207d
instruction Manual
Aphex Systems Ltd. Model 207D
Page 6
207d
2-ch tube mic preamp with adc
Page 7
Aphex Systems Ltd. Model 207D
2.1 WHAT DISTINGUISHES THE MODEL 207D
There are certainly a lot of mic preamps available
in the world. It seems that every audio equipment
company has at least one model to offer. A study
of currently available products shows that a large
percentage use similar circuits based on one or two
popular commercial i.c. chips. The basic design has
been done by the chip maker and the chips do a
competent job. We could have brought out such a
“me too” design, but it is important to Aphex that we
offer products that are more than just “competent”.
They must also be different and better. That is why
we did not introduce our first mic preamp until we
invented something that would make all the differ-
ence.
That invention turned out to be a new and unique
way to use a vacuum tube in a circuit that yields the
clear and detailed tube sound yet has none of the
limitations of conventional tube circuitry like short
life, noise, heat, and low bandwidth. That invention
is called the Reflected Plate Amplifier (RPA), and was
granted U.S. Patent #5,450,038. We introduced our
first microphone preamplifier incorporating the RPA,
the Model 107, in 1996 and it soon became one of
the most popular mic preamps in the world. People
appreciated the difference it made in the quality of
their work. Tens of thousands of 2-channel units were
sold.
More recently, we came up with another invention
pertaining to mic preamps. We had the idea that if
we could build a mic preamp that not only sounded
great, but also had a way to automatically prevent
input overloading over a significant dynamic range
above normal clipping, then we would have another
innovative hit on our hands. Many months of research
went into inventing a method to achieve this goal.
When we succeeded, we called it MicLim™. Later,
we introduced the Aphex Model 1788 Remote Con-
trolled Mic Preamp including the MicLim™ feature.
Months of trials proved it to be extremely useful in live
sound reinforcement applications. Additional testing
showed it is also useful in recording. When we next
introduced our very high-end Aphex Thermionics™
Model 1100 Thermionic Mic Preamp, we included
the MicLim™ feature and it has received high acclaim
among some of the world’s top sound engineers.
Meanwhile, our Model 107 remained a solid prod-
uct in the marketplace because of its low cost, high
2.0 Introduction
performance and value. However, after enjoying
many years of sales, we thought we owed it to the
world to update the Model 107 with the new things
we have learned and developed since its inception.
Hence, the 207 was born. Production of the Model
107 was discontinued. In the present configuration,
a digital output is added and the model updated to
the 207D.
In addition to improving on the Model 107, the
Model 207D is a whole new product. We transported
the front-end and RPA components that character-
ize the sound of the 107 but we completely revised
our thinking about every other detail. We added the
MicLim™ feature and a professional quality instru-
ment input. We even added a processing insert jack
so you can insert EQ, gating, or compression after
preamplification but before the tube output stage.
In this way you always get the sonic benefits of the
tube. We created a totally new and attractive style
for the chassis and panel that makes it look as great
as it performs.
With the Model 207D you are getting exclusive
Aphex design advantages and legendary sonic quality
at a very modest price. We hope you enjoy using it for
many years to come.
2.2 WHAT DOES THE TUBE ADD?
The Model 207D uses a discrete solid-state
transformerless front end carefully crafted for
extremely low noise and high common mode rejec-
tion. It runs without feedback, making it nearly ideal
as an input stage, never reflecting any feedback cur-
rent back out to the microphone. Certainly, the input
stage has a measurable distortion level, but it is very
low and does not impart any appreciable tonality. The
tonality for which our tube preamplifiers are famous
is due exclusively to the tube.
Our unique and stable RPA tube circuit retains the
tube’s transconductance and grid characteristics
while at the same time creating a much more effi-
cient amplifier stage that runs on low power supply
voltages. We designed the RPA in the Model 207D
to deliver a specific tube distortion curve that subtly
“voices” the preamp. If you have been using the
Model 207D or its predecessor, the Model 107, then
you know what that means. The preamp is character-
ized by most users as very transparent and detailed,
but not colored. The beauty of tubes is that their dis-