Myth: low-power high-efficiency


The past 6 - 8 months I have been living with very efficient speakers (~ 109dB/m/w) driven by low-power SET amps. The amps use 300B output tubes for about 7 wpc. On paper, this should be a match made in heaven. In fact, the combination is capable of wonderful nuance, subtley, harmonic richness, and tonality. It is really pleasing, especially on chamber and jazz music. Except for one thing - dynamic energy. I am not referring to loudness. It can deliver more undistorted volume than I care to listen to. I'm referring to immediacy, presence, power, and punch - the life of the music. If you go to the symphony, or live blues, than you know what I am talking about. Next week I'm taking delivery of a 90wpc PP amp, to audition in place of the SET. I need an amp that can maintain the purity of tone and harmonic texture of the SET, while delivering more power, to grab hold and take control the 15" bass driver in my horns.

I searched the archives, but have not found a similar post. Are there any other high-efficiency low-power people who moved to a higher power amp? Are you satisfied now?

Scott
skushino
I've been through this kind of transition in the past couple of years, slowly making a transition to high-efficiency speakers + SET amplification which was fully completed in 2005. I began a few years ago by buying KT88 and 300B single-ended amps to experiment with on a second system set up in a small space. A move allowing me to replan my audio systems from scratch instigated completion of the transition with the purchase of Zu Druids for one system and Zu Definitions for the other. Of course, going to 101db/w/m efficiency simply forced attention back on the amplification.

In a 24' x 12' room, 7/7 watts of 300B power went quite far. And the same was true in another room, 20' x 14' I tried a number of 300B amps and some were quite slow and undynamic, while others were quite lively. My experience has been that there is remarkable variety of sonic signatures in 300B amps. The liveliest 300B amp for me was by Audion. Their circuits all have a characteristic fast, dynamic sound.

However, a single 300B per side didn't have as much ability to project sound into the room and push snap energy into the acoustic space as a single-ended KT88 amp. I had a couple of those, one by Acoustic Masterpiece and another by Audion. The Audion amp had 18/18 watts per channel, by comparison. It had firmer bass than the 300B and more dynamic aliveness to the sound, but didn't have the ultimate focus and intimacy of the 300B.

In a conversation with Sean Casey at Zu, on another topic, he casually mentioned that he really liked the drive of the KR T1610 tube, available in a Cary or KR amp, and second to that he liked the 845 tube. I hadn't heard either up to that point in time, and wasn't really thrilled with the idea of having a tube amp with $1800 power tube replacement costs, so ignored the T-1610 for now. I went looking for an 845 amp and coincidental to my interest found that the last pair of factory Audion Black Shadow 845 monoblocks were available. I bought them. At 25 watts of triode power per amp, I then had the holistic sound of an SET with the muscle of a KT88. This was a quite lively and dynamic sound on Zu Druids.

I went through the same experimentation on the Zu Definitions and ended up with 30 watts per side via a pair of Audiopax 88 monoblocks, which use a dual KT88 circuit that ingeniously models triode behavior from a commodity pentode.

I thought I was settled. And then I began to hear some of the very high end 300B amps, which were at prices that allowed the designers to get more out of the tube. I finally got the dynamic behavior I wanted in a 300B, from a pair of Audion Golden Dream Level 6 parallel single-ended monoblocks, each using a pair of 300Bs for 25 watts per amp.

I was fortunate to have the resources to churn through some auditions in my home to settle my amp/speaker match. I can say that even for a 100+db/w/m speaker, having 25-30 watts on hand sounds like a lot more drive than having 6 or 7, even though the actual SPL the power should drive isn't large. You get more of the sense of reserve and effortlessness that you hear putting something like McIntosh MC1201s on an 88db/w/m mainstream speaker.

I observed a few other things. One is that most 300B amps are change their signature quite noticeably from tube to tube. Various KR 300Bs were dynamic and had a hard attack on transient information, whereas a Full Music or Sophia mesh plate tends to be very smooth. I haven't listened to current production WE 300Bs yet. Some of the very affordable Chinese 300Bs, including the Shuguang solid plates have a lot of snap and sound quite lively, while giving up the lushness that many people buy 300Bs for. Point is, if you have a 300B on efficient speakers, tube rolling has to be part of your strategy for getting the right sound for you.

Also, I had a chance to try a few PX25 amps. At 6/6 watts, the PX25 is distinctly livelier than the 300B, with much less bass bloat. In fact, the PX25 amps had some of the best tube amp bass I've heard from any design. That tube had a very clinical, objective sound, but conveyed less spatial information than a 300B. If I hadn't had the means to look for and find more triode power, I might have settled on a PX25 based solution.

If you're on a budget, don't ignore single-ended pentode/tetrode amps. They solve a lot of problems evident in entry-level 300Bs. For instance, at a local Zu demo held in a 24' x 36' x 16' hotel event room, a little $800 Almarro A205 amp was very impressive with all of 4.8/4.8 watts. That amp has just 3 tubes, with power coming from an EL-84 per channel. While a watt is a watt is a watt, the dynamic behavior of similarly-rated single-ended amps varies considerably by tube and design.

