This model has now been superseded by the Series IVe
This model has now been superseded by the SQN-5S
SQN Electronics Ltd
SQN-4S Miniature 4:2 Sound Mixer
The original broadcast quality stereo portable mixer for
TV, film and radio locations
The SQN-4S has been the unrivalled Industry standard portable audio mixer since it was the first to arrive on the scene back in 1984.
The new SERIES IV is the culmination of an extensive development
programme to ensure that the SQN-4S remains at the forefront of
location sound technology. Extending the control panel to include
all the required functions on one face of the mixer has made it
even easier to use than before.
Newly designed tranformerless input amplifiers, larger output
transformers for low distortion bass, virtually unbreakable
analogue level meters, pre-fade listening, slating microphone,
logic processing of many switching functions leading to a minimal
length audio path, optional feed for four output channels and
improved filtering and screening have all contributed to making
it a welcome successor to its illustrious forbears.
The essential information for connecting to and operating the
mixer is permanently printed on the baseplate.
Features and Specification - SQN-4S Series
Four transformerless balanced inputs using XLR-3 type female
connectors. Channels one and two also share an XLR-5 type
connector. Each channel is switchable for:
-78dBu for nominal line level (PPM4, 0VU) with the channel gain
at maximum and the master gain at 0dB
Max Level, Mic Inputs
-20dBu (+4dBu with 24dB attenuation)
-130dBu (A weighted) from a 200 Ohm source.
20Hz to 20kHz +0, -1dB, referred to 1kHz.
Isolation, channel to unrelated channel: 75dB at 1kHz, 60dB at
The mixer is intended to work in several modes. The mode controls
affect channel pairs CH1 & 2 and CH3 & 4. Within the
pairs, channels 1 & 3 are called "first channels" and 2 &
4 "second channels".
The second channel of each pair can have its phase inverted by
means of a front panel switch. This has the incidental effect of
interchanging left and right in an MS encoded signal.
Monitor Return Input
Unbalanced inputs with a range of sensitivity from -20dBu to
+20dBu for loudness parity with the internal monitoring. The
sensitivity is adjusted by a screwdriver preset on the base.
Mixing Bus Inputs
Two inputs directly into the summing amplifiers with their gain
adjustable inside the mixer. Maximum sensitivity is 0dBu for
+8dBu at the balanced outputs with the master gain set at 0.
Two line driver amplifiers provide the output channels and each
output is available on both an individual XLR and a combined
The level at either set of connectors can be attenuated by 50dB
to provide a nominally microphone level feed.
Floating sources (transformer coupled) with a clipping level of
+20dBm into 600 Ohms. Distortion at the nominal peak level of
+8dBm is less than 0.01% with a 600 Ohm load 20Hz to 20kHz. The
output resistance is switchable from 60 Ohms to 180 Ohms. At 180
Ohms, with the limiter switched on, the mixer can be worked into
an arbitrarily low impedance load with acceptable distortion. The
balanced Mic-Level send is derived from a separate winding on the
output transformer and has an essentially resistive source
impedance of 200 Ohms.
A subsidiary connector carries separately buffered outputs at
10dB below the level of the main line drivers.
CH3 & CH4
Buffered outputs at 10dB below the level of the main line
drivers. Channels three and four may also be switched out of the
mixing bus so that they can be recorded separately.
Twin peak reading, logarithmic level meters with Peak Programme
Meter (PPM) dynamics. Scaling may be
BBC PPM, Nordic Norm, or SMPTE.
VU meters can also be provided. The meters are normally calibrated with the mixer driving a bridging load of 10k Ohms. Meter illumination is by permanently lit glow tubes which consume no electrical power.
