The main parts of your question have been answered (The first rule is that there are no rules! - I am running SS preamplification with tube power amplification right now), so I'll try to answer your last question. The only real qualification that occasionally arises has to do with impedance mis-matches: Tube preamps *can* have highish output impedances, and SS power amps *can* have lowish input impedances, and the two factors combined *can* roll-off bass response. Axendo said it though - you rarely have to worry about this happening as a practical matter with most gear. One other thing to think about: The well-established existence of 'hybrid' gear, where tube and transistor circuits are combined within a single amplification chassis. |
OK, I'll put my unqualified neck on the chopping block...
Webnick: It's the ratios, not the absolute values involved, that matter most. Convention says that there should be a factor of at least 10X between the output impedance of the soucre component (the lower of the two) and the input impedance of the load in order to minimize LF frequency response roll-off (keep in mind that in actuallity, these impedances will vary with frequency, which is usually not specified). Again, the vast majority of preamp/amp combo's will satisfy this criteria. (The other thing that should be watched for if one is using a tube preamp having a highish output impedance, say more than a few hundred ohms, is to avoid long runs of highish-capacitance interconnect, the combination of which can cause premature HF roll-off.)
Philojet: Simplistically speaking, the differences between tubes and transistors that people talk about as far as distortion spectra go has a lot to do with the way they behave when driven into or near clipping (tubes behave more 'nicely', meaning higher overall levels of THD can be less objectionable with tubes). Below clipping, the main differences between distortion spectra have as much to with circuit design as the type of active device(s) used, although tubes will usually display higher overall distortion and noise levels. Simpler tube designs (triodes) are usually considered to display 'nicer' distortion properties than the more powerful tetrodes and pentodes, and a similar characterization is often applied to FET's as compared with bipolar transistors.
As for the distortion spectra themselves, low-order products (mostly the 2nd and 3rd harmonics) are considered less undesirable ('nicer') than higher-order harmonics, a smoothly descending harmonic series (from low-order to high-order) is considered preferable to an unevenly descending/ascending series, and even harmonics tend to be surpressed by typical push/pull amplification circuits (yielding a harmonic series that emphasizes the odd-order products, which by definition are higher-order than the even-order products, and results in an uneven roll-off of the harmonic series). This description ignores a lot of other considerations and types of distortions, including the questions of distortion levels vs. distortion qualities vs. other considerations (such as higher power capability) that may come into play as design trade-offs. (EE's forgive me...) |
Webnick, are you sure you meant to say "passive" preamp, not linestage? The two are different (though not mutually exclusive) things. You probably know this, but "linestage" just means there's no phono pre-preamplification included. "Passive" means the inputs and outputs are not actively impedance-buffered and the 'preamp' offers no gain, just attenuation. Going passive *could* offer a theoretical advantage in ultimate transparency under ideal conditions, but there's the rub - it can be very condition-sensitive. I'm guessing that for a relatively non-tweaky audiophile and bass-enthusiast like you seem to be, an active linestage preamp might be the safer bet, especially if you listen at a wide range of volumes.
(My presumptive description of you as a listener and audiophile - if correct - could also point towards SS power amplification over tubes, which generally won't give quite the bass or carefree operation that SS can. This is why many audiophiles who want to incorporate some tubes go the tubed preamp route, but that's another kettle of fish, and as a tube-lover myself I don't want to discourage tubed experimentation. In any case though, you should be able to improve greatly on the Adcom stack, whether you go all-tubed, all-SS, or a combination of the two.)
