested Retail Price:	$5000 ???
Description:	Class A, Push Pull, Interstage Transformer Coupled, Monoblocks
Manufacturer URL:	Sun Audio
Model Picture:	View

Review by Willie The Squid ( A ) on May 19, 2002 at 00:04:10
IP Address: 12.228.193.136

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for the SV300B MKII

This is a review of the Sun SV300B MKII push pull monoblock amplifier. That's the starting point, at least.
A bit of history. Dr. Harvey "Gizmo" Rosenberg was among the first voices I ran across that preached the gospel of direct heated triodes (DHT) like the 300B, 2a3, 45, etc. Contemporaneously, Gizmo preached the gospel of single ended triodes (SET). But DHTs don't have to be used in single ended designs only...and in fact can sound simply wonderful in push pull circuits.
I had the good fortune of running across and owning (for two years) a Cary 300B stereo amplifier which was a 300B push pull amplifier, using the 6SL7 as the inverter/driver, and the GZ37 as the rectifier. It was a fine amp, boasting 25 wpc and the classic 300B DHT "sound". I believe that Dennis Had of Cary designed and manufactured this amp before heading into single ended land. It had some design drawbacks (if all four(!) 300Bs werenâ€™t closely matched, the amp had quite a hum...and since Centron 300B tubes were at that time $250 each, the amp was expensive to keep quiet...moreover, the 6SL7/5691 tube selection had a rather dramatic impact on the sound....)
Since it wasn't single ended, I required a change and finally made the jump to single ended amps. Over the next 5 years I had the pleasure of owning two classic single ended amps -- the Cary 300B SE monoblocks, and George Wright's 3.5 (2a3) monoblocks. The Cary amp was "THE" breakthrough single ended triode product. More than any other amplifier the Cary broke the herd mentality that said simple 8 watt amplifiers simply COULDN'T sound good. And besides, they tested horrible. Some of you may remember the debate. Fact was, as a midrange amplifier, the Cary 300B SE monoblock was a splendid amp, with magic. There was a reason it was a breakthrough. When they arrived just 3 years ago, the Wright 3.5 monoblocks were much better yet, at a far lower price point -- extraordinary balance and harmonic "rightness" in a small, inexpensive package. I believe their introduction into the market at less than $1,300 a pair was indicative of the progress designers had made in a very short period.
My 5 years of living with "smallish" single ended amps have clarified certain qualities that I would characterize as drawbacks. First, on most modern "dynamic" loudspeakers, little SET amps lack...dynamics! This is a function of most home loudspeakers' inherent inefficiency (83db efficient to 90db efficient) combined with difficult impedance loads. Little SET amps just don't sound their best under these circumstances...and these circumstances are the norm. My "solution" was to find loudspeakers (Epos 14s, then Reference 3a Royal Masters) that were moderately efficient at 87db and 92db respectively, that had flattish impedance curves, and that utilized only a cap tweeter filter as a crossover. As a result, these speakers sounded darn good with those amps...but always there was the limitation that these little amps couldn't really "rock" - they lacked dynamic swing and just didn't have the juice to move a lot of air in any absolute sense. Second, the bottom end sucked on the Cary's, and while it was much better on the Wrights, it still didn't have power. What really was missing is what the English chaps refer to as PRAT: pace, rhythm & timing. I came to really know this when I moved up to truly efficient speakers -- Tannoy System DMT 15 MKII studio monitors that measured 98db efficient. On these speakers, the little Wright amps could fill the room with volume, but just couldn't control the bottom end with speed and precision. The sound was invariably polite - but that wasn't how some music is suppose to sound!
