Atma-Sphere MP-1 Mk II Owner`s manual

model MP-1 Mk. 3.2
Please study this document carefully before using equipment
© 2012 Atma-Sphere Music Systems Inc
1742 Selby Ave.
St. Paul, MN 55104
You have purchased the world's finest preamplifier and certainly one of the most unique. It has seen over
seventeen years of development and represents a level of performance that others will be struggling to achieve
for years to come if for no other reason than we control the patents. At the time of this writing, it is the only fully
balanced differential all-vacuum tube design in the world that also supports the 600 ohm standard.
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 and always feel free to contact us at ATMA-SPHERE MUSIC SYSTEMS. Here's to many years
happy listening!
Ralph Karsten
This warranty on your ATMA-SPHERE MUSIC SYSTEMS product, which is distributed and warranted by ATMA-SPHERE
MUSIC SYSTEMS, shall remain in effect for three (3) 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.
Except as specified below, this warranty covers all defects in materials and workmanship. The following are NOT covered by
the three year limited warranty:
Vacuum tubes are covered for one (1) year, 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.
ATMA-SPHERE MUSIC SYSTEMS will pay for all labor and material expenses for repairs covered by this warranty.
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, 1742 Selby Av., St.
Paul, MN 55104. 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
This warranty is 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 abovereferenced 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
previously purchased.
Unpack the preamplifier and its power supply carefully. Save the shipping container for future shipment
(replacements are $75.00). Warranty may be void if the unit is shipped in a different container. If you do not
have a container, contact ATMA-SPHERE MUSIC SYSTEMS for a replacement.
Normally the tubes are installed; the types are marked on the boards.
During operation, the MP-1 gets warm. Adequate ventilation is mandatory. If the preamplifier is to be placed in a
shelf or rack mount system, allow for at least 12 inches of open space between the power supply and head unit
to avoid overheating and hum problems.
After the preamplifier and supply are properly positioned, make sure that the main power switch is in the OFF
position. Connect the umbilical cable from the power supply to the head unit. The connector operates by lining
up the correct key channels and then pushing on it gently while turning the knurled threaded locking ring. It is
keyed so that insertion is possible only one way- The lowest numbers marked on the pins of the connector should
be aligned at the top of the connector when inserted. You may now plug in the power supply. The "POWER
AVAILABLE" LED should now light. Connect the cables for the various components to be used with the
To maximize performance the MP-1 does not use a muting circuit! Allow the preamplifier to warm up and
stabilize before energizing your power amplifiers. Muting circuits interfere with sound quality and the servo
circuits in the line stage section. Although the DC offsets generated during warmup are low level, this may be a
problem for some amplifiers and speakers.
It takes about 30 seconds from turn on before the preamp is ready for use. During the warmup, 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 (usually a bad 6SN7 tube) which should be corrected to prevent possible damage to
associated equipment. The preamplifier will sound significantly better after about 45 minutes of operation.
The MP-1 takes about 1 or 2 hours to sound its best although it is quite musical after only 15 minutes. There is
no need to run the unit 24 hours a day, but if you do, test the tubes once every four months. Allow for a few
weeks of normal operation to break in the unit; subtle but lucid improvements will be noticed.
The MP-1 supports the use of a low impedance (600 ohm) load at the input of the power amplifier (although it is
by no means required). Such practice can reduce hum and buzz but more importantly eliminate artifact from the
interconnect cables. An optional terminator is available from ATMA-SPHERE for amplifiers without this provision.
Adjust the GAIN TRIM for proper channel balance. Some minor adjustment is sometimes required as the MP-1 is
a zero feedback design. Operate the control SLOWLY. The GAIN TRIM controls are not in the audio path. They
generate a minor and temporary DC offset while they are operated. This effect will vary depending on the
balance of the sections in the 6SN7 used in the line stage section. If possible, keep the controls turned up all the
way and lower the gain of the louder channel. This practice yields the best sound.
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.
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
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).
