Building a signal splitter for MP3 & Satellite radio into car stereo

[B. Jones]

Okay - I guess it's not really a splitter but here's what I'm trying
to do.
I have a Creative Nomdad MP3 player. In the car, I was using a
cassette adapter for the signal (I have no AUX in or CD Changer
controls). Works great, sounds great.
Now I have a Sirius satellite receiver in the car so I have it
connected up instead. I want to have both of them plugged up and
operational. I opted to not just buy a couple of Y connectors that are
used for splitting. Instead, I plan to build my own so I could mount
it neatly.
This is what I was thinking.
__________
|Car Stereo|<----
------------ |
^
-------- |
MP3-->----|________|----/
^
|
Sat-->------

If it's just a straight passthrough (if I just connect the two inputs
to the 1 output), and both devices are transmitting, the Sat output
voltage will be applied to the MP3 output voltage. Is there any danger
here? should I put diodes in line to prevent voltage from travelling
*TO* the MP3 player from the Sat, for example, and vice versa?
Anyone done this?

 

[vic]

Okay - I guess it's not really a splitter but here's what I'm trying
to do.
I have a Creative Nomdad MP3 player. In the car, I was using a
cassette adapter for the signal (I have no AUX in or CD Changer
controls). Works great, sounds great.
Now I have a Sirius satellite receiver in the car so I have it
connected up instead. I want to have both of them plugged up and
operational. I opted to not just buy a couple of Y connectors that are
used for splitting. Instead, I plan to build my own so I could mount
it neatly.
This is what I was thinking.
__________
|Car Stereo|<----
------------ |
^
-------- |
MP3-->----|________|----/
^
|
Sat-->------

If it's just a straight passthrough (if I just connect the two inputs
to the 1 output), and both devices are transmitting, the Sat output
voltage will be applied to the MP3 output voltage. Is there any danger
here? should I put diodes in line to prevent voltage from travelling

Yes there is.
You may destroy the output buffers of the MP3 or Sat devices.

Putting a diode would seriously alter the sound quality (it's not a
linear device), besides the signal going from the player to the stereo
doesn't imply the current flows in the same direction.

*TO* the MP3 player from the Sat, for example, and vice versa?
Anyone done this?

Why don't you use a switch ?

 

[B. Jones]

Yeah, the more I think about it, the more I think I probably will use
a switch.
I've been e-mailing a guy that is doing the same thing in his Ranger
(mine is a Ranger as well) that I'm trying to do in mine and here's
what he came up with:
http://www.ocomik.net/blog/archives/000117.html