SS Preamp with Tube Amp?

If you can understand why the sonic charcter of any system is determined 85% or more by the amp/speaker (and speaker cable) combo, then you'll understand that if you want "tube sound" then you need a tube amp -- i.e., a tube preamp and a ss amp won't do it (contrary to what many people think ;-) Also, tube preamps make tube noise which is amplified by the amplifier. Tube amplifiers by themselves (genreally speaking) make no noise.

I drive my McIntosh MC275 with a Mark Levinson 26s preamp and the system is quiet, fast, and beautifully balanced sonically speaking. The main attributes of a preamp should be accuracy and blackest background. Since preamps do not process (amplify) the signal, but rather simply select sources and attenuate their output (volume control ;-) there's not much they can do to adulterate the signal, so may as well have a quiet preamp and go SS IMO.

After that, the amp and speakers will determine what your system actually sounds like.

The reason for my "pronouncement" ;-) about the 85% contribution of the amp/speaker/speakercable "group" as it affects system sonic character is as follows:

A. The amp is where the signal gets processed the most -- multiplied many many times its original strength and therefore subject to all manner of (possible) modification by the amplifier's electronics: harmonic and intermodulation distortion, variations in frequency distribution, timing changes, noise components and many others. If you ever heard the effects of a microphonic tube for instance, you have some idea what can happen on a less obvious level. All equally true for SS amps as well.

B. Loudspeakers have their own sonic signature(s) as we all know, but that's not the end of it. When an amplifier of one kind or another "looks into" the load characteristics presented by a given speaker (particularly the speaker's crossover network,) bad things can happen (or not) depending on the electrical compatibility of the two devices.

C. Ditto for the electrical characteristics of the speaker cable in use. Example: electrostats require low capacitance speaker cable, which is why it's advisable to stay away from high capacitance cable (almost all Cardas for instance) if you're driving electostats.

Then there's the issue of quality, no matter what kind of gear you want to use -- there are certainly some VERY quiet (and VERY expensive) tube preamps as there are SS preamps. My point was that using a great tube preamp (instead of a great SS preamp) will not get you "tube sound".

So how is it a tube amp produces "tube sound"? And why can't (most) SS amps produce "tube sound"? The answer is quite simple really. but first I need to define what, for me anyway, constitutes "tube sound". To me "tube sound" means that every molecule of signal detail is PRESERVED as the signal is amplified, and then it is sent on to the speakers "whole". In other words, to me it doesn't necessarily mean a "warm" sound, or a "mellow" sound. "Tube sound" is most noticable in an extremely lifelike midrange -- a quality that is less important to rockers for instance, than dynamic range, power, and tight bass.

To understand why tubes 'preserve' the signal better than transistors, you need remember just one thing: "switching speed." Power output devices (tubes OR transistors) are actually valves that normally operate in pairs, often referred to as "push-pull". One valve (tube or transistor) turns on and lets a powerful voltage through that represents a half-wave of the signal. Then it turns off and it's partner opens and lets the other half of the wave through.

OK, here it comes:

Tubes don't turn on/off instantly. They heat up, they cool down. And so there is some overlap between when one of the pair stops operating and the other one starts. There's a bit of -- let's call it lingering -- in handing off the signal; and so "the ball can never get dropped", so to speak. But if the "lingering" goes on too long, the waveform is distorted at the critical inflection point and you get muddy sound. (Some call it warm ;-)

Now transistors are just the opposite. They can turn on and off INSTANTLY. No lingering ;-) But what happens if when one valve turns off, the other one turns on just a nanosecond later? Sound (actually 'signal') was happening (or supposed to be happening) during that nonosecond. Where did it go? Well, it fell through the (nanosecond) crack! Lost! The result can be sound that feels 'hard' or 'etched', but in reality, the signal has simply lost some of it's original microdetail. It's a bit like when you throw away every hundreth pixel of a digital image, the picture seems to 'sharpen', but no longer looks completely "natural".

Very VERY expensive SS amps, like darTZeel, don't have cracks between their pairs of power output transistors ;-) However, it takes incredibly complex circuit design, and component matching, to reduce that nonosecond to a MILLIONTH of a nonosecond ;-)
.

Guido -- there's this marvelous website called Google http://www.google.com where you can not only find out stuff like "waht's a nonosecond?" but you can also look up the correct spelling for common words like what? ;-)

Nanosecond definition here: http://searchcio-midmarket.techtarget.com/sDefinition/0,,sid183_gci212620,00.html
.

The reason I would still choose a SS pre over a tube pre (even assuming the highest quality of either) is because to me, transistors are the device of choice for handling very small/weak signals. There are a number of different reason I feel this way including:

>> transistors don't change their behavior over time
>> transistors don't require large power supplies (compared to a similar tube unit)
>> transistors (except power output transistors) don't generate much heat (which can affect other electronic parts)
>> transistors don't produce electron "rush" (tube noise) which in a low level device like a preamp is bound to be amplified. Tube noise and tape hiss is why Dolby Laboratories was born ;-)

Preamps don't generally amplify the signal. They just select it, balance it, and attenuate it (reduce it's strength) when you don't want to play the music loud.

One kind of preamp that DOES amplify is a phono preamp. And in most cases, it also provides RIAA equalization to reduce record surface noise and strengthen the high frequencies. Frankly, I'm divided on this one. On one hand, I like tube PHONO preamps because you can mess with the tubes ;-) On the other hand, they DO make noise, and what I really dislike is the fact that if you want enough gain for MC cartridges, you almost always have to use a step-up transformer before the preamp; and I really dislike those! Transistor phono preamps can deliver plenty of noise-free gain, even for the lowest output MC cartridges. But you can't "roll" transistors; so if you want to tailor the sonics, why you're just SOL ;-)
.

Mapman, you understood I was talking about phono preamps right? With regular preamps, tube rolling generally doesn't seem to have much effect on sonics, compared to tube rolling in amps, so I tend to lean toward SS for those. Now of course if someone allowed me to audition a Nick Doshi, or perhaps the new CAT, or a Calypso, I might give in ;--)