Owner`s manual

MUSIC PREAMPLIFIER SETUP AND OPERATION
Unpack the preamplifier and its power supply carefully. Save the shipping container for future shipment
(replacements are $75.00). 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.
Normally the tubes are installed; the types are marked on the boards.
During operation, the MP-1 gets warm. Adequate ventilation is mandatory. If the preamplifier is to be placed in a
shelf or rack mount system, allow for at least 12 inches of open space between the power supply and head unit
to avoid overheating and 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- The lowest numbers marked on the pins of the connector should
be aligned at the top of the connector when inserted. 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.
To maximize performance the MP-1 does not use a muting circuit! Allow the preamplifier to warm up and
stabilize before energizing your power amplifiers. Muting circuits interfere with sound quality and the servo
circuits in the line stage section. Although the DC offsets generated during warmup are low level, this may be a
problem for some amplifiers and speakers.
WARNING! DO NOT TURN ON THE AMPLIFIERS IN YOUR SYSTEM UNTIL THE PREAMPLIFIER
IS STABILIZED. DAMAGE TO SPEAKERS, AMPLIFIERS OR BOTH MAY RESULT!
It takes about 30 seconds from turn on before the preamp is ready for use. During the warmup, 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 (usually a bad 6SN7 tube) which should be corrected to prevent possible damage to
associated equipment. The preamplifier will sound significantly better after about 45 minutes of operation.
OPERATING NOTES
The MP-1 takes about 1 or 2 hours to sound its best although it is quite musical after only 15 minutes. There is
no need to run the unit 24 hours a day, but if you do, test the tubes once every four months. Allow for a few
weeks of normal operation to break in the unit; subtle but lucid improvements will be noticed.
The MP-1 supports the use of a low impedance (600 ohm) load at the input of the power amplifier (although it is
by no means required). Such practice can reduce hum and buzz but more importantly eliminate artifact from the
interconnect cables. An optional terminator is available from ATMA-SPHERE for amplifiers without this provision.
Adjust the GAIN TRIM for proper channel balance. Some minor adjustment is sometimes required as the MP-1 is
a zero feedback design. Operate the control SLOWLY. The GAIN TRIM controls are not in the audio path. They
generate a minor and temporary DC offset while they are operated. This effect will vary depending on the
balance of the sections in the 6SN7 used in the line stage section. If possible, keep the controls turned up all the
way and lower the gain of the louder channel. This practice yields the best sound.