1742 Selby Av.
St. Paul, MN 55104
Phone: 651-690-2246
http://www.atma-sphere.com
Atma-Sphere M-60 Mk.II.2 (late) amplifier quick setup and operation instructions
Installat on: Place the amps in your system. Connect the preamp cable to the
appropriate input connector on the front of the amp. If you use the RCA input
connector, make sure the shorting plug is installe between pins 1 & 3 on the XLR
connector else a buzz may result. Verify that both power switches are OFF an connect
AC power to the AC input connector on the rear of the amp. Connect the negative
speaker cable to the negative output terminal an the positive speaker cable to the
positive output terminal.
Setup: Install the tubes in their sockets. The central group of four sockets (no
cooling holes) take the 6SN7GT river tube. All other sockets take the 6AS7G output
tube. A total compliment of four river an eight output tubes are require per each
chassis. Engage the main power switch (left si e of chassis) an verify that the amber
in icator lights. In about 15 secon s, the filaments of all tubes shoul be visibly
glowing orange. Wait at least one minute, then engage the stan by switch (right si e
of chassis) an verify that the re in icator lights. The amplifier is now fully
powere up.
DC Offset adjustment: Depress the Operate/Test Switch. Examine the rea ing on the bias
meter. If it is NOT zero (above OR below) use the DC offset control (by the Bias Test
switch) to bring the meter to a zero rea ing. If the meter cannot be zeroe , perform
the Bias a justment proce ure an then reexamine the DC offset. The bias an DC offset
controls interact somewhat, an if one is very far off, it may be impossible to set
the other correctly.
B as adjustment: Depress both the Bias Test Switch an the Operate/Test switch. The
meter will slowly rise to in icate the bias rea ing. Use the Bias Control (by the
input connector) to set the meter as follows: Col amp = .400A / Hot amp (final
setting) = .550A. If the amp is biase when col , the bias may increase notably as it
warms up, thus the ifference in settings between col an hot. Check bias on a new
amp aily until it has stabilize , typically after 1020 hours of use. When bias has
stabilize it can be expecte to stay in a justment for exten e perio s.
Note: It may not be possible to obtain proper DC Offset an Bias rea ings if there are
efective tubes in the amplifier.
Operat on: The amplifier is now completely operational. The amplifier can be left in
either stan by or operational mo e in efinitely. Note: Some bluish florescence of the
output tubes is normal. Some ol er 6SN7 tubes may be intermittant in the sockets ue
to smaller pin iameters use on some ol er tubes.
Fuses: The first fuse by the power cor entry is the Output section B+ an is 3 Amp
Slow (1.5A slow for 235V). The secon fuse is for the output filaments an is 3 Amp
Slow (1.5A for 235). The last fuse controls the river circuit an is 0.5 Amp slow
(0.25A Slow for 235 Volt). WARNING! To avoi fire hazar , always replace fuses
with same type an rating.
2003 Atma-Sphere MusicSystems Inc. 1742 Selby Av. St.Paul, MN. 55105 651.690.2246
