D104 Mark II Audio Processor
This is a new version of the K7DYY D-104 audio processor with features used in broadcast type audio processing chains in addition to the compression and limiting of the original version.
The phase rotator circuit has been used for many years in the broadcast industry to provide louder audio without introducing distortion. Here is a link to an article by Gary Blau W3AM, a broadcast consultant engineer describing the technique:
Jim Tonne has written an excellent article about the phase rotation
audio processing method which is due to be published in QEX. Jim has generously offered his permission to link to his article. Here is the link.
The new D-104 MK2 processor incorporates the phase rotator while retaining the same size as the original D-104 processor. The new MK2, like the original audio processor, still fits in the base of the venerable D-104 microphone stand!
The compression averaging time has been extended to avoid having the noise gate open between words. The noise gate threshold has also been lowered. In addition, a jumper has been added to allow the noise gate function to be disabled completely for operation in a quiet room.
A low pass filter has been added to provide a gentle rolloff above 6khz to reduce broadband noise from the D-104 microphone.