Brilliant Corners #13: The EM/IA Remote Autoformer and Listening with Master Jazzman Jerome Sabbagh

Ever notice that the language we use to talk about sound can be pretty aggressive? Reviewers often write about amplifiers "taking control" of a speaker, possibly "ironfisted control," especially if the amplifier in question happens to be a "juggernaut." In this particular linguistic trash fire, we also find "razor-sharp transients," "hair-raising dynamics," and that ickiest of descriptors, "bass slam." If words could smell like hair gel and drugstore cologne, these might.

All this verbiage is describing brute force, which we might use to push open a heavy door. But there's another kind of force that we encounter in the world, and consequently in audio, captured in the expression "life force." It denotes a sense of vitality and presence that isn't readily perceived by the senses—something lingering just out of reach of our rational minds. This force can be experienced in the terse saxophone solos of the young Sonny Rollins, the eerie abstract paintings of Mark Rothko and Pat Steir, and the deceptively quiet poems of Elizabeth Bishop. If you've ever been drawn in by one of the squat, gouged, lopsided jars made by a traditional Japanese potter, you know what I'm talking about.

One way that force—in both these senses—manifests in audio is in the phenomenon of drive. Generally speaking, drive tends to feel good. Lots of drive tends to feel better. A system with plenty of it has the first kind of force: a sense of shove, juice, volition. It's likely to make you dance. And it leaves you reassured, in the way you might be by a full tank of gas or a flush checking account. But it also possesses the second kind of force: With lots of drive on tap, music tends to feel vigorous, corporeal, and present. When you put the two kinds of force together, you get a high probability of being emotionally engaged or at least having fun.

That's the main reason I enjoy active preamplifiers. In addition to providing input selection and volume control capabilities, an active preamp (often called a line stage to distinguish it from phono preamps) usually brings a greater sense of drive. What's not to like about that?

Some listeners, though, use passive preamplifiers. Presumably this is because they prefer the sound, but it is also partly based on the somewhat controversial belief that passive preamplifiers, which of course don't contain amplification devices like transistors and vacuum tubes, are quieter and introduce less distortion (footnote 1).

During a brief period in my 20s when I fancied myself handy, before I decided to never again burn myself with hot solder, I built a rudimentary passive volume control using an ALPS potentiometer, some RCA jacks, and a few bits of wire, mounted in a wooden cigar box. It probably won't surprise you that it sounded kind of shitty. Replacing my beloved tube preamp with the cigar box made my system sound a bit clearer but also tentative, unengaging, and feeble. Less force, less feeling.

Since this admittedly unpromising experiment, my feelings about non-amplifying volume control devices haven't shifted. I fancy myself a right-brain, ecstasy-motivated, more-is-more listener, and trading some transparency for fun has always struck me as worthwhile. Besides, with a high-quality active line stage, how bad could the tradeoff really be? When it has come to listening, I've always preferred whatever preamp I have on hand to the passive solutions, whether digital or analog.

The EM/IA Remote Autoformer
This disdain for passive volume controls was with me until quite recently, when I spent time with the unglamorously named EM/IA Remote Autoformer (footnote 2). An inscrutable-looking black box with an LCD readout on the front panel, it offers an unusual approach to getting your music from your source into your amplifier: inductive attenuation, in which two autoformers (one for each channel) with multiple taps allow the volume to be stepped down. To generalize slightly, think of a phono step-up transformer but placed between your source and amplifier and working in reverse. Why would anyone want such a thing when there are plenty of far smaller and cheaper potentiometers, like the Japanese ALPS unit I used in my cigar box and those in many preamplifiers today?

According to EM/IA's Dave Slagle, inductive attenuation preserves more of the signal and presents it to the amplifier in a more useful way. A conventional—ie, resistive—potentiometer reduces volume by turning excess signal voltage into heat. As it does this, it adds noise and distortion and raises output impedance, making the source less capable of driving an amplifier. In contrast, an autoformer volume control works like a gear box, decreasing voltage by selecting taps on a coil. The result of this decrease in voltage is an increase in available current, which substantially increases drive, while the entire process results in less noise and distortion.

The EM/IA, sometimes referred to online affectionately as the Slagleformer, takes this concept to its logical and decidedly deluxe conclusion. The custom autoformers inside the box are wound from copper or silver wire using 80% nickel cores, sometimes known by the trade name Permalloy. (The copper version costs $4875; the silver, $7525.) Each unit offers 60 positions at 1dB intervals for a fairly fine-grained choice of loudness levels and a gain range of –54dB to +7dB. There are three inputs and two outputs. The whole thing can be operated via a lovely metal remote, allowing one's buttocks to remain safely on the couch.

For me, the hidden superpower of the EM/IA is its ability to adjust channel balance without introducing a separate, sound-degrading circuit. With the push of a button on the remote, you can turn one channel up or down, and the unit will maintain the balance setting as you control the volume. The readout even reminds you where you set it in case you forget. This is the single smartest and most convenient balance control I've encountered in a hi-fi component, an all-too-rare function that I find essential for real-world listening.

