What's the best EL84 amp?

@pdreher

Let me begin (oh no, here he goes again ;-) by recommending you head over to the AudioCircle site, where you will find a Music Reference section in the Forums. Roger was eventually kicked off it, but before that happened he posted for a number of years, providing his thoughts on a lot of technical issues, including those related to the design of all his amplifier models. Really fascination stuff.

As I previously posted in a thread here on Audiogon, Roger told the story of Tim de Paravicini (one of the few hi-fi amplifier engineers/designers with whom he felt "aligned") telling Roger he could predict the bass response of a power amp by looking at it’s output transformers. It is well known that the more "iron" there is in a transformer, the better will be it’s reproduction of bass frequencies. Conversely, the worse will be the sound of the reproduction of high frequencies. Everything in hi-fi design is a matter of design choices, trade-offs that must be made. Every design choice comes at a cost.

Roger Modjeski was not a "normal" hi-fi company owner. He freely admitted he didn’t enjoy running a business, or even building "product". What he liked was designing, finding solutions to engineering challenges. He stated every amp he offered was an answer to a design challenge, not just another amp. He didn’t design or build an amplifier to have a certain sound, but rather to be stable, linear, and distortion-free. To have no identifiable sound of it’s own. Of course, that is the oldest mantra in hi-fi, but imo he took it more seriously than do most amplifier designers. To hear Roger discussing amplifier design in the flesh, search for the YouTube videos of the talks he gave (three of them) at the annual Burning Amp Festival in San Francisco.

In the RM-10, Roger set out to prove that 35 watts could be created by a pair of EL-84 tubes, twice what anyone else had ever been able to coax out of that tube. Damned if he didn’t do it! And without sacrificing tube life. You can learn how he did it by watching the Burning Amp videos and reading the Music Reference sections in the AudioCircle Forums.

The RM-200 was Roger’s answer to the challenge of designing a tube amp that 1- was optimized for powering low-impedance loads, and 2- produced a hundred watts out of a pair of KT-88 (or 6550) tubes. Again, twice the normal power created by those tubes. I got myself an RM-200 specifically to drive the midrange/tweeter panels of my Magneplanar Tympani T-IVa, a notoriously inefficient planar-magnetic speaker. 100 watts is not nearly enough power for a T-IVa run full range, but the speaker is very easy to bi-amp, something Magnepan urged Tympani owners to consider. Used with a brute amp on the bass panels, the RM-200 is enough for the m/t panels when used in a moderately-sized room.

I got myself an RM-10 for a specific application, one for which the amp is perfect: the Quad ESL. Roger used that loudspeaker and the 16 ohm LS3/5a as his speaker load in the design phase of creating the RM-10, the Quad a notoriously difficult speaker to drive. If an amp can remain stable, linear, and distortion-free when driving the Quad, powering just about any other speaker is a breeze. Not an inefficient, low-impedance speaker, of course (for that he offered the RM-200).

As for the bass characteristics of the RM-10, that was immaterial to me. I have always used subs with my Quads, as did Roger. Removing the low frequencies from the bass panels of the Quad and the amplifier driving them results in a significant improvement in the sound of the combo, PROVIDING one has a sub/woofer of sufficient quality. I have the best: the Rythmik/GR Research OB/Dipole Sub, THE woofer for any and all dipole loudspeakers.

The RM-10 and RM-200 came years after the RM-9, Roger’s first and most "conventional" amplifier. Roger started his hi-fi electronic career the same way Bill Johnson of ARC did: by repairing broken stuff. Johnson owned a repair shop, Roger worked in one while attending college. Roger made a point of investigating and analyzing the design of every amp he repaired, taking note of what caused them to fail. Building a dependable, trouble-free amplifier was a very high priority for Roger. In the RM-9, Roger’s goal was to create the most stable, linear, distortion-free push-pull/ultra-linear tube amp he could. One that provided long tube life, and of course superior sound. In his review of the RM-9 Mk.2, Dick Olsher asked the rhetorical question: "When we have the RM-9, who needs the McIntosh MC-275?" I haven’t owned a lot of amps, but I can tell you the RM-9 is a better amp than the ARC’s I owned in the 1970’s (of course that was a long time ago, and ARC designs have greatly evolved).

In the 1980’s (I believe it was) Roger was hired by Harold Beveridge to design and build the tube amps included in the Beveridge ESL. Roger had previously discovered and become intrigued by the Futterman OTL amplifier, and he worked hard at solving the engineering problems that amp design presented. Roger’s final product was not just his own ESL loudspeaker, but one with no input transformers (the cause of a lot of non-linearity). Already an unheard of idea! But Roger went further, designing and building an OTL amp specifically to drive his hand-built, transformer-free ESL panels.

Think about it: the output tubes of an OTL amp directly driving the ESL panels themselves. Talk about transparency! By the time the ESL/OTL had gone into production, Roger had moved from Santa Barbara up to the Bay Area. I was out in Palm Desert, and was unable to make it up to his new operation to hear his masterpiece before Roger’s illness made that impossible. The biggest regret of my hi-fi life.

The Fisher (chassis) SA 16. Find one rebuild it and enjoy.  Supper great under the radar tube amp originally used in a counsel why it’s called a chassis amp.  One of the best little el84 amps I’ve heard ever. 

