THERMIONIC CULTURE TheEarlybird 4 valve microphone pre-amplifier 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 Controls 4 2.1 Gain 4 2.2 Bass filter 4 2.3 Pad 4 2.4 Z 2.5 +48V 4 2.6 Phase reverse 4 2.7 Output trim 4 3 Metering 6 4 Operational suggestions 7 5 Specification 8 ©Thermionic Culture Ltd.
1 Introduction The Earlybird 4 is a four-channel mic-amp employing a balanced push-pull all valve circuit, which as far as we know, is unique in this application. The use of this type of circuit gives seriously low noise, plenty of headroom and means a very natural interpretation of whatever sound the microphone is picking up, whether the mic is valve, dynamic or FET. The Earlybird 4 mic amps are improved versions of the Earlybird 1 and 2 series.
2 Controls 2.1 Gain The gain is varied in steps of 5dB from 40dB to 60dB, as stated on the front panel, though actual max gain is 2 – 4 dB more with 300 ohm input .impedance and a low impedance source. 2.2 Bass filter The response is flat when this switch is fully anti-clockwise. It acts at 50 & 100Hz. The effect becomes more drastic as the frequency drops. 2.3 Pad Cuts down the input level by 20dB. Use with Z set to 1200Ω for cleanest results. 2.4 Z Switches input impedance between 300Ω and 1200 Ω.
electronics is available when the controls are set to maximum. These controls are designed to be both ‘fine’ level controls and to reduce the output to feed -10dBV systems. ©Thermionic Culture Ltd.
3 Metering The meters are of a VU type, but they have a compressed scale above 0VU. They measure the actual output of the electronics, less 2dB, not necessarily the actual output as they precede the Output Trim controls. They will only measure the actual output when the Output Trim is set to the ‘M’ position (with a load impedance of 10kΩ). NOTE:- 0 VU is set to the original British standard of +8 dBm rather than the usual US standard or +4 dBm. ©Thermionic Culture Ltd.
4 Operational Suggestions For most microphones 300Ω will give best results. 1200Ω is recommended by Neumann for FET mics (though we like the sound of the U67 on 300Ω). 1200Ω is good for SM58s. For high level inputs, eg. kick drum, use the Pad to reduce level. With Pad in the input, Z will be 2kΩ. Keep Output Level controls near maximum for cleanest results, low and increase Gain control if a bit of distortion is what you want.
5 Specification Included are the figures for noise, distortion and EQ. They are all measured with the Earlybird set up for 44dB mic gain / 0 dB line gain and a 10kΩ load. Input impedance With Pad in: Output impedance (a) Output level control at max (b) Output level control at min Maximum gain Maximum output level (MOL) Distortion (THD) @ 1kHz/100Hz, unweighted, at 40dB gain Frequency response ±0.
Typical values for Distortion, Noise and Phase shift THD (%) @ 100Hz * to 10kHz Noise (dB ref. MOL) Phase shift (°) @ 100Hz 1kHz 10kHz 20kHz ©Thermionic Culture Ltd., July 2014 40dB 50dB 60dB 0.003 0.015 0.03 -117 -113 -104 0 (0%) 1 (0.3%) 14 (3.9%) 28 (7.8%) 0 (0%) 1.4 (0.4%) 17 (4.7) 35 (10%) 3 (0.8%) 2 (0.6%) 31 (8.
Thermionic Culture Ltd., Harlow, Essex, UK Tel: +44 (0)1279 414770 email: technical@thermionicculture.com ©Thermionic Culture Ltd., July 2014. Printed in UK.
