Demultiplexing the aux input

I'd like to connect my phone to my empeg's aux input, but I'm already using it for my XM Radio receiver.

I know there are A/B switches that let you switch between inputs, but I was wondering if there was any sort of specialty dongle/adapter that did this sort of thing more elegantly -- perhaps mixing the inputs rather than requiring switching between them. I realize that this problem is a bit harder to solve than a simple A/B switch since the inputs may be vastly different in terms of the overall loudness, but I figure someone has to have run into this sort of problem before and come up with something. My googling has not found anything that will do the job, so I thought I'd post here to see if anyone knows of such an animal, or if I'm going to be stuck with an ugly A/B switch in my dash somewhere.

IIRC I saw someone on another forum years ago had the same problem and wasn't happy with the results from a simple resistive mixing circuit.

Haven't tried it myself and result may differ depending on the sources, but it's easy enough to try (~5kOhm on center of each source with the
other ends tied together and to center of input. Repeat for each channel (L/R))

I think he went with a small VOX (voice activated switch) kit that had a dual pole dual throw relay and so could switch from a default to
a secondary stereo source as it sensed signal on the secondary source input.

I think it reacted and switched in less than 0.1 second and would hang on for up to a couple of seconds (both adjustable)

Also I think he had to slightly mod the kit as that wasn't exactly how it was intended to run/operate, but I think it was just a matter of rerouting the in/outs of the relay a bit.

If one source is - consistently, and not adjustable - much louder than the other the maybe stick a simple resistive divider on that input/aource?

Yeah, I found a tutorial on how to do one in an Altoids can, but I wasn't really looking for a new project.

I guess my Google-fu is stronger today, because I just discovered the PAC ASAI21 that looks like it might do what I want (diagram). It goes the switching route rather than the mixing route, but it does so automatically, which might work out pretty well.

I'll keep looking for something that mixes or cross-fades or something, but if I can't find that, I can probably do just fine with one of those.

I've built a simple adapter to mix multiple line-level AUX inputs to a single input on my home stereo, and it's worked fine. Incredibly simple, just some female RCA plugs and resistors.

The only reasons that you might not like it in the car is:

- You might run into ground loop noise issues. But honestly, a complex switching system is going to be MORE likely to induce this than a simple resistance mixer would.

- If both devices do not have a volume control for their aux outputs, then you would not be able to control their relative volume. Maybe not an issue if you plan to mute the tuner by hand when you get a call.

I seem to recall that it was the EmpegBBS that told me how to make a resistance mixer, let me see if I can find the thread.

Aha, yes, here it is. Super simple:

http://www.epanorama.net/circuits/linemixer.html

Scroll down to the part where it says "Can I make this circuit even simpler?"

This is what I did to combine three different devices onto a single RCA AUX input pair on my home stereo. Works perfectly without any noise or problems. Remember that the circuit shown is only one half of the system: i.e., it's just one of the two RCA plugs. You need to make a second one for the second RCA plug in a stereo pair.

Yeah, that looks doable, though I'm wondering if the lack of amplification might be a problem. The XM radio unit audio signal comes out really hot, whereas the headphone jack on my phone comes out pretty quiet. If I try to balance them without any sort of preamp, I'll end up sending a really weak signal into the empeg's AUX in. Maybe I can correct for that with whatever the Hijack setting is for that, but it seems like there might be less noise if I found something that would amplify the signal before going into the empeg.

This looks like it might be an attractive mini mixer option, with an integrated preamp. If I don't end up needing the amplification, I just won't bother to wire the 12V DC in, but it'd be nice to have the option. Looks like it can be had for around $50.

Or, if I wanted to try to go the switching instead of mixing route, I could pony up about $50 more for this guy which will do either automatic switching based on silence detection or manual switching with a remote pushbutton. It's a bit more of a hassle to install, and I don't like the non-configurable 10-12 second delay when switching from the higher priority source, but it seems like a pretty elegant, if expensive solution to the problem.

I think I might have found a winner:


It's a switcher, not a mixer, but the delay is configurable from half a second up to several minutes, and the audio sense level is configurable as well. It's 12V DC @75 mA, so I should be able to just drop it on the amp remote line, which I already split out to power my XM direct receiver. And it's only an inch high, so it should fit easily under my carpet where the XM receiver already lives.

Looks like they can be had for about 60 bucks.

Hm, it even has a "status" output that it sounds like I might be able to plug the telephone mute line into. Here's what the manual says about it:



So that should work without any need for pull-up/pull-down resistors, right?

Found one on EBay for $50 and pulled the trigger. It won't do anything about balancing the levels between the two devices, but I think I can probably boost the volume of the phone using the DSP Manager that comes with Android, and if not, I can just attenuate the volume coming out of the XM tuner with one of these.

The Speakercraft LL-One arrived in the mail today. I installed it this evening, and it seems to do exactly what it says on the tin. Switching from XM receiver to phone is almost instantaneous when the phone audio comes on, and I have it configured to switch back to XM when the phone is quiet for 5 seconds, which seems pretty reasonable.

I didn't have time to dial it in to make sure it stays on the phone audio when the music is softer, but I'll test it out some tomorrow and adjust this weekend if necessary. Audio levels between the XM receiver and the phone are pretty balanced with the phone volume pegged, and there doesn't seem to be any clipping.

I haven't hooked up the telephone mute line yet, but I plan on doing so once I figure out how to wire it properly.

All in all, I'm pretty pleased with the device. For $50, it's a pretty elegant solution to the "not enough inputs" problem.

Happy Birthday!

Thanks! It was very happy indeed.

How "almost instantaneous" is the LL-One? Would it work for interrupting music with sat-nav instructions?

It seems to drop at least part of the first syllable -- I'd say maybe a quarter second? Enough that you'll notice, but not enough that it impacted my ability to follow the directions.

Hmm, worst case I guess I could make a custom voice set with half a sec of lead silence...

Except that wouldn't trigger it -- you'd probably have to have a short beep/tone and then *maybe* a tiny bit of silence. But really, the delay isn't so bad that I'd bother, personally.