Aphex
Thermionics
- Division of Aphex Systems Ltd.
Model 1100 MkII Mic Preamp - Owner’s Manual
Page A-5
Introduction
The Model 1100 MkII is an extraordinary micro-
phone preamplifier.
Every detail met with laborious attention during
development. Not until we exhaustively tested our
design both in the field and in the laboratory did
we resolve to release it to production.
To complement the technical achievements inside,
we styled it with a beautiful new look. Chromed
side brackets provide an attractive and very robust
means for rack mounting. The control windows
are illuminated for easy viewing in darkened stu-
dios. The front panel is 3-D machined from billet
aluminum then finished in brightly polished deep
blue anographics. The text and lines are deeply
embedded in the anodizing and can never rub
off. We sincerely hope that our styling efforts will
enhance your enjoyment of this preamplifier.
By looking at the block diagram to the left of this
page, you will see how the signal flows through
the Model 1100 MkII. You may find it useful
to refer back to this diagram later as you read
through other sections of this manual.
You will notice that the microphone input is cou-
pled to the preamp first stage by going through
a series of relays. The first relay selects the 20dB
pad while the second serves to flip the polarity of
the signal lines.
The first stage is a class “A” PNP ultra low noise
variable gain differential amplifier having a gain
ranging from -3 to 41dB. The second stage,
directly coupled to the first stage, is a patented
“Reflected Plate Amplifier
1
” differential tube stage
with a fixed gain of 21dB. The combination of
these two stages provides a novel and unique
front end yielding from 18 to 62dB of gain.
The mute element shown comprises a series-shunt
dual optocoupler to provide noiseless switching
and high attenuation.
The patented Reflected Plate Amplifier output
stage adds 3dB of gain to the front end yielding
the specified gain range of 21 to 65dB.
Because of graduated power rails, the front end
clip point matches the output stage clip point
very closely. Therefore, metering the output of the
front end accurately displays the headroom of the
total system. Also, connecting the A/D converter
to the front end allows precise calibration of the
digital dynamic range to that of the preamp.
You will notice the function called LoCaf
TM
. This
is an Aphex exclusive low cut cancellation filter
that provides increased headroom for frequencies
below the cutoff. Garbled overload from handling
noise, wind, or breath is completely eliminated by
LoCaf.
48 volt phantom power is sourced from a slowly
ramping voltage generator that eliminates thumps
when powering up or down.
Later in this manual you will be more fully taught
about MicLim
TM
. You will notice that there is a
MicLim optocoupler element located immediately
across the mic input lines. The MicLim element is
controlled by the peak detector monitoring the
front end output. When enabled, MicLim will
make the Model 1100 MkII virtually overload
proof. A switched input resistance has been
added to the Model 1100 MkII to extend the
MicLim headroom when using low impedance
microphones such as Neumann Condensers.
The 700Hz tone generator is a unique feature
with many useful purposes. Read about it later in
this manual.
Power is supplied by a linear voltage regulator
assembly and a toroidal power transformer. The
ac supply voltage can be selected by the user to
work with all world standards.
You should find this manual easy to use. Please
do use it even if you are quite familiar with micro-
phone preamplifiers. There are special features we
want you to properly understand and use.
Thank you for purchasing the Model 1100 MkII
from Aphex Thermionics.
1. Reflected Plate Amplifier, U.S. Patent No.
5,450,034. See, in this manual, “Aphex Therm-
ionics: The Story”.
