These new conrad-johnson
linearized-pentode amplifiers are designed to meet the needs of industry
professionals and audiophiles who seek audio perfection for their reference
systems. While the demand for precision and musicality is the common denominator
of these systems, the power requirements can vary considerably. To meet these
varying needs, we offer the LP70S stereo amplifier rated at 70 watts per
channel, the LP140M monaural amplifiers rated at 140 watts and the LP275M
monaural amplifiers rated at 275 watts.
The LP amplifiers share the same
basic audio circuit. This circuit consists of three stages. The input signal is
amplified by a triode amplifier. The signal is then direct coupled to a cathode
coupled phase-inverter. This high current, triode phase-inverter stage provides
a balanced, low impedance drive to the output stage. Output power is developed
by 6550 output tubes, chosen for their musical accuracy, high power, and
reliability. Each channel of the LP70S uses one pair of 6550s to produce 70
watts per channel, the LP140M uses two pair to produce 140 watts per each mono
chassis, and the LP275M uses four pair to produce 275 watts. The output tubes
are operated in ultralinear configuration which offers an optimal combination
of high power and low distortion. The massive conrad-johnson transpectral
output transformers have intricately interleaved wind-ings designed for
extended bandpass and high phase linearity. A small amount (about 12 dB) of
loop negative feedback reduces distortion and achieves a sufficiently high
damping factor to control reactive loudspeaker systems.
Separate, low impedance, discrete
dc power supply regulators are provided for the input and phase-inverter
stages, preventing the output stage from modulating these stages through the
power supply. These power supplies are designed to maintain a rock solid supply
at all audio frequencies. The main power supply reservoir uses a bank of
massive custom polypropylene capacitors. No electrolytic capacitors are used in
any of these power supplies.
These amplifiers require no complicated
adjustments or specialized equipment to maintain. To assure continued peak
performance, the owner need only make a simple bias adjustment when new tubes
are installed. Built in LED bias indicators allow the user to make this adjustment
using only the supplied screwdriver.
At conrad-johnson we are fully
aware that component parts contribute importantly to the sonic performance of
any circuit design. The LP amplifiers maintain the exacting quality standards
for which con-rad-johnson is internationally known. Resistors are precision
laser-trimmed metal foil types. Coupling capacitors are the new Teflon CJD caps
and all other audio-circuit capacitors are polystyrene, while the power
supplies use large value polypropylene in parallel with polystyrene capacitors. There are no electrolytic capacitors in the audio circuits or in the related
power supplies. Proprietary wide-bandwidth output transformers contribute to
excellent high frequency performance. Even the machined gold plated OFC
connectors and the internal wiring have been carefully selected for optimal
sonic performance. Attention to details of this kind enable us to extract the
full potential from our circuit designs and ensure that our products will perform
to this potential for years to come.
