Groove Tubes Vipre
TM

www.groovetubes.com

Vipre
FAQs

GROOVE TUBES CUSTOM SHOP PRODUCTS

VariableImpedancePreampTM

What's theGroove Tubes Vipre?
Vipre stands for Variable Impedance Preamp. It’s amono-block, fully-differential Class A, all-tube
preamp with variable input impedance and adjustablerise time.

What's “variableimpedance” – and why
do I need it?
Altering the input impedance changes the load
against which the microphone has to push – thisdramatically alters the performance of any mic, fromclassic ribbons, vintage and modern condensers –even dynamic mics.

Some vintage mic preamps (like Neve modules)
can be internally hard-wired to one of two different
impedances. Vipre is the only preamp we know of with afront-panel selectable, truly variable impedance
transformer.

What's a “fully-differential,Class A” design?
Class A means that the same amplification device (inthis case, tubes) are doing the entire waveform, boththe maxima and minima of the wave.
Class AB and Class B use separate amp
devices to do the maxima (or top side) and minima (lowside) of the wave. Those are more efficient, but notnearly as accurate or true.

The Groove Tubes

Vipre

FREQUENTLY
ASKED
QUESTIONSAll microphones will
respond similarly in that theapparent proximity gets‘closer’ when the impedanceis lowered, but since you'rechanging the load on themic – you're altering theperformance of themicrophone, not theGROOVE TUBES LLC
preamplifier.
CUSTOM SHOP PRODUCTS
A transformerless, balanced bridging
Fully-differential means that the signal remains
input selection is also available.
balancedthroughout, never becoming unbalanced orBottom line: You haven't heard your microsingle-ended.
phones until you've heard them loaded at different
Almost all amp circuits break the balance. (In aimpedances. Anyone with even a modest mic selection
console,the signal is single ended from the time it
can multiply the selections by using Vipre.
comes into the preamp, until bridged at the output.)
This is accomplished by using identical, mirror-image
signal paths throughout – and why we use ceramic
Don't other mic preamps
deckattenuators instead of potentiometers for gain
offer this feature? (I've seenadjustments.
impedance matching before.)
Common mode-rejection ratios are significantly
improved, as are signal-to-noise ratios.
Avalon’s 2022 and Joe Meek’s VC-1 both have an“impedance matching” circuit, consisting of a resistor
network placed AFTER the load is already terminated.
This is NOT at all the same thing.

Aren't there a lot of tube
microphone preamps
available now?
What's the difference?
Why is yours so much more
expensive than, say, the ART
Tube MP, or the Peavey?
Most “tube” preamps really aren't. They use a tube as
an effect in a transistor-based circuit.
Many times the plate voltage is severely
starved to add distortion, which is what many people
think gives the "tube sound."Very few preamps on the market today are alltube throughout – and all are priced similarly or higher
than the Groove Tubes Vipre – and none with thefeatures that the Vipre has.

What's this “rise-time” stuff allabout?
Rise-time is very much the same as “slew-rate” – therate of speed at which the amplification circuit canamplify the signal.
You can't go from zero to five volts in no time –and how fast a circuit can amplify is part of what
imparts its sound. Vintage circuits were much slower
than are today's, and – in theory – faster is better.
Faster amplification circuits retain the leadingedge of the transient signal, especially apparent on thehigher frequencies. But slowing the rise time down canmellow or smooth out the signal, often rounding-out
harsh sibilants from vocals or edgy tones ofinstruments.
In a way, you can think of rise-times as a “timemachine” for preamplifiers – the slower the rate, themore vintage the sound. No other preamp has thisspecial feature.

Is there a stereo Vipre
available?
Sure. It's six rack spaces, retails at about $6000, andlooks very much like two Vipres.
Wait a minute... it IS two Vipres! (No stereo
model is planned.)
Because of the precision of the components
and gain staging, you should be able to get identicalresults from two units. Finding two as precisely matchedmicrophones would be far more challenging.

Are there line or instrument
inputs available?
Both. A 470K-ohm instrument input is convenientlylocated on the front panel just below the input selector
switch, with a -20dB pad available for "active" guitars
and basses with hotter outputs. This input doesn't gothrough the variable impedance transformer. A balanced
XLR line-level input is also available on the rear
panel, with all the same options available as formicrophones.

GROOVE TUBES LLC
Groove Tubes LLC
Custom Shop Products
1543 Truman Street
San Fernando, California 91340 USA
Tel 818 361 4500
Fax 818 365 9884
www.groovetubes.com©2001 Groove Tubes LLC. All rights reserved. Groove Tubes, the GT in a circle logomark, Groove Tubes Custom Shop,
Groove Tubes Custom Shop Products and Vipre are trademarks and service marks created and owned by Groove Tubes LLC.
All specifications subject to change without notice.