Thermionic Culture THE FREEBIRD 3 channel equalizer User Manual

THERMIONIC

CULTURE

THE FREEBIRD

valve equaliser

OPERATING MANUAL

WARNING

For your personal safety, please read this operating manual and
warning thoroughly before using the equipment.

This unit must be installed in such a manner that operator access
to the mains plug is maintained. Where the product is to be rack
mounted, this may be achieved by having access to the
disconnection device for the whole rack.

To reduce the risk of electric shock, it is essential that the unit is
disconnected from the mains supply before removing the cover.

Please also note that the power supply capacitors within this unit
can remain charged even after the mains supply has been
disconnected. It is essential that these capacitors are discharged
after the mains supply has been disconnected and the covers
have been removed.

In the event that this unit has been dropped or has suffered an
impact, an electrical safety test must be carried out before
reconnection to the mains supply.

This equipment is not intended for use in explosion hazard
environments. It must be used and stored in studio conditions,
such that the ambient relative humidity does not exceed 80%, nor
is the temperature to be allowed to drop to a level, which would
cause dew point to be reached.

Please ensure that adequate ventilation is provided and that the
ventilation slots are not obstructed. When rack mounting this
equipment, a fan may be required to provide sufficient airflow.

It is not advisable to operate this equipment if all valves are not in
place and working, as voltages will rise and components may
overheat and fail.

©Thermionic Culture Ltd., May 2011 1

CONTENTS

Section Page

1 Introduction 3
2 EQ Style 4
3 Circuit Design 5
4 Controls and Operation 6

4.1 Gain 6

4.2 Top 6

4.3 Mid Cut 6

4.4 Presence 6

4.5 Bass 7

4.6 HPF 7

4.7 Bypass 7
5 Servicing and Maintenance 8

5.1 Valves 8

5.2 Operating Voltages and Fuses 9
6 Specification 10

©Thermionic Culture Ltd., May 2011 2

1 Introduction

The Freebird is one of a new line of products from
Thermionic Culture Ltd. These products all share the same
basic front panel size and casing design, which uses a half
rack 4U size and a detachable power supply. We have
selected this format specifically to increase the tactile feel of
the front panel controls and to allow us to create a modular
product range.

The Freebird offers three channels of all valve EQ. Each
channel has a transformer balanced input, a transformer­less unbalanced output and uses two valves.

The input valve is a 5965 as found in our Fat Bustard
summing mixer. The output valve is a PC86. These valves
are run in a single ended configuration which, we feel, gives
a good balance between smoothness, clarity and harmonic
distortion.

The EQ circuit is an active design, part of which is derived
from a circuit created by Vic Keary in 1961. It was used in
several valve consoles which were used from the early
1960's until present. The circuit has been refined and
enhanced in order to make The Freebird as versatile as
possible.

We feel that having three channels available, will allow the
user to approach this equaliser as a multichannel type EQ,
rather than simply a traditional mono or stereo EQ. The
difference being that this can then be used in many
applications rather than permanently consigned to only the
mix bus or only lead vocal, for example.

The Freebird would do a great job in both applications at the
same time or in whichever combination the user desires.

©Thermionic Culture Ltd., May 2011 3

2 EQ Style

The Freebird EQ is based around a Baxendall type circuit.
This gives the user two shelving controls, one each for low
and high end frequencies. There is a switch adjacent to each
shelving gain control which changes the frequency at which
each shelf operates between two positions. The type of
control provided by the Baxendall circuit is incredibly
versatile despite the apparently broad parameters. The
overall tone of a sound can be quickly and effectively
changed with a high degree of musical feel given to the user.

The presence control gives a very unique EQ curve, which is
a combination of shelf and bell curves. The given curves are
set at different gains and frequencies for each switch
position. The presence control is a feature unique to The
Freebird that is derived from Vic's early design. Extra
frequencies and gain settings have been included to make
the control as versatile as possible.

©Thermionic Culture Ltd., May 2011 4