Atma-Sphere MP-3 User manual

Atma-Sphere Music Systems
160 So. Wheeler
St. Paul, MN 55105
Phone: [phone]
FAX: [phone]
ATMA-SPHERE® MUSIC PREAMPLIFIER
Model MP-3
OWNER'S MANUAL
Please study this document carefully before using equipment

CONGRATULATIONS!
You have purchased one of the world's finest preamplifiers and certainly one of the most unique. It was
over fifteen years in development and represents a level of performance that others will be struggling to
achieve for years to come. At the time of this writing, it is the only fully balanced differential vacuum-tube
design in the world and undoubtedly heralds a new breed. You do not have to wait-- all you have to do is
set the preamplifier up by following the simple instructions in this manual.
Every part of the preamplifier has been extensively tested and engineered so the product will perform
flawlessly for years to come, with little if any service.
Please read the manual carefully and follow the instructions closely. If you have any questions, do not
hesitate to contact your dealer or ATMA-SPHERE® MUSIC SYSTEMS. Here's to many years of happy
listening!
Sincerely,
Ralph Karsten
ATMA-SPHERE® MUSIC SYSTEMS, 160 So. Wheeler St., St. Paul, MN 55105 651-690-2246 FAX: [phone]

LIMITED WARRANTY ON ATMA-SPHERE® MUSIC SYSTEMS PRODUCTS
This warranty on your ATMA-SPHERE® MUSIC SYSTEMS product, which is distributed and warranted
by ATMA-SPHERE® MUSIC SYSTEMS, shall remain in effect for two (2) years from the date of
consumer purchase, provided the enclosed registration form is completed and returned to ATMA-
SPHERE® MUSIC SYSTEMS within ten days of purchase.
WHAT IS COVERED:
Except as specified below, this warranty covers all defects in materials and workmanship. The following
are NOT covered by the three year limited warranty:
* Tubes are covered for 90 days, with the following exclusions, as per the rest of the warranty:
* Damage occurring during shipment (present claims to carrier).
* Damage resulting from failure or inability to follow proper instructions.
* Damage resulting from the performance of repairs or modifications by other than ATMA-
SPHERE® MUSIC SYSTEMS.
WHAT WE WILL PAY FOR:
ATMA-SPHERE® MUSIC SYSTEMS will pay for all labor and material expenses for repairs covered by
this warranty.
HOW TO OBTAIN WARRANTY SERVICE:
If your unit requires repairs covered by this warranty, you MUST obtain a return authorization number
from Atma-Sphere® Music Systems. You are responsible for transporting the unit to Atma-Sphere®
Music Systems, 160 So. Wheeler St., St. Paul, Minn. 55105. You must pay the initial shipping charges,
but Atma-Sphere® Music Systems will pay the return charges, if the repairs are covered by the warranty.
All products MUST be shipped in the original carton(s) or in replacement cartons supplied by Atma-
Sphere® Music Systems. Contact Atma-Sphere® Music Systems for replacement cartons and cost.
LIABILITY IS LIMITED TO THE REPAIR OR REPLACEMENT, AT OUR OPTION, OF ANY DEFECTIVE
PRODUCT AND SHALL IN NO EVENT INCLUDE INCIDENTAL OR CONSEQUENTIAL DAMAGE OF
NY KIND.A
This warranty is not transferable. Implied warranties of merchantability and fitness for a particular
purpose are limited in duration to the length of this warranty. This warranty sets forth all expressed
warranties made with regard to the above-referenced product. We neither assume nor authorize any
other liability in connection with the sale or any shipment of products. This warranty gives you specific
legal rights and you may also have other rights which vary from state to state. We reserve the right to
make changes and improvements in our products without incurring any obligation to similarly alter
products previously purchased.

