Very easy audio switch box?

[jdonnici]

I've got an idea for a very simple project, but have been unable to
find some info for it online... before I make a go of it "blind", I
figured I'd post for some ideas.

Basically, I've got 3-4 audio devices in my office and one set of
speakers. All the audio devices have 1/8" stereo jacks for ourput
while the speakers use a 1/8" stereo plug. Currently, I unplug and
plug those speakers as needed, but it can be unwieldy. What I'd
like is a simple little box with some switches so that I could
quickly switch between source devices. I don't see a need for
having more than one device selected at a time.

Radio Shack makes a simple little "stereo audio source selector"
switch box, which would be perfect, but all the I/O on it is RCA
phono. By the time I buy it and all the little adapters to go from
RCA phono to 1/8 jack/plug, I could probably do it cheaper on my
own... or at least have more fun with it by the time I'm done.

Now... is it safe to assume that I can just buy a small project
box, some jacks and some switches, and wire it all up inside the
box? Or will I need to do something with resistors or other
components to not screw up the sound quality (and/or the
equipment!)?

I know very little about the inner workings of electronics, but I'm
happy to learn and this seems simple enough. I do own a soldering
iron (from a project waaay in the past), as well as other various
tools... and RS is right around the corner. :)

Any insights or pointers to relevant URLs would be most
appreciated. I tried googling on all sorts of combinations of
"stereo audio switch box", etc, but mostly seemed to find amp-
related projects.

Thanks in advance for any help,

J

[Kevin McMurtrie]

In article >,
jdonnici > wrote:

>I've got an idea for a very simple project, but have been unable to
>find some info for it online... before I make a go of it "blind", I
>figured I'd post for some ideas.
>
>Basically, I've got 3-4 audio devices in my office and one set of
>speakers. All the audio devices have 1/8" stereo jacks for ourput
>while the speakers use a 1/8" stereo plug. Currently, I unplug and
>plug those speakers as needed, but it can be unwieldy. What I'd
>like is a simple little box with some switches so that I could
>quickly switch between source devices. I don't see a need for
>having more than one device selected at a time.
>
>Radio Shack makes a simple little "stereo audio source selector"
>switch box, which would be perfect, but all the I/O on it is RCA
>phono. By the time I buy it and all the little adapters to go from
>RCA phono to 1/8 jack/plug, I could probably do it cheaper on my
>own... or at least have more fun with it by the time I'm done.
>
>Now... is it safe to assume that I can just buy a small project
>box, some jacks and some switches, and wire it all up inside the
>box? Or will I need to do something with resistors or other
>components to not screw up the sound quality (and/or the
>equipment!)?
>
>I know very little about the inner workings of electronics, but I'm
>happy to learn and this seems simple enough. I do own a soldering
>iron (from a project waaay in the past), as well as other various
>tools... and RS is right around the corner. :)
>
>Any insights or pointers to relevant URLs would be most
>appreciated. I tried googling on all sorts of combinations of
>"stereo audio switch box", etc, but mostly seemed to find amp-
>related projects.
>
>Thanks in advance for any help,
>
>J

A simple switch is all you need; no terminators or mixers. RS sells a 2
pole, 6 position rotary switch.

There is one possible problem, though - a ground loop. If you get AC
hum, you'll need a 3 pole switch so you can switch the ground too. Some
electronics stores have switch components so you can build any custom
switch.

[dB]

jdonnici > wrote in message >...
> I've got an idea for a very simple project, but have been unable to
> find some info for it online... before I make a go of it "blind", I
> figured I'd post for some ideas.
>
> Basically, I've got 3-4 audio devices in my office and one set of
> speakers. All the audio devices have 1/8" stereo jacks for ourput
> while the speakers use a 1/8" stereo plug. Currently, I unplug and
> plug those speakers as needed, but it can be unwieldy. What I'd
> like is a simple little box with some switches so that I could
> quickly switch between source devices. I don't see a need for
> having more than one device selected at a time.
>



You can do it with a two-pole rotary switch with the number of
positions corresponding to the number of audio sources you have - or
maybe one or to more to allow for future additions.

You will need to decide how to connect the sources to the box, (1/8"
stereo jacks and leads with a plug on each end, for instance.)

The "ground" side of each of the inputs need to be connected together
and to the output "ground".

The left channel "hot" inputs each go to a switch position on one
section of the rotary switch, the right channel "hot" inputs to the
corresponding positions on the other switch section. The switched
(moving) contact of one section goes to the left connection on a 1/8"
output jack, and the switched contact of the other section ...... you
can guess the rest.

If you have a choice between a "make before break" and "break before
make" switch, choose the latter.

