Lecson Sfm2 User manual

INSTRUCTION
MANUAL
Lecson Systems Limited
Burrel Road St.Ives Huntingdon Cambridgeshire
England PE17 4LE Tele hone 0480 64124
TELEX 32562 Lecson G

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1. INTRODUCTION
Your Lecson SFM2 Tuner is a superbly en ineered instrument desi ned to
ive the best quality reproduction of stereophonic VHF/FM radio
pro rammes. The SFM2 has been ele antly desi ned to match the existin
Lecson ran e of Hi-fi equipment and to blend aesthetically with domestic
surroundin s. The SFM2 may be operated in conjunction with any ood
quality amplifiers and tape recorders. It has been built with hi h
quality components to ensure r e l i a b l e o p e r a t i o n u n d e r n o r m a l
c o n d i t i o n s . W e w o u l d p a r t i c u l a r l y recommend that the SFM2 Tuner be used
with the matchin ran e of Lecson Amplifiers and Loudspeakers.
Please read this Handbook carefully as it is provided so that you may
take full advanta e of the facilities of the Tuner and thus obtain the
very best performance from it. Your dealer is there to advise and help
you should any difficulties arise.
2. BEFORE SWITCHING ON
The SFM2 Tuner is fitted with a 3-core double insulated mains cable.
This cable should be wired as follows:
Brown .......................... to Live line
Blue ........................... to Neutral line
Green/Yellow ................... to Earth (Ground)
THE TUNER MUST NOT BE CONNECTED TO A TWO WIRE MAINS SYSTEM, OR THE EARTH
LEAD CUT BACK
. This wire forms an inte ral part of the SFM2 internal
circuitry and screenin ; a loud hum will therefore result if the unit is
incorrectly earthed.
When used with the AC1 pre-amplifier the two units should be wired
separately to the mains supply. They should only be linked usin the
recommended type of audio lead.
Under no circumstances should the SFM2 be opened unless the mains supply
is disconnected.
3. INTERCONNECTIONS
Facilities are provided to enable the SFM2 to be connected to a VHF/FM
aerial havin an impedance of 75 ohms (Co-axial cable) or 300 ohms
(Balanced Twin Feeder).
The audio output is via a 5 pin DIN socket which should be connected to
an audio input on an amplifier or tape recorder havin a flat frequency
response and an input impedance reater than 50 ohms. When a 'strai ht'
DIN lead (pin 1 connected to pin 1 etc.) is used, the output level can be
varied from zero to 1V by ad just me n t o f t h e pre s et vol um e co ntr o ls
adjacent to the output socket. (See fi . 1). Connection to the Lecson
AC1 is shown in the AC1 instruction manual, fi .4

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EARTH EARTH
2 2
AUDIO OUTPUT REMOTE OUTPUT
Rear view of plu
Fi ure 1
NOTE: If connection is made to the accessory socket in error, no dama e
will result but only one channel will be connected to the pre-
amplifier.
The accessory output can be used to drive a centre-zero tunin meter after
removal of an internal link connected across the socket. Please note that
once this link is removed, the tuner will not operate unless the two AFC pins
are connected externally.
Do not push in or pull out DIN plu s while the tuner is switched on.
The SFM2 is protected by a fuse located adjacent to the mains lead entry.
Replacement fuses must be of the correct type: 20mm 1 amp anti-sur e.
Mains supply (220-240V only) to the system is made throu h the 3 core lead
supplied with the SFM2. It should be connected as shown in Fi ure 2. The
SFM2 can be adjusted for operation on 110-120V at the factory if required.
Fi ure 2
5 Left Variable
3 Ri ht Outputs
Ri ht 4
Left 1
N/C 6
5 N/C
3 AFC line
7 AFC line
N/C 4
N/C 1
5 WAY 180 7 WAY
Green/Yellow
Brown
Blue

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4. CONTROL FUNCTIONS
Fi 3 shows the top face of the SFM2, and the control functions are
described below.
4.1. Indicator Lamps
.
4.1.1. Tunin Scale
. The tunin scale consists of a line array of Li ht
Emittin Diodes. Usually one of these diodes is lit to indicate
the tunin frequency selected by the tunin control. Occasionally
two diodes will be lit where the frequency selected overlaps
between two discrete steps. Naturally where only a finite number
of steps are possible, the display cannot be absolutely accurate,
but serves as a strai htforward easy-to-use indication of the
tunin frequency selected.
4.1.2. Tunin Indicator
. This LED indicates the accuracy of the settin
of the tunin control. When the station is correctly tuned, the LED
lows. If the Tuner is more than 40KHz from a station centre
frequency, the lamp will extin uish. NOTE: In 'Mute' mode this lamp
also indicates output Muted when extin uished.
4.1.3. Si nal Stren th Indicator
. The si nal stren th indicator is
composed of an array of 5 li ht emittin diodes that are pro ressively
lit up as the si nal stren th increases. When all 5 lamps are lit,
the incomin si nal stren th is in excess of 10mV.
4.1.4. De-emphasis Indicator
. This indicator is lit whenever the 25 micro-
seconds de-emphasis is selected, for instance whenever a Dolby*
encoded si nal is received. It does not in any way indicate that the
received si nal is encoded, only that the de-emphasis of this tuner
has been chan ed.
4.1.5. Stereo Indicator
. This indicator is lit whenever a stereo si nal is
received and the mono/stereo switch is set to Stereo or to Stereo
blend.
* Trademark of Dolby Laboratories Inc.

