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 very high volumes.
PHONOGRAPH
HOOKUP
Almost all phonograph cartridges are balanced sources. Thus the MP-3 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 adaptor 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.
The 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.
RF problems may be encountered if the tone arm tube is not grounded. 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.
Aviod using NOS 12AT7s in the MP-3. Most such tubes are much too noisy for proper operation! Please
purchase new 12AT7s from your dealer or Atma-Sphere Music Systems. Most 12AT7s tend to get noisy
after only a few thousand hours so if you leave the preamp on 24 hours a day the phono tubes should be
replaced every 3-4 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. We have found for the most part that very few are acceptable.
For very low output cartridges you may wish to have the step-up transformer option installed. Contact
your dealer for details.