While I respect Dave Slagle and his partner Jeffrey Jackson's engineering knowhow and design skills, all the theory in the world isn't worth a canceled credit card if it doesn't make listening to music at home more engaging. And to be frank, I wasn't excited to hear another passive volume control; I was pretty certain it would sound like watered-down gravy. Then again, one of my favorite things about being a reviewer is poking holes in my pet theories. So one night not long ago, I set the admirably petite copper version of the EM/IA on my Box Furniture rack beside the PrimaLuna EVO 400 preamplifier. The sources were a Garrard 301 turntable, a Schick 12" tonearm, and an Ortofon Cadenza Bronze cartridge in a Box Furniture plinth passing the signal to a Manley Steelhead phono stage. On the digital side, a Totaldac d1-streamer-sublime fed a d1-unity DAC. A pair of Manley Mahi amps operating in pentode mode drove the Klipsch La Scala speakers. And Ken Micallef was over for a visit.

To begin, we listened to "It's Funny" from a UK pressing of John McLaughlin's 1969 debut, Extrapolation (LP, Polydor 2434 012). Years before McLaughlin became a maximalist fusion demigod to guitar shredders the world over, he released this sinuous, melancholy, forward-looking date, which for me remains his finest recording. We heard it first through the PrimaLuna. The superb-sounding Dutch preamplifier was outfitted with six vintage Amperex signal tubes and a pair of Mullard rectifiers, and through it the jazz record sounded tonally rich, fast, and admirably transparent, with oodles of drive. This was a sound I knew and liked.

After swapping the EM/IA in for the preamp, we listened again. To my relief, the music still sounded satisfyingly forceful if not quite as fun as before. But that's where the similarities ended. The recording was now obviously, disconcertingly clearer. And though the impression of drive had diminished slightly, McLaughlin's playing actually sounded faster and rhythmically more in the pocket.

Unsettled by the magnitude of change we were hearing, we listened to the track again through the PrimaLuna. I could now hear that, compared to the autoformer, the active preamp was adding some electronic sludge to John Surman's soprano sax and John McLaughlin's guitar. The strings of Brian Odgers's bass were also less audible and distinct, and there was less ambient information throughout. These differences were not at all subtle. Ken and I exchanged a round of wows.

The following day, I compared the EM/IA to my Shindo Aurieges preamplifier and heard a similar result: The autoformer sounded clearer, cleaner, faster, and more detailed. I want to note here that these impressions in no way reflect poorly on the PrimaLuna or the Shindo, which are among the finest preamps I've heard at their respective prices. What I was experiencing was a whole other paradigm.

Footnote 1: This is disputed, and for my part I'm with the skeptics. Counterintuitively, passive devices—even resistors—cause more, not less, noise and distortion. The best way to control noise and distortion is to lower impedance, which requires (or at least benefits from) active devices, as eloquently argued in a technical note by John Siau, Benchmark Media's talented designer. See—Jim Austin

Footnote 2: EM/IA. E-mail: Web:


georgehifi's picture

J. Austin: "Counterintuitively, passive devices—even resistors—cause more, not less, noise and distortion".

So you and the skeptics are saying that a say 10kohm Alps pot as a passive preamp creates more noise and distortions than the same 10kohm Alps pot in an active preamp??
(Yeah, good luck with that theory)

Cheers George

Glotz's picture

And not what he was getting at... active circuits vs. passive ones.

Jim Austin's picture

From the Application Note cited in footnote 1, by Benchmark Media's chief engineer John Siau:

"Noise and Distortion Analysis of Fully-Passive Attenuators

In the fully-passive designs we examined, the thermal noise produced by high impedance resistors exceeded what could have been achieved with a well-designed fully-buffered design. Furthermore, the loading imposed by the passive attenuators tended to cause distortion in upstream devices"

Jim Austin, Editor

Glotz's picture

I was impressed by this and many of the other products they have. Zero bling factor unless you look inside or listen. Other reviews have echoed their impressive performance. I wish I had the dosh to look more seriously.

mcrushing's picture

If you DIY: on Slagle's other site,, he offers the parts in various configurations.

You could get what I suspect is an equivalent silver-wound stereo unit in the EM/IA for a LOT less. And if you can live with copper, dual mono knobs and a 16-step switch, you can pick one up for about $400. Or even less, if you really like to solder.

Glotz's picture

I did briefly check that DIY area out and I really like what I see. I can solder cleanly and the price is very right for a phono transformer too.

I triangulate good reviews from respected sites for insights much the way I would to pin down sound of a recordings/equipment with cd and lps. Good column!

georgehifi's picture

Any passive preamp volume control in the correct "i/o impedance environment" has less noise/distortion and coloration than any active preamp could possibly hope to have, and just as much "drive & dynamics", than an active pre using the same volume control in it's circuit.
Sure if you put a $1 Chinese pot in a passive pre and then use $100 pot in an active pre then things could be closer.
Cheers George

georgehifi's picture

Quote:"During a brief period in my 20s when I fancied myself handy, before I decided to never again burn myself with hot solder, I built a rudimentary passive volume control using an ALPS potentiometer, some RCA jacks, and a few bits of wire, mounted in a wooden cigar box. It probably won't surprise you that it sounded kind of shitty."

This statement says nothing about i/o impedances with this, as he had no knowledge that's very important to get right with passives, and it shows because of the self confessed lack of soldering experience.

Cheers George