For your proposed combination of SS preamplification and tubed power amplification, I've found this can work very well, provided of course the gear is up to snuff. In particular, forgoing tubes in the preamp can eliminate some potential hassles with tube noise and finding decent tubes, while I feel that a tubed power amp is the main contributor to providing the greatest traditional strengths of tubes (as well as some weaknesses, but in areas I don't value as highly; I should note that this assessment is probably a minority view). Impedance concerns won't be a factor here: SS preamps (active ones, that is) have low output impedances and tube amps have high input impedances, so the minimum 10X ratio differential rule of thumb will be handily exceeded and no roll-offs will occur. Your options are pretty wide-open, but the way I'd approach it personally would be to get your speakers first, then find an amp that works well with them and your room and tastes, and save the preamp for the crowning touch (well, relatively speaking...next you'll start itching about your source, cables, power... :-) |
Webnick, I think if you consider setting your sights a bit higher (and maybe spending a bit more) than another Adcom - even a more powerful one such as the 565 - you'll be happier in the long run. The speakers you plan to get deserve it. Get the speakers first, then audition some amps, maybe in comparsion to a 565; I don't think you'll be very hard-pressed to find something better. Most audiophiles will allocate at least as much, and often more, to the power amplification than to the speakers. Getting yourself a pair of fairly expensive and revealing speakers, and then trying to power them on the cheap, will rarely work out well - the speakers often wind up highlighting the amp's inadequacies. Listen for yourself and you'll likely agree (and don't neglect trying a speaker cable upgrade at the same time).
You are correct in thinking that you can buy more power for less money going the SS route, although that will not necessarily translate into better sound, or even sound that sounds 'more powerful' - lower-powered tube amps have a habit of exceeding expectations in this area compared to moderately-priced SS amps, so don't get bogged-down in the numbers game of counting rated wpc. Go for quality over quantity.
Bass will usually be more "sharply-defined" with equivalent-quality SS amplification than with tubes. Again, this won't automatically mean 'better' (as in 'more natural') to many listeners, but these things are why you might want to try and hear some tubed amps for yourself before committing, if you can.
To answer your other question, a tubed amp will be turned all the way off when not in use, but it will arrive at fully-warmed-up sooner after being turned on than a SS amp would if it were not on stand-by. Stand-by on preamps is not new, but is more common for SS than for tubes, and running tubes continuously can shorten their life, although so can turning them on and off frequently. Probably most audiophiles turn their tube preamps off when not it use, but there is a large contingent than leaves them on - if you get a tubed pre, you can try this and decide for yourself. |
Webnick, I'm not sure any more what the main thrust of your question is. Listen to some amps of both types if you can. Tube amps aren't made for the mass market, so quality will be at least "acceptable" or better, but sound and quality tend to be pretty comensurate with price until you get above the price range you're likely to be looking in. As for your present speakers, I'm not qualified to offer advice on powering them, but focus on sound quality, not watts. My point is that if you want the better speakers, get a better amp than an old Adcom - be it tube or SS - and I recommend either getting the speakers first or auditioning your amp options through those speakers if you plan on buying them later. The tube options you'll want to look at in your range will not be triode, and basic stereo amps don't have many features to compare. Let your ears be your guide. :-) |
Webnick, I was not trying to say "...that in general, tube amps tend to be of a higher sound quality than SS amps" - both can have their strengths and weaknesses, and I don't like to generalize sonics as far as 'tube sound' or 'SS sound' types of characterizations. I wasn't clear whether your question was about build quality or sound quality, but all I was trying to say is that tube gear is a specialty product, not made in the hundreds of thousands for general consumption, and will likely have acceptable build quality. My comments about quality being roughly comensurate with increasing price, at least in the sub-several-thousand-$ range, apply to both sound and build (beyond a certain point, you're into luxury cache goods, where all bets are off and image, status, and fetish play equal roles to sound and build quality).
But some brands off especially good value while eschewing fanciness, and VTL and Quicksilver are prominent among them as far as made-in-USA goods go. I can't comment on the current Quickie offerings, but I have heard the VTL ST-85 sounding extremely good with SS preamplification powering 6 1/2"-woofered small floorstanders, so I would certainly give it a listen with the Veritas 2.3's if you're so inclined. (BTW, David Manley hasn't had anything to do with VTL for a number of years, or for that matter the company he founded after he left VTL, Manley Labs. VTL is run by David's son Luke Manley plus Luke's wife Bea, and Manley Labs is run by David's ex-wife EveAnna Manley; David Manley had gone back to Britain or Europe the last I read, and I don't know if he has any industry involvement now. His design concepts do seem to continue to influence both companies to a fair degree, if not always in the same ways.) |
