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SQN-3M Series 4000 User's Handbook
CONTENTS
INTRODUCTION MONITOR HEADPHONES
LINE INPUTS OUTPUT CONNECTIONS
LEVEL METER OUTPUTS
LIMITER POWERING
LINE-UP TONE PRE-FADE LISTENING
MASTER GAIN SLATE MIC
MICROPHONES SERVICE
MONITOR RETURN INPUT HISTORY
1. INTRODUCTION All of the information necessary for a recording engineer to operate the SQN-3 Miniature Mixer is permanently displayed on its baseplate and cannot be lost. In seeking to amplify certain points in this manual we apologise in advance to those whose training or experience has rendered such explanations superfluous, but they often stem from enquiries the manufacturers have received. Notable features of the SQN 3M are:
The SQN-3 achieves an extremely low noise performance which equals or surpasses the standards commonly achieved by studio desks. This large signal-to-noise ratio enables the SQN-3 to be used in any situation and with digital recorders and the highest quality of microphone without any fear that the mixer could restrict the overall results obtainable.
2. POWERING
3. MICROPHONES The three identical microphone inputs are wired to conform with the IEC standard (pin 1 earth, pin 2 in phase and +ve for T powering). The SQN-3 is designed to accommodate all professional microphones, and assumes a source impedance in the range 150-600 Ohms. It is outside the scope of this manual to describe in any detail the various types of microphone which may be employed, but the type will determine the setting of the front panel Attenuator switches and the Mic. Power Selector switches set into the baseplate of the SQN-3. While the SQN-3 has sufficient current capacity to supply any make of condenser microphone, the use of microphones which have a particularly large current drain with battery-powered equipment will need careful consideration. Some marked improvement in performance or special tonal characteristic should be required as compensation for the reduced battery life. The primary purpose of the Mic. Attenuators is to provide a rough level match between the input signals of microphones of differing sensitivities, so as to allow comfortable handling of the gain controls. In the SQN-3, incidentally, this is not achieved by the usual method of introducing resistor pads into the circuit, which will produce as much noise from a costly capacitor microphone as from a dynamic type, but by altering the gain of the input amplifier. It is of course, a dangerous practice to rely on attenuators (or gain controls) to achieve a signal reduction when using sensitive condenser microphones in proximity to loud noises, such as motor sports or pop music, since such signals may well overload the microphone's own first stage. In those conditions the ambient noise level can even prevent such a disaster being detected on your headphones. Dynamic microphones may be found more suitable in these situations. Rotary faders had to be selected for the SQN-3 because of their proven sealed construction, but the specially designed control knobs incorporate some advantages of the slider in that they can be pushed from the side and their position is unequivocally seen and felt. The knobs cannot be gripped, and turning over a considerable arc is achieved with the tip of the finger resting on the point of the arrow design. A bass cut switch for each mic. channel is situated next to its gain control allowing for attenuation of the signal by 4dB with a 6dB per octave slope or 10dB with a 12dB per octave slope at 100Hz. These are employed for a variety of purposes, such as the reduction of 'boominess' in hard or 'live' acoustic locations or from male voices, as well as reducing extraneous traffic rumble, hum related to the frequency of the supply of electrical appliances and so on. Perhaps the most common use for bass cuts is to assist in the reduction of wind noise outdoors, but a suitable windgag on the microphone is also essential.
4. LINE INPUTS The fourth XLR-3 connector on the left hand side of the SQN-3 Series 4000 allows the connection of a balanced input over the range of -10dB to +20dB sensitivity. The input level is controlled by a small knob so labelled above the Cannon sockets. On a small microphone mixer like the SQN-3 the source for such a signal may be expected to be at a fixed level, such as the output from a radio mic. receiver or a public address system; hence this control is treated more as a pre-set. When this channel is unused set the control to zero to avoid the possibility of unwanted noise being generated. Each MIC channel also has a slide switch on the baseplate which will add -50dB attenuation before the Mic input allowing the Mic channels also to be used for Line level signals, with the added refinement that the Attenuator and Bass Cut controls can still be employed if needed. Note that it is necessary to set the MIC POWERING to DYNAMIC when using the channels as line inputs.
5. MONITOR RETURN INPUT The SQN-3 Series 4000 mixer features an Auxiliary amplifier for a balanced input (Pins B2 (earth), B4 (live) and B5 (return)) over the range -19dB to +11dB chiefly used for monitoring. The input level is set by adjusting the screwdriver-operated potentiometer recessed in the XLR-3 connector block and in the absence of instruments can generally be set with sufficient accuracy by ear when operating the Phones Mixer / Aux switch situated below the Master fader to and fro. This feature allows Before / After comparisons of off-tape signals, or, when used with a recorder which lacks off-tape monitoring , it can be used as a check that the mixer output is at least reaching the recorder input. Many E.N.G. recorders feature an Earphone Monitor output on a 3.5mm jack intended for the cameraman's use, often with warning of tape end or other problems, and because it is fed from the recording head the practice has grown of using it for audio monitoring (confidence) even though this signal is usually degraded by time-code and noise reduction encoding and is an unbalanced signal of 8 Ohm impedance and very low level (typically -16dB). This may be connected to Pins B4 and B5 (without earthing). Interface leads are available from SQN which carry the audio feeds and monitoring return in a single flexible cable (6mm diameter in coiled or straight versions). Please refer to the manufacturer's current list. The Phones Mixer / Aux switch only affects the headphone signal and has no effect on the SQN-3 output or metering. If the Auxiliary Input is not being used, the more common 3-pin DIN connector may be used to take an output from Socket B.
