One of the more important functions of a line section is control of the interconnect. That is why you see so many posts on this thread preferring the (allegedly) more colored sound of various preamps over passives. Passives cannot control interconnects, so their sound changes (coloration) depending on the setting of the volume control.
Once you've heard what this is about its hard to keep using passives. They just don't work, unless the volume control is located at the input of the amp itself. This can be really inconvenient if you have monoblocks!
In an ideal world, the interconnect is always neutral as the line section completely controls it. In the real world, this is more closely achieved by balanced line stage operation. But any line section that has a low enough output impedance will drive a single-ended cable quite well- this is how 50 ohm cable for video can work.
I'd think twice about selling off a good Line section in favor of a passive! If you really do like it better, it suggests to me that there is a bad synergy elsewhere in the system that the passive is compensating.
Good Luck! |
Hi Herman, Obviously I don't hide who I am :) I also cannot escape facts- and I outlined them above. Yes- a few inches of wire (often unshielded) can be a *lot* different from a few feet of cable. If you've not tried it, then do so! You will see what I mean. There is a good and simple reason there are so many comments on this thread favoring active line stages: the issue is real.
Integrated amplifiers often share power supplies and limit the ability to keep short speaker cables while at the same time putting the sources at a distance from local sound fields. There can be no question that while they might be very good, they are a compromise in these areas and always have been. But if you have no space to start with they can be a good choice. |
"I had to laugh at Mr.Sphere's comments about passives not being able to drive the cables... that's a pretty broad statement. With the right source some of these passives(TVCs) will spank an active all day long driving cables. Being he designs and builds active preamps..I'm not surprised at the negativity towards passives. Man.. this jet black background coloration is working for me.;-)"
It might surprise you that we've built passives too. Of course, we do think that our line stages exhibit a new possibility of line stage capability (and we are who we are- no surprises there- if you think I ought not offer comments I'm open to suggestions).
I like to take advantage of the capabilities of monoblock amplifiers by putting them very close to the speakers, thus keeping the errors introduced by any/all speaker cables to a minimum. This means that the interconnect has to have some length. There are no passives that we have found that are able to drive the distance without an audible artifact. Our line sections can drive 30-100 feet with no difficulties. Simply out of the question with passives unless the control is at the input of the amp. |
"Also from what I've read the PLC with autoformers doesn't electrically isolate input from output like a TVC. This means you'll have less noise filtered with the PLC."
In theory then, that would be a good thing.
FWIW, the task of the volume control is *not* to filter noise! I would suspect that there are other reasons for a preference. |
"Still waiting, but maybe they'll arrive today. Atmasphere. let me ask you a question. If you could design a passive preamp, choose an appropriate source with just the right output impedance, select the cabling to be used (for appropriate electrical properties- and lenght)and they were feeding one of your OTLs or some other quality 100KOhm load - that is you could optimze the variables that determine successful versus unsuccessful implementation of the passive approach - could you conceive that a passive, minalmist approach might work better, sound better than an active, any active preamplifier. I would accept that the passive might not be as flexible, be more fussy, and may be less universally marketable."
Here's the problem that passives are up against (if done my way). 'My way' is to eliminate the interconnect cable as a sonic variable so that any cable will work as well as any other (right now you have to go balanced to do that BTW).
Anyway, to achieve the above for me would mean a very low resistance passive system- probably about 100 ohm control would do the job. This is a challenging impedance for a CD player to drive with low distortion and enough voltage to drive the power amp. Please keep in mind that I am expecting the system to be immune to the effects of the cable. You are not going to get this if the value of the passive is much higher than that. IOW, its impractical with current CD players and phono sections. |
"Yes I agree, I suppose it is how one looks at it. I'm not designer like yourself,but don't you use something inside your equipment to filter noise or keep it to a minimum? Capacitors or something? If you did then your amplifiers or preamps would also do the job of lowering the noise floor..correct? This wouldn't be any different from a TVC having the same ability would it?"
In the audio path, we do everything we can to insure bandwidth. OTOH, we do all we can to prevent noise from the AC line from leaking in. The two are definately *not* the same! The idea that a volume control would filter noise of some sort is to say that it is really a tone control as well. In the world of high end audio, the idea is to get away from tone controls so as to get to the truth of the matter. |
Hi Gmood1, I don't agree with your statement for several reasons, not the least of which is that equipment exists that seems to lack 'tone control' qualities and in fact is able to fool jundiced audiophiles. This is a forum for high-end, not mid-fi so we won't be leaving too many 'in the dust'. Finally, we're getting off-topic, but if you would like to discuss this further perhaps we could start a new thread?
All the Best! |
"The same with tubes..come on..I know you have a favorite type tube for your equipment... most designers do. Give up the goods!LOL"
Its true. I prefer the tubes that I do because I can get them to be neutral. How neutral? Neutral enough that the state of the art has to evolve to hear the colorations. Even then we find that changing things elsewhere (power supply, wiring, coupling caps etc.) will often deal with it (in effect we still are not hitting the limits!).
I agree that all things make a difference, and I know that creating a system around a coloration will not work in the face of creating a system around no coloration. Synergies in effect do not work. |
Yes. It took us years to get around this problem. A big key was working with master tapes! This allowed us to know exactly what the recording really did sound like. |
Unfortunately this is not the case. You listened to tapes that were slowly deteriorating over time played on a tape deck that added it's own colorations played through speakers or headphones that also added colorations. This is not exactly true- the tapes were new, the tape machine was rebuilt and very stable and calibrated. This is the sort of thing that you apparently have to do in order to understand how powerful it is as a reference! I've seen audiophiles turn ghost white after being fooled by the direct microphone feed (startled at how *real* it sounds- far more so than any stereo using a recording can!). The value of working with master tapes is that you are there at the recording session so you *know* what the music is supposed to sound like. |
FWIW, the issue you face with TVCs is hysteresis loss, which introduces low level distortion whenever the signal changes polarity (IOW- loss of low level detail). Additionally there will be changes in bandwidth depending on the tap selected. Careful design can minimize the latter but there is nothing to be done for the former- its a fact of life for all audio signal transformers except those in the current path of a single-ended device.
Since a single-ended device (tube or transistor) biases the core of the transformer, the zero crossing of the signal occurs at 1/2 the total saturation of the transformer- in effect there is zero hysteresis loss.
So- if you wanted to use a TVC this would be one way of doing that for those of you who are DIYers- combining the technologies. |
