1/4 inch jack noob question

[micro]

Whats the difference between an open and closed circuit 1/4 inch jack?

Im new here.

[GibsonGM]

Well, I'll take a stab at it (welcome, BTW!)....this must be referring to 'switching jacks'...closed circuit being that the 'switch' is closed with no plug, and open circuit implying that a contact is made when a plug is inserted.  Check this link for a definition for ya:

http://en.wikipedia.org/wiki/Jack_plug

[John Lyons]

Micro

An open circuit jack has two lugs, sleeve/ground and hot/tip. When you plug in a cord you connect the tip of the plug to the hot connection of the jack and the sleeve of the plug to the sleeve/ground of the jack.

A closed circuit jack has three lugs. One of the lugs (usually the tip lug) has a finger that connects to the third lug internally when there is no cord inserted. When the cord is inserted the connection is broken and the tip lifts away from the third and no connection is made. It's like a switch built into the jack. You can get jacks with two or more of these switched connection built in.

For most FX you want open circuit 1/4 jacks for the output and A stereo 1/4 jack for the input which will switch on and off the battery connection.

John

[CGDARK]

Whats the difference between an open and closed circuit 1/4 inch jack?

Im new here.

Welcome.
Here you can find useful information for the beginner and as reference for the future.
http://www.diystompboxes.com/wiki/index.php?title=DIY_FAQ

CG

[micro]

Thanks alot guys. Now, is this used for normaling two jacks? Is the battery power switch the only use as it applys to guitar pedals? Trying to understand the application...

[Mark Hammer]

A closed-circuit jack "does something" when no plug is inserted.  Or rather, it has the capacity to do something, depending on how you wire it up.  For instance, some of those Marshall-type plastic phone jacks can come with 6 legs, 3 per side.  When a plug is inserted each of the three spring-leaf contacts inside (tip, ring, shaft) is moved out of the way of a second set of contacts (i.e., their normal no-plug-inserted contact is broken).  This sort of a jack is a sort of generic jack that could be wired to accomplish any of several possible switching actions.  Of course, if you simply ignore the second set of contacts, it works like any old stereo jack, and if you ignore the ring contacts, it works like any old mono open-circuit jack.

Since closed-circuit jacks complete specific connections when nothing is inserted into them, they are often used for the convenience  of establishing "default" connections, commonly referred to as "normalized".  So, imagine you had a pair of mono closed-circuit jacks used for send and receive in an effects loop on an amp.  If you aren't using the loop, do you really want to have to stick a patch cord between those jacks just to  mimic a direct connection?  Nah.  So the jacks are wired up using the alternate contacts to provide a normalized connection.  If nothing is plugged into the send jack, then the hot lead is automatically connected to the hot lead of the receive jack.

Normalizing is also used in older analog synths.  If a VCF, for instance, has no external envelope voltage patched/plugged into its CV-in jack, then it will take a feed from the ADSR generator included in the synth, by default; i.e., the "normal" connection.

Closed circuit jacks come in a several flavours.  You can get some stereo switching jacks that can have multiple sets of SPDT contacts.  For example, headphone jacks on some audio equipment will automatically  redirect the output signal in multiple ways when a headphone plug is inserted into it.  In these instances, insertion of the plug pushes a plastic actuator that indirectly accomplishes the switching action.  This is in contrast to the more common type where inserting the plug directly brings the plug into contact with something, and lifts that contact out of the way of something else.

The long and the short of it is that switching-type jacks provide you with possible connections.  These possiblities do not HAVE to be used.  If you scored a great surplus deal on 9-lug 1/4" headphone jacks and had room for them in your projects (they ARE a little bigger), you could simply use 2 of the lugs as if they were mono open-circuit jacks.

Do keep in mind that as the number of solder lugs add up, the number of possibilities for wiring them up "wrong" also increase, so don't be shy about using any means at your disposal to keep track of whcih lug conencts to where.  We've heard more than one story here about folks who wired up a stereo input jack and couldn't figure out why their batteries were always dying so fast!

[axg20202]

Yes, normaling is an application for these jacks. Switching sockets are not actually required for a mono signal and power switch since this can be achieved, as mentioned in previous posts, by using a 3-pole (stereo) jack, with power ground connection to the 'ring' tab of the socket, forming the switch - when a mono jack is inserted, the power circuit is completed because the jack itself makes a connection between the ring tab and the ground tab. So, if you have a stereo jack socket that has actual switches for each of the 3 terminals you don't actually have to use them for this arrangement.

The normaling function you speak of is possible though. The common use for these is if you want to divert a signal to various points depending on whether a jack is inserted or not. The 'normal' is the signal routing that is exists when no jack is inserted. Jack fields (patchbays) use this principle.

Here's an example use for a stompbox. You have two effect circuits (or two stages of the same effect) connected in series and contained in a single box. With the use of a switching jack, you could create an 'Effect 1 OUT' jack which taps off the single from the first effect in the series only when a jack is inserted, otherwise the signal is routed (in the normal, no jack inserted state) to the input of Effect 2 in the box.

Here's another: you have two intruments that you want to share the same FX pedal board but you want one instrument to only use the last few pedals in the chain and you don't want to unhook it every time. Solution: build a small box that has standard in an out sockets connected as a 'thru' direct connection (what comes in goes straight out), but with the in socket also wired up to a further 'insert' socket on the tob of the box (your switching jack socket). The normal could be setup so that when no jack is inserted to the switching jack, the signal flows directly from in to out. When you insert a jack (your instrumenet that only requires the subsequent pedals in your pedalboard), the switching jack disconnects the in socket from the out and routes the inserted jack to the out jack instead and on to the downstream pedals on your board.

Just some applications I have used them for.

Andy.

[micro]

Wow, thanks so much for the detailed replies. It makes complete sense now!