Thermionic Culture THE PHOENIX SB Stereo valve compressor User Manual

T

HERMIONIC

C

TPHE HOENIX

valve compressor

ULTURE

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.

NOTE: When switching on from cold ensure that the STANDBY
switch is in the UP position (red light on). L eave for at least 20
seconds before switching down for normal operation. See
section 2.

©Thermionic Culture Ltd, July 2011 1

CONTENTS

Section Page
1 Introduction 3

2 Standby and metering 4
3 Controls & Operation 5

3.1 Output trim 5

3.2 Gain 5

3.3 Attack 5

3.4 Release 5

3.5 Threshold 6

3.6 Bypass 6

3.7 Link 6

3.8 Sidechain 7

4 Servicing & Maintenance 8

4.1 Valves 8

4.2 Operating voltage / Fuses 9

5 Specification 10

©Thermionic Culture, July 2011 2

1 Introduction

The Phoenix is a stereo compressor which can be used as a
pair of mono compressors. It has a ‘soft knee’ or ‘variable
mu’ characteristic in that the compression ratio increases
with the amount of compression being used. Initial
compression is 1.2:1 increasing to 5:1 at 15dB compression.

The Phoenix is being updated continually and this unit is the
‘2011/12’ version (suffix QSB) with sidechain filter and
standby switch.

The sidechain works by filtering out bass frequencies from
the compressor's detector circuit and this makes the
compression less sensitive to the low frequencies present in
the audio signal.
It is due to the nature of bass frequencies that this is a
desirable effect. Bass frequencies tend to contain a lot of the
energy present in a full band signal and large fluctuations in
the amplitude of these frequencies can tend to dominate the
performance of the compressor.
A classic example is found when using a compressor over
the mix buss. If the music contains a bass instrument that is
not in all the way through the mix, it is noticeable that the
overall volume of the other instruments in the mix can go
down when the bass instrument is introduced. This is
especially noticeable when using heavy compression.

The sidechain can also be useful on single instrument
sources, perhaps a vocal that needs to be dynamically
controlled in the mid-range frequencies for example.

Another useful effect of the control is that it is possible to
make more use of the faster attack times available on the
Phoenix. When the sidechain control is activated the
Phoenix will be responding to the higher frequencies. As
these frequencies are commonly associated with transient
responses it is now possible to speed the attack time of the
Phoenix up so that it predominantly compresses these
transients.

©Thermionic Culture Ltd, July 2011 3

2 Standby and metering

The Standby switch is provided to extend valve and
capacitor life. When the Phoenix is on 'standby' the HT
current through the valves is less than 50% of normal. The
meters, which read the current through the input valves, will
be at about half full scale. Always have the switch up (red
light on) when switching on from cold and leave for at least
20 seconds before switching down. Once switched on its
best left on all day, but switch to standby if not actually being
used. It will come back to normal operation instantly.

When warmed up and settled down off standby, the meters
should read '0' for no compression. The meters will vary a
little with mains voltage and may drop as valves age. The
zeros should be adjusted by inserting the tool provided into
the pre-sets between the meters. The meter adjustment
does not affect the performance of the compressor so having
the meters reading exactly '0' is not critical, but its best if
they are the same when compressing a stereo track. The
small screws actually on the meters are only to adjust the
needle so that it is horizontal when the unit is switched off.

©Thermionic Culture Ltd, July 2011 4

3 Controls & operation

3.1 Output Trim Control

This control is used to trim the output levels when
compressing a stereo mix. Its function occurs after the
electronics and therefore reduces the maximum output
level (MOL) and noise.

For operation at line level (+4dBV), this control is best
left at around 7. For -10dBV operation it should be set
to 2.

3.2 Gain Control

For line level and medium compression, this control
should be set, typically, to between 3 and 5.

3.3 Attack Control

The attack control varies the rate at which the
compressor starts to react. Attack rates of between
4ms (fully anti-clockwise) and 120ms (fully clockwise)
can be achieved. This control is typically set to 3 for
normal operation. Slow attack rates make the
compressor less efficient, but can be effective for
percussion.

3.4 Release Control

The release control varies the rate at which the
compressor ‘lets go’ of the input signal. Release varies
from 40ms (fully anti-clockwise) to 2.4s (fully
clockwise), typically. Faster release times can give
rise to low frequency distortion. A typical setting for
normal operation of the release control is 3.

©Thermionic Culture Ltd, July 2011 5

N.B. The compressor will become inefficient if very
slow attack and very fast release times are used.
However, this can be used to advantage if ‘thumping’
bass effects are required.

3.5 Threshold Control

The threshold control is used to adjust the amount of
compression in conjunction with the input level. With
the control in the fully clockwise position, there will be
no compression. Turning the control anti-clockwise
increases the amount of compression.

