Dynamic Mic Aging?

Discussion in 'Microphones, Speakers & Audio Processing' started by VK4QP, Feb 4, 2020.

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  1. VK4QP

    VK4QP Ham Member QRZ Page

    I have acquired a Yaesu FT-107. I was also given a Yaesu YM-34 desk mic. The FT-107 seems to work fine, except audio out of the Mike seems to be very low and requires having to crank up the mic gain quite high.

    I have check all the obvious things like the grille over the mic being blocked with crap, but it looks fine. I cleaned the PTT switch contacts...

    The question I have is can dynamic mike inserts age? Given the mic is probably at least 30 years old.

    My idea is to replace the dynamic element with an Electret insert, as there's a 5v line on the mic socket for the biasing.

    Before I do this is there anything else I need to check? Trying to work out how a Mic element would age...

    Guess it could be the preamp in the FT-107, I need to get another Mic and check it.
     
  2. N7EKU

    N7EKU Ham Member QRZ Page

    Hmm,

    Is the impedance selector on the correct setting?

    I guess a dynamic mike element could go bad if its cone suspension warps or wear out, shifting the voice coil into the magnet. I've seen that happen in speakers. I've seen cones made of mylar too, where the mylar cracks with age.

    73,


    Mark.
     
  3. W1VT

    W1VT Ham Member QRZ Page

    I can't remember exactly what it was, but I have a spare dynamic mike element. :oops:

    If you can, I'd measure the output of the mic element directly at its output terminals.
    I think dynamic mics are pretty rugged. They survived lots of portable operations in less than ideal weather.
     
    Last edited: Feb 4, 2020
  4. N7EKU

    N7EKU Ham Member QRZ Page

    Good idea,

    When viewed on a scope, I usually could get about 50mVpp when given a loud "aaaaaaaaaaaaaaaaaa" in the microphone. Never tried it on a DMM, but it should be measureable there too.

    73,


    Mark.
     
  5. N7EKU

    N7EKU Ham Member QRZ Page

    Hi,

    I just check a couple old dynamic mikes using just my DMM set on the mV range. The output was quite variable, but generally a stout "AAAAAAAAAA" (not yelling) close to the mike (about half inch away) would generate ~25mV. Saying "AAAAAA" more at a conversational level and staying an inch away would make about 5-10mV.

    73,


    Mark.
     
  6. KF5FEI

    KF5FEI Ham Member QRZ Page

    Does the desk mike have a blocking cap to prevent the DC from being applied to the mic element?
     
  7. K1LKP

    K1LKP Premium Subscriber QRZ Page

    TIM,

    AS YOU MENTIONED IN YOUR POSTING"

    Given the mic is probably at least 30 years old.


    YES, YOUR MIKE IS NOW GOING THRU THE CHANGE OF LIFE.


    DEPENDING UPON THE ENVIRONMENT THE MIKE WAS STORED IN,
    WILL DETERMINE THE AMOUNT OF DETERIORATION TO THE ELEMENT.

    FOR INSTANCE, IF THE LAST PERSON WHO HAD THE MIKE LIVED NEAR
    A BEACH AREA, THAT SALT WATER ENVIRONMENT AREA WOULD
    ACCELERATE THE
    DETERIORATION.


    YOUR MIKE HAS OVER 100,000 MILES ON IT.

    IT'S TIME TO CHANGE THE TIRES.......HIHIHI.....

    73 CARMEN.jpg
     
  8. W4EAE

    W4EAE Subscriber QRZ Page

    The only reasons to use a microphone (an inexpensive, technically low-end one like the radio manufacturers make*) that old are nostalgia or absolute lack of any funds.

    Microphones and speakers do degrade. A 30-year-old microphone or speaker will necessarily not sound as good today as it did 30 years ago.

    *microphones sold for $40, $60, $100 for 'ham radio' wouldn't fetch 10% of that in the audio world.
     
  9. W8AAZ

    W8AAZ Ham Member QRZ Page

    Most mics are sealed on the back and the diaphrams are sealed on the front with plastic diaphrams that are immune to normal environments. And necessarily have an insulation on the coil wires to protect them. Thus the only way I see it going bad is if some current was passed thru the coil or some sort of abuse took place. Or if it was a poor quality element to begin with. I have seen plenty of vintage dynamic quality mics and they work just fine as they always did. Electret mics can lose charge over decades and supposedly their output can slowly taper off, but they only drastically change if exposed to heat or abuse. Crystal mics die with age due to the crystals cracking or absorbing moisture from air. Electro-Voice used to give lifetime warranties against manufacturing defects. That apparently went out the window when they changed hands. I have seen problems with solder joints where the voice coils connect or the tiny wires breaking, but then you get dead, not weak. Could not hurt to take it apart and examine it for any issues like corrosion of connections or bad switch connections or anything like that. How about a continuity check for very low resistance between the element connections and the plug at the rig.
     

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