Joule Electra LA-150 MkII Line Preamplifier
Tip #108
Dick Olsher (August 2024)

By any audio industry standard Joule Electra was a most unusual company. It was founded in the early 90s by the late Jud and Marianne Barber, a husband and wife team that was perfectly happy with an artisanal approach to high-end audio. Rather than relentlessly extending the product lineup Jud focused his attention on a subset of products, and in particular a mu follower line preamp, a popular circuit at that time. Unlike most designers, Jud was first and foremost interested in capturing the music’s elusive perceptual attributes rather than perfecting bench top measurements. And this led to some remarkable line preamps. The LA-100 gave rise to the LA-150, and then the LA-150 MkII which arrived circa 2006 after over a decade of evolutionary progress. According to Jud, the new version was much more musical and fleshed out than the original LA-150. An upgrade to MKII status was offered in 2006 by Joule Electra for $500.

According to Jud Barber some of LA-150 MKII highlights were as follows:

TUBES ONLY – Eight tubes in a line stage only preamp. They are carefully selected New Old Stock (NOS) 6350s tubes for the Gain Stage and Mu Follower. The power supply uses two 6EM7 regulator tubes and two OA2 voltage reference tubes, a pair for each channel.

POWER SUPPLY ISOLATION – The first thing you will notice is two separate construction boards. The larger one contains the power supply, and the smaller one is the “Signal Board”. The power supply board uses broad copper traces to connect the major components, but some of the heavy current is direct connected with separate insulated conductors.

HIGH ENERGY STORAGE – The next thing you will be aware of is the large number of capacitors; over 150,000 microfarads of energy storage. They are used in the two regulated filament power supplies and two separate tube regulated B+ supplies. HIGH COST TUBE REGULATION is usually found in very expensive custom built hardware.

POINT-TO-POINT WIRING – Then you will notice that the smaller board, the “Signal Board” is unique in that it has NO traces. That’s right, all the connections are point to point with the components lead wire being the only wire on the board, each connection point is a large copper pad on the board where all the leads are sealed together with silver bearing solder. This construction technique is unique to Joule-Electra.

PREMIUM QUALITY PARTS – Further examination will reveal that all the resistors are of the “Holco” or “Vishay” brands. We auditioned several different brands of metal film resistors and the Holcos and Vishays were head and shoulders above the rest. Unfortunately they are pretty expensive, but we need to use what sounds best. The prominent white caps are MITs, the best available at any cost. And cost they do; triple the cost of other high quality caps. Cardas jacks and Cardas wire are used in point to point configuration to avoid lost definition and detail in the signal. Purist Audio wire is available as an option.

WE LISTEN – The LA-150 has a stereo/mono switch by popular demand. To prevent this feature from causing crosstalk between channels a four pole switch is used with the center contacts grounded. Channel cross talk is -80 dB.

PURE DC – Now you will notice something funny. At the bottom of the signal boards there are two batteries (yes the batteries are included). They are part of the adjustable bias circuit and insure that pure DC is on the signal grids of the gain stage. Critical listening has shown this to be significant in producing the sonic signature of the LA-150. The result is clear, open treble; rich, full upper midrange; warm balanced lower midrange; and a solid, deep bass presentation. Again unique to Joule-Electra.

MAXIMUM CHANNEL SEPARATION – The next funny (read innovative) thing you will notice is the brass shaft that connects the selector switch to the front panel. You will see this on a lot of preamps but the switch won’t have multiple docks and wide spacing like the one found on the Joule. This arrangement shortens the length of the signal inputs and reduces cross talk between the channels. The multiple decks allow paralleling of the contacts which reduces the lack of transparency caused by the single contact arrangements found on most preamps, even the Joule’s competition.

SIMPLICITY -The second duty this switch performs is to allow all switching functions to be done with one switch. The tape monitor loop is available between each of the selector points eliminating the need for another switch. Each input is “virtual direct”.

