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General Asylum General audio topics that don't fit into specific categories. |
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In Reply to: Tubes or Solid State? posted by Eric on October 28, 1999 at 08:59:26:
My very first stereo (in 1969) was a tube rig. Dyna PAS-3 preamp and Stereo 70 power amp. The latter has become a cult item and now sells for more than it did new. I now have a Krell KAV-300i integrated amp. Between those two, I've had a variety of solid state gear from Dyna, and a couple of solid-state receivers. And, of course, I've auditioned contemporary tube gear in shops. Leaving the subjective part for last, there are a few objective things that can be said, IMHO.
First, tube poweramps do not deliver a flat frequency response into a reactive loudspeaker load, even though they may deliver a flat response into an 8 ohm load resistor. Their high output impedence interacts with the speaker's impedence and can produce response variations of several decibels, depending upon the particular amp and speaker. This is clearly audible, and no doubt accounts for part of the "tube sound." If you look at any recent Stereophile test of a power amp, they will show you a graph of the amp's measured response into a reactive load. This means that "synergy" is not just a buzzword when buying a tube poweramp; it's a must. You must select the particular tube poweramp/ speaker combination that you like. Having done that, if you later replace one of the units, you can not count on a better sound. It could even be worse. Transistor amps have a very low output impedence and do not display this charcteristic.
Second, in my experience, even with the equipment I was using 30 years ago (AR 2ax speakers), as the EL-34 output tubes on my Stereo 70 aged, the sound changed, and not for the better. And we're talking months here, not years. After a while, I would notice that the amp did not sound quite so good. It was kind of dull. Then I would buy a new set of output tubes, and everything was all better. And, yes, I kept the tubes biased correctly with a VTVM (Although, I checked them frequently,the tubes' bias held steady, even though the sound deteriorated). And also yes, Mullard EL-34s (now worth their weight in gold if you can find them) did make the Stereo 70 sound noticeable better.
Third, there is the matter of price -- which you did not specify. At price-is-no-object levels, I guess there's no advantage. But at more "real world" levels, I think tubes are more expensive for the same equivalent (more or less) output. In my own experience, I shopped the Krell integrated and the Audio Research CA50 tube integrated. The Krell lists for something like $2300; the AR is substantially more. Both units have 4 inputs and a tape loop; both units have a remote. The Krell rates 150 wpch @ 8 ohms; the AR 45 wpch 20 - 20K (I think it makes 50 watts at 1 Khz, but less at the frequency extremes). I auditioned these amps driving Joseph Audio RM7si signature speakers and Aerial 5 speakers, both standmount speakers. Both sounded very good within their operating limits. However, the AR did not have enough power to run the Aerials at a moderately loud level with symphonic music. If the AR had sounded way better than the Krell, I might have bought it knowing that I had to be careful about speaker selection. But, for me the question was: why spend more money for an amp that will drive only some speakers well?
Third, to some degree, all tubes are microphonic. This is not much of a factor with power amps that provide only a little voltage gain, but it is a factor with preamps. While I'm suspicious of claims of great sonic benefits of vibration damping and isolation of solid-state electronics, I have no doubt that such damping is very important for tube equipment, especially preamps.
Fourth, I suspect that, long term, tube equipment is going to require more service, even if you can do your own biasing or have a self-biasing circuit. It's true that tubes tolerate conditions of extreme abuse (i.e. shorted outputs) better than most solid-state stuff, which can go into thermal runaway almost instantly if shorted or if heat sink ventilation is inadequate or blocked. But, in normal use, transistor stuff is pretty bullet-proof. The only problem I've ever had with any of the solid-state stuff I've owned is with bad contacts on the output relays that some solid-state equipment has, and my oldest piece is a solid state receiver (the original Luxman) that I'vehad for 20 years.
Subjectively, I agree that some solid-state stuff has a glarey, nasty sound. My receiver has it when called upon to deliver more than a watt or two, and I've heard it in some Adcom stuff demoed in a store. Tube equipment, especially power amps, typically is "softer" at the frequency extremes. I think this has to do with the presence of impedence-matching output transformers in the tube power amp's output circuit. (I have never auditioned any of the OTL (output transformerless) tube poweramps; but my house does not need any additional heating. OTLs have a lot of tubes, and a pair of them will dump anywhere from 500 watts to a kilowatt of heat in the room. That can be a problem.) For some people, this characteristic can be a virtue. Although not all of them are that way, a lot of CDs have a nasty, edgy sound that is helped by a tube amp's soft topend. Also, if you're using standmount speakers, they're not giving you much bass below 50 Hz, so whatever happens (or doesn't happen) below that doesn't matter.
I can't say much about tube preamps. The PAS-3x I had was noisy at the phono inputs, compared to later solid state preamps and integrated amps that I had. I'm sure today's stuff is better, and the PAS 3x did not pretend to be state of the art, even for its time. You may not even be interested in vinyl, so the question may be academic.
I hope these thoughts are helpful.
Good listening!
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Follow Ups
- Re: Tubes or Solid State? - Bruce from DC 10/29/9906:56:21 10/29/99 (0)
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