6. MASTER GAIN CONTROL The Master fader not only allows the whole programme mix to be faded in or out but permits its level to be increased by up to to 3dB from the nominal setting.
7. LEVEL METER The level meter is of fast
response peak reading design with a log calibrated linear scale,
and uses full wave rectification.
8. LIMITER The Limiter is of original design and may confidently be employed at all times, since it gives rise to none of the undesirable audible effects, such as clicks and other extraneous noises often associated with such devices. Coming into operation just below peak level, it accommodates overloads of +18dB with an attack time of half a millisecond (100ms release time). A red LED below the meter lights when the Limiter is functioning. It should only flash on in the event of unexpected peaks and if it remains lit for most of the time, too high a level has been set; when 'riding' the Limiter in this way it would be too much to expect that its functioning will pass unnoticed as described above.
9. MONITOR HEADPHONES The SQN-3 is fitted with a 6.25mm stereo headphone jack able to accommodate Gauge A or B connectors, but unless specially ordered is supplied wired for a mono plug. Headphones with impedance in the range between 50 Ohms and 1k
Ohm may be employed. Those of lower impedance may not provide
sufficient volume. 10. SLATE MIC The mixer now incorporates a slate or announcement mic with an automatic gain control. The microphone is placed behind the front panel between the TONE / MIC switch and the CH2 Fader. It is activated 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 is automatically returned to internal while the slate mic is active. This is so that the recordist will not be troubled by having to speak over a possibly delayed off-tape monitoring of his voice. 11. PRE FADE LISTENING A third sprung right hand position on the MXR / AUX switch allows Pre Fade Listening to Channel 3.
12. OUTPUTS The output amplifier of the SQN-3 has a clipping level of +18dB into 600 Ohm loads and over 20dB where the load impedance is higher which will usually be the case. This means that overload distortion is virtually impossible so far as the mixer is concerned. However the recordist must ascertain the relevant clipping level of the recording amplifiers into which the mixer output is fed and the relevant parameters for recording tape being used to know where he stands. If in doubt, use the Limiter. Series 4000 SQN-3 mixers offer three different outputs, all of which can be used simultaneously:-
13. LINE-UP TONE Pressing the TONE / MIC switch
on the front panel to the left (where it will latch) generates a 1.
1kHz tone for lining up external equipment at -8dB (=PPM 4) in
accordance with standard practice in British broadcasting. In other
territories or to special order this level may be pre-set
differently (internal adjustment - see Service Data manual).
14. OUTPUT CONNECTIONS With balanced and unbalanced outputs at line and mic. levels, there is scarcely any device which cannot be fed from your SQN-3. Possible modes of connection are as many and various as the types of equipment that require a feed. The manufacturers produce many types of standard interface ex-stock and can supply special looms to user's requirements.
15. SERVICE The SQN-3M is guaranteed to be free from defects in workmanship and materials for a period of 24 months following delivery from the factory (increased from 12 months in April 2002). If any problem should be encountered during or after this warranty period, the owner is urged to return the mixer to the factory where it will receive prompt attention. This small instrument contains hundreds of components, the majority of which are on just two multi-layer PCBs. The scope for costly damage in the hands of the inexpert is therefore quite considerable, and if incorrect parts are substituted it is unlikely that the original specification will be maintained.
16. HISTORY The SQN-3 was conceived as a 4-channel mono mixer for Kudelski's Nagra SNN tape recorder by the design team which produced the original SQN-1 Control Unit for the SN in 1973. The SQN-3 intended for SN use was designated Type C (for Control Unit) and first appeared in June 1980. At the same time a mixer without SN controls - the Type M - was released for users of 1/4 inch Nagras and other recorders, since no portable mixer with the facilities and performance of the SQN-3 had previously been available. These models had a serial number commencing 1000 (SERIES 1000) and the SQN-3C continued unchanged until it was discontinued in September 1988. In September 1981 the SQN-3 Type M was considerably modified to meet the growing needs of broadcast video users. This model (known as the SERIES 2000) with Serial Numbers commencing 2000 or 20000 remained in continuous production for exactly ten years with only small modifications in the light of continuing development. The SERIES 3000 with Serial Numbers from 31000 was introduced in September 1991 and differed from the Series 2000 only in that the side connector panel was re-modelled to provide for a Cannon XLR-3 male output, with an unbalanced output available from a 3.5mm jack socket and the same 4-way Hirose powering / charging socket as our other mixers. At the same time the output mic / line level switch was moved to the baseplate and provision was made for Channel 3 to be switched to accept line inputs in situations where two had to be accommodated. The SERIES 3000 (version II) with Serial Numbers from 34000 was
introduced in January 2001. The internal electronics of this
version were totally revised with the addition of extra functions
while the mechanical construction remained the same and only the
front panel appeared different. The limiter circuit was changed to
be similar to that used in the current stereo SQN mixers. The
meters were illuminated by light emitting diodes, giving a brighter
light than the original glow tubes.
The SERIES 4000 (version III) with Serial Numbers from 35000 was introduced in June 2002. The modifications are:
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