Stereo or mono jack: a newbie question

[zener]

Do all stompbox have to come with 1 stereo and 1 mono jack? What is the difference between the two? Can't it be both mono or both stereo?

[Rob Strand]

Usually at least one is stereo (usually the input) because the socket's "Ring" connection is used to switch the battery on/off when the jack is inserted.  For the non-switched jack it doesn't matter what you use.

[smoguzbenjamin]

There's a siple difference between a mono and stereo jack    Mono has one ground lug and one channel, and a stereo jack has one ground lug and two channels.

But in a stompbox, the ring and sleeve lug are indeed used to switch the battery, because when you plug in a mono jack, the ring and sleeve lug are connected. At least I know that much!  

[Mark Hammer]

They don't ALL have to use one stereo and one mono.  As is pointed out, the stereo input jack has become a standard way of dis/connecting the power by un/grounding the battery.  Of course, if you don't *use* a battery, either because the pedal draws too much current for battery use, or because you've made a conscious decision to power all your pedals from an external power supply, there is nothing for the stereo input jack to do, other than carry a signal, so in those cases you can use mono jacks at the input and output.  I have an old Boss flanger that doesn't have a hope in hell of running off a 9v battery (there IS no battery snap inside), so the jacks are both mono.

Some players/builders prefer to have the option of leaving pedals plugged into each other on a pedal board, in which case you either have to use an external supply, or else have some means for turning the battery off, even while plugged in.  There are pros and cons to using switches instead of stereo jacks.  One advantage is that you can leave things plugged in.  A second is that turning on 2 batteries for a bipolar supply is trickier with jacks (although RG has a method to do it with one jack).  One disadvantage is that using switches means more machining and planning for where it should be installed.  A second problem is that you can accidentally turn a switch on and be draining batteries without realizing it (as opposed to unpugging a cable, which you'd obviously know if you had or hadn't done).  Fortunately, you can get fairly low profile slide switches that won't be moved unless you really want them to.