As someone who worked with Roger Modjeski for the last 5 years of his life, and to who (along with a couple other long time friends) he entrusted his business and legacy with upon his passing, I see I need to clear the air here.

A lot of facts about what Roger did and how he did it have gotten twisted over the years, to the point of becoming myths. Roger tried to set the record straight a number of times but finally gave up. I think he eventually came to view the myths as a source of humor, to the point of proliferating them. Roger and I spent his last few months speaking daily at length about many things audio (including the myths vs. reality) and personal. We listened diligently to his interviews with audio luminaries like Julius Futterman and Saul Marantz. I have all his notebooks and designs (at least the ones he documented) that I have been reading and studying so I think I have a pretty good idea of the man and his legacy when it comes to audio.

@bdp24

I got myself an RM-10 for a specific application, one for which the amp is perfect: the Quad ESL. Roger used that loudspeaker and the 16 ohm LS3/5a as his speaker load in the design phase of creating the RM-10, the Quad a notoriously difficult speaker to drive.

The Quad ESL was never used in the design process or as the load for the RM-10 and it’s debatable that his Chartwell LS 3/5a speakers were either. The Quad just happened to be the speaker Roger was using in his system when the amp was designed so after playing it on them just to get a listen to it he felt it was a good amp for the speakers, but a bit lean in the bass.

I have always used subs with my Quads, as did Roger.

Maybe you did but not Roger, although he certainly felt that it would be a benefit to do so, which is what he told me as he sat next to me listening to my RM-10 power my Quads. So next day at his shop we made up some woofers, I grabbed a solid state amp off the shelf, and Roger gave me a Beveridge RM-3 active crossover so I could biamp the Quads in my system and I never looked back.

In the 1980’s (I believe it was) Roger was hired by Harold Beveridge to design and build the tube amps included in the Beveridge ESL.

It was the late 70’s when Roger worked at HBI and this was probably the classic of all the myths. Roger never designed or built those direct drive amps. He did test all of them which is why you will see his name inside them, but design and build - no. Roger did design the Beveridge RM-1 preamp, it’s RM-2 power supply, and the RM-3 active crossover. Roger remembered this period of his career fondly as he got to focus on what he truly loved which was design work. As he often told me, at HBI I designed it, someone else built it, and someone else sold it.

Roger’s final product was not just his own ESL loudspeaker, but one with no input transformers (the cause of a lot of non-linearity).

Not by a long shot.

Thanks for the corrections, clarification, and additional information @clio09 (in spite of your subtly churlish tone ;-) .

May I ask you to elaborate on your "Not by a long shot" response to my statement that the ESL/OTL was Roger’s final product? I know he had also introduced a number of single-ended amps in his final years. Or was "Not by a long shot" said in relation to something other than whether or not the ESL/OTL was the last product Roger introduced?

My first hi-fi amplifier was the Fisher X-100-A integrated (bought used in 1968), which used the 7189 tube, an EL-84 variant. A nice place to start ;-) . My first guitar amp was a 1966 Fender Deluxe Reverb, also a sweet little amp.

@bdp24 Sorry if you felt I was churlish. Just trying to set the record straight and it's probably something I picked up from Roger himself after many years of listening to him trying to set people straight about all things audio. He certainly didn't suffer fools gladly.

The ESL direct drive amps designed by Roger were never meant to be a product per se. The first ones were actually designed as a custom project for some Acoustat owners down under who wanted to replace the pitiful step up transformer that was originally designed for the various Acoustat full range ESL models. Roger appreciated Strickland's ESLs and they influenced his ESL designs. Roger was also very familiar with the Acoustat direct drive amp and designed a tube input stage modification for it that a few folks have benefited from. So he designed an all tube direct drive putting 5000V on the panels without that pesky interface for those very lucky Acoustat owners.

When Roger decided to build an ESL of his own, the earliest of which I knew of was around 2003, it wasn't used with a direct drive amp and it wasn't full range, it only went down to 100 Hz (as it was with all his other ESLs) and was biamped. I remember going over to his house to pick up a box for my RM-9 and he invited me in to listen to them with none other than Kavi Alexander who had dropped off his Beveridge ESLs for Roger to fix. It wasn't until he built the direct drive amp for the Acoustat guys that Roger built one for his ESLs (which required less voltage, I think around 3500V).

I would have to say Roger's last "product" was the RM-9 Special Edition. Limited to 20 pieces it is an all point-to-point wired circuit using an additional pair of driver tubes, 6BQ7s at that, and adding another 25 watts of power. Just about everything else was the result of custom orders and small batch efforts (ex. EM7 amp). Even the OTL 1 amp had only 6 pieces produced (on a RM-200 top plate where Roger didn't even bother to hide the RM-200 logo).

Roger's idea of "product" was very different than industry norm. He felt that as the designer he could make changes whenever he wanted without having to document or re-badge the designs. This is why there are 4 versions of the RM-10 MkII sitting out there. He kept most everything in his head but in the final year we pulled enough out of him to hopefully bring forth some posthumous designs that audio enthusiasts can enjoy. So yeah, in more ways than one that ESL direct drive amp was not Roger's final product by a long shot.