How the "AM Stereo" sound is generated at WA2FNQ


Audio from the center channel microphone (Marshall MXL 2003/Rolls pre-amp) is fed to the main mixers channel 1 input. The left channel microphone (Marshall MXL 2003/Rolls pre-amp) goes to channel 4 of a Behringer MX802A used as a sub-mixer. The right channel microphone (EV 635A) goes to channel 2 of the MX802A. The sub-mixer appears on channel 6 of the main mixer. Outputs of the main mixer pass through a Behringer Dualflex audio enhancer. The secondary outputs from the Dualflex feed a bucket brigade type reverb and a Behringer Virtualizer. The bucket brigade reverb is used as the mono reverb and is set set for a short duration. The Virtualizer is used for longer duration stereo effect and is set to the "Virtual Cathedral" mode. The wet outputs of both units are sent back to aux. return 1 and 2 of the MX802A. The primary output of the Dualflex goes to a Behringer Autocom audio processor, then to dBx 163X compressors and audio distribution amplifiers. One set of outputs from the left/right audio distribution amplifiers is mono-summed and sent to an Inovonics model 222 limiter. Here the audio can be made NRSC compliant if desired. An audio equalizer is used to optimise the frequency response through the transmitters. A second set of outputs from the distribution amplifiers feeds a stereo Volumax. An equalizer is used to optimise the frequency response. It is followed by a L-R processor and then the Magnavox stereo generator. The output of the stereo generator is summed with a 25 Hz pliot tone generator to enable CQUAM receivers. This signal is then used to modulate the VFO of the transmitters. A CQUAM receiver will be able to detect stereo with good separation but some distortion. The audio output of the equalizer also feeds a Broadcast Techniques unit which is used to place the WA2FNQ transmitters in the ISB (Kahn/Hazeltine) AM stereo mode. This is currently experimental.

Block diagrams

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