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JOULE ELECTRA 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
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