Owner`s manual

MUSIC PREAMPLIFIER SET-UP AND OPERATION
Unpack the preamplifier and its power supply carefully and save the packaging containers for future shipment if required. Warranty may be void if the unit is
shipped in a different container. If you do not have a container, contact ATMA-SPHERE® MUSIC SYSTEMS for a replacement. The replacement container is
$30.00.
Place the tubes in the appropriate sockets as shown in the tube chart elsewhere in this manual. There is no tube in the power supply.
During operation, the MP-1 gets hot! Adequate ventilation is mandatory. If the preamplifier is to be placed in a shelf or rack mount system, allow for at least 2
inches of open space above the power supply and head unit. Make sure that the preamplifier is at least a foot away from the power supply, to avoid hum
problems.
After the preamplifier and supply are properly positioned, make sure that the main power switch is in the OFF position. Connect the umbilical cable from the
power supply to the head unit. The connector operates by lining up the correct key channels and then pushing on it gently while turning the knurled threaded
locking ring. It is keyed so that insertion is possible only one way. You may now plug in the power supply. The "POWER AVAILABLE" LED should now light.
Connect the cables for the various components to be used with the preamplifier.
The MP-1 does not use a muting circuit! Allow the preamplifier to warm up and stabilize before energizing your power amplifiers. A muting circuit is
not used as it would interfere with the servo-loop operation in the output section of the preamp. Its presence in the circuit would be audible as well. Although
the DC offsets generated during warmup are low level, this may be a problem for some amplifiers and speakers.
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WARNING! DO NOT TURN ON THE AMPLIFIERS IN YOUR SYSTEM UNTIL THE PREAMPLIFIER IS WARMED UP AND STABILIZED! DAMAGE TO
SPEAKERS, AMPLIFIERS OR BOTH MAY RESULT!
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Get in the habit of turning down the volume or switching to an unused input anytime you turn your amplifier on, when you change a record, etc.
After the preamplifier is turned on, it takes about 30 seconds before it is ready for use. During the warmup of the preamplifier, one or both of the "DC
OFFSET" LEDs on the front panel may light up. This indicates that the servo circuit has detected a DC voltage at the output of the preamp and is trying to
correct it. If the indicator stays lit for more than a minute, a fault is indicated and the preamplifier must be turned off immediately to prevent
damage to associated equipment. The preamplifier will sound significantly better after about 45 minutes of operation.
OPERATING NOTES
Normally the preamplifier can be left on all the time. Adequate ventilation is required in any event. If the unit is operated continuously, have the tubes tested
once every six months. The unit will sound substantially better three hours after turn-on.
It takes time to break in the internal wiring of the MP-1. Therefore it will sound better with use. This is true of all inputs. Thus if an unused input is put to use,
expect it to require a break-in period, even if the preamp has been in use for a long time.
The MP-1 may be used with a low impedance (600 ohm) load at the input of the power amplifier. Such practice can reduce hum and buzz. An optional
terminator is available from Atma-Sphere for amplifiers without this provision.
Invariably you will have to adjust the GAIN TRIM for proper soundstage effect, because the MP-1 is a zero feedback design. Operate the control SLOWLY.
The GAIN TRIM controls are not in the audio path. They may generate a temporary DC offset while they are operated. This effect will vary depending on the
balance of the sections in the 6SN7 used in the high level section.
Due to the low impedance operation of the MP-1, cable quality between the preamplifier and power amplifier is usually unimportant. You may hear
differences in the cables, but they will be minor compared to the differences you may be used to hearing in single-ended cables. Thus we have no
recommendation for cables to be used between the preamplifier and power amplifier. On the other hand, the input cables may be very critical, depending on
the source.
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