VX2500 Low Mic Audio HELP

[cdesigns]

Guys, I bought 2 VX2500 from ebay without mics, I bought some MH-67 microphones for them and everything seems to work fine but I get reports that my audio is very low. I also have some HT VX400 and they can hear me very loud with those portables, but with the VX2500 and the MH67 mics they hear me very low.

Any ideas?

 

[cmdrwill]

MH-25 A8J
Standard
Microphone

So you have the wrong mic.

 

[cdesigns]

MH-25 A8J
Standard
Microphone

So you have the wrong mic.

Everywhere I go online says:

MH-67A8J Vertex Mobile Microphone
(Replaces MH-25A8J)

That's why I bough this mics, now I'm confuse, do they have different mics inside?

This is from another website
The MH-25A8J has been discontinued as of 12/04/08.....it has been replaced by the MH-67A8J
You can still order the MH-25A8J but you will recieve the MH-67A8J instead

 

[cdesigns]

After hours of looking on google, I found a modification that helps 10x better the audio output of this microphone with vertex radios, it consist on removing one resistor and adding a small capacitor, I tested the modification and WOW, super clear audio with deep tone, while putting everything together by mistake I damaged a second resistor and somehow it sounded even better, super loud, just like those nice amplified microphones.

Tomorrow I'm receiving a new microphone and I will take pictures on how to make the modification and a video of before and after. I'm pretty sure this will help a lot of people, since I read reviews of people buying this radios and the audio is low, but the problem is the microphone, the MH-25A8J is different than the MH-67A8j, the MH-68A8J works great on ham radios where you can raise the gain of the microphone, but on this radio you only have Standard Mic Sensitivity or Low.

 

[cdesigns]

Here is a PDF of how to make the modification. I just tested 2 modded microphones on (2) VX-2500 and the audio was loud and clear.

Hope this mod helps others, its a big improvement.

 

[cmdrwill]

Here is a PDF of how to make the modification. I just tested 2 modded microphones on (2) VX-2500 and the audio was loud and clear.
Hope this mod helps others, its a big improvement.

Good catch Sir, I shall put that in my Vertex bag of tricks.

 

[cdesigns]

Good catch Sir, I shall put that in my Vertex bag of tricks.

It brings the audio loud and clear, 10 times louder and no distortion.

 

[k5gu]

MH-67A8J Wiring Question

While I had the mic opened to apply the 4.7uf mod, I noticed a green wire connected to the mic hanger fastener. Anyone know the purpose of this green wire? There's also a wire (black) connected to the hanger in the MH-25A8j. BTW, the 4.7uf mod worked very well, big improvement in mic gain!

 

[cmdrwill]

While I had the mic opened to apply the 4.7uf mod, I noticed a green wire connected to the mic hanger fastener. Anyone know the purpose of this green wire? There's also a wire (black) connected to the hanger in the MH-25A8j. snip

Part of the 'Off Hook' monitor requirement in Part 90, you must monitor the frequency before transmitting.. When the mic is in the 'hook', hung up in the clip, the receiver Tone Squelch IS enabled. Picking up the mic out of the 'hook' the radio receiver reverts to carrier squelch so the operator can hear co-channel radio traffic. Kinda like looking in the mirror before changing lanes.

 

[k5gu]

Thanks for that explanation. I'm assuming the "Off Hook monitoring" requirement, and thus the green wire application, is only for "Trunked" systems, as specified in FCC Part 90.187(b), using sub-audible tones, etc. For conventional communications, it is still best practice to "look in the mirror" before transmitting...

 

[MBill]

If the VX-2500 "Mike Off Hook" function works the same as the VX-2200 radios, you have to have
the mike hangup bracket at the same ground potential as the radio. Quick way is to observe the
LED Tx/Rx light. If the green LED goes out (on a VX-2200) when you place the mike in the hang-up
bracket then the tone circuit is working. If the green LED does not go out, then you have to ground the
mike hang-up bracket. Usually this is to any convenient chassis ground. That is of course, if you are
using the Coded Tone Squelch. Otherwise you will hear anyone that transmits.

 

[k5gu]

Thanks MBill. I'm slowly learning how these legacy Vertex radios work, thanks to you all. Apparently because of the original purpose of these radios, there's more technical info. available, but only if you're a dealer or Vertex technician, eh? Thanks again.