Line Output Level
The nominal line level is normally set at 0dBu for PPM metered
mixers and +4dBu for VU metered mixers. Peak level, which is used
as a reference for the limiters, is considered to be 8dB above
this setting. Other calibration levels are readily available to
Switchable [O]ff [M]ono [S]tereo (ganged). Approximately 40:1
compression over a 17dB range. Attack time constant 0.5ms,
release time 100ms. The limiter threshold is set 1dB below the
nominal peak level. An LED indicator for each output channel
shows when the limiter is attenuating the signal.
A tone at 1.05kHz which is injected into both channels upon
operating a front panel switch. Two modes are available, [M]ono
in which the tone is injected at a fixed level into both outputs
and [S]tereo in which the left hand channel tone is interrupted
for 250ms every 3s. The tone displaces the normal channel
Headphone amplifiers with adjustable gain capable of driving most
headphone types to a suitable level. The use of headphones with a
resistance of between 200 Ohms and 600 Ohms per side will make
best use of battery power. The gain control is on the connector
side panel. Please note that with some sets of headphones it will
be possible to produce sound levels capable of damaging the
hearing if the phones gain is set too high. Pre-Fade listening to
each of the input channels is possible as is MS matrixing of the
two output channels so that an MS recording may be monitored in
the equivalent AB stereo.
Monitoring Mode Selector
The monitoring mode rotary selector switch on the front panel
[PHONES] has the following functions.
Monitoring Source Selector
A front panel toggle switch selects the monitoring source as
either internal [MXR] or external [AUX]
A microphone mounted behind the front panel at the right hand end
of the mixer is brought into operation by pressing a button on
the side panel. The output of the microphone is levelled by a 2:1
compressor and overrides the main audio, appearing on the mixer
outputs and in the monitoring system. While the microphone is
active, the monitoring mode automatically reverts to the internal
or [MXR] setting.
Eight AA size cells housed in a quick-change compartment. The
acceptable range of voltages is 6 to 24 Vdc allowing the use of
most cell technologies. Battery life with alkaline cells will be
10 hours when using unpowered microphones.
The right channel meter is fitted with a suppressed-zero scale,
brought into operation by a front panel push button, which
indicates the battery voltage directly.
A supply in the range 6 to 24 Vdc may be used. The maximum
consumption will be 2.5W and quiescent consumption, without
microphones, 1.6W. The input terminals float with respect to
ground. Either (or neither) side may be grounded at will, thereby
allowing the use of floating supplies or grounded supplies of
either polarity. There will be no possibility of hum-loops being
The mixer carries two four-way connectors, one of which [DC]
gives access to the internal batteries for charging and also
serves to connect to an external power source. The second
connector [PT] is an output which provides a switched, short
circuit proof connection to the power supplied to [DC]. This
allows the mixer to be used as the focal point for a system of
interconnected devices, all controlled from the mixer’s
The mixer is designed to work over the temperature range of -20
to +60 °C.
The dimensions of the mixer case are: Height 47mm, Width 297mm,
The outer case of the mixer is made of aluminium. The end blocks
holding the connectors and the panpots are milled from solid
aluminium bar. Inside the mixer is an inner compartment of steel,
tin-plated after forming, which contains all of the circuitry
that might be sensitive to radio frequency interference. The top
and bottom of this compartment are sealed by copper screens and
rf gasket material and all inputs to and outputs from this
compartment are filtered. The circuitry is constructed on
multi-layer printed circuit boards with internal ground and power
planes which ensure the integrity of the internal grounding
All control knobs are special to SQN and are turned and milled from solid aluminium bar. The internal battery compartment is milled and bored from a solid block of polyacetal engineering plastics material and the moving parts are aluminium and stainless steel.
All labels and legends on the mixer are permanent. On the end blocks they are engraved; on the front panel they are printed into the hard-anodised surface; on the baseplate they are reverse printed on a polycarbonate label.
The mechanical construction is a development of a system which
has proven in the past to be resistant to mechanical
The weight of the mixer without batteries is 2.2kg
The SQN-4S series IV mixer offers the professional
©1998 SQN Electronics Ltd