Thermionic Culture Snow Petrel User manual

Thermionic Culture Ltd, October 2019 1
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.
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, October 2019 2
CONTENTS
Section Page
1 Introduction 3
2 Installation 4
3 Controls 5
3.1 Pad 5
3.2 Input Z 5
3.3 Gain 5
3.4 HPF 5
3.5 Air 5
3.6 O/P Trim 5
3.7 Atten 6
3.8 Phantom Power 6
4 Operational Hints 7
5 Servicing & Maintenance 8
5.1 Valves 8
5.2 Operating Voltages/Fuses 9
6 Specification 10

Thermionic Culture Ltd, October 2019 3
1 Introduction
The Snow Petrel is designed as a two channel microphone
amplifier for all types of microphones, especially certain ribbons,
eg. Coles 4038, which have a lower output level than others but
offer superb quality. Their full potential can be realised with this
high gain unit as it has a natural valve sound with very low
background noise and distortion. The passive “AIR” control is
provided to lift the very high frequencies as many ribbons suffer
a little loss there and this compensates for that perfectly.
It will give excellent results with any microphone and we have
included +48V phantom power and -20dB pad for use with FET
and self-amplifying microphones.
There are 3 valves in each channel of the Snow Petrel, the first 2
acting as the main amplifier preceded by a specially designed
Sowter input transformer, then after the passive HPF and Air
controls comes the Tung Sol (6189) output valve and Sowter 1:1
transformer. This combination is capable of a clean output in
excess of +25dBu. Of course many users may want valve and
transformer colouration to give a bit more “edge” to the sound so
we have provided 2 attenuators, O/P trim comes after the 1st 2
valves and can be used to provide a little 2nd harmonic
colouration, then the “ATTEN” is at the actual output so if the unit
is driven hard it will add transformer as well as valve distortion.

Thermionic Culture Ltd, October 2019 4
2 Installation
Ensure that the voltage selector at the rear is correctly set for your
mains voltage!
The Snow Petrel is designed primarily for vertical rack mounting
and there is no need to leave gaps above or below it, as long as
there is reasonable ventilation to the rack. However, if it is
mounted with the face plate horizontal you must leave a 1U gap
above it for heat to escape.
Standard XLR cables are fine for ins and outs. We do not
recommend jack type patch bays for the inputs.

Thermionic Culture Ltd, October 2019 5
3 Controls
3.1 Pad
A 20dB attenuator before the input transformer.
3.2 Input Z
Switches the input transformer from 850Ω to 2400Ω to suit
different microphones. If the Pad is used, switch to Hi.
3.3 Gain
Changes the gain of the main amplifier. Figures on front
panel are correct if Input Z is set to Lo, a low impedance
source is used, and the output feeds a 10kΩ load with no
attenuation. If input Z is set to Hi, there will be a reduction in
gain of around 6dB, depending on the microphone
impedance.
3.4 HPF
This is a 6dB/octave roll-off designed to reduce proximity
effect, being 3dB down at selected frequencies.
3.5 Air
When set to 10 will give a lift of 5dB at 10kHz, peaking at
22kHz.
3.6 O/P Trim
Reduces the output of the input stages by up to10dB. Note:
the figures on the front panel do not represent dB reduction
except 0 and 10.

Thermionic Culture Ltd, October 2019 6
3.7 Atten
This switch follows the output transformer and will attenuate
the signal by 7 or 15dB allowing distortion in the output stage
and transformer. Figures are correct with a 10kohm load.
3.8 Phantom Power
The 48V enabling switch needs to be pulled out to switch on.
Preventing accidental application, to protect ribbon
microphones, etc.

