Passive preamps - differences between technologies

You might want to consider how someone that designs a passive implements it and don't underestimate what the "switch" adds to the mix. For example, in a resistor-based passive you can have shunt, ladder, or series type attenuators. You might also just have a "pot" in the box. A simple attenuator with a wiper. Magnetic passives can use transformers or autoformers, and there is a difference in how these work and why one might be a benefit over the other. I also don't agree that a TVC imparts a warm sound. Any passive I have had or built, and there have been many, has been very transparent.

That being said a good yet simple LDR design that still makes the rounds in my system is the Lightspeed Attenuator. Don't let the price or looks fool you. It's an amazing passive if all you need is one input. The benefit of a light dependent resistor is it takes the switch out ouf the equation. I have had passives with Seiden, Shallco, Khozmo, Elma, and other switches, as well as NOS Noble potentiometers, and a simple well designed LDR is clearly different and shouldn't be overlooked if you are serious about going down this path.

Maybe I didn't convey it correctly. I'm not saying a TVC adds warmth. But it does have a signature. Yes it is transparent, but not as much as other designs. TBH, I like them all with the exception of a cheap "pot in a box". And I didn't care for the Placette either.

Bottom line is that even though being passive, they all sound slightly different.

Passive preamps are simple but the quality of components can vary tremendously. Quality transformer based volume control (a passive preamp is basically volume control) are excellent and coveted.

a resistive ladder style can be excellent with good components.

Both are going to require a high quality multiple step selector switch.  

Avoid the sliding contact resistors as cheap and noisy.

I like passive vs active because it has the least impact on the signal (some of us call it coloration and some members here don't like that, we will agree to disagree).

Jerry

Maybe I didn't convey it correctly. I'm not saying a TVC adds warmth.

A TVC certainly can add warmth, due to ringing caused by the transformer not being properly loaded. That loading changes with each tap but the designer can't predict the load of the amplifier being used so it will only be exact at one input impedance only.

PVCs have the problem where when you turn the volume down from full up, the bass impact is often reduced. If you listen closely, you'll find that the impact it likely affected across the entire audio spectrum. The reason this happens is because the PVC is a resistance in series with the input and so the source can't control the interconnect cable (reduce its artifact) as well as it would otherwise.

You'll also find that you have to audition the interconnect cables to find one that sounds acceptable. If you've auditioned cables before and heard a difference then you know what I'm talking about.

You can see that in both cases, a buffer is handy to prevent these issues occurring. Its possible to make something too simple and PVCs and TVCs are a good example.

I've used a range of Stepped Att', with the DACT Brand being the most expensive.

A few lesser types than DACT, when used in my system put a lot of their traits into the end sonic, I recollect not much being an attraction. 

I also use the Slagle AVC and know the Promethius TVC very well.

Both are in my view, as a Standalone an improvement over a Stepped Att'.

The AVC and TVC do add a hint of Richness, but that is probably the result of the windings. The overall presentation is where the design wins favour. 

I have heard a Khozmo used as an upgrade VC and this was quite a substantial betterment. 

On the same design Pre' as the one that had the Khozmo, I have heard it with the Prom' TVC as the VC. In comparisons the Khozmo was the one with the most attraction.

I have had Bespoke Stepped Att's made for my own pre' that is close in design to the pre's being referred to, as a result of the Khozmo. 

It looks like systems are able to be quite influential on how the VC types are perceived. 

There is also the digital VC designs, such as the 'Muses' that have been very much liked in user reports.