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

3 Circuit Design

The design of The Freebird was also initially based around
the type of valve selected.

We felt that the simple single ended design particularly
suited this unit and that the input 5965 valve combined with a
PC86 output valve, gave a very desirable quality to the
sound of the unit.

An input transformer was added to counteract potential
problems that might be found with certain combinations of
electronically balanced equipment. The output was left
unbalanced because we love the 'open' sound this gives the
unit.

©Thermionic Culture Ltd., May 2011 5

4 Controls and Operation

4.1 Gain

The rotary gain control is located at the top of each
channel. It allows the channel gain to be attenuated
continuously at the input to give a channel gain of
between -12dB and +5dB (when the EQ is set to flat).
This can be used either to adjust the EQ'd channel to
unity gain or to change the gain so as not to distort the
unit if high levels of positive EQ are added.

4.2 Top

The rotary gain control allows the amount of top EQ to
be adjusted continuously between +14dB and -16dB.
The EQ has a shelving type curve, reaching it's
peak/trough at either 9kHz or 15kHz depending upon
the position of the two way frequency selector switch.

4.3 Mid Cut

The rotary gain control allows the amount of mid cut
EQ to be adjusted continuously between 0 and -20dB.
The EQ is set at a fixed frequency of 700Hz. The Q of
the curve increases as the trough level is increased.

4.4 Presence

This switch allows for five different preset presence
EQ curves to be applied to the signal. The curve is
quite unique to this equaliser. It acts partly as a high
pass shelf curve, but has a peak near the beginning of
the curve, followed by a drop at the upper audible
range of the curve.

The curves are set at:­L: +3dB @1kHz H+: +5dB @3kHz
M: +4dB @1.5kHz H++: +8dB @3kHz
H: +3dB @ 3kHz

©Thermionic Culture Ltd., May 2011 6

The 'M' setting is the original design, which simply
gives a very broad lift to mid and top.

The lowest setting 'L' gives a very useful thickness to
instruments like guitars.

The 'H' settings are three increasing amounts of curve
which focuses around the high mids of the signal. This
can be useful for vocals or anything that needs to be
brightened and brought forward.

4.5 Bass

The rotary gain control allows the amount of bass EQ
to be adjusted continuously between ±11dB. The EQ
has a shelving type curve, reaching it's peak/trough at
either 50Hz or 100Hz depending upon the position of
the two way frequency selector switch.

4.6 HPF

The high pass filter switch gives the user a 12dB per
octave filter which is 8dB down at either 25Hz or
65Hz.

These frequencies and filter slope work very well in
conjunction with the 'Bass' control. This effectively
allows the user to simply remove problem frequencies
from a sound, or to allow the bass frequencies to be
enhanced dramatically, without any danger of
producing frequencies that interfere with the action of
loudspeakers.

4.7 Bypass

This switch provides a hardwired bypass that simply
connects the unit's inputs and outputs together,
completely bypassing the unit's electronics. When the
switch is up, The Freebird is in circuit and when down
it is completely bypassed.

©Thermionic Culture Ltd., May 2011 7

5 Servicing and maintenance

The Freebird comes with a 12 month warranty covering all
parts, including valves. It is essential that in the event of a
fault occurring it is returned to our factory or to the dealer
from which it was purchased for repairs to be carried out
otherwise the warranty will be invalidated. There is however
one exception to this rule:

5.1 Valves

If a fault occurs, the most likely cause is one of the
valves, probably the input valve. There is one input
and one output valve per channel. The inputs are the
ones closest to the front panel. If a fault (eg. a crackle)
occurs on Ch 1 then swap the input valve with the one
from Ch 2 and check whether the fault moves. If not,
try the same with the output valves.

To change a valve, unplug the mains power lead,
unscrew the top cover, remove the valve screening
can by pushing down gently and twisting it anti-

clockwise, then pull the valve straight out. WARNING

valves run very hot so you may need to use a cloth to

remove the valve. ALSO be careful not to touch any

exposed component leads as potentially lethal
voltages lurk there, even after disconnecting the
power source.

If you find a faulty valve, contact your dealer or
ourselves and a new one will be sent to you (free of
charge if still in warranty). PLEASE send back any
faulty ones.

Do not try to operate the unit without all of the
valves plugged in.

Valve complement:

Input: 3 x 5965
Output: 3 x PC86

©Thermionic Culture Ltd., May 2011 8

5.2 Operating voltages / fuses

The Freebird can be set to operate from either 230V
or 115V 50/60 Hz AC. The appropriate mains input
voltage can be selected on the red switch located next
to the mains inlet.

Note: Mains fuses must be replaced in accordance
with the following table.

230V T315mA
115V T630mA

©Thermionic Culture Ltd., May 2011 9

6 Specification

Frequency response

±0.5dB
±1dB

Input impedance
Output impedance
Distortion

THD @ +4dBu 1kHz
THD @ +4dBu 100Hz

MOL (1% THD)
Noise
Gain

(all controls flat)
20Hz-80kHz
15Hz-130kHz
10kΩ
200Ω

≤0.05%
≤0.1%

+22dBu
100dB below MOL

-17 to +5dB

NB. Noise and distortion measurements made unweighted,
with 30kHz filter to remove any radio pickup.

Loading=10kΩ. Can be loaded with 600Ω but MOL will be
reduced and distortion increased.

The BYPASS switch completely removes the electronics
from circuit.

The gain of the unit is set to zero for a 10k

trimmer near to the gain control for fine adjustment. This is
accessed by removing the lid.

Ω load. There is a

©Thermionic Culture Ltd., May 2011 10

20

15

10

The Freebird - Frequency Response Curves

Bass+5@50Hz

5

Bass+5@100Hz

0

Bass-5@100Hz

Bass-5@50Hz

-5

Gain (dB)

-10

HPF 25Hz

HPF 65Hz

Mid Cut

-15

Top+5@50Hz

Top+5@100Hz

-20

-25

-30

0111.010.0

Frequency (kHz)

20

15

10

The Freebird - Presence Curves

5

0

L

M

-5

Gain (dB)

-10

-15

-20

-25

-30

0111.010.0

Frequency (kHz)

H

H+

H++

Thermionic Culture Ltd., Harlow, Essex, UK

Tel: [phone] Fax: [phone]

www.thermionicculture.com

©Thermionic Culture Ltd., May 2011. Printed in UK.