Reproduction of acoustic instruments with tube amp

I too find Dburdick's findings surprising. The VTL ST-85 should be able to drive the Sparks no problem. I haven't heard the combo myself, but when I recently auditioned the new Thiel 1.6's with both my own c-j MV-55 and the store's VTL ST-85, I thought the latter was outstanding for acoustic (and electric) music, with a vast soundstage and very 3-D imaging. It did strike me as possibly a touch overripe through the midrange, but not excessively colored for enjoyment, and still quite transparent for the money. In that system (with Transparent wire), it frankly made my c-j sound small and pinched. Fortunately, the MV-55 sounds better at my place (Thiel 2.2's, Cardas Cross) - full, spacious, and neutral (and it far outshines my previous SS amps, especially with acoustic material). If in Dburdick's system the VTL didn't offer separation and definition with acoustic music, I would suspect a wire mis-match and/or poor tubes as possible culprits.

Yeah, it's worth giving it another try. Your ancillaries are good stuff. The reasons tube amps can sound best with vocals are generally the same reasons for the way they handle acoustic instruments. I just call the whole gestalt an ability to sound "natural", having a lot to do with the way the harmonic structure is preserved, and the way images are cast in their acoustic environments. SS bass slam and weight tend not to matter as much as these qualities when it comes to vocals and acoustic instruments. But in addition to trying better tubes themselves, it seems to me that you don't favor a "tubey" characterisic warmth that might compromise separation and definition. This would point to trying an amp (still push-pull, probably not in triode mode if switchable) with a large, wide-bandwidth output transformer (for un-rolled bass and treble extension), possibly running higher-output tubes than your VTL's EL-34's such as 6550's (and maybe more than one pair per channel?) for higher undistorted output capability (in conjunction with a beefy power supply), and possibly using an ultralinear output topology and somewhat greater negative feedback (both as opposed to the VTL) for lowered output impedance (less frequency response deviation into a 4 ohm load) and a higher damping factor (increased bass control). If you spend the money to get these things, you should also get passive parts quality on par with your Plinius, bettering transparancy and detail. The result may be a sound that, within the scale of tube amps, is more "dry" and less "luscious", with images that more favor focus over breadth and a soundstage favoring intimacy and clarity over distance and reverberance, and a small-scale dynamic character that may lean less toward "freewheeling" and more toward "controlled" traded off against increased large-scale dynamic resistance to sounding "amorphous" during complex passages. Obviously, many folks prefer tube amps for just the qualities opposite these, but you may not. Then let us know how things turn out. Good luck!

61, of course you are right about an amplifier's being supposed to reproduce the input signal it's fed - in theory. But in the real world, no amplifier can do this perfectly. So amplifiers introduce colorations, have strengths and weaknesses, sound different from one another, and may have characteristically indentifiable traits within design types - meaning that certain design schools may tend to broadly share some relative strengths and weaknesses.
By the same token, different types of music will tend to differ in the characteristic demands they place on the equipment reproducing them. Tube gear is commonly considered to be capable, when well-executed, of standard-setting reproduction of pure harmonic overtones and sonic recreation of space and objects. These strengths correlate well with the demands generated by naturally recorded and live-captured acoustic music and voice. With electronically produced and studio recorded and processed multi-track music (like most rock), the demand for the above qualities can be lesser because little genuine space or acoustically natural harmonic overtone content may be present. The traditional solid state virtues (again, when well-executed) of separation, definition, and bass weight and slam can be of more relative importance here. Obviously, and as previously intimated, these are broad generalizations, and quality amps of all types can do a capable job with many sorts of music types. But differences will still exist, and an audiophile's preference in types of music listened to will often have an impact on which set of amp characteristics are weighted with the most importance for the job.

Amen. Yes, it's imperative to keep in mind that everything is part of a *system*! No one has ever listened to *just* an amplifier...