[Robert Rowton]

Hello,
This is a very simple project, and all the parts needed are available
at Radio Shack. And you won't need any resistors. I recommend using an
aluminum box for shielding purposes, and the common ground connection
can be made through the box itself by simply mounting the jacks on the
panel, so you'll just need two wires from each jack going to the
switch. Here's a parts list:

Switch:
2 pole 6 position non-shorting rotary
P/N 275-1386
$2.99
(This switch has 6 positions which is more than you need, so you can
leave the other positions unconnected, or use 6 jacks for future
expansion.)

Jacks:
1/8" 3 conductor open circuit chassis mount
P/N 274-249
$2.99 / pkg. of 2

Minibox:
P/N 270-238
$2.99

Of course, you'll also need some wire, rosin core solder, a drill and
bits for making the holes, pliers and wire strippers, and a knob if
you want. Here's a crudely drawn wiring diagram that should get you
through. If you're using a text-only server, you can get the diagram
from my site at
http://mywebpages.comcast.net/bobrowton/diagram.gif

While you're there, you might check out the very cool Honda ad at
http://mywebpages.comcast.net/bobrowton/index.html

Good luck.

[Kevin McMurtrie]

In article >,
"Bullwinkle Jones" > wrote:

>"DarkMatter" > wrote in message
...
>> On Tue, 15 Jul 2003 07:49:45 -0600, Robert Rowton
>> > Gave us:
>>
>> Hey dumb****! Do NOT post binaries into non binary groups!
>
>Wowee.. lets not get _too_ angry. It was only a 10k binary, after all. Even
>the poor soul out there who still uses a 14.4kbit modem wouldn't even have a
>problem.
>
>

You still can't do it. Most news servers filter out binaries from text
groups. Some people also run bots that cancel binaries in text
newsgroups. Whatever the case, it never arrived here.

[Kalman Rubinson]

On Tue, 15 Jul 2003 23:05:47 -0600, jdonnici
> wrote:

>1 - Is that possible, or would that screw things up in terms of the
>signal flow and/or make it much a more complex effort?

Not more complex but, potentially, a problem for the devices. Multiple
simultaneous loads might exceed the capability of your source device.
It also makes it possible for their to be nothing connect although
this is less of a problem in general.

>2 - If it is possible, which type of switch would be the most
>correct to use? I saw plenty of SPST, SPDT, and DPDT switches... I
>could see the differences on them visually, but wasn't sure which
>would be most appropriate. Also the RS packaging doesn't have any
>type of wiring diagram, so it was hard for me to see precisely how
>I'd wire it all together.

Stick with the diagram/circuit you have.

>3 - Would it be reasonable for the output side of each toggle
>switch to be wired to the output jack? Seems I'd have 4-6 pairs of
>wires going into that one jack and may need to be more creative to
>make that work.

Vide supra.

>Next.. I did find the 2-pole, 6-position rotary switch and that
>diagram was very helpful in terms of helping me see the way that
>would all be connected.
>
>The concern I had with that is that the "post" for the switch
>seemed like it was much longer than any of the matching knobs would
>really work for.

Intentionally. You cut off as much as necessary to make it work.

>In other words... I drill a hole for it, mount the rotary switch to
>the inside of the box, and then stick a knob on the end of it --
>but the base of that knob could be sticking out a half-inch or some
>from the box's external surface.

Vide supra.

>How is that normally handled? Was I not looking for the right knob,
>is that post usually trimmed to size (yikes... I'd be afraid of
>ruining the switch), or am I missing something else altogether?

Vide supra.

Kal

[Bullwinkle Jones]

"Kalman Rubinson" > wrote in message
...
> On Tue, 15 Jul 2003 23:05:47 -0600, jdonnici
> > wrote:
>
> >1 - Is that possible, or would that screw things up in terms of the
> >signal flow and/or make it much a more complex effort?
>
> Not more complex but, potentially, a problem for the devices. Multiple
> simultaneous loads might exceed the capability of your source device.
> It also makes it possible for their to be nothing connect although
> this is less of a problem in general.

Well, he could do this, he'd just need to buffer it with an op-amp or
somesuch.

[Robert Rowton]

On Tue, 15 Jul 2003 23:05:47 -0600, jdonnici
> wrote:

>In article >,
says...
>
>> If you're using a text-only server, you can get the diagram
>> from my site at
>> http://mywebpages.comcast.net/bobrowton/diagram.gif
>
>Thanks to all who responded. This was very helpful info. I actually
>went to RS tonight and found these parts. I stopped short of
>picking them up, though, because I had a few questions...
>
>Suppose I were to have 4 inputs and each input had a toggle switch
>instead of using the rotary switch to move between them? It seems
>that it would be possible in that case to have two devices "on" and
>connected to the speakers at once, or for various combinations of
>devices to be "on". Could be a cool option...
>
>1 - Is that possible, or would that screw things up in terms of the
>signal flow and/or make it much a more complex effort?

