Single-Knob Mic Preamp Gain-Trim and Fader for Low Noise
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Solution Overview
Problem
Microphone pre-amplifiers often require separate gain-trim and fader controls to manage varying microphone output levels, but existing solutions that eliminate gain-trim control result in increased noise and harmonic distortion due to high initial gain settings.
Innovation Solution
A microphone gain-trim and fader circuit that combines gain-trim and fader functions using a fully differential amplifier and a fader amplifier, with a common adjustment apparatus mechanically tying the gain-trim and fader settings, allowing for simultaneous adjustment of gain and attenuation across a range of settings, including natural logarithmic and anti-logarithmic scaled potentiometers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate gain-trim and fader controls are used, then noise and harmonic distortion performance is maintained, but device complexity and physical space requirements increase
Solution Approach 1:
The patent combines separate gain-trim and fader controls into a single integrated control mechanism. The gain-trim circuit and fader circuit share common components including a differential amplifier, fader amplifier, and mechanically linked adjustment apparatus, allowing both functions to be controlled through one interface while maintaining distinct signal processing paths to preserve audio performance.
Solution Approach 2:
The single control apparatus serves multiple functions by mechanically tying together the gain-trim and fader adjustments. This universal control structure allows one mechanism to simultaneously manage both gain trimming and fader operations, reducing the number of separate controls needed while maintaining full functionality of both features.
2Device complexity
If gain-trim control is eliminated, then device complexity is reduced, but noise level and total harmonic distortion increase
Solution Approach 1:
The patent integrates gain-trim functionality within the fader circuit architecture rather than eliminating it. The differential amplifier and fader amplifier work together with mechanically linked adjustments to provide both gain trimming and fader control in a unified structure, maintaining audio performance while reducing overall control complexity.
Solution Approach 2:
The control system employs dynamic adjustment capabilities where the gain-trim and fader settings are mechanically linked but can be independently optimized. The logarithmic and anti-logarithmic scaled potentiometers allow dynamic range adjustments that adapt to different operating conditions, maintaining low noise and distortion across varying signal levels.
3Adaptability or versatility
If high gain is set upfront for all microphones, then all microphone output levels are accommodated, but noise level and total harmonic distortion increase
Solution Approach 1:
The patent applies local quality by providing gain trimming at the specific location where it is most effective - in the gain-trim circuit before the fader amplifier. This allows each microphone channel to have its gain optimized locally rather than using a high fixed gain for all channels, reducing noise and distortion while maintaining compatibility with various microphone output levels.
Solution Approach 2:
The system enables parameter changes by allowing the gain setting to be adjusted via the mechanically linked gain-trim control. Instead of a fixed high gain setting, the gain parameter can be dynamically changed to match the specific microphone being used, optimizing the signal-to-noise ratio and minimizing total harmonic distortion for each microphone type.
Data Source
AI summary
According to a first aspect of the embodiments, a microphone mixer is provided comprising: an input adapted to receive differential microphone (mic) output signals; a gain-trim circuit adapted to receive the differential mic output signals, and which includes a substantially fully differential amplifier adapted to amplify the received differential mic output signals through use of a gain-trim output adjustment device that provides a variable gain amount ranging from a first gain-trim gain value to a second gain-trim gain value, to produce differential gain-trim circuit output signals; a fader circuit adapted to receive the differential gain-trim circuit output signals, and which includes a differential amplifier adapted to attenuate the received differential gain-trim circuit output signals through use of a fader output adjustment device that provides a variable gain amount ranging from a first fader gain value to a second fader value; and a common adjustment apparatus that mechanically ties the gain-trim output adjustment device with the fader output adjustment device such that the first gain-trim gain value and first fader gain value are obtained substantially simultaneously at a first position of the common adjustment apparatus, and the second gain-trim gain value and second fader gain value are obtained substantially simultaneously at a second position of the common adjustment apparatus.