Owner`s manual

TROUBLESHOOTING TIPS (continued)
Distortion
Check the output tubes (6SN7, upper right in diagram) and the associated 6SN7 in front for defects. If any of the
output pins of the main output XLR connectors other than pin one is at ground potential, distortion may result.
Low output from one channel
Check tubes.
One or both channels out
Check all tubes. If OK, there is a fuse located on the rear right side edge of the circuit board (as you face the
front of the unit). Replace with the same type slow-blow fuse (.75 Amp for 117 Volt units, .35 Amp for 230 Volt
units). If you are not qualified, do not remove the cover. Hazardous or lethal voltages are present with the cover
removed. Refer servicing to qualified service personnel.
Microphonics
If the MP-3 exhibits a ringing or 'bell' sound when at operating volume, One or more of the tubes may be
microphonic. Usually the 12AU7 in the line stage is the most likely to cause this fault. The 12AT7s in the phono
section can do this too. If the MP-3 is OK on AUX inputs, but rings on the phono, then a 12AT7 is most likely at
fault.
Noisy phono section
Replace the 12AT7s in the phono section. AVOID 'NOS' (New Old Stock) TYPES AT ALL COST! Despite claims
to the contrary by NOS tube suppliers, all NOS 12AT7s are just too noisy if you intend to use low output moving
coil cartridges. All brands, including Mullard, Telefunken, etc. will be noisy regardless of manufacture. The quiet
ones were purchased decades ago.
DC Offset LED lit up continuously
Check the 6SN7s (rear right two on circuit board) in the channel associated with the LED.
NEVER, EVER, USE TWEEK OR ANY CONTACT ENHANCER ON TUBE SOCKETS! “Tweek” is resistive at
vacuum-tube voltages. This will destroy the tube sockets and possibly the circuit boards!
If none of these suggestions help, contact your dealer or ATMA-SPHERE MUSIC SYSTEMS.
USAGE SUGGESTIONS
For use with sub woofer and other bi-amplified systems: Have your crossover updated with correctly balanced
inputs. If this is not possible, a specialized balanced-to-unbalanced sub woofer-optimized line transformer is
available from Atma-Sphere and works quite well. If you do not use one of these techniques, it is likely that you
will encounter a buzz.
When ordering from any source, specify tubes for a differential circuit (matched tube sections). The 12AT7s at
the input of the phonograph section and the 6SN7 at the input of the high level section (right front on circuit
board) are perhaps the most audible. We find NOS 12AT7 tubes to be too noisy.
Harmonics of the power line frequency have been shown to be far more problematic for good sound then all
other types of power line problems (RF, spikes, etc.) put together. Be sure that the conditioner you use can filter
line frequency harmonics, particularly the fifth (300 Hz on 60Hz line). A pronounced 5th harmonic can cause
any power transformer to become mechanically noisy! Beware that any line conditioner with a transformer in it
can add harmonics if operated at more than 50% of its capacity.