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-3 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 cables for the various components to be used with the preamplifier.
For superior sonic performance, the MP-3 does not use a muting circuit. Although the DC offsets generated
during warmup are low level, they could be a problem for some amplifiers and speakers. Allow the preamplifier
to warm up and stabilize before energizing your power amplifiers. A muting circuit would interfere with the servo
loop operation in the output section of the preamp. When not in use, its presence would have an audible artifact
as well.
WARNING! DO NOT TURN ON THE AMPLIFIERS IN YOUR SYSTEM UNTIL THE PREAMPLIFIER
IS STABILIZED. DAMAGE TO SPEAKERS, AMPLIFIERS OR BOTH MAY RESULT!
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.
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-3 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-3 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.
The GAIN TRIM is provided to adjust for proper left-right balance effect and to allow for range on the volume
control. The MP-3 is a zero feedback design so tube condition can cause a gain difference between left and right
channels. Adjust the GAIN TRIM for proper channel balance. 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.