Joule-Electra Information Library
Reproduced from old Joule-Electra Literature
LA-150MKII Line Stage Design Goals
By Jud Barber
Why does a preamp costing less than half the price of other high end products have sonics judged to be as good as (some say better than) these marks? Let’s look at the details of the design and build quality of the goals Joule-Electra LA-150. Here is where the secret is; but it’s really no secret. All you need to do is pull the cover and start looking,
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 wile 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 -80dB.
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!
TUBES ONLY – And now last but not least – seven, yes 7, 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.
None of this is snake oil… all of it is what makes the Joule-Electra giant killer. Audition one in your home today.
This historical information is provided courtesy Signature Sound.
We provide support, service and upgrades on Joule-Electra products.
Click here to go back to our main Joule-Electra resource and information page