One of the advantages of most single driver speakers is their limited bass output as it relates to synergistic amp pairing.
With my Fostex F200A driver (rated 30 - 20,000 Hz, 8 ohms, 90 dB/w/m) based speakers I've found bigger tube amps (10 wpc and bigger) to provide bloated, uncontrolled, muddy bass and smaller tube amps lacking in power or any deep bass output. Conversely I've heard good results from 35 wpc tube amps with smaller single driver designs (that have similar bass output to the Omega speakers). In my experience many SET/single driver fans have simply accepted lack of deep bass and have grown completely accustomed to a lean sound.
That's why I'm a Clari-T owner. A bit more juice might be nice in my 2,000 cu. ft. room but I'm most satisfied to wait and see what Vinnie or others can come up with to take things to the next level.
You're right about most SET's lacking deep bass. When you take a look at a frequency response graph from (say) a 2a3, they start to roll off gently below 30Hz. Coupled with the typical single driver speaker like the Omega, the rolloff is a non-issue because it can't produce 30Hz anyway.
I haven't found the bloated bass that you mention from the SET's. Even though I use mine to drive the Lowthers (while don't do anything under 60Hz) we've plugged my 2a3 along with Willies PP 45, Handmades basic 45, several 300's, plus some triode strapped EL34's, into a pair of Altec 19's (15" woofer), a pair of Klipsch horns (15" woofers), LaSalla's, and Cornwalls. None of the SET's exhibited the bloated sound. I have to qualify that by saying that we typically rolled the tubes to get the best sound with the speakers.
The DRD mean Direct Reactance Drive. Essentially, its Ron's terminology to describe a direct coupled design. Direct coupled means that there is no coupling cap between the driver tube and the output tube. The Handmade utilizes a .22uF coupling cap between the (in the case of the Handmade) 6C45Pi driver tube and the 2a3 output tube. This is 'typical' most SET designs.
The DRD and Handmade DC designs eliminate that coupling cap. The result is veil after veil are lifted. The veiling comes from that cap. I've only played one (maybe two) caps that don't veil the sound. Both of them are Teflon and very expensive (V-Cap and the Audio Cap used in the Handmade Deluxe design). I haven't installed the V-Cap in the 2a3 to do a side by side so I can't firmly say which is better.
What I have done is listen to the DRD beside the 2a3. The DRD smoked my 2a3. Granted they are two completely different presentations. The 2a3 has a lovely relaxed sound. Tons of detail without the appearance of being veiled. I still haven't figured out the best way to describe the sound of teh DRD other than it just sounded cleaner.DRD Schematichttp://www.welbornelabs.com/drd.htm
If you notice, the only thing in the signal path is a single resistor, two tubes and the output transformer. This is as close to a 'straight wire' as you can get. Result, little (if any) 'coloration' from passive parts installed in the signal path.Typical SET Design
As you can see with this 2a3 design, this one utilizes a coupling cap between the driver tube and the output tube. Some designs utilize 'chokes' to couple the driver to output tubes.
Eliminating the coupling cap or choke cleans up the sound dramatically. Thats not to say that a capacitor or choke coupling sounds bad because it doesn't. I love the sound of my 2a3 and will keep it forever. In fact, after listening to Willie's (drummerwill in the GAS circle) PP 45, I'm going to build one of those too.
Hey Lonewolf, Thanks!
Here's anonther one of my favs....http://www.tnt-audio.com/casse/lowtherpm2a_e.html
The AudioNote gear sounds great too. I've listened to several of their SET's and they are really impressive and the kits are a great value.
Maybe it's just me, I've played with the little digital amps and found them lacking. Not that they don't sound clean, accurate and all that stuff but when you compare them side by side to quality SET, they fall short. There is something about them that seems to strip the harmonics. I find the same thing with solid state gear too.
I'm not saying that to slam the digital or solid state gear or start a flame war, it's just my personal opinion. I've got a heavy preference for tubes. With all their quicks, the fact that they are picky about speakers, cables, IC's power quality, brand of tubes, all that negative stuff, I* still prefer them over the best solid state or digital gear. I guess part of it is I'm a cronic tweaker. The simplicity of tube design lets be roll up my sleaves and get dirty.
On the other hand, if your not into tube rolling or have the patience (sp) to carefully assemble a tube based system, the digital and solid state amps do a fine job.