Icom M700 Mods ★ Latest
The IC-M700's stock audio is optimized for voice intelligibility in a noisy engine room on a fishing trawler. It's punchy but lacks low-end "warmth." For amateur SSB operation, where you want a fuller, less fatiguing sound, the audio coupling capacitor mod is essential.
The Problem: The audio path uses small-value capacitors that roll off frequencies below 300 Hz. This kills bass response, making your receive audio sound "tinny."
The Solution: Increase the value of two specific capacitors on the Audio (AF) unit.
Why this works: These capacitors form high-pass filters in the receive audio chain. By increasing their capacitance, you lower the cutoff frequency to approximately 80-100 Hz, allowing natural voice fundamentals and low-end richness to pass through. icom m700 mods
Bonus Audio Mod: The M700's microphone preamp is designed for dynamic marine microphones. If you are using a modern electret condenser mic (like a Heil headset), you need to add a 5-10 µF capacitor in series with the mic line (pin 1 of the mic connector) and also install a 2.2k ohm resistor to provide bias voltage. This will boost your transmitted audio to "broadcast quality."
The stock M700 has wide SSB filters (typically 2.4 kHz or wider). For CW, FT8, RTTY, or weak-signal work in a crowded band, this is terrible. You get adjacent channel interference (QRM).
The M700 was designed for intelligibility on a pitching ship, not for musical SSB audio. The stock audio path rolls off highs above 2 kHz, making voices sound "boaty" and muffled. The IC-M700's stock audio is optimized for voice
| Mod | Difficulty | Tools Needed | Benefit | |------|------------|--------------|---------| | MARS/CAP (full TX) | Medium | Soldering iron, diode cutter | Ham band transmit | | TX audio mod | Easy | Soldering iron, capacitor | Clearer voice | | CW filter add-on | Hard | Oscilloscope, filter, PCB | Weak signal CW | | Fan control | Easy | Resistor/thermal switch | Quiet operation | | PLL recap | Medium | Desoldering pump, caps | Reliable lock |
The M700 has a spot on the main board for an optional mechanical or crystal filter (often a Murata CFJ455K or equivalent). Many surplus units have an empty slot.
How to do it:
The "Pseudo-CW" Mod: Some hams wire a small SPST switch to the filter board. When flipped, it swaps the 2.4 kHz SSB filter for the 500 Hz filter. This lets you use the radio for CW with the clarity of a dedicated contest rig.
The M700 relies on convection cooling. For contesting or FT8 (high duty cycle), it gets scorching hot.
