Using guitar jack input to switch circuit voltage on/off

[ziggy]

Hi folks,

Building a small pre-amp circulit to sit between the tone/volume control circuit and the (female) 1/4" output jack connector on an acoustic guitar.

Just now getting to the part were I wan't to make sure that the pre-amp circuit is only powered by its 9-volt battery when a (male) 1/4" jack is inserted.

I have heard that this can be done by ensuring that the female output jack (on the guitar body) is stereo and that the input jack is mono, and then running the negative off the 9-volt battery to the ring connector (on the stereo input) which is then shorted to the sleeve connector (on the stereo input) when a mono jack is inserted? But not sure if I have got all of that right as I cannot find any clear instructions :-S

But then I have heard others saying that this approach is a hack and not recommended ... and I do wonder what would happen if you inserted a stereo jack ... hmmmm?

And then I heard that there were "switched jacks" out there that had this power-on-off functionality built-in, but cannot find any clear information on them either that shows the connections, how they work, etc.

So that is why I am coming to you guys ... help!

Can someone explain all this to me ... or point me to a site that does?

Thanx

Ziggy

[rullywowr]

Welcome!

Yes, you have heard it correctly.  While you can get a more expensive switched jack, you can simply use a stereo jack as you described.  The sleeve of a 1/4" plug is ground anyways. 

If you hook up your battery ground to the ring connection, and the ground to the rest of your pedal with the sleeve connection...then when you plug in a mono 1/4" jack it will connect the battery ground to the pedal ground and complete the circuit.  When the plug is disconnected, there will be an open circuit and no battery drain will occur.

Here is a pic of what's happening from beavis audio's excellent website (http://www.beavisaudio.com/).  The tip goes to your input of effect, and the ring and sleeves will be tied together when a mono jack is inserted since there is no "ring" stripe on a mono plug.  If you are not using a DC jack, just ignore it and run the neg of battery to ring of stereo jack and the pos of battery to your effect.

[midwayfair]

But then I have heard others saying that this approach is a hack and not recommended ... and I do wonder what would happen if you inserted a stereo jack ... hmmmm?

Who told you that? Using the ring as a switch with mono plugs is one of the main uses of stereo jacks. What about it could someone possibly believe is a "hack"?

[jkokura]

But then I have heard others saying that this approach is a hack and not recommended ... and I do wonder what would happen if you inserted a stereo jack ... hmmmm?

Who told you that? Using the ring as a switch with mono plugs is one of the main uses of stereo jacks. What about it could someone possibly believe is a "hack"?

I think because technically these are designed as tip-ring-sleeve jacks, not as a switched jack. In essence, it is a 'hack' to do it this way. Largely we do it because proper switched jacks are actually more expensive than the typical #12B stereo jacks. If you can buy a Mono #11 and a Stereo #12B for about the same money, you can do the 'hack' method instead of paying the extra whatever for the proper #49x (made up number alert) to do the job 'correctly.'

That said, it's a common practice, and so I can see why you wouldn't view this as a hack.

As to the OP's questions, if I understand you, what you're trying to do is run 9V up the cord to the pre-amp in the guitar? My first thought is that you can't do that with Mono jacks, and my second is to wonder if you really even should be. Wouldn't it be easier to use a 9V battery in the guitar? That's how my guitar is setup, and I only need to change the battery every once in a while. (thinking of it... I should go check my battery in my acoustic)

While I don't recommend it, what I'm thinking you'd need to do is use a stereo cord setup with a stereo jack on both the guitar and the preamp. Essentially, you're running hot signal from the guitar to the DI using a the tip of the cable. The sleeve is still ground. What you need to do is include a 9V power source on the ring, and it get's sent from whatever box you're using, up the cord and to the preamp.

The reason I'm not sure this is a good idea is because as you plug your cord from your guitar into whatever, you essentially make contact between the tip and this 9V power source, and I'm not sure that's going to be healthy for your equipment. Not saying it isn't, I just think there are other ways to do this.

Have you thought about putting the preamp in a pedal and just running your hot signal from the guitar into a preamp on the floor, rather than in the guitar? What about including a battery in the guitar itself? You don't need to modify the guitar at all, you can simply apply some stickyback velcro on the inside by the neck block.

