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Model SP9 MKIII
utes. The automatic muting circuitry timer is adjust-
ed for about 45 seconds. (This is because recurrent
interruption "settling" time is much less. You would
not want to wait for 5 to 10 minutes each time such
an interruption occurred.)
The Mute/Operate Switch allows manual disabling
of the SP9 MKIII outputs during any moving of the
tonearm or switching of equipment. Use of this
switch will minimize stress on your amplifier even if
it is "Off". It
is
also highly recommended that manu-
al muting be employed during the initial 45 second
warm-up period as well as during tum-off for maxi-
mum protection.
While it is true that the automatic muting will pro-
vide reasonably adequate protection against speaker
burnout during these periods. it has limitations. At
the 45 second point the automatic timer "releases"
the output, and since full subsonic stabilization has
not yet occurred, some sonic unpleasantness may oc-
cur. Although this is normally adequate protection.
utilization of the manual mute provision will com-
pletely avoid this stress to your speakers, as well as
the associated sonic unpleasantness.
Some solid-state power amplifiers have a DC offset
present at their input connections. (This, of course.
should not be.) Operation of the manual muting
switch with such an amplifier connected will result
in a "click" or "pop" in your loudspeaker (commensu-
rate in level with the amount of the offset) each time
the switch is activated. Repair or replacement of
such amplifiers is suggested.
The automatic muting operates as follows:
1. The manual mute switch al ways disables both
"Main"
outputs and overrides any automatic provi-
sions. even when the SP9 MKIII is turned off.
(The "Operate" position of the manual mute
switch is functional only when the unit is not in
the automatic mute mode.)
2. The 45 second warm-up timer will restart auto-
matically and the LED will dim if the power is
temporarily interrupted for 0.1 second or more.
Note: Power supply regulation of the SP9 MKIII is ef-
fective down to lO0VAC without serious sonic de-
gredation.
3. The automatic muting of the SP9
MKIII
is
de-
signed to be effective only against power supply
interruptions and power line failures.
It
will
not
mute against subsonic signal transmissions from
your turntable, etc. Proper Fusing of speakers ls
essential to protect against excessive audlo level
or power amplifier faults.
Shut-Down
1. Set "Mute" switch to "Mute" position.
2. Rotate "Gain" control counter-clockwise to
minimum setting.
3. Deactivate power amplifier(s).
4. Deactivate all input sources.
5.
Set SP9 MKIII Power Switch to "Off" position.
Input Impedance Adjustment
For the best sonic performance of your phono pick-
up cartridge, it should connect to the proper load im-
pedance recommended by the cartridge manufactur-
er. Your SP9 MKIII comes wired with a standard
load of 47K ohms for most high-output moving-coil,
or moving magnet cartridges. A kit of precision load
resistors is supplied with your SP9 MKIII for the
more common low-impedance load requirements of
10, 33 or 100 ohms for typical low to medium output
moving-coil cartridges. Consult your cartridge manu-
facturer or dealer to determine the optimum load im-
pedance for your needs. You may wish to connect
the load resistors at the output of your turntable,
rather than in the SP9 MKIII. especially if you may
be using more than one turntable or cartridge, with
different load requirements.
The use of precision fixed resistors provides better
load accuracy and sonic performance at lower cost
than most adjustable or switchable loads. Audio Re-
search can supply audiophile grade non-standard
load resistor and capacitor values upon request ac-
companied by $10.00 to cover order processing costs
(certified funds or money order).
Solder the desired resistors to the turret terminal
posts on the bottom of the main circuit board near
the phono inputs (see illustration). First wrap the re-
sistor leads around the posts 1/2 to 3/4 tum. Then
solder using the special alloy solder supplied with
the resistors. Connect one resistor between the left
and center posts and the other resistor between the
center and right posts.
5
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