3.6 Bypass

This control totally bypasses the compressors, by
linking the inputs to the outputs.

3.7 Link

Links the two compressors for compressing a stereo
track. All controls are still in use, so both channels
should be set to around the same setting. Ideally, a
1kHz tone should be used to setup the levels so that
both channels’ inputs and outputs are equal. In
practice, this is not always necessary.

In another application, the link control can be used to
allow one compressor to control the other in a mono
application. For example, to increase the high end
compression, use the channel 1 compressor as the
signal path and feed an equalised version of the same
signal with additional top lift into channel 2. Turn off
the compression to channel 1 by turning the threshold
control fully clockwise. The opposite applies to

©Thermionic Culture Ltd, July 2011 6

channel 2. Channel 2 controls channel 1 when link is
in.

3.8 Sidechain

The sidechain filter operates only on the control
voltage part of the Phoenix, it is not in the signal path
so no audio that you will hear has passed through it.
The sidechain filters operate as high pass filters
operating at either 150Hz or 300Hz. This is denoted
by the symbols for high pass filtering on the control.
In use the filters will alter the response of the Phoenix
to bass frequencies. The compression will become
less responsive to bass frequencies either below
150Hz or 300Hz, depending on the position of the
switch.
It’s worth noting that as the Phoenix has a true stereo
link, it is possible to set the sidechain control in a
different position on each channel. The result will be
an average of the two settings when in link mode. So if
channel 1 has a sidechain control set at 150Hz and
channel 2 has a sidechain control set at 300Hz,, the
overall sidechain response will be a high pass filter at
225Hz.

©Thermionic Culture Ltd, July 2011 7

4 Servicing & Maintenance

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

4.1 Valves

It is quite safe for the user to change the valves, but

the unit must not be operated without all valves
plugged in. If a fault occurs, it may be a valve, so
unplug the mains and remove the top cover.

Looking from the front of the unit there is a row of 4
valves going from left to right and 2 smaller ones at
the back. Going from left, the 1st 2 are
input/compression, the next 2 are output. The 2 at the
back are in the side chain and almost never give any
problem. If a fault occurs on 1 channel try swapping
the 2 input valves over and if the fault (usually crackle
or level loss) changes side then you have located the
problem. If not, replace the valves where they were
and do the same with the output valves. Make sure
that the valves are put back in their original positions.

If a valve fault is located Thermionic Culture will
replace, under warranty if applicable. If an input valve
(PCC 85) is faulty, BOTH must be replaced as a
matched pair and they will be matched at our factory.
If an output valve is faulty, then the faulty one can be
replaced on its own, though it may be best to replace
both if more than 2 years old. Output valves must be
accurately matched so that the 2 halves of the valve
are equal, then soaked and re-tested. We do this with
all valves supplied.

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Input valves can be just plugged in and used with the
zeros re-adjusted. The output valves have a more
complex procedure, details of which will be supplied
with the new valve(s) if requested.

4.2 Operating voltage / Fuses

The Phoenix Valve Compressor is factory set to
operate from a 230V 50/60Hz AC mains supply It can
be set to operate from 115V AC by sliding the voltage
selector switch on the rear panel to the ‘115V’
position.

NOTE: If the mains supply voltage is reduced to 115V,
then the mains fuse MUST be increased to 1.6A in
accordance with the following table:

Operating Voltage Fuse Rating

115V T1.6A 20mm type
230V T800mA 20mm type

©Thermionic Culture Ltd, July 2011 9

5 Specification

Max. o/p level (MOL): +19dB into 600Ω
+24dB into 10kΩ

Max gain: 30dB.

THD (at no compression): better than 0.06 % @ 100Hz &

Noise, IEC weighted: better than 100dB below MOL.

Input impedance: 15kΩ.

Frequency response: <1dB variation over range of
12Hz to 56kHz.

Attack time: 0.004s to 0.12s

Release time: 0.04s to 2.4s

Output impedance: 600Ω

Distortion will increase with compression, typically 0.2% &

0.25% at 1kHz & 100Hz with 8dB compression. Attack and
release controls are somewhat interdependent, for instance
a change of attack setting may affect the release time
slightly. Therefore, no times are given on the front panel.

VALVE COMPLEMENT (2 ea):

Input/Compression: PCC85 (equiv. 9AQ8)

Output: ECC81 (equiv. 12AT7, CV4024)

Side chain detector: EB91 (equiv. 6AL5, CV4025).

1kHz

©Thermionic Culture Ltd, July 2011 10

Thermionic Culture Ltd., Harlow, Essex, UK

Tel: [phone] Fax: [phone]

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