High Level Hookup
The auxiliary inputs are high impedance. Thus you may use any input as a source for the MP-1. A single-ended
source can also be used, by applying the signal between pin 2 of the input XLR and pin 1 (ground). The unused
pin three may have to be shorted to pin 1 to prevent noise. Pin 2 of all the XLR inputs is the non-inverting 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 10Kohms.
The tape monitors are a single-ended, non-inverting, high impedance input and may be used with any singleended line source.
A note on tubes: As mentioned previously, avoid NOS 12AT7s. Older 6SN7s, on the other hand, can often
provide some improved performance. Only buy from a reputable vendor, with proper assurance that the tubes
can be returned if they are unsatisfactory! We advise that you do not go overboard with NOS tube types, as the
prices paid for the results can be high compared to other changes you can make, fleeting, or both. Especially in
the case of the phono tubes, the investment is often not worthwhile.
1) The 12AT7s in the rear left of each board are the most critical for low noise phono operation. DO NOT use
NOS tubes: noise will be unacceptable.
2) The constant current sources (6SN7s in the center of the boards) should be chosen for low noise.
3) Matched sections in the front-most 6SN7 of the preamp will reduce noise
during operation of the front panel GAIN TRIM control. This 6SN7 is also the most important to the sound of the
line stage.
4) Tube damping rings are recommended.
5) Do not remove tubes while unit is operating. Hazardous or lethal voltages are present!
6) *NEVER* use Tweek or other contact enhancers on vacuum tubes, their sockets or the volume control!
Such use voids the warranty.
Front panel LEDs on the power supply don't light up
Check the rear panel fuse and verify that the power cord is plugged in.
Buzz, hum:
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). If you are trying to operate the output of the preamp with singleended equipment, buzz may occur if the conversion from balanced to single-ended is not handled properly.
Contact Atma-Sphere for assistance. In some situations an isolation transformer can be helpful.
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.
One or both channels out
Check all tubes. If OK, there are two fuses located on the right side of the power supply circuit board (as you
face the front of the unit), one for each channel. 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 service to qualified service personnel.
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.
Low output from one channel
Check tubes.
DC Offset LED lit up continuously
Check the 6SN7s (rear right two on circuit board) in the channel associated with the LED.
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.
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.
The power cord can have audible effects! A good cable is recommended.
The Sound Anchors equipment stand and the Silent Running stands are the finest we have seen. They are highly
recommended. Use them in conjunction with the Ultra Resolution Technologies vibration damping platform.
NavCom Silencers or other anti-vibration pads can be helpful as are tube damping rings.
Most cartridges with more than 0.15mv seem to work fine. The higher the output the better, tempered with a
musical presentation. Some recommended choices: The Grado Statement and Master Reference, Lyra series, ZYX
and Micro Benz. There are of course many others.
If a high output cartridge is used, a jumper plug that replaces one of the phono tubes can be installed to reduce
gain. Contact Atma-Sphere for details.
A moving coil step-up transformer option is also available for cartridges of less than 0.1mV. It can be used to
reduce noise, even with higher output cartridges, at a slight cost of musicality. The technique is to use the
aforementioned jumper plug as well. The gain tends to be similar to the normal phono section without the
transformer, only with about 15 db less noise. If you can, avoid the transformer option, it is likely that the sound
will be better; all transformers cause signal degradation.
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.
NAME: ___________________________________________________________________________________
Address: __________________________________________________________________________________
City: _______________________________________________State: __________zipcode: _______________
Country: __________________________________________________________________________________
Name of dealership: ________________________________________________________________________
MP-1 Mk. 3.2
Date of purchase: _______________serial #____________price paid: ______
Comments concerning your dealer: ___________________________________________________________
Comments concerning this product: __________________________________________________________
Components in your system: ________________________________________________________________
Suggestions: _____________________________________________________________________________
© 2012 Atma-Sphere Music Systems Inc
1742 Selby Ave.
St. Paul, MN 55104