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.
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 6 Servicing and Maintenance 8 5.1 Valves 8 5.2 Operating Voltages and Fuses 9 Specification ©Thermionic Culture Ltd.
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.
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.
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.
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.
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.
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.
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 115V ©Thermionic Culture Ltd.
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 Freebird - Frequency Response Curves 20 15 10 Bass+5@50Hz 5 Bass+5@100Hz Bass-5@50Hz Gain (dB) 0 Bass-5@100Hz HPF 25Hz -5 HPF 65Hz -10 Mid Cut Top+5@50Hz -15 Top+5@100Hz -20 -25 -30 0.01 0.
The Freebird - Presence Curves 20 15 10 5 L Gain (dB) 0 M H -5 H+ -10 H++ -15 -20 -25 -30 0.01 0.
Thermionic Culture Ltd., Harlow, Essex, UK Tel: +44 (0)1279 414770 Fax: +44 (0)1279 412233 www.thermionicculture.com ©Thermionic Culture Ltd., May 2011. Printed in UK.
