Condenser Microphone Low-Impedance Head Unit Connection
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Solution Overview
Problem
Condenser microphones with interchangeable head units experience noise generation due to high impedance at signal output parts, especially when exposed to external electromagnetic waves, and existing solutions do not adequately suppress noise to satisfactory levels, particularly with low signal levels and varying phantom power supply voltages.
Innovation Solution
A condenser microphone design featuring a field-effect transistor (FET) on the head unit with an emitter-follower current gain transistor for amplifying sound signals, connected to a microphone body with a 3-pole output connector and current regulative diodes, allowing a single low-impedance connection for attaching and detaching the head unit, and using voltage divider resistors to maintain maximum output levels across different phantom power supply voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sound signals are extracted from the drain side of the FET to simplify the structure with one connection, then device complexity is reduced, but sound signals are easily distorted due to low signal levels
Solution Approach 1:
An emitter-follower current gain transistor is introduced as an intermediary component between the FET drain and the output connector. This transistor acts as a buffer that isolates the low-level signal from the FET while providing current gain and driving capability, thus preventing signal distortion while maintaining the simplified single-connection structure.
Solution Approach 2:
The invention changes the electrical parameters at the output stage by using the current gain transistor to transform the high-impedance, low-current signal from the FET drain into a low-impedance, high-current output signal. This parameter transformation enables the use of a single connection without signal distortion.
2Object-affected harmful factors
If an inductor is connected in series between grounds to suppress noise, then noise suppression is improved, but the impedance remains extremely high and noise is not suppressed to satisfactory levels
Solution Approach 1:
The invention fundamentally changes the impedance parameter at the output stage by introducing the current gain transistor. This transistor transforms the extremely high impedance of the condenser microphone into a low output impedance of approximately 200Ω, which inherently provides better noise immunity without requiring complex inductor-based filtering.
3Reliability
If two connections are used to separate power and signals from the source side of the FET, then signal distortion is reduced, but device complexity increases
Solution Approach 1:
The invention merges the power supply and signal output functions into a single connection by using the emitter-follower transistor. The transistor's emitter follower configuration provides both power supply rejection and signal transmission through one shared path, eliminating the need for separate power and signal connections while maintaining low signal distortion.
4Ease of operation
If the head unit is connected to the microphone body with one connection, then ease of operation is improved, but achieving low impedance for noise suppression becomes difficult
Solution Approach 1:
The invention changes the output impedance parameter to approximately 200Ω through the use of the emitter-follower current gain transistor. This low impedance state is achieved while maintaining the single-connection structure, thus providing both ease of operation and noise suppression capability simultaneously.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design achieves low output impedance of approximately 200Ω, enabling noise suppression and allowing the head unit to be attached and detached with a single connection, while ensuring maximum output levels across varying phantom power supply voltages, thus reducing signal distortion and complexity.
Implementation Method 1
a head unit including an FET for converting capacitance changes in the condenser microphone unit into sound signals
Implementation Method 2
an emitter-follower current gain transistor for amplifying the sound signals appearing at source of the FET
Implementation Method 3
a feed circuit having first and second current regulative diodes fed from the phantom power supply for applying a drive current to drain of the FET
Data Source
AI summary
To provide a condenser microphone having a removable head unit on the microphone body, wherein the head unit can be attached and detached to and from the microphone body through one connection at a low impedance. A second pin 22h and a third pin 22c of a microphone body 20, which has a 3-pole output connector, is connected with current regulative diodes D2 and D3 as a feed circuit for the drain D of the FET Q1. A first AC coupling electrolytic capacitor C3 is connected to one of the current regulative diodes, D2, and a series circuit of a second AC coupling electrolytic capacitor C4 and a resistive element R3 is connected between the anode of the other current regulative diode D3 and a ground line L3. The resistive element R3 has substantially the same impedance as an output impedance of the transistor Q2.