The last thing I did was to try 100w - 500w solid state amps to see whether a dramatic power increase would gain anything useful. What I gave up wasn't worth the small amount of reserve that was gained, however. The same was true trying push-pull tube amps. 25 - 30 watts of SET on a 101db/w/m speaker has plenty of dynamic projection in rooms my size.

Phil
Hi Gang, Interesting thread here and many good observations. When one contemplates the many factors involved in the equation here it can be a little overwhelming indeed. I would hazard to guess that the room size would probably dictate ones priorities and perhaps have the biggest influence regarding the power issue. As many here have already pointed out, all watts are not created equal regardless what topolgy we wish to choose....the type of tube employed in set amps,push/pull,triodes, pentodes or SS for that matter. In many cases the quality of the transformers and/or the power supply can have more of an influence than the type of tube employed in the amplifier itself. I am not denying here that power doesn't matter however,if your speakers crossover is a reasonably begign load and the speaker anywhere close to 100 db sensitive, I can assure you that 25 to 50 watts of power is more than enough to simulate the volume levels of a live event in most rooms.... unless of course your room is the size of an auditorium. My main rig is in a huge room....34ft x 27ft with a 16 foot ceiling. I use a pr of Tannoy Westminsters [98 db efficient] and have many amplifiers on hand to pool from.Both high powered tube and solid state as well as both low powered tube and low powered solid state. I can also bi-amp with any number of combinations. SET amps? The wright 2a3's.... nice,clear and vibrant but don't quite cut it full range for anything but chamber music or simple acoustic stuff. When used as the tweeter amp only... more than enough,300b's for tweeter only?.....way more than enough. The 300b set amps [western electric 300b].....a greater sense of the venue,a larger soundstage with more of a holographic presentation,slightly rolled off on both frequency extremes but somewhat soft and lumpy below 100 hz. But what a fabulous midband, incredibly nuanced and fluid though not your rock and roll amp for full tilt boogie. Higher powered 845 based set amps bring a whole higher dynamic presentation to the table. The cary 805 will rock with the best of them,and will handle any and all musical genre at any sane volume level one chooses to listen at,and does so without any hint of compression,glare or collapsing of the stage...although it possess decent bass power and weight, it's still somewhat soft and overly ripe in the bottom two octaves. By contrast, the Antique Sound Labs parrallel 845's 60 watt 1009 monos have a similiar presentation,seemingly unlimited dynamic range with a far superior bass range akin to the better high powered push/pull tube amps like the el-34 based VAC pa-90's,the kt-88 based mfa 120's or the Jadis Defy 7 and as good as any tube amp I've had the pleasure of listening to in my room.When compared with high powered solid state.... The Bryston 4bst just flat out boogies at any volume levels with recorded rock n roll music.As does the Krell KSA 50,classe dr3 or the little bedini 25/25. Bass energy and power that is second to none, a percussive vibe that most tube amps only hint at. Funny thing here is: [to my ear anyway] I much preferr the sound of the lower powered [high current] classe A ss amps to the higher powered solid state stuff, at least when powering the Tannoys. They seem to be a little more articulate in the bottom octaves as well as possessing a sweeter sounding treble with less of a grain structure in the midrange.Any one of the SS amps above will play to well above 100 db in my room without any sign of dynamic compression or diminished dynamic range. At times: when I have a room full of people over for social gatherings [read party here]sometimes things can get a little carried away with regards to SPL's. Yup... 50 watts is way more than enough in my room.Just recently had a pre Christmas gathering with around 30 people over.Many of them are professional musicians that stop by regularly to jam. A friend had been restoring a pair of old vintage 30 watt Eico monoblocks . These are a parrallel push/ pull design from 1959 that employ the el-84 output tubes.The circuit was stock,original transformers but obviously tweeked and updated with modern coupling caps as well as power supplies. WOWZA!!!! These babies just flat out rocked the room and with a bass punch that knocked me out. They simply made music believable and in a room full of people no less.Hey, I think I'm getting a little carried away here but: Big power....it has it's own vibe I suppose,different stokes for different folks.
Hi Scott, after trying many amps over the last year (including 45&300b SET) on Westminster royal HE(99db). I also prefer a bit more power for many of the reasons stated by others.
I am really enjoying Nagra VPA's 845 push/pull, also still use McIntosh 2102.
Happy new year!!
Rob.
Sonus Faber Stradivari and Nagra 845 is a fine match that I am fortunate to hear at the home of a friend of mine.No lack of dynamics, bass depth that goes thru the floor, and great detail even at low listening levels. Need I mention that there is no listening fatigue?When this fellow hosts listening nite,we always stay longer.
The best option I can come up with is something like the new Jordan JXR6 HD 2" driver which goes to 80hz and useful bass into the 60's. Maybe put two drivers in each cabinet. This is good for vocals etc. Fostex is anothere option for higher efficiency.
Combine this with self powered 15" stereo woofers which kick in with dynamic bass heavy music.