MUSIC PREAMPLIFIER SET-UP AND OPERATION
Unpack the preamplifier carefully and save the packaging containers for future shipment if required.
Place the tubes in the appropriate sockets, if required, as shown in the tube chart elsewhere in this
manual.
During operation, the MP-3 gets warm. Adequate ventilation is mandatory. If the preamplifier is to be
placed in a shelf or rack mount system, allow for at least 2 inches of open space above the unit. Make
sure that the preamplifier is at least a foot away from any power supply, to avoid hum problems.
After the preamplifier is properly positioned, make sure that the power switch is in the OFF position.
Connect the cables for the various components to be used with the preamplifier.
For sonic performance reasons, the MP-3 does not use a muting circuit! Allow the preamplifier to
warm up and stabilize before energizing your power amplifiers. A muting circuit is not used as it
would interfere with the servo-loop operation in the output section of the preamp. Its presence in the
circuit would be audible as well. Although the DC offsets generated during warmup are low level, they
could be a problem for some amplifiers and speakers.
══════════════════════════════════════════════════════════════════
WARNING! DO NOT TURN ON THE AMPLIFIERS IN YOUR SYSTEM UNTIL THE PREAMPLIFIER IS
WARMED UP AND STABILIZED! DAMAGE TO SPEAKERS, AMPLIFIERS OR BOTH MAY RESULT!
══════════════════════════════════════════════════════════════════
Get in the habit of turning down the volume or switching to an unused input anytime you turn your
amplifier on, when you change a record, etc.
After the preamplifier is turned on, it takes about 30 seconds before it is ready for use. During the
warmup of the preamplifier, one or both of the "DC OFFSET" LEDs on the front panel may light up. This
indicates that the servo circuit has detected a DC voltage at the output of the preamp and is trying to
correct it. If the indicator stays lit for more than a minute, a fault is indicated and the preamplifier
must be turned off immediately to prevent damage to associated equipment. It is normal for the
indicators to flicker at high volume settings. The preamplifier will sound significantly better after about 45
minutes of operation.
OPERATING NOTES
Normally the preamplifier can be left on all the time. Be sure to provide for adequate ventilation. The
12AT7 phono tubes should be checked every 6 months if the unit is left on continuously. The unit will
sound substantially better three hours after turn-on.
Use the MP-3 with a low impedance (600 ohm) load at the input of the power amplifier if possible. Such
practice results in reduced possibility of hum and buzz in most cases.
Invariably you will have to adjust the GAIN TRIM for proper soundstaging effect, because the MP-3 is a
zero feedback design. Various tubes will result in differing amounts of gain between left and right
channels. Operate the control SLOWLY. The GAIN TRIM controls are not in the audio path. They may
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 MP-3, 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 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.

High-Level Hookup
The auxiliary inputs are high impedance. Thus you may use any input as a source for the MP-3. If you
are using a low impedance source, a low impedance termination is recommended for better sound. A
single-ended source can also be used, by applying the signal between either pin two or pin three of the
input XLR, and ground. The unused input (pin three or pin two, respectively), may have to be shorted out
to prevent noise. Pin two of all the XLR inputs is the noninverting input, per industry standard.
The tape outputs are high impedance. Use a high-quality cable for best results and keep the cable as
short as possible. The minimum drive impedance is 20K-ohms. The tape 2 output is inverted while tape 1
is non-inverted.
The tape monitors are a single-ended, non-inverting, high impedance input.
MP-3 tube locations
NOTES ON TUBES
1) The 12AT7s in the upper left of the board are the most critical 6) NEVER use Tweek® on vacuum tubes.
for low noise phono operation. 7) Long live analog!
2) The constant current source tube is outside of the signal path.
3) Matched sections in the 12AU7 of the high level section will
reduce DC offset during operation of the front panel GAIN TRIM control.
4) Tube damping rings are recommended.
5) Do not remove tubes while unit is operating. Hazardous or lethal voltages are present!

TROUBLESHOOTING TIPS
Bottom front panel LED won't light up: Check the rear panel AC connector and verify that the power cord
is plugged in. If so, the internal 1.5Amp SLOW BLOW (.75A if 235 Volts) fuse may be blown.
Buzz, hum and/or RF interference: Make sure that the power cord is plugged into a properly grounded
outlet and that no other equipment in the system is grounded (resulting in a ground loop). Sometimes RF
can get into the phonograph through poorly shielded wiring in or from the tone arm. This is common with
modern straight-tracking arms. Buzz can also occur if the input of the amplifier is not properly balanced.
Distortion: Check the output tube (6SN7) and the associated 12AU7 for defects.
Both channels dead, unit lights up: 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.
LED lit up continuously: Check the 6SN7 in the channel associated with the LED. If the LED remains lit,
replace the TLO82 opamp ICs beside the associated 6SN7. They are in sockets and the ICs are
available from Radio Shack or other electronic supply houses.
NEVER, EVER, USE TWEEK® ON TUBE SOCKETS! Tweek® is an organic compound and is capable
of forming resistance paths if it breaks down.
If none of these suggestions help, please contact your dealer or ATMA-SPHERE® MUSIC SYSTEMS.
MORE TIPS AND TWEAKS
You can reduce the noise level beyond the specification by using low noise tubes. When ordering from
any source, specify tubes for a differential circuit (matched tube sections). We have found that the 12AT7
at the input of the phonograph section, and the 12AU7 at the input of the high-level section are perhaps
the most audible.
We recommend line conditioning. The fifth harmonic of the powerline frequency has been shown to be
far more problematic for good sound then all other types of powerline 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).
We have found that the power cord can have audible effects! A good cable is recommended.
The Sound Anchors equipment stand is the finest we have seen. It is highly recommended. Use it in
conjunction with the Ultra Resolution Technologies vibration-damping platform. Nav-Com Silencers or
other anti-vibration pads are also recommended. Tube damping rings are highly recommended.
A cartridge with .3mv or more is recommended.

NOTES

WARRANTY REGISTRATION FORM
IMPORTANT: This form must be filled out and returned to ATMA-SPHERE® MUSIC SYSTEMS within 10 days of purchase to validate the warranty! Please
type or print clearly.
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Optional section for our records and information:
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list the components in your system________________________________________________________________
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MAIL TO: ATMA-SPHERE MUSIC SYSTEMS, 160 So. Wheeler St., St. Paul, MN 55105 USA