Groove Tubes VELO-8 Reference Manual

© Groove Tubes LLC.All Rights Reserved.

Groove Tubes

Velocity (Ribbon) Microphone

Reference Manual

VELO-8

For the latest information on your

Groove Tubes product, visit our web site at

www.groovetubes.com

Or call us toll-free at

[phone]

1 VELO-8 REFERENCE MANUAL

A little background on “Velocity” mics

The VELO-8 name stands for “velocity” microphone, with a traditional
“figure 8” polar pattern; hence, VELO-8. “Velocity microphone” is the
original name used by RCA, Electro-Voice and others for what we commonly
today call “ribbon” mics. They actually worked on reacting to sound wave
velocity (or audio wind), so the name fits if you understand the technology.

Most ribbon mics have a very thin aluminum element that looks like a silver
ribbon. It is moved (activated) by very small amounts of sound (or air velocity)
from instruments or voice. This ultra-thin strip of metal is a double-edged
sword.

First the positive: its ultra-thin element can capture details with a smoothness
not found in any other microphone technology. It can make a saxophone sound
sweet, not harsh. Ribbon mics can do the same for voice and many other
instruments that might record too bright or harsh using modern condenser mics.

Now the downside: while its thinness affords highly detailed sensitivity to
sound waves, it is also easily damaged or torn if the accompanying air waves
are too strong. Higher air pressure levels, like those generated by a closely
miked strong vocalist or a bass drum on axis, can easily rip the thin aluminum
ribbon element resulting in a costly and time consuming re-ribboning repair
adventure. Replacing the torn ribbon is a delicate maneuver, and only possible
if performed by a highly experienced mic tech or a factory repair department.
Unfortunately, both in the early days and today, a broken ribbon element is
quite common. If you find a good mic tech who can repair your ribbon
element, it can take weeks or months before you’re back in business. The old
RCA and Capital studios usually employed a full time tech whose only job was
to maintain their array of ribbon mics so studio time was not lost. But those
old ribbon tech guys are mostly gone today, and few younger techs have the
training and/or experience to do a good ribbon repair. So today, we usually
have to search for that rare “ribbon mic guru” and send it to him, or in the case
of a newly produced ribbon mic, it would have to go back to the factory... and
you wait!

This is one reason velocity mics fell out of favor with most the larger studios,
who embraced the more modern and highly detailed condenser mics which are
not as easily damaged from higher levels of wind or air velocity common to
rock recordings.

GROOVE TUBES 2

Another factor of the ribbon mics’fall from favor with modern studios was that
they had very low signal output as compared to the electronically activated
higher output condenser mics. They therefore required more preamplification
to get similar output levels, which add noise floor to the signal from the
increased amplification factor. For an example, listen to the hiss on Elvis’s
“Love Me Tender” or Patty Cline’s “Crazy”, both recorded with early ribbon
mics.

In fact, ribbon mics can be up to 20dB weaker than condenser mics. This is
really a problem today, as most mixers and preamps do not have the low input
impedance to match the relatively low output impedance of the typical ribbon
mic (which uses a transformer to boost the impedance from 1 Ohm to maybe
100-200 Ohms). Also, the ribbon element’s output signal levels are too low as
well. Therefore, the “loading” is usually too high, and the preamp too weak to
effectively boost the level to the strength of the more common condenser mic.
Our ViPRE and SuPRE mic preamps were specifically designed to load the
ribbon with a matching balanced transformer winding of 300 Ohms, instead of
the industry standard of 2,000 Ohms or higher. These preamps also amplify
over 70dB, so this feature set was specifically intended to allow ViPRE and
SuPRE to address the special needs of preamplifying a ribbon mic, and
duplicate the loading and amplification designs of the old RCA consoles when
velocity mics populated the studios in the USA.

How the velocity mic works

Ribbon mics, both then and now, all work on the same basic principle; a thin
conductor (usually a strip of aluminum) is suspended and “tensioned” between
a magnetic field and is activated by sound waves, and this generates a small
signal voltage. This is similar to the way the more common dynamic mic
works, which uses its diaphragm suspended in a round magnetic field to
generate a signal voltage from its movement activated by sound waves, like a
small speaker in reverse.

3 VELO-8 REFERENCE MANUAL