Passive Pre - No Regrets?

There is a lot of confusion about this. The volume control in a passive is no different than the volume control in any active preamp. It is in a different box so you neeed cables to hook it up, that's the only difference. The volume control inside a preamp is also a passive device. You can build either one with a transformer, pot, stepped attenuator, whatever.

You can successfully use a passive if:

1. the rest of system has enough gain to drive the speakers to the desired level

2. the input impedance of the passive is high enough to properly load the source

3. the output impedance of the passive is low enough to be a good match to the amp

4. you don't try to use cables that are too long or have high reactance

Those that had poor results failed to meet one or more of these requirements and finding a passive that meets all of the above for a given set of components may be impossible. Trying to use one in a system that requires the extra gain from an active preamp is doomed to fail. Many don't understand what these requirements mean, choose an ill suited passive for the job, and end up with lousy sound. That's not the fault of the passive but of the person putting together the system.

The big problem with volume controls of any type is that they always take something away. The advantage designers of preamps have is they can optimize their design for the type of volume control they choose. Unless the user of a passive takes the same care in choosing they will likely end up with poor results.

Here's another one for you. Intact Audio

A transformer winder from hell. With discussion on how to tune the transformers to your system. Not for the faint of heart but results can be stupendous if you are willing to invest the time and effort to optimize it.

Gmood, where did you put your buffer and what did you use?

What you have is basically an active preamp broken into several sections. An active preamp usually consists of some switching - maybe an active gain stage that also acts as a buffer - passive volume control - maybe another gain stage which also acts as a buffer.

Most go switching - volume control - active stage, but some, like at least some VAC preamps, go switching - active stage - volume control.

The beauty of the active is that the designer can optimize the interaction of the gain stages and the volume control. Much tougher to do out here in the real world. So people try a pasive and fail and dismiss them and blame it on the fact that it is passive. Kind of ironic really considering that at the heart of their active preamp is a passive volume control.

Mr. Sphere, So if the volume control is connected to the first stage of an amp by a few inches of wire that is OK, but if it is connected by a few feet then that is bad? I don't buy it. The difference in impedance of 3 feet of wire vs. 3 inches of wire is negligible.

Maybe, and that is a big maybe, at the very lowest volume settings it will come into play, but if you are operating down there most of the time then the system has too much gain to begin with.

And even though I'm sure you are a stand up guy, and many people here know that you are a mnaufacturer of active, balanced preamps, it should be disclosed so your advice can be properly evaluated. I'm sure if Mr. Placette answered this question we would get a completely different response.

Unless I missed something, all of this talk of transformer vs. autoformer is pure speculation. I don't see where anybody posting has actually compared.

Neither have I, but the link I gave to Intact Audio has an active forum with people I know, and who's ears I trust, who's passion is transformers and inductors, and FWIW they say there is no contest; an autoformer is clearly superior to a transformer when used as a volume control.

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.

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.

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.

I agree that it is a worthwhile goal to build a component that is completly neutral (straight wire with gain) but since we are all using different speakers that in relative terms are all highly colored, couldn't you end up feeding a speaker with a completely uncolored signal and still have sound that is crap.

As long as we have highly colored speakers further complicated by room interactions, it seems we will always be tweaking the system to color it in a way that compensates for speaker and room colorations.

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. Perhaps better than the CDs and vinyl I have but still not perfect. There is no way around this problem.

I just received my Placette RVC that I had them build with a 100K input impedance. I tried the stock unit but it was lifeless due to the high output impedance of my phono stage. This one works wonderfully. There is a price premium for the larger resistors due to an increase in his costs, but if you have the need as I did then it is well worth it.

I just love having a remote volume control!