Yes, that is an option, but it's ill-advised. You'd be shorting the
various outputs together, which is a load they weren't designed to
drive. Most consumer gear is pretty fault-tolerant so it probably
wouldn't damage anything, but you never know. Also, unless at least
all but one of the sources in question has an output level control,
you wouldn't be able to adjust the relative volume of the sources. The
proper way to mix audio signals is with a mixer.

>2 - If it is possible, which type of switch would be the most
>correct to use? I saw plenty of SPST, SPDT, and DPDT switches... I
>could see the differences on them visually, but wasn't sure which
>would be most appropriate. Also the RS packaging doesn't have any
>type of wiring diagram, so it was hard for me to see precisely how
>I'd wire it all together.

Since you'd be switching stereo (two-channel) sources, you'd need DPDT
(Double Pole - Double Throw) switches. A wiring diagram is shown
below.

IN 1 L OUT L IN 2 L
O O O

O O O
IN 1 R OUT R IN 2 R

>3 - Would it be reasonable for the output side of each toggle
>switch to be wired to the output jack? Seems I'd have 4-6 pairs of
>wires going into that one jack and may need to be more creative to
>make that work.

The way to avoid the resulting rat's nest of wires going to the
output jack would be to connect the outputs of the first switch to the
outputs of the second switch and the outputs of the second switch to
the output jack. Actually, this just relocates the rat's nest to the
second switch.

>Next.. I did find the 2-pole, 6-position rotary switch and that
>diagram was very helpful in terms of helping me see the way that
>would all be connected.
>
>The concern I had with that is that the "post" for the switch
>seemed like it was much longer than any of the matching knobs would
>really work for.
>
>In other words... I drill a hole for it, mount the rotary switch to
>the inside of the box, and then stick a knob on the end of it --
>but the base of that knob could be sticking out a half-inch or some
>from the box's external surface.
>
>How is that normally handled? Was I not looking for the right knob,
>is that post usually trimmed to size (yikes... I'd be afraid of
>ruining the switch), or am I missing something else altogether?

The shaft is an industry standard length; you just hacksaw off the
excess.

>Thanks again for the help... I really appreciate it and am looking
>forward to the project later in the week.
>
>Regards,
>
>J

[Kalman Rubinson]

On Thu, 17 Jul 2003 03:39:55 GMT, "Bullwinkle Jones"
> wrote:

>
>"Kalman Rubinson" > wrote in message
...
>> On Tue, 15 Jul 2003 23:05:47 -0600, jdonnici
>> > wrote:
>>
>> >1 - Is that possible, or would that screw things up in terms of the
>> >signal flow and/or make it much a more complex effort?
>>
>> Not more complex but, potentially, a problem for the devices. Multiple
>> simultaneous loads might exceed the capability of your source device.
>> It also makes it possible for their to be nothing connect although
>> this is less of a problem in general.
>
>Well, he could do this, he'd just need to buffer it with an op-amp or
>somesuch.

He's having technical difficulties wiring a switch; why advise him to
start messing with buffers?

Kal

[jdonnici]

In article >, kr4
@nyu.edu says...
> He's having technical difficulties wiring a switch; why advise him to
> start messing with buffers?

Fair question... and not to worry -- I'm going with the nice simple
rotary switch. ;)

I picked up a couple of 'build it yourself' kits the other day, as
well as a book called something like 'electronics projects for
musicians' -- in the hope of learning more about this new world.
I'm a software developer by day, so I'd love to start learning
something about circuits and hardware logic.

[jdonnici]

> Yes, that is an option, but it's ill-advised.

Good to know... I don't want to mess with anything that could screw
any of the devices up, so I'll stick with the rotary.

> The proper way to mix audio signals is with a mixer.

Understood... I've got a couple of those, but the notion of
actually wiring one or trying much beyond a "solder by numbers" is
foreign to me right now. :)

> The shaft is an industry standard length; you just hacksaw off the
> excess.

Ok... that makes sense. I'll need to makeshift a vise so that the
vibration of the sawing doesn't damage the rotary switch.

Thanks again VERY much for your assistance. I really appreciate it!

I picked up Craig Anderton's book on 'electronics projects for
musicians', as well as a couple of project kits, so I'm hoping to
learn my way around this stuff a bit more.

Thanks again,

J