Signature Sound
Joule-Electra Information Library

Reproduced from old Joule-Electra Literature

JOULE ELECTRA
LINE STAGE AMPLIFIER
LA-150MII

General Description

The JOULE ELECTRA LA-150 line stage only pre-amp employs tubes throughout, including a tube reference and tube voltage regulator for each Stereo half. The overall gain is 11 dB and four inputs are provided as follows: CD, Aux-1, Aux-2 and Tape. The separate balance and volume controls can be operated by remote control and two outputs are available from separate output jacks. The input selector functions as a passive buffer which is unique in the industry and provides for complete separation of the tape recorder from the input circuitry when not in use.

Circuit Description

The LA-150 is a dual mono design with separate voltage regulators and power supplies for both halves of the stereo circuitry. The circuit is called a “Mu Follower” and is unique in that the cathode follower acts as a very high resistance buffer between the B+ and the plate of the gain stage. This is sometimes referred to as “totem pole” design. This allows the gain tube to see almost an infinite resistance at the plate, enhancing sonics and minimizing distortion. The Joule Electra LA-100 was the first commercial product using this unique circuit topology and the LA1150 follows in this tradition.

The circuit of the LA-150 is phase inverting. This design approach reduces the number of stages from three to two which has a very positive effect on the overall sonics. If you are concerned about system phasing and already have the preferred phase established, then it is only necessary to switch the hot and ground leads to both of your speakers if you have been using a non-inverting pre-amp.

The Mark II version of the LA-150 uses the work horse of the Joule line, the 6350, in both the gain and Mu Follower positions. This exceptional tube is NOS and no longer in production. We have several thousand of these on hand so availability will not be a problem. The power supply uses a zeiner diode as a voltage reference and a 6EM7 as a voltage regulator. In case you are interested, the schematic for this supply appears in the 1957 edition of the RCA tube manual. Completely independent regulation is provided for each channel and the only common ground for the LA-150 is found at the input terminals, as they are grounded to the chassis. Individually regulated filament supplies are provided for the gain stage and the Mu follower stage.

The astounding sonics of the LA-150 are not achieved by unique circuitry or clever design schemes. It is the result of using the simplest possible gain and follower stages and the use of parallel switch contacts in the input block. In addition to this, the sonic signature of every component in the signal circuit was evaluated and each of these parts was selected for maximum neutrality. The last and possibly the most important aspect of the design is the extremely large current capacity of the power supply. The circuit is so sonically revealing that changing almost any part including the wire will result in a detectable sonic affect.

Sonic Objectives

The LA-150 was designed with the following sonic objectives in mind

1. Extended range from below 5 Hertz to above 100 Kilo Hertz +- 1 db.
2. Clean open treble with no edge or glare.
3. Enhanced sonic detail in the mid range, with full rich tonality and clean spacious harmonic structure.
4. Solid extended lows with depth and authority.
5. A broad, deep sound—stage, with proper placement of instruments both laterally and behind the plane of the speakers.
6. Instruments occupy their own space, with good separation and vivid tonal accuracy.
7. Ambience recovery maximized for the presence of the original performance.
8. Provide both low impedance and very low impedance outputs for maximum sonic benefit.

We think you will agree with us that we have reached this goal