Groove Tubes Speaker Emulator
Last Update 02-19-2012
Groove Tubes designed this pioneering speaker emulator for the guitar
world - they received a patent on it in 1990 and licensed the design to
other
famous amplifier brands. Many guitarists, a notorously
conservative lot leaning to simple controls and copycat tactics, fail
to grasp the details and/or market for this device. Guitar
speakers from different brands and indeed different models from the
same brand sound different from one another. Groove Tubes, by
then having acquired an impressive collection of vintage tube guitar
amplifiers, acquiesced that the speaker of choice for guitar amps was
the Celestion Alnico G12 which was the stock speaker in early british
amps such as Vox, Selmer, and Marshall guitar amps and were often
scavenged from inferior "Thomas Organ" Vox solid state amps to be
installed in vintage Fender guitar amps for their superior tone.
So their design goal for the Speaker Emulator was to emulate the
Celestion G12. It is a very different sounding speaker from other
later Celestions such as the Vintage 30 or others in the ceramic range
used in later configurations so if you are looking to emulate the sound
of a cabinet loaded with later speakers you are going to be very
disappointed. Because many guitarists do not grasp this important
detail, many of them write gear reviews on the 'net slamming this
device - another reason why I take internet gear reviews with a grain
of salt.
As the stock picture suggests, the SE was designed for the vintage
enthusiast. The SE is designed to be a 16 ohm speaker load for
the speaker output of your tube amplifier and has a power capability
maximum of 100 watts. The 16 ohm load was deliberately chosen as
a universal load that is safe to use with any amp designed to be used
with a 8 or 4 ohm load (although some loss of level will result).
The SE is designed as a replacement for
the speaker and does not have a "thru" jack for external speakers (a
later version called the SE-II includes a THRU jack and was designed
for touring systems). A reactive dynamic load was meticulously
designed by the world's leading speaker engineers and audio
mathematicians to "model" the reactive properties of the Celestion G12
speaker, which creates negative feedback to the tube amplifier that
impacts the tone. This negative feedback responds to playing
technique and power level. This is a design detail that is
missing from purely resistive power attenuators such as the Tom Sholtz
Power Soak. The load circuit attenuates the amplifier output by
30dB to the OUTPUT jack to produce a preamp level suitable for direct
input to recording systems
or monitor systems of higher volume. If you loved cranking that
vintage Marshall Plexi to "Nigel Tufnel" 11 for that tube power amp
overdrive but hated the earaches from the volume, the SE is a great
solution and keeps you on friendly terms with your neighbors. If
you loved the tone of that vintage Tweed Deluxe but can't loud enough
to be heard over a stage band, the SE allows you to take the speaker
tone and route it to a louder monitor system.
Gain staging has an impact on the clarity of the sound. The INPUT
control governs the level of speaker output to the reactive load and
will distort unpleasantly if it is too high. For low wattage
amplifiers you use high input levels, for high wattage amplifiers you
must back the input level down. The OUTPUT control governs the
level out of the SE, which should be high for recording systems but may
need to be reduced when using with another guitar amp as a
monitor. With proper gain staging of the INPUT and OUTPUT
controls you can achieve maximum signal-to-noise ratio with no clipping.
The TOP BOOST control restores high frequencies that were attenuated in
the reactive load circuit as a necessary evil to avoid parasitic
oscillations. Usually this is effective for clean tone, but can
get too brassy with flat out overdrive. The EQ section has
boost/cut controls at frequencies of 220hz, 1700hz, and 3500hz to
simulate resonances of different cabinets - open back versus closed
back cabinets have different tone and the EQ is a tool to emulate the
cabinet as opposed to the speaker - a nice option when playing back a
reamped signal. When played back through a full bandwidth system
such as a stage monitor or studio speakers, the EQ also rolls off some
high frequencies to more accurately reproduce the constricted bandwidth
of a guitar speaker cabinet (the upper limit of a guitar amp tops out
around 5Khz). This is why proper gain staging is important - the
EQ will clip harshly if the INPUT control is too high, and noise will
increase if too low. If you are using an external guitar amp as a
monitor it is advised to bypass the EQ.
Other benefits to a studio-friendly output level is you can use the SE
signal to drive studio processors like compressors, digital reverb,
modulated effects, etc which tend to be wider bandwidth and lower noise
than pedal effects units. With pro audio digital reverbs or
delays you can easily simulate the room sound which lifts the guitar
above the mix without overwhelming the mix. These were benefits
that made the SE a popular tool in the studio and on the road.
Curiously my unit neither has a serial number or any badge to hold one.
My original intention of acquiring the SE was to boost the output of my
Selmer Twin
Thirty amplifier being driven by my Fender Rhodes
piano. I love the sound of the Rhodes through the Selmer amp, but
the optimum preamp level without distortion resulted in a volume that
isn't loud enough in a stage band. I already had the Hughes &
Kettner Red Box but that emulates ceramic speakers designed for guitar
overdrive, and I wanted to emulate the clean tone of the Celestion G12
Alnicos in the Selmer which is a big part of the tone I was
getting. I had read of the SE in an old edition of Aspen
Pittman's Tube Amp Book and
after studying the patent I decided this was the box I was looking
for. I quickly found one for sale online. It achieved
exactly the result I needed - with the SE providing a processed signal
designed to emulate the tone of the Celestion G12, I could route it to
a louder amplifer and the Rhodes could compete with a stage band.
The SE also serves me well with my Vox Valvetronix amp which I
use with
a 2x12 cabinet loaded with Celestion Alnico "blues" G12s, and with my
1958 tweed Fender Harvard as the
original speakers were alnico Jensens which sounded close to the G12s.
Players with amplifiers with higher than 100 watts will have to be
cautious and keep their output level of their amp down to avoid
damaging the
SE. If you damage the device with too much power, you are in for
a world of trouble because the reactive power inductors are ENCASED IN
EPOXY AND THEREFORE NOT CAPABLE OF REPAIR. The process of
dissolving the epoxy will also destroy the encased components, which is
a pet peeve of mine that is shared with ARP synthesizers. There
are no
schematics known to exist and Aspen Pittman has sold the Groove Tubes
assets to Fender back in 2009. The patent does not disclose any
details on the inductors - Groove Tubes wanted to keep that crucial
design
detail a trade secret to deter infringing copycats.
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