Owner`s manual

OPERATING NOTES (continued)
Due to the low impedance operation of the MP-1, cable quality between the preamplifier and power amplifier is
considerably less important. 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. Atma-Sphere offers a variety of interconnect cables for this purpose. Contact your
dealer or Atma-Sphere for details.
PHONOGRAPH HOOKUP
All phonograph cartridges with four signal pins are a balanced source. Thus the MP-1 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 NO hum whatsoever. Many tone arms use a five pin connector that
plugs into the tonearm. If you have such an arm, you may order a tone arm cable with the right connections
from almost any cable manufacturer. Sometimes a copy of this page sent to the cable manufacturer is helpful. If
your arm has RCA connectors at the output, an adapter cable can be made that will work. The shield connection
of the RCA becomes 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 will result in a loud hum.
The cartridge loading is accomplished by installing resistors on the loading terminal above the phono connectors
on the rear panel. A screwdriver is all that is needed for attachment. You will have to experiment to obtain the
correct value. 100 to 150 Ohms is common with many low output moving coil cartridges in use since the early
1990's.
The MP-1 is highly resistant to Radio Frequency Interference (RFI) problems. Certain tonearms that are not
grounded may still pose a problem (usually air bearing straight tracking arms, which cannot be properly
grounded due to the air bearing). RF beads installed in the interconnect cable can sometimes
alleviate this problem. The trick is to eliminate the RF before it gets into the preamplifier, so treat the ground
connection with RF beads also. For best results, the phono cable should be shielded.
Note: To avoid noise, avoid New Old Stock (NOS) 12AT7 tubes in the phono section. Most are far too noisy to
be of any real use.
A step-up transformer is available for very low output cartridges (0.1mv or less).