SONIC EXCELLENCE – You will now note the high quality Noble potentiometer in the input path and the separate balance control. We have tried others (Penny & Giles, Alps, and TKD controls), but found the Noble to be sonically superior in this circuit. The balance control also uses shunt to ground technology and allows very small changes in left and right channel level to be dialed in with perfection.

HIGH-TECH CHASSIS – Now for the icing on the cake, and you may argue that it was the first that you noticed. The signal board is mounted on an exotic tri-flex suspension system to isolate it from the cruel world of vibrations and feedback. State of the art materials are used for this including EAR vibration bushings and ISO-DAMP sheets. Where have you seen this before? Probably nowhere!

I recently picked up a used LA-150 that had been upgraded by Jud Barber to MkII status in October of 2006. During 2013 Jud had retired and closed shop. Sadly, he passed away in 2022, about 15 years after the passing of his beloved wife Marianne. Fortunately, support and repair service are still available from Rich Brkich, Signature Sound (www.sigsound.com). Rich maintains a Joule Electra info page and has been a big fan of Joule Electra gear for many years. He tells me that there are no official schematics as Jud kept it all in his head. And further that the circuit is a bit unusual, not your standard mu follower, because of some unusual design touches such as feedback loops. This probably accounts for my unit’s measured voltage gain of x5.4 (14.7 dB), well below the 6350’s mu of 18. I think that Jud was always aiming for a gain factor in the range of 4 to 8, probably the sweet spot for a tube preamp.

One major purchase incentive was Harry Pearson’s Golden Ear Award in 2007. He raved about the sound of the LA-150MkII. Quoting in part:

“Not everyone, putting it mildly, has 25,000 dollars to live with and experience the component whose lack of an electronic “signature” is at the current state-of-the-art, a component in which the line between the music and the illusion of the music becomes paper-thin. Nevertheless, a master designer—and make no mistake, Judd Barber of Joule Electra is that—can use his craft to achieve a wizardly concatenation of the ingredients that make up a linestage to get a kind of musical magic. This unit is so seriously seductive that many a veteran listener will accept its version of the musical “truth” and be happy exploring old favorites in his collection. Part of what makes a great-sounding component has to do with balance, that is, the relationship between the spectra of sound. The LA-150, in its new edition, has bottom-octave response—and this includes the dynamic, as well—that you seldom get in any linestage, much less one at $5200 or so. Oh yes, you can have deep, deep bass (vide, the Burmester 011 preamplifier), but you almost never, in any price range, get the explosive transient dynamics you get here. (Try the last minute of Cut 9 of The Thin Red Line soundtrack.)

What is more remarkable—and to these ears, a bit of legerdemain—is the midbass response, which is even more propulsive, dynamic-contrasty, and three-dimensional. It almost never happens that you get this kind of jolt from the bottom two octaves without one of them being obscured, usually the very bottom (that is, below 40Hz). There is a price to be paid for this, but first let me suppose that I know why Barber has done this. Most speaker systems these days, and maybe even the one that Barber himself uses, really do not have much in the way of a bottom octave, and among their number are some highly touted and highly expensive big systems, say, from out West. With the LA-150, you’re going to think your speakers have bottom-end response like they never did before. And it won’t sound “wrong,” either. That’s because Barber has elicited from the electronics a correspondingly alive and dynamic upper midrange, though not enough of one to make you think it’s a euphonic coloration, so skillful is the design. And all this is bathed in glorious “tube” sound, like a darker version of the classic gear when Audio Research ruled the waves, and with even lower distortion.”

For the record, after living with the unit for several weeks, I fully agree with Pearson’s assessment. This is one remarkable line preamp.Textures are sweet and luxuriant. In particular, the upper midrange is a thing of beauty: expressive, tonally rich, focused, and 3D to the point of conjuring up a startling impression of the real thing. In these respects, it exceeds the performance of all other line preamps I’ve lived with. The LA-150 MkII doesn’t often materialize on the used market, but when it does, do yourself a favor and snap it up.