2000GTL AUX jack modification idea

[loosecannon]

Just thought about this, and haven't tried it yet, but will be opening up the 2000 in a day or two for another mod, and might give it a shot.

I thought i'd put it out there to the great minds of this forum for a little perusal before i do.

so, the AUX jack on the 2000GTL is meant to allow you to hook the radio up to a tape recorder in order to record both the received, and the transmitted signals of the radio.

There is another use for it, and that is to connect it to a home stereo system and equalizer in order to tailor the audio to your liking, and maybe filter out some extraneous noise.

The issue with doing this is that as soon as you key up, you have talkback through those speakers, and in my case, a whole lot of feedback.

My idea is to connect the transistor controlling this jack (TR51) to a receive only voltage source.

as can be seen in this diagram, the collector of TR51 is connected to pin 1 of the voltage regulator through a couple of resistors:



i would think that if this connection were moved over to pin 6 of the regulator, that the jack would only be active on receive, thereby removing the talkback.

so, am i missing anything?
has anyone else tried this?

thanks for any input.
LC

 

[Shadetree Mechanic]

Interesting idea. Might be easier to use the speaker out and pad it to line level.

 

[loosecannon]

I could do that as well.

although, i think the frequency response would be different because this record out jack takes a sample before the audio amp circuit which defines the response to 300-2500hz.
thanks for the reply.
LC

 

[loosecannon]

now that i look at the circuit a little closer, i would think that i would want to disconnect it from C121 as well, as that's where the TX audio sample is being taken from.

LC

 

[Dmans]

LC,
I think you are on to something.

No input from me- but a Cool Idea!

73
David

 

[loosecannon]

ok so i just did this mod and it works great!

here's how to do it:

lift the ends of R249 and R250 from the trace where they meet, and stand them straight up from the PC board.
connect their free ends together and solder a wire about a foot long to that point.

now connect the other end of that wire to pin 6 of the MB3756 voltage regulator.
this will provide the receive only voltage we are looking for.
there is a convenient hole near the front of the PC board you can put the wire in that goes to pin 6. just follow the jumper off of pin 6 and follow that trace up towards the front of the board and you will find the free hole.

Now remove C121.

that's it!

now you can use your AUX jack connected to your home stereo system and equalizer without having talkback/feedback when you transmit.
LC