DACS Clarity MicAmp Technical Specifications:

Description
The DACS MicAmp is a very high performance unit. At this level we believe that every effort needs to be made to avoid compromising the quality of the signal path. We have examined every aspect of the process, from the power supplies to wiring to external connectors. Probably the changing of any one factor would make no noticeable difference, but cumulatively we believe that the attention to detail is worthwhile, particularly in long term performance and reliability.
Below are some notes regarding the technical aspects of the MicAmp which we believe make this unit one of the best Microphone Amplifiers available.

Power Supply Units
The Dual Rail supply used in all our products uses LM317 variable regulators. These have been shown in a number of tests to be lower noise than standard 78/9 series regulators. We have also implemented additional ripple reduction circuitry. In addition most capacitors are Tantalum, not standard electrolytic. The main smoothing capacitors are 4700µF per rail.
The Phantom Power Supply is an op-amp based regulator giving extremely stable regulation.
Power distribution uses a star system to minimise any interaction between circuit elements.

Earthing
The unit uses a star earth system where all earths go to the 0V tag using heavy cable. In addition the transformer and the PSU circuitry are screened with galvanized steel screens.

Wiring and Fixing
Where connections are crucial we have soldered directly to the PCB. This forms a more reliable long term connection than connectors. All cables are loomed and firmly cable tied to the board. The audio cable is OFC, again producing a small benefit over the long term. No external connectors are PCB mounting. This ensures long term reliability.

Components
The input DC decoupling capacitors are metallised polyester of 5% tolerance. The input is protected by four ultra fast diodes. The transistors are stacked to improve thermal coupling and reduce lead length. They, are mounted in a turned pin socket. The gain switching uses a self cleaning rotary switch which is screwed to the PCB, then soldered, and the switching shaft is fixed to the screwed down portion of the switch body so that there is little or no mechanical stress on the PCB. The pot (conductive plastic tracks) is also mounted on a bracket to minimise PCB stress. The filter stage uses 5% metallised polyester capacitors too, to give accurate and stable filtering. The amplifier stage is decoupled from the filter and trim stage by a 100uF bi-polar electrolytic capacitor. The trimmers are all low noise trimmers with a wide track. Throughout we have used Burr Brown OPA604s which are extremely high specification op-amps optimised for audio applications. In listening tests they have been preferred to NE5532s.

Noise and distortion
EIN is -133dB relative to a maximum output of +22dBu. Distortion is very low, with THD+N figures of around .00025% @ 1kHz (measured in the audio frequency range). Input impedance is ca 1kOhm.

Frequency response
-3dB point at 48kHz, roll off at 6dB/octave
Flat to less than 20Hz on phantom with subsonic roll off at 6dB/octave, DC coupled on non phantom inputs.

Bass Roll-off Filters

Common Mode Rejection Ratio