3
resistor, controlled by a light that changes in proportion to the
audio signal. This is how classics like UA's LA2, LA3 and LA4 - among
many others - work, but we use a somewhat faster resistive element,
giving a much wider range of control.
The sidechain "sense" input for the compressor is taken either from
the input or the output of the equaliser section, in effect making it
up to you to decide if you want the compressor before the EQ, or the
EQ before the compressor. This is selected with the "Comp" pre/post
switch (15), which also doubles as a compressor bypass switch in it's
middle position.
The Compressor is fully adjustable, giving you access to Threshold
(7) - at what input level the compressor starts working, Ratio (9) -
how much it will do once it starts, Attack time (11) - how fast it
will attenuate over-threshold signals) and Release time (13) - the
amount of time it takes to release the attenuation).
For most real-world recording tasks this compressor works well, but
again - like the EQ - you shouldn’t expect it to do something overly
dramatic. It is designed with signal integrity in mind, not as an
destructive effect.
The working of the compressor - actually the gain reduction
introduced in this circuit - is monitored on the large VU-meter (18).
This is controlled by the Meter switch (16), allowing you to monitor
input level, output level, or gain reduction. When set to the "input"
position, it gives you an idea of how "hot" you're running the
internal circuicy - when reading 0VU, you'll still have about 10dB of
headroom before anything nasty happens. If you select "output",
you're monitoring the unit's output stage condition. 0VU is +14dBm,
still allowing plenty headroom. Note, however, that operating the
meter switch is not recommended while recording, as switching clicks
can (and will, in the middle of the fantastic take) be audible on the
output due to the passive action of the VU-meter.
After the compressor circuit, we reach the output level control(17),
setting the level for the final output driver stage, responsible for
driving your further line of equipment. The output is - like the
input - floating transformer balanced to get rid of potentially
problematic hum loops. The output resistance is less than 1K Ohm, so
driving all sorts of modern equipment - or even long cable runs -
won't be a problem.
