SQN-4S IVe User's Handbook
3. EXTERNAL POWER FEED. When the mixer is being powered from an external
supply, that supply is also made available at the 4-WAY connector [PT] on the main
connector panel. This is intended to supply power to other devices with which the
mixer may be working. This power feed is short-circuit protected by self resetting
thermal fuses and is switched on by the mixer’s power switch in either the [BAT] or
[EXT] position. Many users of these mixers prefer to power them and several extra
pieces of equipment from an NP-1 camera battery, the whole being kept together in a
special carrying bag. An extremely long endurance can be expected from the NP-1 but
it is necessary to be careful that the battery is not allowed to discharge below the
manufacturer’s recommended minimum of 10V (use the [BATT] test); the mixer will
continue to work but the battery will have its life reduced.
3. OUTPUTS The mixer is provided with two balanced line driver amplifiers of substantial capacity.
The output transformers of these amplifiers also carry windings providing isolated, nominally
‘Mic Level’ outputs. Additionally, unbalanced feeds of the two main outputs and the ‘Post Fader’
outputs of all input channels are available at a nominal line level of -10dBu with 200 Ohm source
resistance. All of these signals are made available on the connectors at the end of the mixer. The
connection lists for the multi-way connectors are given in sections 17 and 18, reproduced from the
mixer base label.
The connections for the two XLR-3M connectors are to the usual convention :
1 GND, 2 LIVE, 3 RETURN.
Two switches on the base of the mixer allow the feed to the [MAIN] connector [A] or the XLR
connectors to be taken from the Line Level or Mic. Level outputs .
4. LINE-UP TONE A calibration Tone of 1kHz with distortion below 0.1% may be injected into both
output channels by setting the 3-way front panel [TONE/MIC] switch to the left. The form that the
tone takes depends on the setting of the [GANG 1-2] switch. When this switch is in the unganged [0]
position the tone is continuous in both channels. Either of the other two positions gives an EBU
coded tone signal (the left channel interrupted for 250ms every 3s) to indicate that the recording
which follows is true stereophony. The tone mutes and replaces the main audio. The calibration level
for a given meter reading is indicated on the baseplate of the mixer and, unless specially requested, it
will be at the Nominal Line Level (see the next section).
5. CALIBRATION OF THE RECORDER The recorders that are used with the SQN-4S are almost
invariably fitted with some form of input gain control. In these circumstances the absolute calibration
levels of both the mixer and the recorder become irrelevant: what must be considered are the relative
calibration points Nominal Line Level (0VU) and Nominal Peak Level on the meters of both
instruments and how they are to be related.
The basic calibration used at SQN is to place the Nominal Line Level at PPM4, ‘TEST’ or 0VU and
then to treat the Nominal Peak Level as being 8dB above this, in the case of the PPM or VU meter or
6dB above in the case of the Nordic type of meter. The limiter is then set to come into operation on a
steady tone at 1dB below the Nominal Peak Level. This ensures that the mixer output will not exceed
the Nominal Peak Level when measured using a Peak Programme Meter. The Line-Up tone is then
usually set to the Nominal Line Level. In any case, the calibration points, including the limiter setting
are shown on the individual mixer baseplate.
When interfacing to an analogue recorder with its typical slow overload characteristic, what is
required is to place the mixer’s Nominal Peak Level at the correct point which will ensure that the
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