Recording - April 2014 - 44

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

Studio Projects SPM5 500 Series Mic Preamp
A classic design plus beautiful extras equals a great value in a 500 preamp
A Wolff in Studio Projects clothing
Studio Projects is part of the PMI Audio
Group. PMI also distributes the classic
Trident, Joemeek and Valley People product lines, as well as the Paul Wolffdesigned Tonelux brand, which built its
reputation on custom configurable modern recording consoles.
In addition to his innovations for
Tonelux, Paul's previous associations also
include a little company known as API...
the originators of the 500 Series. This is
significant for today's review because
Paul is the designer of the SPM5, establishing a great pedigree for this module
right at the start.

Studio Projects is a California-based
company with a 15-year legacy building
highly affordable quality microphones
such as those found in their B, C and CS
Series. In addition to offering these wellrespected mics, Studio Projects has also
ventured into the audio hardware realm in
past years. Notable examples include the
VTB-1 tube microphone pre amp, as well
as the now-discontinued SP828 which
was both a Burr Brown-based 8-channel
mic preamp and 8x2 mixer in one.
Now Studio Projects is expanding its
hardware line with a trio of 500 Series
modules that cover a typical channel
strip. The line features the SPM5 Mic
Preamp under review today, as well as
the SPE5 Equalizer and the SPC5
Compressor, both of which are still forthcoming.
44

RECORDING April 2014

The SPM5 up close
The SPM5 is a single-space module
designed for use inside any one of the
growing number of 500 series of enclosures on the market. For this review I
tried it in an original API 600 Lunchbox,
the Radial Workhorse (reviewed October
2011), and the new Aphex USB 500
Rack (review forthcoming), and it worked
flawlessly in each.
Out of the box it is solid, heavy and
well-built, with a dual layer jam-packed
circuit board protected by a 3-sided
brass surround. Since the circuit board's
surface is exposed, the first thing I
noticed was a large custom-wound transformer. This transformer, known as the
TX100, is the same one that can be
found in the Tonelux MP5A microphone
preamp and was chosen by PMI's Alan
Hyatt as best for the preamp.
The SPM5 uses a discrete input stage
coupled with the transformer-based output. Its published specs include: Input
impedances of 2 kilohm (mic input) and
1 Megohm (instrument input), commonmode rejection of 70 dB, equivalent
input noise of -127.5 dBu (unweighted,
150 ohm source), 0.001% (+4 dBu output, 1 kHz) total harmonic distortion, a
frequency response of 10 Hz to 70 kHz
(with a tolerance of -3 dB), 70 dB of
total gain (60 dB preamp gain plus 10
dB output gain), a max input of +4 dBu
(mic) / +22 dBu (instrument) before clipping and a max output of +28 dBu (10

kilohm load) before clipping, +4 dBu
electronically balanced nominal output
level, output impedance of 100 ohm,
and lastly an output noise floor of -85
dBu (typical, with -40 dB mic gain).
Features, functions and controls
The front plate of the unit is quite thick
compared to most 500 Series modules
and is dressed in a laminated reddish
gradient design. Starting from the top
down, signal flow starts with a 40-position detented input knob with a range of
3 to 60 dB gain. I love detented knobs
like this, as they make settings reliably
reproducible and generally induce confidence. Just to the right of the Gain knob
is an 8-segment LED meter which goes
from green to yellow to red for signal levels and clipping. Note that there is an
internal jumper where you can choose to
view input signal or output level.
Below the input is a fully variable output
knob which offers an additional 10 dB of
fine tuning for the output level. This classic
input/output preamp design allows the
SPM5 to start out clear and clean with the
input set low and the output set high. But
if you wish, you can induce subtle levels of
grit and weight all the way to full-on solid
state overdrive by pushing the input hard
into the preamp while bringing the output
level down. If you are looking for a preamp that can give you a nice Jack Whitestyle breakup or even a ripping Nine Inch
Nails vocal distortion, the SPM5 can handle either with ease.
To the right of the output knob and running down the length of the unit are five
function buttons. The first is a 12dB/
octave highpass filter with a 70 Hz corner frequency, meant to help get rid of
low-end rumble. There is no published
graph, but it sounds like there is a classic
resonance bump happening here as
well, to keep the musical part of the low
end punchy while the extreme lows are
being cut.
The next button is marked POL for
polarity or phase flip. The next button,
marked IMP, changes the input impedance from 2 kilohms to 50 ohms. This
button changes the load seen by the mic,

Recording - April 2014

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