Owner`s manual

generate a temporary DC offset while they are operated. This effect will vary
depending on the balance of the sections in the 12AU7 used in the high level
section.
Due to the nature of the MP3, expensive cables between the preamplifier and
power amplifier are less important. The cable differences you hear will be
minor compared to 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.
NOTE:
Some flashing of the DC Offset L.E.D.s is normal at high volumes.
PHONOGRAPH HOOKUP
Almost all phonograph cartridges are balanced sources. Thus the MP3 allows you
to set up your turntable as a fully-balanced source, with considerable sonic
advantage. For best results, follow the connection scheme outlined below:
1) Use a cable that has two signal conductors PLUS a shield for each channel.
The two conductors are for the plus and minus outputs of the cartridge, and the
shield connection becomes the tone arm/turntable ground connection and is
common to BOTH channels.
2) Pin number one of any XLR connection should always be ground as per industry
standard.
3) Pin two of the XLR phono input corresponds to the "+" or non-inverting
output of the cartridge, and pin three is the "" or inverting output of the
cartridge. Absolute system phase can be corrected from the front panel.
4) There is no need for an independent ground wire from the arm to the preamp.
If you set up the cable correctly, there will be little or no hum. Many tone arms use
a five pin connector that plugs into the bottom of the arm. If this is the case in
your system, you may order a tone arm cable with the right connections from almost any
cable manufacturer. If your arm has RCA connectors at the output, an adapter cable can
be made that will work. The shield connection of the RCA must become the connection to
pin 3 of the XLR connector, and the tone arm ground connection should be made as
described above. ON NO ACCOUNT should you allow the shield connection of the RCA to
become the shield for the cable, as this may result in a loud hum.
Cartridge loading is achieved by installing resistors on the loading terminal on the
rear panel. A screwdriver is all that is needed for attachment. You will have to
experiment to obtain the correct value.
Avoid using NOS 12AT7s in the MP3. Generally, and despite claims to the contrary, most
such tubes are too noisy for proper operation in the MP3! Please purchase new 12AT7s
from your dealer or Atma-Sphere Music Systems, Inc.. Most 12AT7s tend to get noisy
after about 3 thousand hours so if you leave the preamp on 24 hours a day the phono
tubes should be replaced every 34 months. They will last longer if the preamp is
turned off when not in use. In any event, be VERY suspicious of any NOS 12AT7s. Most
of them are unacceptable.
For very low output cartridges you may wish to have the step-up transformer option
installed. Contact your dealer for details.