Communications headset tester

[mister_e]

Ok,
so i guess it's probably miles away... or not. mmm, all beltpack/base station etc etc, were connected together via 3 pin XLRs. They called that Party-Line.

Try to draw a schematic of your existing tester board. It may reveal some interesting stuff. Same for the transistor board on the headset.

Sure it's doable... If it worked.. it can work again.

Don't give up!

[bcd]

Is it possible the inline box it could be some kind of volume limiter circuit for the headset? I know in European broadcast stations that all the headphones have to be fitted with dB limiters to stop the operators from damaging their hearing.
http://www.canford.co.uk/commerce/it...1_2001812.aspx for example.

Most of them use back to back diodes, but if it is military gear they have the money to do things the expensive way...

Bill.

[skimask]

Is it possible the inline box it could be some kind of volume limiter circuit for the headset? I know in European broadcast stations that all the headphones have to be fitted with dB limiters to stop the operators from damaging their hearing.
http://www.canford.co.uk/commerce/it...1_2001812.aspx for example.

Most of them use back to back diodes, but if it is military gear they have the money to do things the expensive way...

Bill.

Interesting thought. The 2 transistors on the board, while they aren't diodes, can sure be set up to act like it.
JDG

[Luciano]

Hi,

Original headset:

The original headset uses an electret microphone. (Phantom powered).

* * *

Modified headset:

The circuit board is an amplifier for the dynamic microphone.
The circuit emulates an electret microphone.
The circuit is phantom powered.

Best regards,

Luciano

[skimask]

Hi,

Original headset:

The original headset uses an electret microphone. (Phantom powered).

* * *

Modified headset:

The circuit board is an amplifier for the dynamic microphone.
The circuit emulates an electret microphone.
The circuit is phantom powered.

Best regards,

Luciano

Correct me if I'm wrong.
Electret mike - don't need power, just am amp, like the earpiece.
Dynamic mike - Feed power to the mike on one pin, like a pre-bias voltage; connect an amp on the other pin.

I probed the connector without the headset plugged in and didn't get any power on any of the pins (well, a few mV, but it was very jumpy, so I figured it was being induced from somewhere).

How are you guessing that the original configuration might've been electret? Is that 'just the way it's always been' ?


Jeeze...this would be so much easier if I had a datasheet for the things!!!!
JDG

[Luciano]

I probed the connector without the headset plugged in and didn't get any power on any of
the pins (well, a few mV, but it was very jumpy, so I figured it was being induced from somewhere).

Did you measure that on the functional station 12 miles away or did
you measure that on the headset tester?

If the station uses an electret microphone then you will have
about 3-9V DC between the microphone line and the microphone GND.


Example of similar circuit:
http://www.tkk.fi/Misc/Electronics/c...tretinput.html

Best regards,

Luciano

EDIT: 3-9V DC with the electret microphone disconnected.
-

[skimask]

Did you measure that on the functional station 12 miles away or did
you measure that on the headset tester?

If the station uses an electret microphone then you will have
about 3-9V DC between the microphone line and the microphone GND.


Example of similar circuit:
http://www.tkk.fi/Misc/Electronics/c...tretinput.html

Best regards,

Luciano

EDIT: 3-9V DC with the electret microphone disconnected.
-

The shop is 12 miles from where they use the headsets. The place where they use the headsets has multiple stations.
The headset tester seemed to be totally dead until I started messing with it
And like I said before, now all I can get is some serious squeal in the headsets when I plug them into it (except when I'm at the extremes with the volume pot that's on the tester).

I'm taking notes on all this good stuff for when I go in next week to beat this project up some more!

EDIT:
I just looked at that epanorama site. I remember looking at that site a few years ago, forgot all about it.
Yes, those diagrams (and others in that site under the audio section) look like they might have something to do with what I'm messing with.
My problem with the tester box circuit might be that I'm treating it totally wrong, possibly treating it like it has a dynamic mike instead of an electret mike, which that little circuit might do the 'conversion'.
I should be 'biasing' one input coming (for lack of a better phrase) from the mike with the battery instead of grounding it, and then sending it off to the + input of the LM386.

I'm going to have a good read of those pages, compare notes, etc. Hopefully this thing will work by noon on monday when I get it re-wired.
JDG

[skimask]

Ok,
so i guess it's probably miles away... or not. mmm, all beltpack/base station etc etc, were connected together via 3 pin XLRs. They called that Party-Line.

Try to draw a schematic of your existing tester board. It may reveal some interesting stuff. Same for the transistor board on the headset.

Sure it's doable... If it worked.. it can work again.

Don't give up!

That's just it. The tester box itself is almost stupidly-simple, just an LM386 amp. Shouldn't be a problem with that right? Not so much.... As near as I can figure, the guy that designed/built the tester box is probably around 115 years old by now. Not much of a chance of getting useful info from him.

And the schematics will come next week sometime. It will probably be clear as day as soon as I draw it out.
JDG