Is my preamp useless?

^^ The quick answer is here:
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1426779273&openflup&16&4#16 (earlier in this thread).

The longer answer is that mathematically, no passive control is going to work perfectly as intended if it is driving an interconnect cable. The longer the cable the more noticeable the artifacts become (one solution is to build the control into the amplifier, which works very well). These artifacts can be so profound that a properly designed line section can actually sound more neutral.

Consider the source, which has an impedance, usually no more than a few hundred ohms and often quite a bit less. It is driving an interconnect cable. The lower the source impedance, the longer the cable it can drive and less artifact will be heard from the cable. If you install a passive volume control, essentially the source impedance driving the interconnect cable after the volume control (and the amplifier as well) is raised by the value of the volume control setting. This is often a multiple of the original source impedance.

The result is that the capacitance, inductance and resistance of the interconnect cable is no longer shunted by a low impedance (the source impedance). Instead the shunt impedance is much higher (the value of the control dominates this value and changes with the setting; you can see that as the control setting is changed it may be that the sound changes with it, and indeed many people experience this).

In this situation the resulting system is very sensitive to the issues of the cable and cable artifacts result. Anyone who has set up a successful system with a passive volume control knows this: the choice of cable in such systems requires careful selection as the cable artifacts are so easily heard.

There are other issues/phenomena; some are source dependent and others are amplifier dependent and so do not occur in all systems. Hence the extremely variable results that cause so many of these threads to exist.

Atmasphere,

"A preamp does these things:
1) provide volume control
2) provide any needed gain
3) provide switching for various sources
4) control artifact from interconnect cables."

Looking at the post you referenced on what the preamp does, I have a question. I've heard this before, where people list these things and say that's all a preamp does, almost like its a trivial matter. (In general, I'm not singling you out.). Why is it then, when you put different active preamps in a system, the sound changes so much? Imaging changes, dynamics, contrast, etc... And a related question. I hear all the time comments to the effect of, a preamp can't add anything. It can only take away. If that's the case, how do account for something like image size getting much larger when switching from a passive or source with a volume control, to an active line stage? There are some big differences, not subtle ones. It makes perfect sense that a preamp can't add anything to a recording, but listening clearly proves otherwise. (Maybe no proves, but something is going on that's audible.)

Going direct like the OP can do, will not add or subtract anything that the source is presenting. As his source (PSA) has perfect impedance match and voltage output to drive his Cary amps and the "interconnect".
Any active pre that is put between, will colour the sound, he may wish to do that but, he will also get way too much gain as well.

Cheers George

^^ This post is incorrect, as the problem is not the control but the interconnect it drives, and of course the drive actually comes from the source- I explained this in my prior post.

Why is it then, when you put different active preamps in a system, the sound changes so much? Imaging changes, dynamics, contrast, etc... And a related question. I hear all the time comments to the effect of, a preamp can't add anything. It can only take away. If that's the case, how do account for something like image size getting much larger when switching from a passive or source with a volume control, to an active line stage? There are some big differences, not subtle ones. It makes perfect sense that a preamp can't add anything to a recording, but listening clearly proves otherwise.

Thanks for your thoughtful question! The first comment I have is 'compared to what?'. Is it that the line section is reproducing the image incorrectly or is it the passive? This really is very system dependent! Some line sections introduce colorations without any doubt, so I am usually careful to qualify my statements about what a line section should do with a phrase like 'properly designed' or similar.

IMO/IME it is a statement on how dreadful some line stages are that a passive control can sound better; if the line stage is designed and built correctly that simply can't happen. But in real life it does so that says to me that there are a lot of marginal line stages in use otherwise this debate would not occur over and over.

Atmasphere,
With all due respect - have you heard all possible permutations/combinations of amp+preamps that exist in the world? If not, then it is simply YOUR view that actives are always better than passives. Folks have been very happy about TVC preamps, which are considered to be passives. I love my TVC. Does it mean, it will work in all systems? Heck no! Try my preamp with a power amp that has a sensitivity of > 1.5V and it will sound pathetic at best. If you have heard a passive that was introduced in a system that needed the gain, I am sure it would sound bad. At the same time, in my system I cannot introduce any source that gives out less than 2V.
So, it is all system dependent. A properly put together system can shine as much or better than an active line stage, if it used a passive preamp. It has been asked before - why would Nelson Pass make active line stage, if he likes passives? The simple reason could be - because people have behemoth loudspeakers, whose sensitivity is so low that they need tons of GAIN in their system. The amps that drive these loudspeakers are low sensitive amps, mostly >1.5V for full power.