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Spec. Handbook

SQN Electronics Ltd

SQN-3M Miniature 4:1 ENG Audio Mixer
The original broadcast quality mono portable mixer for TV, film and radio locations
3M View
Click on picture for closeup
Starting with serial number 34000, the circuitry was revised using elements from our SQN-4S to make the SQN-3M Series 3000vII.

The important facilities added were

  • New Limiter Circuit with increased transparency
  • Slate or announcement mic
  • Pre-Fade listening to Channel 3
Starting with serial number 35000, the layout was revised to bring the CHANNEL ATTENUATORS onto the front panel and the Mic Power Selectors and Mic/Line attenuators were changed from rotary to slide switches. 12V Phantom powering was dropped. This is the SQN-3M Series 4000.
The SQN-3 Type M four input miniature audio mixer was designed to provide all the basic functions found necessary in using professional microphones for location recording. Since its introduction in 1980 it has been adopted as the industry standard for mono work in most European countries and further afield and has established a solid reputation for quality, reliability and longevity.
3M Baseplate

Click on picture for closeup
It remains the smallest truly professional mixer today offering comprehensive microphone powering, peak metering, a peak limiter and off tape monitoring.

Battery Compartment
Powered by 6 AA size internal alkaline cells, the SQN-3 Type M commonly functions for a week or two in professional use without reloading. Its unique sophisticated power supply delivers 48V phantom power until the battery dies, and the quick change battery compartment permits reloading in a few seconds. Provision is also made for accepting an unusually wide range (5V to 18V dc) of external supplies of either polarity without adjustment and with good efficiency.

Features and Specification - SQN-3 Type M Series 4000

Three identical channels using industry standard XLR-3 type female connectors. Each channel is individually switchable for:
  1. Powering:
    • a) 12V T [DIN A-B]
    • b) dynamic or self-powered microphones
            (150-600 Ohms)
    • c) 48V phantom
  2. Input attenuation:
    • 0dB, -10dB, or -20dB
  3. Bass Cut:
    • Flat, -6dB or -12dB at 50Hz
  4. Line Attenuation:
    • Adds -50dB before the mic preamp

Mic. Input

-70dBu for 0dB (peak level) on the meter with the channel gain at maximum and the Master Gain at 0dB.
Max Level
-20dBu (0dBu with 20dB attenuation).
Mic. Polarity
The unit is normally shipped wired to IEC standards, i.e. pin 2 in phase and positive T powering.
Noise Figure
-129dBu (A weighted) with 200 Ohm source resistance.

30Hz to 20kHz +0,-1dB
Line Input 1
Dedicated balanced input by way of fourth XLR-3 female connector with side panel fader control.
Line Inputs
2, 3, & 4

The mic channels 1, 2 & 3 may also be switched from mic. to line input mode, retaining their effective input attenuator and Bass Cut controls.
Aux. Monitor Input
Balanced input carried on same 5-way D.I.N. connector as line output.
Aux. Input Level
Minimum level -19dB; maximum level +11dB.
Microphone Faders
Recessed front panel rotary controls. Knobs contoured for ease of adjustment allowing fader position to be judged by touch or viewed from a distance.
Master Fader
Front panel rotary control governing all 4 inputs and allowing the level of mix to be adjusted from zero to +3dB (detent at 0dB).
Level Meter
Fast response peak reading meter with a log calibrated linear scale; full wave rectification. Nordic Norm and VU versions are available to special order. The meter scale is permanently illuminated by light emitting diodes for low light applications.
Switchable; operates on the metered output to give approx. 20:1 compression ratio over an 18dB range. Attack time 0.5ms. Release time 100ms.
Line Up Tone
1.1kHz tone operated by a front panel TONE / MIC switch. The output level is internally adjustable and is usually set 8dB below peak level.
Line Output 1
Balanced, floating source with a clipping level of + 18dBu, or +20.5dBu into 10k Ohms. The output level is preset so that 0dB (peak level) on the meter corresponds to +8dBu. Distortion at +15dBu is less than 0.1% over the range of 30Hz to 20kHz. The output connector is a standard XLR-3 male type and the output impedance is 160 Ohms.
Line Output 2
Derived from Line Output 1, a second balanced line output is available from a 5-way D.I.N. locking connector which may be switched to Mic. level (-50dBu) by a toggle switch set into the mixer baseplate. Monitoring return on this socket facilitates single cable connection to recorder.
3.5mm Jack
Unbalanced output at -40 dBu allows connection of ancillary equipment such as transcription recorder.
Output Monitoring
The phones output level is adjustable from zero to 1.5V by a control on the side panel. The connector is a 6.3mm stereo jack, normally wired with tip and ring joined, accepting Gauge A or B connectors.
Monitoring Switches
Monitoring is selected by the MXR / AUX switch on the front panel. Choices are:
  • Mixer Output
  • Aux. Monitor Input
  • Pre Fader signal from CH3 input amplifier

Pre-Fade Listening
Pre-Fade listening is available on CH3. The output of the CH3 Mic. amplifier may be monitored in the headphones even when the fader is closed. This is selected by a third, biased position on the MXR / AUX switch.
Slate Mic
The mixer now incorporates a slate or announcement mic with automatic gain control. The mic is placed behind the front panel between the TONE / MIC switch and the CH2 Fader. It is selected by pressing the TONE / MIC switch to the right. The mic output replaces the main audio. The switch is biased to return to the off position when released. If the monitoring is switched to external, it automatically returns to internal while the slate mic is active.
Six AA (UM-3) size cells housed in a quick change compartment. The acceptable range of battery voltages is 5V dc to 18V dc allowing the use of Nickel-Cadmium rechargeable cells, Alkaline-Manganese cells or even Lithium cells. Access is provided to the battery terminals for recharging. A fresh set of Alkaline-Manganese cells will power the unit for more than 12 hours when using dynamic microphones.
External Power
A supply in the range 5V dc to 18V dc may be used. The maximum consumption will be 1.5W and quiescent consumption, without microphones, 700mW. The power input terminals float with respect to the SQN-3 ground so that external supplies of either polarity may be used. Alternatively, a power supply which does not share a ground with the SQN-3 may be used e.g. a camera battery.
Battery Test
The meter is fitted with a suppressed-zero scale, brought into operation by a front panel push button, which indicates the battery voltage directly.
Case Size
210mm x 120mm x 44mm.
The outer case of the mixer is made of aluminium. The end blocks holding the connectors are milled from solid aluminium bar.

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 polymer 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 damage.

1.37kg. (1.51kg with batteries).
Temperature Range
The working temperature range is -40ºC to +70ºC.

The SQN-3M mixer offers the professional recordist:
  • Unsurpassed sound quality
  • Industry standard acceptability
  • User friendly ergonomic layout
  • Tried and tested electronic design
  • Superior mechanical engineering
  • Lowest running costs
  • Highest resale value
  • Long trouble-free service
  • The utmost in portability
  • Efficient factory back-up service
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©1999 & 2002 SQN Electronics Ltd