Yaesu MD-100 A8X Go to product viewer dialog for this item. is a popular dynamic desk microphone featuring built-in audio filtering and scanning controls. Its schematic highlights a sophisticated pre-amplification and filtering circuit centered around op-amps like the PC4572C. 🛠️ Wiring & Pinout Guide Go to product viewer dialog for this item.
typically uses a reversible cable that supports both 8-pin round and RJ-45 modular jacks. Color (Standard) 1 UP / Fast Scan Pink / Yellow 2 3 4 FAST / MIC Yellow / White 5 6 PTT (Push-To-Talk) 7 MIC Ground / Shield 8 White / Red Note: Wire colors may vary by manufacturing batch. 📉 Audio Filtering Controls
includes a "Main" bypass switch and two specialized filters located on the bottom of the base: Low Cut Filter: Position 1: -3dB roll-off from 1000Hz down to 150Hz.
Position 2: -3dB roll-off from 1000Hz down to 300Hz (for noisy conditions).
High Emphasis: Boosts higher frequencies by +6dB at 3000Hz to improve clarity in pileups.
Main Switch: Must be set to "FILT" for the Low Cut or High Emphasis settings to take effect. 🔍 Technical Resources YAESU- MD-100/100AX schematic.pdf - QSL.net
Yaesu MD-100A8X Go to product viewer dialog for this item. is a desktop dynamic microphone featuring a cardioid element designed for high-fidelity amateur radio communication. Its schematic reveals a sophisticated active filtering system located in the base, allowing operators to tailor audio response for clarity or "DX punch". Core Circuitry and Schematic Components
The MD-100 schematic illustrates several critical functional blocks: Active Filtering Stage
: Unlike basic hand mics, the MD-100 base contains active components—including $\mu$PC4572C op-amps —that power the selectable filters. Switchable Tone Controls Low Cut Filter
: A three-position switch (Off, 1, 2) that provides rolloff at approximately 150 Hz and 300 Hz. High Emphasis Filter : Provides a +6 dB boost at 3,000 Hz to help voice signals cut through interference. Dual Connector Interface
: The schematic features internal wiring for both a standard 8-pin round jack RJ-45 modular jack Yaesu Md 100 Schematic
, making it compatible with a wide range of Yaesu HF transceivers. Scanning Control
: A rotary dial on the base connects to the radio's "Up/Down" and "Fast" lines, allowing for remote frequency tuning. Microphone Pinout (Standard 8-Pin)
According to official technical documentation, the pin assignments are: : Up (Scan Control) : +5 Volts DC (Powers active filtering) : Down (Scan Control) : Fast (Scan Speed) : Ground (Chassis/Circuit) : PTT (Push-to-Talk) : Mic Ground (Shield) : Mic Audio Common Modifications and Enhancements
Enthusiasts often explore the internal schematic to improve performance: Level Modification
: Some users bridge specific paths before the op-amp to achieve a 10 dB increase in microphone level without causing distortion. Element Upgrades
: While the stock cardioid dynamic element is highly rated for warmth, some operators replace it with alternative elements to further customise the audio profile.
To see the internal circuitry and how the filter switches impact the audio signal: The Yaesu MD 100 desk microphone. Fred in the Shed YouTube• 17 Sept 2017 against the newer Yaesu M-100 dual-element model? YAESU- MD-100/100AX schematic.pdf - QSL.net
The Yaesu MD-100A8X is a high-fidelity dynamic desk microphone designed for Yaesu transceivers. Its schematic reveals a combination of a high-quality dynamic element and active filtering circuitry powered by the transceiver's 5V DC line. Schematic and Circuit Overview
The MD-100 circuit is centered around an internal preamp and filter board. This board allows operators to tailor their audio profile directly from the microphone base.
Filter Switch: Switches between "THRU" (bypass) and "FILT" (active filters). Yaesu MD-100 A8X Go to product viewer dialog for this item
Low Cut Filter: Cuts low frequencies to improve clarity in noisy or crowded bands.
