Intentionally Unbalanced mixer?

[dlciii]

Hello all,

I was wondering if the teeming masses could help me with a circuit.

I am trying to make a line mixer with 3 source inputs, one output, and have it powered off 12 v. I am trying to put the 3.5mm stereo outputs from my gps, ipod, and radar detector into the factory aux input for my car radio.

I would like the mp3 to be attenuated once the radar or gps have a message.

My question:

If I use fixed resistance instead on pots, will that accomplish an intentional unbalancing of the 'mix' when the gps/radar has signal?

Do you think that I could get away with a passive mixer for this situation, or would the sound quality just fall off?

Is there a simplier solution to this problem then a mixer?

I have a bunch of plans for mixers but I welcome any input.

Thanks for your time sincerely,
Don Crawford

[Eva]

You need an active circuit to detect the presence of signal from the alternate sources and attenuate the main source (MP3).

Also, you need an active mixer with balanced inputs (word not used in the same sense as you did) to get rid of the ground loop noise.

[dlciii]

I don't think it has to be that complicated.

It would be easiest if I didn't attenuate the signal and used NO circuits on each input.

But did it make sense what I was trying to describe by using fixed resistance for the inputs instead of potentiometers or variable resistance.

That was went the auxilary signal is sent they always affect the summation the same way every time.

Tell me why I am mistaken with on my use of balance. I am really new to audio but I am not new to signals and electronics. I am talking about the resistance of the circuit for each input will be fixed. The peak current of just the mp3 will generally be less than the mp3 + auxillary inputs peak current. If you have appropriate fixed resistance than the signal for the mp3 should get weaker naturally when the signal of aux is activated?

I don't know if that made any sense.

I guess I am just thinking while I type but I should have some sort of extra resistance on the mp3 line that is added when the aux signal is activated.

Right?

But the above doesn't need anything beyond passive mixing right?

thanks for helping me think this out,
Don

[Perry Babin]

How about relays to switch signals going to the aux input?

That would eliminate the input buffer or transformer required for a mixer.

[dlciii]

could I use something like the ic New Japan Radio 2754?


It looks good but I don't know what will happen when I activate multiple inputs.

[Perry Babin]

Can you post a link to a datasheet?

[dlciii]

http://semicon.njr.co.jp/njr/hp/file...?_mediaId=7231

[Perry Babin]

That appears like it may work but it does the same thing as the relays and will add to the complexity of the project.

[dlciii]

You have a relay in mind?

Because my understanding is that a relay would not be a summation of signal. It would be a switch. Of many inputs, one could be selected and sent to the output.

I am looking to select one or more inputs that will be combined in a fixed manner to one output.

[Perry Babin]

This IC, as far as I can see, is only a switch. It will not allow the mixing of signals.

Relays would do the same thing but with relays, you could switch all of the connections (including signal grounds) so that there would be no chance of creating ground loops.

Any good quality 4 pole double throw relay would work. You'd need two of them. Use relays that have sockets so that it will be easy to change the relay if it fails.

You'll have to build a trigger circuit that will drive the relays on when the other devices produce audio.

Do you know how much AC voltage the GPS and radar detector produce when they have audio output? Do they both have volume controls for their output signals?