Switching two audio sources between two different outputs

[ToddW]

I've got a little project I'm working on that integrates my iPod, iMac, as well as my headphone amp, with some speakers basically I want it to work like the following:

source1 to output1 or output2
source2 to output2 or output1

I'm thinking of using relays to do the switching and was wondering if anyone has any better ideas on a way to do this. I just do not want to degrade the audio signals any.

 

[Blueiz]

How about this.... not sure if it is exactly what you are looking for or not. I have one and it is very nicely constructed...

http://www.phonopreamps.com/tc716pp.html

 

[ToddW]

Thanks for the link, however, i'm looking to make it myself. I've got an idea, I'm just thinking of using relays instead of switches. I want to make it when I switch the ipod to the speakers the computer switches to the headphone jack automatically and vice versa.

 

[splaz]

Well from the last time I asked relays have very little degradation, unless somethings wrong with them of course.

But yeah from what I was told although cheaper relay should be fine, telecoms relays are probably the best choice for signal.

I quickly worked out a way of doing it, can't say if it's ideal or not. Uses 2 DPDT relays. I do realise and apologise in advance as I probably massacred all sorts of standards and practices and that those are switch symbols not relay symbols, however I'm just doing it to more visualise how it'll work, not flesh out a schematic just a mud map really. As I said before not sure it's the best way to go about it.

Well here it is quickly drawn up in paint.

 

[blip]

This is something I've been planning on building for quite some time. There are a multitude of different ways of doing this but they more or less break down into either a physical switch or relays. Since you want a somewhat intelligent solution, relays are probably the way to go.

Could you explain the behavior you are after a bit more clearly? If I understand you correctly you want Input A to connect to Output b whenever Input B connects to Output a. (i.e. Ab-Ba, with the other state being Aa-Bb) So in other words the connections are supposed to swap? I'm not quite clear why you would want this, but it could be accomplished a couple of different ways. Either you could do something tricky with logic to accomplish this (should be pretty simple but I've never been good with discrete logic) or you could use a micro controller driving the relays.

Something like a PICAXE 8 could accomplish the task for $3 or so (plus another $5 to build a serial programing interface). The program would only be three or four lines long... quite simple indeed!

As for relays, I'm still waiting on a definitive answer as to which kind is the best. My guess is that latching relays designed for low-level signals would be great in this application... but would require a more complex circuit to control.

 

[splaz]

Well as blip said there are a lot of ways to go about it.

Goes to show, I was tired last night, just crashed form a caffeine high and now I wakeup and wonder what I was thinking. The way I put up is a bit unnecesarily complex.

Threw this much simpler version together in a fraction of the time, 2 SPDT switches/relays this time around.

What I think he wants blip is to choose which of the two inputs he wants and then which of the two outputs he wants to play it.

Don't have much experience with relays but it shouldn't be too hard to put together, I'd agree latching would be the better choice. I'm buying a lot of latching DIL DPDT telecoms relays cheaply to mess around with for audio. Might not need a microcontroller if it's the way I think, just the circuitry to operate the relay and maybe two buttons that decide input and output respectively. Although if it is what I think it probably would be a lot easier just with switches.

 

[blip]

Ahhh... He just wants the two to be selectable independently then... That should be simple enough to implement.

Basically think of the problem as two separate modules, one is for the input, the other is for the output. This is more or less the way that splaz has them drawn right now.

Now what you are going to want is some way of energizing each relay coil (in a burst if you are using latching, constant if not). Lets start with a simple circuit block:

http://img147.imageshack.us/my.php?i...erelay1ig5.png

In this diagram the first input enters at PAD 1 + 3 and the second input enters at PAD 2 + 4. The outputs are PADs 5 + 6. When the switch (S1) is closed the coil is energized meaning that input 1 (PADs 1 + 3) are connected. If it is not then the second input (PADs 2 + 4) are connected.

Reverse this and you have the output side of your switch. It really is as simple as that.

Now if you want to use latching relays things are more complex. You will want to put some kind of logic (I'd imagine) into the circuit. Things also get more complex if you want more than two outputs/inputs... Suddenly you either need to use a separate bank of relays for each output/input or you have to find a 3 pole relay. Things get yet more complicated if you want to integrate a delay into your relays.

 

[MASantos]

Twistedpearaudio has a produt that may be what you're looking for. It is the darwin selector board. It uses relays and you can switch between several inputs, two outputs or even a loop out. I never used it but many have over at www.diyaudio.com with sucess.

Manuel


ps: i don't have any connection with Twisterpearaudio, I just think they offer a good product.

 

[mrarroyo]

I have been using a line routere LR1 from Dr. Lloyd at Mapletree and I am very pleased. It can be custom made with up to 6 devices in any combination of input and output. Here are some pictures.

 

[blip]

That twisted pear board is pretty sweet! I like that it is so basic... just relays and pads for control. It looks like a perfect time saver during a project. (Plus I love that they just sell the PCB... I'm thinking about using a microcontroller and only need 3 in/ 2 out so I might have to look into going that way.)

One thing struck me... Anyone know if you could plunk a preamp module/volume control in between the inputs and outputs? I've been planning on a passive line stage, but I'd like the option of going active later on.

Edit: Oh wait a minute, you could probably use the loop for that couldn't you?

 

[ToddW]

Quote:

Originally Posted by splaz /img/forum/go_quote.gif Well as blip said there are a lot of ways to go about it. Goes to show, I was tired last night, just crashed form a caffeine high and now I wakeup and wonder what I was thinking. The way I put up is a bit unnecesarily complex. Threw this much simpler version together in a fraction of the time, 2 SPDT switches/relays this time around. What I think he wants blip is to choose which of the two inputs he wants and then which of the two outputs he wants to play it. Don't have much experience with relays but it shouldn't be too hard to put together, I'd agree latching would be the better choice. I'm buying a lot of latching DIL DPDT telecoms relays cheaply to mess around with for audio. Might not need a microcontroller if it's the way I think, just the circuitry to operate the relay and maybe two buttons that decide input and output respectively. Although if it is what I think it probably would be a lot easier just with switches.

Thanks for the help everyone it seems that the the quick drawing that splaz worked out seemed to be the way i was going to do it. When I get something drawn out I will post a schematic, hopefully in the next couple of days with the holiday around maybe i can get something that i want to do instead of real work!