Adapting PC Headset to Aviation Radio.. ( NEED HELP PLEASE )

[(*steve*)]

That was Resqueline, not me

You can't just build this because there are still several unknowns, the values of the capacitors for example. Also I think the diagram is incomplete as we can't see what is below the trimpot.

 

[roland_xp_80]

Hi steve and resq,

Ok, as soon as I get home I will open the circuit,

Would that is the only picture that u need to see??

How about the number 3? What do u need for the number 3?

 

[(*steve*)]

1) you may need the gain control
2) I looked up the numbers printed on the part, but found nothing. Chances are it's a fairly vanilla jfet though.
3) true, but see 1.

and also

4) we don't know where the ends of that trimpot go yet.
5) this circuit is for an electret element, possibly quite different from what is in the microphone you have.

I have looked (briefly) for schematics of amplifiers operated from the power delivered to an electre mic without success. I have no doubt that something is possible, but I'm not willing to design something from scratch without any sort of test rig .

 

[roland_xp_80]

hi thanks for your reply steve,

Appriciate your help, right now I'm out of town, but I will be at my house tonight, and I will then take picture of the circuit board 1 more time without the trimpot, and I will take out the trimpot to get the model number.

Thank you once again for your help..

 

[Resqueline]

I don't quite think you'll need to remove the trimpot, just look around its legs (and possibly beneath it) to see where the tracks are going.
The resistance value should be printed on its (curved) side.

 

[roland_xp_80]

Hi guys, sorry for the rate reply,

this is the photo of the peak.. let me know this image is sufficient.. if not I will take another one..

thanks.. appriciate your help..

 

[roland_xp_80]

Hi steve and Resqueline,

Is it correct if the number 2 is NPN transistor??

thanks..

 

[Resqueline]

Like Steve stated above, I too believe it's a JFET, not a bipolar transistor.

I'm not quite able to make out where the track from the pot' is going in that picture. How about the other side? Any tracks going from that pin?

 

[roland_xp_80]

in the other side is not visible, I have tried to open it, but I do not have specific tools to suck the solder liquid and to pull it out..

Hmm steve or Resqueline if you could create something for me that would be fine, I'm more than willing to try those circuit..

u don't need a rig, I will test it by my self.. I will try to upload the pic again tommorow..

 

[roland_xp_80]

The other side is just like the picture I attached.

can u help me to complete the circuit today? I want to buy this components and start building it..

thank you..

 

[Resqueline]

Can't complete the circuit w/o proper pictures showing the tracks in question..
You have the circuit in hand and it should be an easy task for you to follow the tracks on the PCB, comparing them to the diagram, and so completing it yourself.
As for the capacitor values I'm sure we can make an educated guess based upon the impedances present and common cutoff frequencies.

 

[roland_xp_80]

hmm I'm removing this amplifier now, and try it with my PC headset and bring it to fly tommorow.. I will update how does it work..

could you please guess the capacitor values for this circuit and where to put it?

I have no clue of how to read this small chip compared to this circuit. But I will keep trying as we go.. never give up..

thank you very much Resqueline..

 

[roland_xp_80]

I have tested above circuit to work(the original) picture.. can u advise what kind resistor should I use in number 3?? and what is number 2??

 

[Resqueline]

Ok, so if I understand you correctly then the PC headset works with the air-radio when connected via this circuit.

Like I said before, the value of the potentimeter (3) is something you have to read (and tell us). It's written on the curved side of the component,.
And like Steve said before, and I said before, we are unable to dechipher the number on component (2) but believe it to be a completely ordinary JFET (transistor).

Lastly, looking at this picture; surely you are able to see the similarity between the diagram lines and the light green lines on the circuit board, connecting the components.
It should be possible for you to tell where the light green lines from the potentiometer are going. You'll have to do this mental connection if you're to build the circuit anyhow.

 

[roland_xp_80]

Correct it does work perfectly..

OK now it does make sense.. Just I still have some question,

Based on my latest attachment:
Number 2 is connected there
the potentiometer is Piher Spain.. but there is no information how big is it.
For some reason Number 5 has no leg to anywhere.
I have question what is different between Number 3 and Number 4?

And the JFET 304 transistor, which one is the right one? which you guess, check below:
http://search.digikey.com/scripts/D...dkc_sep&site=us&lang=en&keywords=FDN304PTR-ND

thank you again for all help for you guys..

 

[Resqueline]

If there's no labelling on any of the sides of the pot then you have no other option but to measure it with an ohm-meter (measure between pins 2 & 5).
It's quite normal for a pot to have a free connection. It's then termed as a variable resistor.

I'm not quite certain that I have the 680k resistor connected correctly to the transistor in the diagram. You'll have to verify where that track actually goes by measuring too.
Also verify/double-check where pot track #2 ends up.

Capacitor #3 seems to be transferring the signal to the transistor, while #4 seems to decouple the supply to the mike - making the signal appear across the upper 2.2k resistor.
Cap #3 might have a value of 33nF, while cap #4 might have a value of 470nF. The first (unlabelled) cap might have a value of 22nF (or less).

The FDN304 is a P-MOS transistor. I can't tell at the moment if that's what is used there or not, or if it'll work. The diagram actually makes no sense to me as an amplifier.
There's no difference between the three part #s other than packaging and minimum quantity. Choose the middle one (FDN304PCT-ND) if you want to take the chance on it.

 

[roland_xp_80]

Ok Resqueline, Thank you for your reply, I will start seeking and let u know the progress. thank you..

 

[Manyacarb]

this is an old post, but Did you guys get this preamplifier work?

I have a very simple one transistor preamplifier that I use in my David Clark headset (not the M-1 dynamic microphone originally installed) and it works pretty well. I will try to post the schematics if anyone is interested.

Thank you

 

[Manyacarb]

This is the schematic I use on my headset. Basically adapts the electret impedance to a "old" carbon microphone impedance.
If the gain is way too high (in some audio panels/transceivers I noticed that) the second transistor can be omitted. It works really good.
Hope this helps

Regards