I'm looking to build a simple audio switch (4 or 8 inputs, 1 output). The channel selection would be done with some sort of IR remote or perhaps through a serial link connected to a computer. In either case, the project would need some sort of microcontroller. That's the easy part for me, the analog side is what I've come to ask about.

I was looking around for devices to do the actual audio channel switching and it seems to me that the easiest thing to use in conjunction with the uC would be an analog mux. Does this seem like a good idea?

The most common analog mux (there are a lot) I could find was a 4051. However since this will only be used for audio signals I was hoping that somebody could point me to an analog mux that is optimised for audio signals. Cost is not a factor as this project would most likely be built once.

Thanks.

 

Analog devices has a pretty good line of analog switches and multiplexers - http://www.analog.com/en/cat/0,2878,768,00.html.

 

Hi,

Analog devices, Maxim, TI, and more manufacturers make analog switches.

What makes them optimal for audio is another question. Things to look for are gain flatness and low-charge injection. Some are designed so that you will not hear a pop when switching channels, which is what you would want. You want linear gain over a wide range, so resistance flatness is key for hifi stuff.

Steve

 

Thanks for the replies. I was looking through Analog and Maxim's sites for quiet a while before I posted. I didn't find anything fitting that mentioned audio in particular though.

Also, I'm not sure if it would be more appropriate to use an analog switch or an analog mux? A mux seems to make more sense to me but I really don't know what kind of bearing that would have on the audio side.

scubasteve_911, what kind of numbers am I looking for? How low is low charge injection, etc?

Any model numbers in particular that have worked out well in the past or that are known to be good would be truly appreciated.

Thanks a lot.

 

Possibly the MAX4586 (http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2081) ? It says "High-End Audio Equiment" under Application/Uses.

Datasheet mentions:
-5 Ohm on resistance flatness
-3pC charge injection

Anybody know if this is a good one?

 

Look at the DG409.

 

That looks good, it's available as a DIP too (unlike the MAX4586) so that makes life easier. Thanks.

 

Just read an app note somewhere yesterday, talking about audio muxes - can't remember where.

The bottom line was, make certain that any unused inputs to the mux are grounded. Otherwise, they'll float, introducing a great deal of noise into the system, and can actually destroy the mux.

I would be tempted to put in some fairly large-value resistors, say 100k, between ground and each mux I/O channel, just to guard against such an occurance.

 

So I'm finally getting around to building this thing. My question now is: do I need a negative voltage for the analog mux? Since I'm working with audio signals here I'm guessing that I do. If so, what would be the best way to generate -5VDC from +5VDC regulated input (not using batteries for this project). Would the ICL7660 be a good choice for this? Would it introduce noise into the system?

 

The negative voltage will be needed if the signals are standard bipolar (+/-) type audio. If the signals are +5V audio with an offset, you may not need it as long as the signal doesn't go all the way to ground (there would probably be rail issues with the source op amp anyways).

To create the -5V, take a look at the attached MAX764, and look around for anything that may be simpler or a better fit for your project.

Oddly enough, one of the things you can do with the Max764 is create -7V from +5V, and then run the -7V into a -5V low-noise linear regulator (such as a Linear Tech LT1964) for a quiet analog supply (it's not the most efficient, but it's easy and quiet).