Passive preamps - differences between technologies

All are very good. But there are some differences.

Transformer or autoformer volume controls will be slightly warmer, but not quite as transparent as other passives.

The Tortuga is a very nice unit, I have owned two of them. They can be a little quirky, but have lots of flexibility with the adjustable impedance. The sound is more transparent than a TVC.

The performance of resistor based passives will be very dependent on the quality of the resistor used and the design. I am currently using a Hattor "Big" preamp with the AMRT resistors from AMTrans. I would put this preamp up against all others. But I really like the looks and the ergonomics of Hattor offerings.

If a system is passive friendly, all of the above will sound better than most active preamps. But you have to do your homework to make sure it's a good fit for you.

@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.