Is my preamp useless?

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.

Of these the last is the least understood. Since you don't need any gain my recommendation is a buffered volume control. This is a passive control that has buffering circuitry with no gain that allows the control to work properly without artifacts being generated by the interaction that typically occurs between the volume control and the interconnect cable driving the power amp.

So let us assume that I purchase this preamplifier. What happens to the power amplifier, sources and speaker cables? What about power cords? They also seem to have some degree of effect due to cable changes. At least in my system, the speaker cables made a huge positive difference. Or is my system completely wrong in revealing changes because of cable switching?

Your system is fine- being able to hear the effects of cables is what comes with resolution. The only thing is, interconnects are the one type of cable that should never be able to impose an artifact- because we figured out how to stop that a good 60 years ago!

However, speaker cables and power cords are a different matter entirely. They impose (measurable) artifacts too and the physics about why are pretty straightforward although I am not sure if they are germane to this thread.

^^ 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.

^^ 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.

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.

Of course I have not heard everything. But I did go to school and got taught engineering principles, and if you look at my posts you will see I was careful to be talking about PVCs and not TVCs. So as far as I am concerned, your comment is a strawman, as you are attacking an argument I did not raise.

However we can have that discussion if you like...

I think you were generalizing that Actives were better than passives. I do not think I attacked your statement in any way. I was suggesting that we cannot make generalized statements. Isn't TVC a passive component?

No worries- but apparently what you were thinking is not exactly what I was saying since I was careful to not generalize. If you review my posts you will see that I make a point of also saying that not all active line sections are created equal. The phrase I like to use goes like this: 'It is a statement of how poor many line stages are that passive volume controls can beat them'. So I am always careful to use the phrase 'properly designed'.

So far this thread has really been about active preamps vs PVCs (Passive Volume Controls).

TVCs (Transformer Volume Controls) should not be considered in the same realm as PVCs. The math regarding how they function is quite different.

TVCs involve a transformer or autoformer with taps. They have a different set of issues- for example if improperly loaded the device will not express the turns ratio correctly and so bandwidth will not be flat (inter-winding capacitance can start playing a role). This means that the designer has to provide the proper loading for each step in the setup, taking into account that the amplifier (which might have an input impedance anywhere from 10K to 100K or more) is part of that load.

A lot of TVC designers don't take all that into account. So some of them are easily beaten by active line stages because the active unit is more tonally neutral). OTOH, there are TVCs that have all the design parameters sorted out and they can have impressive performance if used correctly.

If a TVC provides gain (and sometimes even if it does not) and depending on the type of amplifier used, the interconnect cable may well play a serious role in the results! Cables have capacitance and TVCs are all about inductance- the two together can result in a high frequency resonance that varies with the control setting.

If you can hear big differences between interconnect cables, what you can safely conclude is that the 'good' cable you have now and the one that didn't make it are both wrong. The why of it is simple- did you audition all the cables out there? Will the manufacturer of the cable you settled for make a better one next year?

A properly designed active preamp eliminates this issue- the cable plays a far less of a role in the tonality and resolution of the system. A good active will force the cable to do its job- to pass the signal without editorial. I don't see PVCs or TVCs really doing that.

I agree that I have not auditioned all the cables that are available. Will the manufacturer make a better cable next year - chances are most likely yes. Isn't advancement in technology supposed to do that? Nordost, Siltech, Shunyata, etc, all come up with new improved cables over a period of some years. Folks have done A-B comparison with the new-old and preferred one of the other. Does it mean that these cables are wrong?
There are tons of users on this forum who use very highly regarded active preamps (probably 3X-10X the cost of my entire system), and have experienced a better sound when their cables were upgraded. Does it mean that all these highly regarded active preamps also have not been designed properly? So which one would you say is wrong: cables or active preamp?

I understand your consternation! It took me a while to get my head around this issue, but to your first question- does this mean that these cables are wrong the simple answer is 'yes'.

What if you had a setup where the cable made no difference in your system and an inexpensive cable sounded just as good a really expensive cable- which is to say that they both played so well it was as if they were simply a direct line to the music? Would that be of interest?

This is what I am talking about when I talk about eliminating interconnect cable artifact. Now if you prefer to throw as much money as you can afford at the cables to get better sound- by all means be my guest. That is one approach and it is the one most commonly used by the 'tons of users on this forum' to which you refer.

But if you want to get off of the interconnect cable merry go round and not have to worry about cables ever again in your whole life then go back and re-read my posts on this thread. That system to allow that has been around for about 60 years and it works really well.