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Using Single-Ended Equipment

with our balanced tube preamplifers MP-3 & MP-1 

La triode de puissance 6AS7G

The MP-1 and MP-3 accept single-ended inputs quite easily. For phono cartridges there is no real need to do this, since all cartridge/tonearm setups are actually balanced sources. The right thing to do in this case is use the proper phono interconnect cable. For line-level applications, the easiest thing to do is to use one of the monitor inputs, which are all single-ended. Otherwise, an adaptor (or better yet, a custom cable) can be used to connect the single-ended input to the AUX 1 or AUX 2 input of the preamp. Pin 3 should tie to pin 1, with the signal being carried on pin 2, for non-inverting results. Of course, the front panel phase inversion switch can change this.

The MP-1 and MP-3 will convert any single-ended input to a balanced output with no degradation of any sort. 

There are several methods of using a subwoofer with either the MP-1 or MP-3. The best method is to have the subwoofer updated to include a balanced input by us or the manufacturer. If this is not possible, the next best solution is to have a 3rd party, such as Great Northern Sound, modify the crossover of the subwoofer with a balanced input. 

Sometimes it is possible to operate the subwoofer from of the RCA inputs of an Atma-Sphere amplifier. Since the RCA is connected to pin 2 of the XLR, and if and MP-1 or MP-3 is driving it, the RCA can serve as a convenient connection for the hookup, provided the subwoofer is nearby. Sometimes a buzz will result from this type of connection, but it is worth a try.

Alternatively, a line transformer can be used that converts from balanced to single-ended. It should be installed in parallel with the input of the balanced amplifier, but can be in its own box or location. Jensen makes excellent transformers for this and they also make a transformer that is optimized especially for subwoofer operation, having no loss of impact at any bass frequency. For many subwoofer situations, this is the ideal solution. 

Finally, the output of the preamp can have one of the XLR pins (usually pin 3) tied to pin 1. This will cause the entire connection to be single-ended, resulting in less performance from the preamp, but works quite well in many cases. 

Single-ended amplifiers can be used one of three ways. The best way is to have the amplifier updated with a true balanced input. This is simple, inexpensive and is a service we provide. This technique, one that we developed, works with all amplifiers and does not change the character of the amplifier in any way. You can also use a transformer to do the same job. This is a bit less elegent but works fairly well. Jensen transformers makes a very respectable unit for this use called the ISOMAX. Finally, you can use a simple XLR-RCA adaptor that connects pin 3 of the XLR output of the preamp to pin 1. These latter two techniques should be considered temporary- a permanent installation is best served by the first method mentioned in this paragraph.


Atma Sphere
1742 Selby Avenue
St. Paul, MN 55104


Tel : +1 651-690-2246