At FM ACOUSTICS it's not just semiconductors that are selected. Each of the special multi-wiper potentiometers is carefully selected by hand for tracking accuracy. The test unit used to
accomplish this task has been specially built by FM ACOUSTICS' engineers.
Using a sample and hold function that displays an initial default value assists in analyses which is done manually by slowly moving through the whole range and watching for any potential tracking difference. If a tolerance higher than fractions of a dB are found, the potentiometer is rejected.
Each selected potentiometer is therefore of high accuracy.
In the above photograph the test machine is hooked up to the oscilloscope. The two traces of an oscilloscope show the difference between the two potentiometer tracks (channels).
This is an example of a Volume potentiometer that is tracking very poorly. Without additional selection procedures even costly high-quality parts like this potentiometer cannot meet the quality standard required at FM ACOUSTICS.
Rather than switched (stepped) attenuators, VCA circuits, digital Volume controls, optical encoders or a relay matrix, in FM ACOUSTICS products laser- trimmed and hand-selected precision potentiometers are used.
With stepped attenuators the limit of resolution is determined by the individual steps. Music levels, however, do not come in steps but rather must be finely tuneable to achieve the most realistic reproduction. Therefore, they must be continuously variable. VCA's (Voltage Controlled Amplifiers) and the circuitry of optical encoders are known to be detrimental to audio quality and therefore must be avoided in order to attain optimal results.
Multiple switched relays have the same limitations as stepped attenuators, in addition to having less long-term reliability (partly due to a massive additional electro-mechanical component count).
While not "fancy", finely selected precision potentiometers, as used in the FM ACOUSTICS range, give better results all around. They are the optimal choice.