Passive preamps - differences between technologies


I have been wondering what are the main differences in the way some passive preamps are designed. 

Some have resistors, some are transformer based.. What are the pros/cons?

More specifically, I'm looking at Music First Classic/Baby Reference V2 vs Hattor the Big or a Tortuga.

I'm looking for an upgrade from Audio Research LS16, considering looking for ARC Ref3 or a nice passive. My amp is ARC Ref150 (which is a lovely thing and I feel like the LS16 is holding it back) and phono pre is RCM sensor2 mk2 - so there's enough gain from the phono, the power amp has 300k ohms input, my DAC can output 1-3V rms, I use interconnects up to 1m so a passive could be an option. 

Thank you. 

Greetings from Prague with the first snow



@ozzy62 That's what I was looking at.. Hattor the Big with AMRT resistors. I was wondering if anyone compared it to Music First Baby Reference, from what I have read most of people prefered Baby Reference against ARC Ref5/6. Still, I imagine these ARC amps to be more juicy or fluid against a passive. 

Someone also mentioned there's a guy in Hungary that makes Music First Baby Ref clones.. does anyone have an idea who might that be or what his products are called? I tried to google it without any success. 

I can't say I like the Hattor design, the logo doesn't really fit in to my eyes. But I love the Music First Audio looks. I was also considering BAT VK52-SE which is absolutely hideous so I'm all after the sound :)

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).


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.