Sound Performance Lab 2711 manual Technology, Ssm, Servo Drive Design

Technology SSM 2019, Servo Drive

SSM 2019

The Preference Mic Pre is suitable for all common dynamic and con- denser microphones. It works along the principles of an instrumenta- tion amplifier which is a technology that is also used in measurement and medical equipment due to its high common mode rejection of stray pick-ups. It is based on the semiconductor SSM 2019 which sounds more balanced than available alternatives. Low noise and distortion values as well as a broad bandwidth and a fast slew rate are its forte.

Servo Drive Design

The main focus during the development of the Preference Mic Pre was its acoustic transparency and its natural representation of the source signal. Reducing DC offsets in the audio signal paths is a decisive part of this design job.

DC offsets are produced in relatively large amounts especially when amplifying a microphone signal because the signal is amplified by extreme factors from the pico volt range to 0dB nominal level. DC off- sets impair the signal quality as they induce noise and distortion that lead to a diffuse sound.

The Preference Mic Pre‘s servo drive design minimizes these problems much more effectively than the common solution based on capacitors by setting the DC offset to almost 0 mV. In addition to that, the active servo drive circuitry tends to produce less distortions than passive capacitors.

The servo drive design incorporates three operational amplifiers. The SSM 2019 is the first op-amp. The second op-amp acts as a sensor to detect voltage differences. These differences are then compensated for in a third op-amp working as summing stage.

Of course an elaborate active servo drive circuitry is a more expen- sive solution than simply using passive capacitors, but especially in a microphone preamplifier this effort pays off with improved sound quality.

14 RackPack: Preference Mic Pre