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realised, with carefully optimised headroom and noise at all stages. The attenuation
switch which follows the phono stage operates by selecting winding taps, avoiding the
problem of variable source impedance that arises when resistors are used to provide
signal attenuation.
As you would expect from such a comprehensively featured product, the 912 has a very
high quality phono stage compatible with practically any cartridge ever made. It is
based on a valve circuit with a unique RIAA equalisation network which gives excellent
stability, high headroom, low noise and low distortion and which (like all the circuits in
the 912) is single-ended and therefore runs in pure Class A. Moving magnet cartridges
connect to the input valve directly, while moving coil types make use of a step-up
transformer which provides optimum matching over a range of input impedances.
All inputs (whether balanced or unbalanced) are selected by relays, thus keeping signal
paths as short as possible, avoiding potential problems due to long internal wiring looms.
A high grade volume control is employed.
The main output circuit is based on a gain block somewhat similar to that used in the
phono stage, but of course with lower gain and flat frequency response. The primary of
the output transformer is in the anode circuit of the output valve, while two secondaries
feed the outputs, one to the unbalanced output sockets and one to the balanced outputs.
Note that some manufacturers have boasted of the vast headroom of their output circuits,
sometimes capable of output voltages in excess of 20VRMS from a low source impedance.
Although this sounds impressive it can have an unfortunate side effect if the preamplifier is
accidentally driven to full level (for instance by a loose connector): some power amplifier
input stages will be physically damaged by such a high level, requiring expensive repair.
There is absolutely no requirement for such high levels, and the 912 has more than enough
headroom, with a sufficiently low source impedance to drive cables of enormous length.
The ‘Mute’ switch is intended to give instant silence without losing the volume setting or
the choice of input. This is most useful when listening is temporarily interrupted.
Metering is provided to give a visual indication of signal level, which can help when
setting up a system. It also gives some interesting information about the dynamic range of
commercial recordings!
Tim de Paravicini has designed this amplifier to give a lifetime of trouble-free
performance. All components in the amplifier have been carefully selected to give
consistent high performance over a long period.
We hope this instruction booklet will help you enjoy your amplifier to the full.