Thermionic Culture Ltd, October 2019 7
4 Operational Hints
The Lo impedance setting is in fact high compared with some
other mic amps and is good for most microphones, though many
mics may sound better with the Hi Z setting, which will give an
extended HF response with low impedance microphones.
Similarly, when the Pad switch is used, the HF response is
extended at Hi Z, whilst slightly rolled off at Lo Z, so giving a
“warmer” sound. Many options.
The Air control will compensate perfectly for the slight roll-off of
hi top in most ribbons, minimising phase shift and giving extra
clarity to these microphones. Legendary engineer Geoff
Emerick of Abbey Road boosted a pair of 4038s by +6 dB @ 12
kHz on The Beatles drum overheads, and this can be replicated
and bettered with the Air control.
As for legendary engineers, Glyn Johns is on record as saying
that part of his drum mic-ing technique was to overdrive the
mixing console channel. The Snow Petrel will give you this effect
by using 2 separate attenuators, one before and one after the
Output stage. The sound can certainly be obtained and made
even more dramatic using Coles 4038s, driving the input hard
with the first attenuator set low and the final output attenuator at
-7 or -15dB settings.
This technique can of course be used for many instruments,
basses, guitars, even strings, BUT don’t forget the natural clear
open sound of The Snow Petrel with no output attenuation!

Thermionic Culture Ltd, October 2019 8
5 Servicing & Maintenance
If servicing is required within the warranty period, which is 2 years
from date of purchase (except valves which are strictly 12
months) then the unit must be returned to the supplying dealer
using the original packaging.
5.1 Valves
The only exception to this rule is in the event of a possible
valve problem. If the user feels confident changing valves,
then he/she can take off the lid by removing the fixing
screws. Assuming that the fault is with 1 channel only, valves
can be swapped in turn to isolate the fault. Try the output
valves first, then work back to the inputs (smaller ones in
cans). Switch OFF when changing valves. WARNING: Very
high voltages lurk in the circuit boards and components. DO
NOT TOUCH!
Valves fitted are usually as follows, close equivalents are in
brackets:
Input: RTC 5654 (Mullard M8100)
Stage 2: Svetlana EF 86 (JJ EF 806)
Output: Tung-Sol or similar 6189 (12AU7A)
If you require spares, please contact your dealer, or
Thermionic Culture Ltd.
Before we supply spare valves we test and select them, then
“soak” them at high power for 48+ hours, then check them
again in a working unit to ensure they are still up to spec
before sending to customers.

Thermionic Culture Ltd, October 2019 9
5.2 Operating Voltages/Fuse
The Snow Petrel can be set to operate from either 230V or
115V 50/60Hz. The approximate 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: -
Operating
Voltage
Fuse Rating
115V
230V
T630mA
T315mA

Thermionic Culture Ltd, October 2019 10
6 Specification
Input Impedance
Lo
Hi
Pad
850Ω
2k2
2k2
Output Impedance
@ 0 Atten
@ -7dB
@ -15dB
250Ω
700 Ω
270 Ω
Maximum Output Level (MOL, 1% dist.)
@ most gain settings >+26dB
Frequency Response (+0.5/-1dB, Air at 0)
@ most gain settings
@ max. gain (75dB)
13Hz to 22kHz
35Hz to 17kHz
Distortion (THD @ 1kHz)
@ 40dB Gain
@ 54dB Gain
@ 68dB Gain
@ Max Gain
0.012%
0.025%
0.1%
0.2%
Crosstalk
@ most settings and frequencies Better than -60dB
Signal to Noise
@ most settings Better than 100dB
NB: The above figures are typical and may vary a little with individual
units. Each unit comes with its own test report. Specifications are subject
to change without notice. For details of how figures are measured,
please contact [email protected]
I/P & O/P Connectors 4 x XLR, wired balanced. Pin 1 GND
Pilot Lamp Bulb 12V 3W
Power Consumption 30W
NET Weight 6kg

-10
-8
-6
-4
-2
0
2
4
6
8
10
10 100 1000 10000
Gain (dB)
Frequency (Hz)
The Snow Petrel Frequency Response - Air & High Pass Filter
Air Half
Air Max
HPF 60Hz
HPF 120Hz
HPF 240Hz
HPF Flat

Thermionic Culture Ltd., Harlow, Essex, UK
Tel: [phone] email: tec[email protected]om
 Thermionic Culture Ltd, October 2019. Printed in UK.