Martinsound Martech Modular Studio Series, Owner'S Manual, Page: 14 / 28

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Many things were taken into consideration when designing the outputs of the MSS-10
to interface flawlessly with other equipment, with no sonic compromise being the most
important. We were faced with three options; a transformer balanced output, an elec-
tronically balanced output, or go with a single-ended output.
The idea of a transformer was not a real contender. The size and weight for a truly stellar
sounding unit that could easily drive +24dB into 600 Ω would have been unreasonable.
Also, the cost to develop a unit that satisfied us aurally was cost prohibitive. We also
realized that an output transformer would put off many people, no matter how good it
sounded. We felt that the only significant advantage of a transformer was that it would
provide a true floating output.
Electronically balanced outputs are heavily used throughout the audio industry. When
evaluating the sonic characteristics of the many different balancing circuit designs we
found all to be seriously lacking. Whether as a result of delay imbalances between the
differential outputs, use of inverting amplifiers, or amplifiers operating on the verge of
instability, none sounded close to a piece of wire. After all the effort to achieve a truly
stellar sounding microphone preamplifier it was unthinkable to destroy the sonic integ-
rity of the design at the final output stage.
What advantage is gained using a balanced output? After careful examination, the key
benefit we found is the identical impedance on both output legs. A transformerless bal-
anced input must see the same impedance on both input legs or its common mode rejec-
tion is seriously compromised. But, if a source presents a matched impedance to both
legs of a differential input full common mode is achieved, whether driven differentially
or single-ended.
The D2024 amplifier developed for the MSS-10 has an extremely low source impedance.
When connecting a D2024 to pin 2 of an output XLR, a build-out resistor is used to iso-
late the amplifier from external influence giving a source impedance of 52 Ω . To mirror
the source impedance of pin 2, a 52 Ω resistor is used to connect audio ground to pin 3
of the output XLR. The lower output impedance properly terminates shielded pair audio
cable, while the balanced output impedance maximizes the common mode rejection of a
following device. And, because audio only appears on pin 2, output level and headroom
are never affected when connecting the MSS-10 to a balanced or unbalanced input.
We believe that this simple but elegant solution provides you with the best sound pos-
sible.
WARNING: The MSS-10 uses a very sophisticated design for limiting output current to
prevent damaging the unit in the event an output is ever shorted. Nevertheless, avoid
connecting the unit to cables or equipment that tie pin 2 to shield or ground.
Balanced Impedance Outputs