Pedal jack question

[Antonio1963]

According to the build diagrams the input jack has three wires. One to ground, one to the board input, and one to " PWC in ring" on the board.  From what I can tell The PWC from the DC power jack also goes to the input jack as well.  My question is if the ground is the outside of the input jack , and the tip is the input signal,  what is the third lug of the jack for? It looks like it contacts the side of the mono plug. Can anyone shed some light on this ?

[Mark Hammer]

Historically, stereo input jacks have been used in pedals as a means of automatically engaging and disengaging an internal battery.  If a mono plug is inserted into a TRS stereo jack, the shaft of the plug will also make contact with the ring connector, connecting the black ground wire from the battery to ground, but leaving it "floating" when the plug is removed.

The 2.1mm power jack does the complementary thing.  It too has 3 lugs: one for ground and two for power.  When there is nothing inserted into that jack, the battery is connected to the circuit board as its power source.  When a plug is inserted, the battery connector is nudged out of the way and the power comes from the external supply.  The power jack trumps the stereo input jack, such that even though inserting a mono plug is supposed to engage the battery, sticking a plug into the power jack disconnects the battery.

NOTE, however, that the location of the tip and ring lugs on stereo phone jacks is not consistent across brands.  Many people here, over the years, have inquired why the battery in their pedal kept dying so quickly, only to find out that they had wired it up to the wrong lug, such that it remained connected even when the phone plug was pulled out.  Always good to verify which solder lug goes to which contact.

[PRR]

Welcome.

--- edit- ah, Mark probably said all this but it's already typed.....

> looks like it contacts the side of the mono plug.

The grandfather of that jack was for telephone patching. Two signal wires and a common. Tip, Ring, Sleeve. This "balanced signal" allows running miles of unsheilded pair without large interference.

A simplified/cheapened form with just Tip and Sleeve was introduced for mono headphones and general jackery. This is what we call "guitar jack and plug".

The jack in the form you show was introduced for Stereo Headphones. Left, Right, Common.

Those are the "proper" uses of TS and TRS jacks and plugs.

*Guitar Pedals* do something strange. Wire signal on T and S as normal. But then we wire the groundy end of the battery to the R contact. With no plug, no connection, battery is not drained when no plug is inserted. When a TS plug is inserted in a TRS jack, as you noted the R is now shorted to S via the TS plug's sleeve. Now the battery circuit is complete and the pedal gets power.

[Antonio1963]

 So if I plan to run this pedal solely on 9 V from a power supply, and not a battery, I don't need that third wire on the input?

[Mark Hammer]

Correct.

[Antonio1963]

Thank you for the help.

[antonis]

Correct.

I shouldn't say it untill I see his power company bill..!!!