WHITE PAPER SERIES“OHM-MAZING” DISCOVERIESSECRETS OF THE GROOVE TUBES VIPRE PREAMPEARLY IN THE ANNALS OF PRO AUDIO,mics and mic preamps were often madeby the same company, and the output
and input impedance between the mic andpreamp were matched to provide the best
possible audio quality.
Those days are long gone now, and mostcondenser mics send a 200-250 ohm load into
an input about 10 times the impedance –roughly 2000-3000 ohms.
Altering the load against which the mic
has to push fundamentally alters the tone andcharacter of the output signal.
At the core of the Groove Tubes Vipre is amulti-tap high-performance input transformer,
with four distinct positions: 300, 600, 1200
and 2400 ohms. This changes the working
impedance or loading of a given microphoneand can strongly influence the sound qualities
by the cumulative effects of small differences.
These differences vary from microphone
to microphone, but all mics respond quite
audibly when the preamp input impedance isaltered. This control feature opens a muchlarger sonic window to each mic, and provides
the ability to magnify certain attractive tonal
shifts in the way it responds to impedancechanges.
Vintage microphones are especiallysensitive to load terminations, as impedance
matching was the norm in early broadcast andrecording facilities.
Ribbon mics, for example, are sought after
for their smooth tonal properties. When
properly terminated or loaded with 300 ohms,
the tonal characteristics change, and the soundseems to “bloom” in a way most people havenever heard.
The equalization changes slightly as well,with the entire spectrum from about 100Hz to
15kHz taking on a very slight tilt, typicallyaround -1dB at the low end, and around +1dB
at the upper registers. Very slight whenlooking at individual frequencies, but thecumulative effect over the whole spectrum is
unmistakable.
This kind of variation would be almost
impossible to recreate with any kind of EQ,
unless the principle of a simple, unclutteredsignal path is abandoned altogether.
Moreover, a balanced-bridged ortransformerless input is provided, bypassing
the variable-impedance input transformer
altogether for a completely different soniccharacter.
An instrument input is also provided on
the front panel of the Vipre for easy access,and can be padded by -20dB to accommodate
the stronger output signals from active
instrument electronics.

VARIABLE IMPEDANCEINPUTS
Altering the input
impedance changes theload against which themic has to push. This
dramatically alters theperformance of any mic –The Groove Tubes Vipre is a mono-block, fully-differential Class A all-tube preamp
from classic ribbons towith variable input impedance and adjustable rise time. It can be set for over 20vintage and moderndifferent tonal variations – all without ever requiring EQ or other signal-degrading
condensers – evendevices to achieve them.
dynamics. All mics
will respond similarly in that the apparent
ALL-TUBE, FULLY-DIFFERENTIAL
proximity gets ‘closer’ when the impedance isCLASS A DESIGN
lowered, but since you’re changing the load
Class A means that the same amplificationon the mic, you’re altering the performance ofdevice (in this case, tubes) are doing thethe mic – not the preamp.
entire waveform, both the maxima andSome vintage mic preamps (like Neveminima of the wave.
modules) can be internally hard-wired toClass AB and Class B use separate amp
one of two different impedances. Avalon’sdevices to do the maxima (or top side) and2022 and Joe Meek’s VC-1 both have anminima (low side) of the wave. Those are“impedance matching circuit” – consisting of
more efficient, but not nearly as accurate ora resistor network placed AFTER the load istrue.
already terminated. But, this isn’t the same
Fully-differential means that the signal
as what the Groove Tubes Vipre offers.
remains balanced throughout, never becomingThis is the only preamp we know of
unbalanced or single-ended.
with a front-panel-selectable, truly variable
Almost all amp circuits break the balance.
impedance transformer.
(In a console, the signal is single ended fromIn short: You haven’t heard your mics until the time it comes into the preamp, until
you’ve heard them loaded at different
bridged at the output.) This is accomplished
impedances. With all the control functions
by using identical, mirror-image signal paths
available on this unit, anyone with even athroughout – and why we use ceramicmodest selection of mics can dramaticallydeck attenuators instead of potentiometers forincrease their tonal options by using a Vipre.
gain adjustments.
Common mode-rejection ratios are
VARIABLE RISE TIMES
significantly improved, as are signal-to-noise
Rise-time is very much the same as “slewratios.
rate” – the rate of speed at which theamplification circuit can amplify the signal.
PRECISION GAIN AND GENUINE VU
You can't go from zero to five volts in noIn order to maintain a fully floated andtime – and how fast a circuit can amplify isbalanced signal path throughout the entire
part of what imparts its sound. Vintage circuits circuit, there are no potentiometers on thewere much slower than are today’s, and – infront panel. Instead, gain controls consist oftheory– faster is better.
ceramic deck rotary switch assemblies
Faster amplification circuits retain thearranged for discrete step attenuation,
leading edge of the transient signal, especiallyproviding repeatability, ultra-wide control
apparent on the higher frequencies. But
range and superior accuracy.
slowing the rise time down can mellow or
To watch over all this signal manipulationsmooth out the signal, often rounding-out
capability, the Vipre is fitted with a genuine
harsh sibilants from vocals or edgy tones ofVU meter for signal observation – complete
instruments.
with five separate types of VU response
In a way, you can think of rise-times as athrough an amplified VU meter driver circuit“time machine” for preamps – the slower thethat allows for an “expanded view” of -20dB
rate, the more vintage the sound. No otherto +4dB – up to a -60dB to +9dB response.
preamp but the Vipre has this special feature.
BOTTOM LINE: ONLY VIPRE DOESGROOVE TUBES LLC
WHAT NO OTHER PREAMP CAN
www.groovetubes.com
Hear the Vipre – along with our full line ofsales@ groovetubes.com
mics at your Groove Tubes audio dealer – or1-800-459-5687
visit us at the New York City AES, booth 1087.