High Emphasis: Boosts higher frequencies to help audio "cut through" during DX contacts.
Power: Typically draws 5V DC from the transceiver via the 8-pin connector. 8-Pin Connector Pinout
The standard wiring for the MD-100/100AX 8-pin round connector is as follows: Pin Number Wire Color (Internal) 1 2 +5 Volts DC 3 4 FAST (Scan) 5 Ground (Digital) 6 PTT (Push-to-Talk) 7 Mic Ground (Shield) Shield/Clear 8 Key Features and Maintenance 🛠️
PTT Lock: Includes a latching switch for long transmissions without holding the button.
Scanning Controls: Features UP, DOWN, and FAST buttons that interface with the transceiver's CPU.
Compatibility: While primarily for the 8-pin round jacks (like the FT-1000 or FT-950), it often includes a modular cable for newer radios like the FT-817/818 or FT-450.
Schematic Access: Full PDF diagrams are available through repositories like QSL.net and RadioManual.info. If you'd like, I can help you with: Instructions for modifying the audio gain How to wire it for non-Yaesu radios (Icom or Kenwood) Troubleshooting common PTT or audio issues
Let me know which radio model you are using so I can verify the exact cable requirements. YAESU- MD-100/100AX schematic.pdf - QSL.net
| Pin | Function | Wire Color (Internal) | Voltage | | :--- | :--- | :--- | :--- | | 1 | GND (shield) | Black | 0V | | 2 | MIC + (Audio out) | White | 0.5-2V DC bias | | 3 | PTT (Push to Talk) | Yellow | 0V when pressed | | 4 | +9V DC (from radio) | Red | 9-13V (via radio’s mic jack) | | 5 | NC (not used) | - | - | | 6 | DOWN (scan down) | Green | 0V pulse | | 7 | UP (scan up) | Blue | 0V pulse | | 8 | GND (second ground) | Black | 0V | Cause: Dried 47µF coupling capacitor (C6 on the PCB)
⚠️ The MD-100 is active – it needs +9V on pin 4 from the radio (e.g., FT-857, FT-991, FTDX series).
The Yaesu MD-100 is a classic microphone that deserves to be kept alive. While the manufacturer has moved on, the ham radio community has not. The schematic is the single most important document you can own for this microphone.
Do not give up after a single Google search. Check mods.dk, ask on QRZ.com forums, or open the mic and trace it yourself. Whether you are fixing a dead preamp, rewiring it for a new SDR radio, or just satisfying your curiosity about how Yaesu engineered this audio gem—the schematic is your roadmap through the silence.
If you found a working schematic, print it out, laminate it, and tape it inside the bottom of the microphone base. The next ham who inherits your MD-100 in 2040 will thank you.
Keywords used organically: Yaesu MD 100 Schematic, MD-100A8X, preamp transistor, PTT relay, resistor ladder, reverse engineer, microphone repair, Yaesu microphone wiring, MD-100 mods.
The MD-100 typically uses an 8-pin round connector or an RJ-45 modular plug for connection to Yaesu transceivers. RigPix Database Wire Color Description Scanning control: Up / Fast speed Power for active filtering circuits Scanning control: Down Scanning control: Fast speed toggle Chassis and logic ground Push-To-Talk control Mic Ground Dedicated audio return ground Microphone audio signal output Circuit Overview
The MD-100 schematic incorporates several active stages to tailor audio response: 777 Yaesu MD-100 Manual | PDF - Scribd
Once you obtain a schematic (official or reverse-engineered), it will typically show four distinct blocks. Let's break them down.
If you visit Yaesu’s official website, you will find manuals for transceivers but rarely detailed internal schematics for microphones. Why?
Searching for "Yaesu MD 100 Schematic" on Google often leads to dead links, suspicious PDF hosting sites, or forum threads that end with "PM me for the schematic."