Stereo and mono jacks

[Dror]

Hi all

Can someone please explain why in some pedals the input is a stereo jack and the output is mono jack  :?:

Thanks  
Dror

[smashinator]

You use the stereo jack to connect the battery when a plug is inserted.  I think there's an explanation of this on geofex, or www.muzique.com.   I can't remember which one it is...

***EDIT***  it might be in the FAQ, also  ***END EDIT***

[Mark Hammer]

The stereo input jack is used for connecting/disconnecting the battery from the circuit in addition to carrying the signal.  The mono output jack serves only one function - carrying the signal.

The input jack can do two things because phone plugs are long.  Where the jack contact for the "other channel" would normally connect if you actually put a stereo plug into that jack, just happens to be part of the lengthy ground connection on a mono plug.  So, if you connect something to that thrid "unused" contact, it remains ungrounded until you insert a MONO plug.  When you inserta mono plug it gets connected to ground.  As luck would have it, you can wire up a battery so that current doesn't flow until one of the leads gets grounded.  In this way, you turn the battery off when you unplug.

The thing about conserving batteries is that while you COULD have a separate switch to turn them on and off, you need to make sure the switch doesn't get turned on accidentally or else you find yourself digging into your gig bag only to find you have a dead pedal that you were all pumped to use.  It also requires extra cost for parts and labour.  Making the battery something that requires an intentional action to turn on (i.e., you have to deliberately insert the plug in the input jack) and exploits an already existing part kills two birds with one stone.

[petemoore]

The sleeve of a mono plug touches the Sleeve and Ring connections of a Stereo jack, making complete the power supply circuit to board, when plug is pulled, the sleeve/ring connection is no longer made, and is a way to disconnect battery without disconnecting battery from battery clip. The ground/negative connection is usually the one lifted when plug is de-inserted.

[Dror]

Thanks  :oops:  it's sounds logical
Sorry for the stupid question, I don't know why I thought it's got something with the ground loop issue.
Thanks

[Mark Hammer]

Not a stupid question.  Mixers will use stereo mic jacks for exactly the reason you suggest - having balanced inputs and a "liftable" ground.  It's just that stereo jacks are used for a different purpose in stompboxes.

[Phorhas]

Can switched Mono jack replace a stereo jack for the power switching pupose?

[Mike Burgundy]

nope - only if you don't mind the pedal being always on. The trick is that the ring gets connected to the sleeve when a plug is inserted. This needs the 3rd connectiuon to work.
There are jacks that include a switch that connects only when a jack is inserted, but theyre rare, probably more expensive than stereo jacks and I'm not even sure it'll work.

[Phorhas]

thanx mike