The MAX Audio Processor For Amateur Radio, LPAM, And Podcasting |
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Information contained on these web pages copyright W8KHK / N1BCG. Amateur or individual use is encouraged. Commercial use of any kind is prohibited without the express written permission of the author, Richard A. Maxwell MAX Audio Processor - General Description
The MAX Audio Processor is a simple yet full-featured audio processor for amateur radio and Part 15 low power AM (LPAM) operators who want loud and clean audio with absolute bandwidth control.
The design is the result of a collaboration between amateur radio operators and broadcast engineers and includes all the key components of sophisticated audio processors. Individually selectable features include compression, limiting, clipping, phase-rotation, high and low pass filters, plus a constantly variable bandwidth filter. Users can connect power, input, and output and get great audio with the default settings. For advanced users or those looking for a specific sound, the modular layout of the MAX Audio Processor enables each section to be bypassed or controlled separately by adding external switches, resistors, or potentiometers, resulting in a fully customizable sound adjustable on the fly. |
MAX Audio Processor - Connections, Controls, And Indicators
Four inputs provide users with the ability to connect a wide range of Hi-Z, Lo-Z, balanced, unbalanced microphones, and line level equipment. The gain for each input can be independently set using internal trimmers. Hum pickup is minimized by the use of an external analog power supply.
The basic model of the MAX Audio Processor features an input control and two LEDs that show normal (yellow) and peak (red) levels. An additional pair of LEDs indicate whether the polarity of the incoming waveform is predominanty positive (green) or negative (blue). This is useful for those who want to check the performance of their microphone(s).
The MAX Audio Processor includes comprehansive waveform processing to ensure loud and clean audio at all times. This is accomplished with a combination of asymmetry control, presence frequency enhancement, average audio maximization, and peak control. Users can tailor the sound instantly to suit preference or band conditions with the "Open/Dense" switch or add optional controls for maximum flexibility. See the Customizations section for details.
The heart of the MAX Audio Processor is the dual section precision SCAF (Switched CApacitor Filter) bandwidth limiting circuit. The three default switch-selectable sharp cutoff frequencies are 3kHz, 5kHz, and 7kHz (6kHz, 10kHz, and 14kHz bandwidth) although users can adjust any or all three using the internal trim pots. This allows instant selection of transmitted bandwidth to suit changing conditions. Alternatively, users can add an external potentiometer for continuous frequency response/bandwidth control. See the Customizations section for details.
Two internally adjustable gain outputs can be configured for balanced or unbalanced line level (0 to +4dBu) or microphone level (-50dBu) to drive virtually any type of transmitter. An additional internally adjustable gain utility output is provided for connection to a VU meter or headphones if desired. |
Max Audio Processor - Circuit Description
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