Passive Pre - No Regrets?

The issue of DC on an output would not be solved by any of these controls, but I should nave been more clear. My point was that even though DC on an output would be a problem for an autoformer, this didn't strike me as a real life problem since resistor based volume controls would have the same issues. In the first place there shouldn't be any DC on the output of a commercial source since many amps are DC coupled and it would cause severe problems. If you are doing DIY like me then it is something you have to decide for yourself.

In any case a transformer would also be a bad choice for a source with DC sitting on it's output. The way to do it (as mentioned) is a cap to block the DC. A transformer would short it to ground, not good. There are some designs such as either a parafeed output or an interstage transformwer acting as a plate load with a tapped secondary that would do double duty; DC isolation and volume control, but then you have to worry about the varying load on the output tube as you change the volume.

Nothing is simple it seems.

"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.

"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."

OK let's look at from another perspective. Since it's the goal of high end to get away from tone controls.. This will leave a lot of members here in the dust. Essentially every component is a tone control. All the way done to the tubes used in a selected piece of gear. How will we ever get away from tone controls? When every piece of gear is basically a tone control? No matter how High End you go...there will always be those darn tone controls.

Ken Stevens, the designer and manufacturer of CAT equipment, once told me that a parts manufacturer (I think they were resistors)asked him what "flavor" of sound he wanted from the resistors (warm, bass-oriented, etc.). That is, these parts could be used as "tone controls" - Ken's answer was I want the flavor of water. The sales reps was a bit confused, but I think Ken's goal and Ralph's goal seem similar - "get away from tone controls so as to get to the truth of the matter". Which gets back to the passive/active debate - can an active line stage ever get as close to the "truth" as a passive (minimal flavor, clear as water) implemented in a properly matched "system". I still think that the active approach is probably necessary for some of the reasons mentioned by Ralph and the need to actually sell this equipment into a variety of listening envrionments and matching equipment.