Passive Pre - No Regrets?

"There is a good and simple reason there are so many comments on this thread favoring active line stages: the issue is real."

There are even more favoring passives. Not that either proves anything.

"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."

My Museatex Bitsream dac has an output of 3V@300ohms. My Art Audio amp has a sensitivity of 0.7V and input impedence of 180kOhms. I don't seem to have any problems and prefer the TVC to any active preamp I have used within my price range.

Different tools for different tastes.

Remember that those interested in autoformers have to be sure that there is absolutely no DC on the output of their sources. Any DC getting through can be bad for amps.

By contrast, one of the primary benefits of transformers is galvanic isolation, or making sure no DC reaches the next stage.

Of course, if a person is sure that all their sources have no DC, then there can be sonic benefits to an autoformer over a transformer for volume attenuation.

A funny story for Atmasphere(and others),

4-5(maybe 3-4) years ago I called Jack Elliano of Electra-Print (of transformers and DRD/Ultrapath amps fame) about winding a transformer volume control for me. At the time, S&B TVC's seemed excessively expensive and I was looking for an affordable US substitute. (I know have S&B)

Jack is a great guy and wealth of knowledge about all things audio, especially transformers. Even better, he loves to talk about the subject just as much for conversation as doing business.

He spent at least a half hour with me outlining all the fundamental engineering reasons why a TVC was inferior to active linestages and why he would never make/sell one even though he had been getting a lot of calls about them. He wasn't being condescending, rude, or defensive about the subject, just the reasons why his 20+ years of experience led him to believe they were a fad and not anything of lasting merit. I aked if he would ever give them a try and he said there was no reason.

Well, low and behold, Jack and Electra-Print now sell a transofrmer based volume control he refers to as a "Passive Volume Attenuator" preamp (bottom of page). His version of the TVC might be slightly different because it was desinged to load the output transistors of your source so they can deliver optimal current. His PVA then converts that current to an equivelent voltage.

Noentheless, I applaud Jack's open mind when it comes to audio and engineering. After intial resistence, he began to seriously look into the subject which has resulted in a 180 degree change in his opinion. So much so, that he is putting his time, money, and company reputation behind it.

"Great story Moebis!! He's still just as stubborn about tube amplifiers being the only amplifiers to use!LOL"

You mean, it's not true? Actually, I'm a low-power SET guy, but not so much so that I don't appreciate other approaches.

"I had to laugh at Mr.Sphere's comments about passives not being able to drive the cables... that's a pretty broad statement."

I don't have a thimble's worth of his experience or knowledge, and he always seems to make very measured and reasoned statements. So, I'm sure there are very good reasons for what he says.

But, it's hard to tell if his statements are directed at all passive controls or just resistor based. He did not address the situation where a source has low output impedence and high voltage output feeding a high input impedence amplifier with low voltage sensitivity via a TVC.

Going one step further would be an all balanced system via the balanced input and outputs of a TVC. Or, single-ended source being converted to true balanced signal via the TVC transformers to the balanced inputs of an amp.

I have a pair of Jensen JT-11P4-1 (1:1.414) for "Balanced Bridging" Input transformers that I am going to add to the end of long balanced cables for converting back to SE at my amps inputs.

Not as good as a truly all-balanced system, but will allow me to use ~30-40 ft. cables to cross my room to my amps right next to each speaker.

Good point about phono preamps, Electoid. My solid state Gram Slee Era Gold mkV phono preamp(+ELP "transformerless" stepup) has an output of 240mV - 1.08V max. That's works for my Art Audio PX-25's 0.7V input, but not really enough for my Welborne DRD 300B monoblock's 1.5V needs. I have to use the +6dB setting on my TVC sometimes, which has it's own drawbacks.

Gotta admit, that used Atma MP-3 preamp that was for sale here at $2k had my bank account shaking, badly.

Jsadurni,

1. What is the output voltage and impedence of your sources? 2. What is the input sensitivity and impedence of your amps?
3. What type of interconnects are you using?

Can't get any better match between source nd amps than that, Jsadurni. "If it ain't workin' for ya, it ain't workin!"

The only other question is what type of interconnects are you using and how long are they? I've heard that capactance and inductance, or the relationship between both, can be a HUGE influencing factor in the performance of a passive pre.

From your August post here, it seems you have settled on short speaker cables and longer interconnects. That's what has also worked best for me.

Herman wrote:
"I don't see this as a drawback as the issue with DC is no different if you use a resitive voltage divider of some sort."

But, both Autoformers and resistive pres are significantly different than a TVC in that regard. Galvanic isolation means that no DC will pass through the TVC at all. Of course, I think most sources have a capacitor near their output specifically for DC blocking.

Anyway, it's best to absolutely sure that no dc is being passed by all sources before making that very expensive leap of faith.

Another major TVC advantage(if needed), is that they can easily convert single-ended signals to fully balanced for driving very long XLR cables with little signal degradation. A big advantage when your equipment rack is on one side of the room and amps next to the speakers on the other.

Pubul57,

Wait until you get 100 hours or so on the Placette, bet things just get better and better. Take your pick as to whether passives actually "burn in" or it takes a little time to notice all the extra fine, subtle, details that get through. But, you should be able to notice things that never came through in recordigns before.

Enjoy! (and let's know how things develop)