Now all this time I had another, second system, upstairs. It consisted of a NAD multi-disc CD player and a Fisher mono tube tuner as sources, Spendor LS3/5a (15 ohm) speakers, and a variety of small, integrated push pull amps and receivers from the 50's and 60's - Fisher, Scott, Bogen, Eico, MacIntosh, etc. So all this time I'm listening to these elegant sounds from my "main" system downstairs, but I'm always cognizant of the "second" upstairs system offering "something" that's just missing downstairs - PRAT, drive, energy, whatever. On numerous occasions I found myself thinking that I could live forever with this simple little system in the living room...but rarely had that feeling about the downstairs system. Hmmm.
So the SunAudio SV300B MKII amps arrive a couple of months ago. I must admit that I was pre-disposed to like them. The design parameters made sense: no coupling caps, a 6SN7 input tube is connected in parallel to a transformer phase splitter which drives the output stage. As a result, gain is low, but that's OK if you have a good driving pre-amp. There's no global feedback, and the power supply has a choke. The 300Bâ€™s B+ voltage is only 320V which is substantially less than the â€œnormalâ€ 400-450 Volts. This operating point helps define the "tone", along with allowing the output tubes to practically "idle", with a maximum output of 20 watts. Parts are high quality, and the Tamura transformers are super high quality. It is very, very simple. Moreover, I had read what Dr. Gizmo had written (mostly raves) about them on more than one occasion. The big "drawback" was that when they first arrived on the scene, they are $6,300 a pair assembled and $5,000 a pair in kit form. Unreachable at that time. I quote Gizmo:
"This the only push/pull amplifier I have ever encountered that is causing me serious doubts about the artistic primacy of single-ended circuits.... This is the best push/pull amplifier that I have ever heard."
My amps (used) arrived from Hong Kong (about $2,500 including shipping and customs) with Sovtek tubes: outputs, drivers, rectifiers. One of the outputs immediately bit the dust, so for my first month I had Sovtek 300Bs in one amp and JJ/Tesla 300Bs in the other. I tried a variety of 6SN7 types in the driver position, and IN THIS SYSTEM, the KenRad 6SN7GT (mid 40s)is absolutely "stunning" - I always found this tube to be out of balance with too much bass in prior systems - but not here! I sourced some NOS RCA 5U4Gs for rectification, and they sweetened and relaxed the sound without loosing any drive or PRAT. Then three weeks ago I finally landed two matched pairs of Sophia 300B Mesh Plates and these output tubes truly completed the amps. I'm sure I can make them sound different, I skeptical that I can make them sound any better.
So here's the deal: these are the best sounding amps I've ever heard. In my experience, nothing even comes close. They give up a "smidge" of midrange magic to the single ended designs, but in every other area they are superior. While the midrange is not as spooky magic, it is much lower in distortion, wider and clearer. There is no homoginization. They are fabulously extended, both top and bottom. There appears to be a real synergy with the Tannoy loudspeakers, displaying dynamics to die for. 20 watts per channel allows for peaks of 110db without clipping. They never congest at volumes that make me fear for my hearing. They create this coherent musical wave, top to bottom, that energizes the room differently than SE, and in a way that I find more captivating. The biggest deal is that no matter what kind of music I put on, it quickly becomes mesmerizing. The system no longer tends to lead me to certain kinds of music. It's all available, in spades. The PRAT is back, and I'm not likely to ever give it up again.

Product Weakness: see above
Product Strengths: see above

Associated Equipment for this Review:
Amplifier:	SunAudio SV300B MKII
Preamplifier (or None if Integrated):	Supratek Syrah
Sources (CDP/Turntable):	Naim CD3; Rockport Xerxes w/Rega 900; Goldring Eroica Low Output MC
Speakers:	Tannoy System 15 DMT MKII
Cables/Interconnects:	Silver Sonic Interconnects & Speaker Cables
Music Used (Genre/Selections):	All
Room Size (LxWxH):	10' x 18' x 8.5'
Room Comments/Treatments:	Carpeted; Stuffed Furniture; Blinds on Windows
Time Period/Length of Audition:	2 months
Other (Power Conditioner etc.):	PS300 on Sources and Syrah
Type of Audition/Review:	Product Owner

Product Weakness:	see above
Product Strengths:	see above