Some queries on the 3.5mm jack plug...

[wakiki]

I'm currenty working on a transmitter which will take its input from the headphone jack (audio out) of audio players. So i need to connect a jack plug to my transmitter. Should i just leave the COM connection? This will actually allow audio to be heard only via the headphone, rite?

**broken link removed**

 

[ericgibbs]

hi wakiki,
You need the Common, as its the common return for the right and left
audio channels. So you need something like a screened pair cable.
One wire of the pair to the right channel and the other wire of the pair
to the left channel. The screen of the cable is connected to the common.

If its important to your project, make sure the right and left channels
do not cross over, otherwise the left channel sound will come out of the
right speaker.
Got the idea.
Let us know.

Regards
EricG

 

[wakiki]

hi wakiki,
You need the Common, as its the common return for the right and left
audio channels. So you need something like a screened pair cable.
One wire of the pair to the right channel and the other wire of the pair
to the left channel. The screen of the cable is connected to the common.

If its important to your project, make sure the right and left channels
do not cross over, otherwise the left channel sound will come out of the
right speaker.
Got the idea.
Let us know.

Regards
EricG

I see, i got your idea...Thanks so much, EricG...

Isit possible to do this using normal wires? Or could you show me some photos on the wires you mentioned?

 

[ericgibbs]

hi,
the problem with 'normal' wires, is electrical interference picked up by non
screened wires. The wire picks up mains hum at 50 or 60 hz also electrical noise from nearby equipment.
If your wires are long, say, 3 or 4 feet and the audio voltage levels are
low, then hum and and noise will spoil your music quality.

If you must use normal wire, twist them around each other, with at least
2 twists per inch. Keep them as short as possible and route them away from
electrically 'noisy' equipment.

You can buy twin screened wire from your local hobby shop, its not very expensive and it will give you better results.

Hope this helps.

EricG

 

[wakiki]

Thanks EricG...

I'll try to get one of those twin screened wires

There's one more thing actually. I need to feed the jack into an attenuator to lower down its voltage before it goes into the transmitter. I got this attenuator design from audioguru.

The twin screened wire looks something like this rite;
**broken link removed**

For the other end of the twin screened wire, is it necessary to connect the screen to the GND node of the attenuator? My intuition tells me to leave it though...

 

[Nigel Goodwin]

For the other end of the twin screened wire, is it necessary to connect the screen to the GND node of the attenuator?

Yes it is!.

 

[ericgibbs]

hi,
as nigel states, it is necessary to connect the screen, otherwise your signals
will not have a return path. Correct connection of screens and grounds in most equipment is important, especially if the signals are low level.

Its also good practice.
Remember: as you progress/advance in your projects you will sometimes not use the screen as a return wire, an internal wire within the cable will be the signal return. The outer screen will be grounded, most likely just at one end.
This is too prevent what is referred as to 'as a ground loop current'.

EricG
If you require an explanation, why a signal return is required, check your
text books, or ask the forum.

 

[ericgibbs]

hi Sceadwian,

I agree, in fact I have pointed this out to him.
For the stereo audio connector, he is using twin screened cable, so
in this instance he has got to connect the screen at both ends or else it
will not work.

Best Regards
EricG