Recording - March 2015 - 36

B Y PA U L V N U K J R .

Ingram Engineering MPA575
A full channel strip-preamp, EQ,
and compressor-in a single 500 Series space
Back in June 2013, Scott Dorsey took a
look at a new microphone preamp by
Ingram Engineering. The MPA685 was/is a
2-channel mic pre with variable mic impedance, DI inputs and a high pass filter.
Designed for cleanliness and accuracy, it also
featured transformer coupling which helped
add just the slightest hint of coloration.
Mr. Dorsey was impressed, concluding
his review with: "This is the kind of preamplifier I want to see more of in our world. It
does what it's supposed to do and it doesn't
add much else to the sound. It has a lot of
Swiss-Army-knife style features that can be
very handy in a modern studio. And it's built
with care and to last several lifetimes."
That's high praise from Scott.
With that in mind, I was quite
excited to take Eric Ingram's latest creation, the new MPA575,
out for a spin. It's a channel
strip with an MPA685 based
mic preamp, a compressor,
and an EQ... all in a singlespace 500 Series module.
Looking at all the 500 Series
boxes on the market, it's surprising how few full channel
strips there are. I would imagine this is because of the difficulty of providing all the necessary controls on the front and
cramming in all of the needed
circuitry-a tall order even for a
double-wide module, let alone
a single-space box! Ingram has
done exactly that, however...
and included some additional
bells and whistles to boot.
Dense-packed but neat
The MPA575 is housed in a
full wraparound metal enclosure. The unit uses a dual circuit board design-not the
common stacked, miniature
daughterboard format, but
two fully loaded full-size
boards, placed on opposite
sides of the enclosure interior,
facing inward and linked.
36

RECORDING March 2015

What I could see inside this "circuit
board sandwich" was neatly laid out; I
noticed the new unit uses a Lundahl
LL1538 1+1:5 transformer vs. the Sowter
transformer found in the MPA685. An
optional output transformer, according to
Ingram, adds "crunch and coloration"; my
review unit lacked this option.
Preamp controls
The front panel is jam-packed with buttons, lights, pots, and switches. It all starts at
the top with the mic preamp section, which
centers around a large black 12-position
stepped gain switch that goes from 10 dB up
to an impressive 70 dB of gain. The steps
are 6 dB increments from 10 to 40 dB, 5 dB
increments above that.
This section also includes a
+48V phantom power switch
with a green LED indicator, a
180 degree phase button, and
a pair of signal (green) and clip
(red) LED lights.
The MPA575 features
impedance switching via a
Mic Load button with a choice
of 600 ohm or 2.4 kilohm vs.
the MPA685's 3-way 600/
1.5k/2.5k switch. The implementation is the same in both
preamps. As Scott Dorsey
pointed out in his review, it's
done "the proper way-by
adjusting input taps on the
input transformer rather than
just adding shunt resistors. You
can tell this because the noise
floor remains low as you drop
the impedance." I can concur
that the noise floor is not
affected at all.
Tonally, when set to 600
ohms, I found the sound a touch
thicker, forceful and gelled. At
2.4 kilohms, the sound spreads
out a bit and opens up in the
high end; the mids even seem
to move out of the way a tad,
and it has a more diffuse low
end signature.

See-saw EQ
The EQ section starts with a switchable,
variable highpass filter with a range of 30 to
400 Hz. Next, rather than a typical multiband parametric, the EQ here is a single
knob with low frequencies on one side and
high frequencies on the other. This EQ does
not simply boost one band or the other like
you might find on an old 1970s car stereo;
instead it's best described as a See-Saw EQ.
Here, 1.2 kHz is the pivot point; as you
raise the high frequencies, it lowers the
low frequencies, and vice versa. There's
a boost/cut range of greater than 15 dB
boost and under 4 dB cut.
Like the highpass filter, the EQ can be
bypassed at the touch of a button. That's
also true of the next section...
Dynamics
The Dynamics section is also controlled
by a single knob. This may seem "limiting"
(sorry, had to), but is similar to how many
vintage compressors work. This one is a
feed-forward design that's program dependent; in use, it adjusts its attack, release,
and ratio depending on how hard it is hit
by the incoming signal. The circuit is a soft
knee design that goes from a gentle 1.2:1
up past 20:1 with a threshold of -30 dBu
to +12 dBu with 1dB of compression.
The Dynamics section can be switched
pre or post EQ. It also has a built-in
sidechain EQ identical in function to the

Recording - March 2015

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