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4.2 CONTROLS
4.2.1. Power Control Switch
. This switch controls mains power to all the
circuits in the tuner when turned ON. When turned OFF it
disconnects all mains power from all tuner circuits.
4.2.2. Preset Switch
. In the normal position, this switch enables the
manual tunin control knob for selection of stations. The remainin
four positions of the switch enable the four pre-set stations. As
the switch is moved to each position it uncovers the associated
pre-set. These pre-sets can be turned to particular stations by
turnin them with a small screwdriver or trimmer.
4.2.3. Mutin Switch
. This switch enables the mutin circuit, which mutes
the tuner output for very weak si nals so that inter-station hiss
is not heard. When it is set to OFF all si nals are fed to the
output re ardless of their quality. If the switch is set to ON when
the SFM2 is tuned more than 40KHz from a station centre frequency the
output will be muted in this mode. The Tuner is muted at any time that
the 'ON Channel' LED is extin uished. Due to the narrow tunin window
for each station with Mute ON, we recommend that tunin is carried out
very slowly to avoid over shootin station centres.
4.2.4. Stereo/Mono Switch. This switch is normally set to STEREO position
which enables stereo stations to be received if they are of a suitable
si nal stren th; durin reception of MONO si nals (havin no 19KHz
Stereo Pilot Tone) the tuner automatically reverts to the mono mode.
The centre position is STEREO BLEND which reduces the noise level when
a stereo si nal is received but at the expense of some stereo
separation. The third position is MONO. When the switch is set at
MONO it is not possible to receive any pro rammes in stereo. Note that
adequate reception of stereo pro rammes requires a much lar er si nal
than that necessary for ood mono reception.
4.2.5. De-emphasis Switch. In the normal position of this switch the de-
emphasis time constant is set to that suitable for the area in which
the tuner is used. In the second position the de-emphasis is
recommended whenever Dolby* encoded si nals are received and enables
the si nal of the correct frequency content to be fed to an external
Dolby type B decoder.
4.2.6. AFC Switch. This switch, the automatic frequency control switch, is
normally set to OFF when the tune control is operated. Once the station
has been selected, settin the switch to ON activates the circuit which
automatically holds the tuner onto the selected station and
compensates for sli ht manual mis-tunin or any tendency for the tuner
to drift off the station.
4.2.7. Tunin Control . This manual tunin control is a ten-turn rotary
potentiometer which sets the tuner to receive any frequency on the VHF
band from 88 Me ahertz to 108 Me ahertz.
4.2.8. Preset Volume Controls. (Located on the rear panel). These are used to
match the audio output of the tuner to the inputs of ancillary
equipment such as amplifiers or tape recorders.
* Trademark of Dolby Laboratories Inc.

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5. TECHNICAL SPECIFICATIONS
Tunin Ran e: 88 to 108 MHz
Aerial Inputs: 72 Ohm unbalanced, 300 Ohm balanced
Sensitivity: 1.2uV for 30 dB Quietin IHF
IF Rejection: >85 dB
Capture Ratio: 1.2 dB
Frequency Response: 20Hz to 15KHz + 1 dB
T.H.D. (Mono): 0.1% (Typically)
Si nal to Noise Ratio (Mono): 70 dB
Pilot Tone Rejection: 60 dB
Stereo Separation: 40 dB at 1KHz
Audio Output: a) Up to 600mV RMS (Variable)
b) Up to 500mV RMS (Fixed)
De-emphasis: 50uS or 25uS switchable (75uS for North
America)
Pre-set Stations: 4 front panel adjustable pre-sets with
visual station indication on LED Tunin
Array
Other Facilities: Automatic Frequency Control. Blend
Facility. Switchable Mute Facility.
Si nal Stren th Level Indicator. Tunin
Indicator
Accessory Outputs: Local Oscillator Feed to DR1.
Discriminator DC Output to DR1
Overall Dimensions: 363mm wide 250mm deep 38mm hi h.