User manual

26
resolution July/August 2014
MODULAR PROCESSING SUPPLEMENT
REVIEW
T
he Powertube is one of
a rapidly growing
number of 500 series
modules produced
by Radial Engineering.
The range, comprising
repackaged versions of
existing Radial boxes
plus some brand new
additions now numbers
some 18 different modules
— no doubt due in part to
the introduction of its own 500
series chassis products under
the ‘Workhorse’ banner (And
there are six variations of the
racks. Ed). The most recent of
these — the Six Pack — was
used for the review, and that’s
important as it unlocks features
in the Powertube and other
Radial 500 series modules that
other chassis designs may not.
As its name suggests,
the Six Pack is a compact
chassis that houses up to six
compatible modules and in
broad terms these are any 500
series modules. An external
power supply connects via a
five-pin XLR connector, and
the supplied carry handle can
be attached to the top or the side of the chassis
depending on preference. Of particular note is the
capacity of the supply — 1600mA is available to
share between the six slots.
At one level it looks pretty straightforward, a
balanced input and output to each card are provided
on XLRs and ¼-inch TRS jacks wired in parallel
but Radial has added some interesting tweaks to
this standard theme. For ease of connection to, for
example, a DAW interface, eight inputs and outputs
are also provided on DSUB connectors. The first six of
these logically connect to the six slots, the remaining
two inputs from the DSUBs are available on the rear
panel on balanced jacks, and a pair of additional
front panel XLRs can be routed to the ‘spare’ DSUB
outputs.
Each of the six slots also has a slide switch on the
rear panel allowing it to feed its output to the input
of the next slot along — useful for recording chains
made up of individual modules without a mess of
patch leads at the rear. But perhaps the biggest
change — and one that moves slightly away from the
original ‘standard’ — is the provision of an additional
rear panel connection for each module, dubbed
the OmniPort. A ¼-inch stereo jack, the Omniport
function is entirely down to the module manufacturer.
For example it could be used as an (unbalanced)
sidechain access point for a compressor, as an
external key-input for a gate, an insert point or an
additional input. While the majority of Radial’s own
modules obviously exploit this feature, they are also
encouraging other 500 series manufacturers to adopt
it by publishing the specs in an Open Source document
(Workhorse Open Source Document).
The Powertube module is a
tube-based Class A preamp. Front
panel controls are extremely
straightforward — a continuously
variable pot effectively trims the
input to the initial tube stage by
up to 60dB, while another pot sets
up to 60dB gain from the discrete,
Class A output stage. Output level
metering is via a 10-segment LED
ladder working across a range of
-20 to +6dBu. Given that the
aforementioned gain staging is
clearly an inducement to drive
the Powertube as hard as you
dare, it would have been useful
to have the upper range of this
extended somewhat. The display
is also configured so that only one
segment lights at a time, rather
than building up from the left hand
side. This works fine up close, but you do lose the
sense of ‘size’ of signal when squinting at a distance.
Below the gain pot are two pushbuttons to engage
filters in the signal path. The first is the ubiquitous
HPF (100Hz @ 6dB/octave), while the other, labelled
‘Air’, adds a gentle presence boost centred around
8kHz or so. Finally, a recessed pushbutton (you
need a pen/matchstick/tweaker to operate it) engages
phantom power. While I can see the thinking behind
this in terms of reducing the chance of accidentally
applying phantom to an aged ribbon mic, after a
while it can get a little tiresome hunting around for a
suitable poking implement.
As well as the front panel controls, there are a
couple of slide switches on the rear of the PCB at the
back of the module. The first of these is a hard earth
lift on the inputs — only really useful for feeding line
level sources or dynamic mics at a push, as phantom
power is going to disappear if it’s engaged. The second
determines which of the two audio power rails will be
used to power the tube’s heater (+16 or -16V). This
enables this part of the total module current draw to
be balanced between the two rails — useful if your
chassis is populated with multiple Powertubes.
Internally, the Powertube uses a Jensen input
transformer that feeds a 12AX7 tube, followed by
a Class A discrete gain stage. If the Six Pack chassis
didn’t already provide enough input options, there’s
also a front panel XLR input on the module itself. The
OmniPort function in this case provides a DI input on
the rear — inserting a jack in here engages a relay
that disconnects the balanced input and presents the
DI input directly to the transformer.
Plugging in a C414 for reference, and with the
trim control set halfway, initial impressions are of a
robust sound that’s reasonably quiet and open. Noise
does increase as the trim control is turned up and the
tube stage driven harder, along with progressively
increasing amounts of harmonic distortion. Adjusting
the relative settings of trim and gain gives a very
broad palette of sonic permutations, ranging from
clean to slightly warm to positively grungy on
line level sources (which the Powertube deals
with quite happily). In practice, unless really
going for effect, I found that the best results on
most sources were found in the bottom half of the
trim control’s travel. Nevertheless, Radial also ships
an additional ToneBone distortion pedal tube with
the module for additional possibilities (the tube is
socketed on its own circuit board inside the module,
so swapping it out is pretty straightforward). The ‘Air’
presence boost is a useful feature, particularly when
exploring the cleaner end of the tonal range. It’s a
fairly subtle little boost, but actually more generally
useful as a result.
I was less enamoured with the DI input which
sounded a little too ‘soft’ for some applications — I
suspect as a result of the relatively low (150kOhm)
load impedance of the DI stage. While this gave a nice
smooth tone on DI bass, it lacks a little detail on other
sources, although dialling in a little extra tube drive in
conjunction with the Air setting helps here.
The Powertube is unashamedly old school in
approach, and coupled with the no-nonsense we’ve
come to associate with Radial Engineering, it’s safe to
say that it isn’t something you are going to turn to for
subtlety. But for a flexible, characterful and compact
preamp it will find a lot of friends. n
Contact
RADIAL ENGINEERING, CANADA
Web: www.radialeng.com
PROS
Wide sonic palette; robust sounding; exible
gain staging for working with line and mic
sources; Air lter subtle and useful; exible
routing and I-O options on Six Pack
DI input a little ‘soft’ sounding for some
applications; metering could have a wider
range; phantom power switch a bit ddly.
CONS
Radial Six Pack
& Powertube
Radial has yet another rack and yet another module to add to its
portfolio of 500 series units. JON THRONTON