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.

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. 

Audio Research is very synergistic with other Audio Research. The REF3 or LS28se are really great preamps.

I can highly recommend the Ypsilon PST 100 Mk2.  It is a passive pre-amplifier that uses transformers to attenuate the sound:  very detaIled, nuanced, with minimal coloration.  It also has an active mode, which affects the SQ.  If you read articles about the Ypsilon, it will give you an idea of how the transformers are used to transmit the signal. 

Hello filipm!  If your speakers are sufficiently efficient, and your amp is sensitive enough, you are wise to skip unnecessary electronics. That's what I do in my demonstration/lab system. Why put money into something you don't need. Mine is a simple volume control with six sets of dual RCA plug inputs chosen by a switch with silver contacts. Enjoy the music!

Look into Townshend's Allegri Reference Passive Preamp.....

https://www.townshendaudio.com/allegri-reference-preamplifier/

@ozzy62 

Thanks for the Hattor reference! 

Yes, the Hattor passive with discrete shunt attenuator is quite good. I have/had 2 of them, the pure passive and the dual mono buffered. The buffered version requires some discrete OA rolling to get the best results (of course). Industrial OA just don’t cut it IME.

Transformers/magnetics do also impose a signature IME. I’ve also had AVC and TVC passive pres. IME, resistor shunts much less so, with wonderful organic naturalness. But alas, the dynamics can be boring unfortunately.

Nor do the magnetic pres solve the issue of coloration vs needing buffering. They might couple the signal a little better than a resistive passive, and I say "might". But the coloration imposed in the process doesn’t cut it IME. OTOH the passive shunt atten definitely needs buffering in most cases.

But that raises the question of exactly how to buffer such that it works the best with 0 ~ coloration. A tall task, and have been working on it personally for years.. But lately that has been solved very nicely via a) an optimized impedance shunt attenuator, b) utterly amazing, no distortion, no coloration, no global feedback discrete buffers that can also drive pretty much anything and c) the topology, ie where exactly do you place the buffers (and where not).

What we need is, the glorious organic, uncolored naturalness of the passive shunt attenuator with say, Z foils. But also the perfect dynamics of a (properly) buffered version. Eureka, it’s been solved and it’s a game changer.

I said "had" the Hattor above because the passive was converted to the above eureka buffered pre a few months ago and my high end audio bud in Dallas wouldn’t let me return home with it. Sold already, the first day of its premier demo lol. And he can use anything; it displaces an expensive Esoteric setup (and a few others). Yes, it really is that good.

Just sharing my experience. Not trying to step on any toes here. YMMV.

TK

The Luminous Audio has the shortest signal path of them all. Just saying. Enjoy, MrD.

Don’t have the technical know-how of most on this thread but I’ve been using a Slagle/Jackson(EMIA) elmaformer for the last few years. I haven’t shot it out vs other passive designs but it did beat out a Levinson no.28 and a McIntosh c220 in my high efficiency horn system. Beautiful large step attenuated volume knob and a three input switch. 
 

looks-wise it’s my favorite piece of gear in any system I’ve had/seen

Thanks for all the recommendations and sharing your experience. 

Slightly added warmth/richness would be a lot more welcomed than any loss of dynamics. 

Simply put, I'm wondering if it's worth it puchasing something like Music First Audio Classic V2 or if the technology advanced so much I'd be better off with something else (I'm only assuming that because there's apparently a big difference between V1 and V2 while the first version isn't that much older).

Townshend Allegri Reference looks absolutely amazing but it's also rare on a used market and very expensive. Maybe it's just wrong intuition but Music First Audio would be probably the best choice in terms of performance and resale value. 

My speakers are 92,5dB, power amp's input sensitivity is 300k ohms and both DAC and phono preamp have pretty strong output capabilities. Especially with the phono (RCM sensor2) I'm suffering with too much gain from the ARC LS16 preamp. Setting lower gain on the phono stage results in muddy sound when set too low. Also, I live in the city center and the mains isn't the cleanest. So I assume my system would welcome a passive preamp with open arms :)

I gave up after ten years use a wonderful sounding dual mono valve preamp in favour of the complete quiet and transparency of detail of an Audion Select TVC line level pre amplifier (copper transformer windings w/ silver internal hook up wires) —sound is colourful, vibrant and dynamic - not in an additive way, just that it’s not greying or shrinking the sound as you would find with most alternative means of adjusting volume. Speakers are 104db horns.

OP, the 300K is the input impedance. The input sensitivity of the amp is 2V for rated output, and the V gain is 24db, a little less than the norm of 26-28 db. Just a friendly fyi. My best, and ENJOY ! MrD.

@mrdecibel Thanks! I was under the impression that the input inpedance is the main factor to determine how friendly a power amp can be to a passive preamplifier. And also the output of a phono stage or a DAC..

Lord to visit Prague again…. pack my REF5se in a flight case and be right there…

Astute read that you don’t want to give up the dynamics… In my experiments… a buffer almost always needed …. hopefully you can find a way to trial a few of tgese devices while retaining the excellent store of value your  ARC preamp represents….

Best to you….

If a Hint of Richness is on the 'to be experienced' list.

A Cable with D.U.C.C Wire has the capability to produce this Tonality e, as a very subtle influence, the thickening up of the mid's and lower frequencies, is a typical  effect from the Cable, that has been perceived across a few systems I have loaned the Cables with this Wire Type to be used in.

Because the Wires Tonality is perceivable when a Group has been at a Demo' of it in use there has been a mixed response/thoughts disclosed on how it is able to create an impression.     

Get the best ARC preamp you can afford.  The synergy will be fantastic.  

I have the EMIA Remote Autoformer (Sliver). It's incredible in my system.

My Tortuga Audio LDR preamp has never disappointed me.

It has a very clean transparent sound, nice detail, clarity is a strong point. It images very well too.

It has a pitch black back ground too that I attribute to its battery power supply.

Very impressive, especially for the $$ 👍

If you have adequate gain, I say the same thing to anybody who will listen, get one of Dave Slagle’s autoformers and be done with typical resistor type volume control.