Jacob

[ziggy]

Hi Folks,

Thanks for all your help so far.

No I am not planning to run 9-volts up the guitar cable, there will be a 9-volt battery in the guitar and a single output jack - that can be stereo - if I use the ring-sleeve switch option. What I was trying to get across was that whereas on a pedal the R/S switch is on the input jack ... for my guitar, the R/S switch would be on the output jack as there is no input jack as the pickups are the input ... gut guessing that doesn't matter?

Can someone tell me how the switched jacks work as the ones I have seen seem to have 6 legs on them ... so what is happening here, what are all those legs for? Guessing 3 of them are T/S/R ... but what about the other 3?

Thanx

Zig

[jkokura]

A switched jack is pretty simple really. Think of ever switch being an on/off connection. So, plug a jack in, the switch is off. Unplug a jack, and the switch is on.

So, if you use tip, ring, and sleeve connections, you can then choose to ground, or not ground something, connect, or not connect something, depending on if a jack is inserted.

For instance, a common example would be if you want to 'ground' your input when there is no jack inserted. To do so, connect the tip-switch lug with the sleeve-switch lug with a bit of wire. You'd connect your sleeve lug (normal) to ground and the tip lug (normal) to your input on the effect, or bypass switch, or whatever. When a jack is plugged in, the switch-lugs are suspended. They don't connect to anything. But if you unplug that jack, not the tip-switch connects to the tip lug (input) and the sleeve-switch connects to the sleeve lug (ground) and your input is grounded.

Another example is in effects loops. An effect loop should only be engaged when an effect is placed in the loop right? You shouldn't need to include a little jumper cable to go from send and then back to return when you don't have an effect in the loop. To avoid that, you can use a switching jack.

You signal goes: Preamp - Effects loop send - effects loop return - power amp.

If you use switching jacks for the effects loop send and return, you can connect the tip-switch lugs of each jack to each other. The regular tip of each jack goes to it's respective input/output location in the amplifier circuit. So, when no jacks are pluged in, the signal goes: Preamp output - Effect Loop Send Jack Tip - Effect Loop Send Jack Tip-Switch - Effect Loop Return Jack Tip-Switch - Effect Loop Return Jack Tip - Power amp input. When jacks are inserted in there, the switches are lifted, and now the signal goes: Preamp - Effect Loop send - effect - effect loop return - power amp. No need for a little jumper cable, when there's no cables plugged in, the switching jack moves the signal on for you.

Jacob

[davent]

The times i've put fx loops in pedals i used a single switched stereo jack to handle both the send and return, one less hole to drill, premium space saved. Handy devices, great for hacking!
dave

[ziggy]

OK ... at the risk of sounding dim ... you lost me.

From what I am picking up, the 6-legged switched stereo jacks have tip(normal), ring(normal) and sleeve(normal) legs plus corresponding tip(switch), ring(switch) and sleeve(switch) legs?

If I am correct so far, then for my 9-volt battery on/off switch what do I do? Do I simply connect the negative terminal of the battery to the sleeve(switch) leg - which is connected to the sleeve(normal) when a jack (of any type) is inserted and disconnected when the jack is removed?

Thanx

[davent]

Connect the negative terminal of the battery to the ring tab of the jack, the sleeve of the jack gets connected to the PCB/circuit ground. You can use a simple 3 terminal stereo jack, no need for anything more complicated if all you are doing is power switching. Plug in a mono plug and the sleeve and ring are shorted together connecting the battery to the pcb.
dave

[ziggy]

Thanks Dave ... appreciate that I can use a standard stereo jack for this but was wanting to understand how the switched jacks work as I gues the advantage of those is that if for some reason you had to use a stereo jack cable in an emergency you would still have a working circuit.

[rullywowr]

There are many different types of switched jacks, however the most popular is the following "D" one (from wikipedia)


A popular use of the "D" style is to have a headphone jack which cuts out the speaker when a headphone is plugged in.  The grounds would be all connected, and then the speakers (L and R) would be connected to the circles where the arrows are (2nd and 3rd from top).  The audio (L and R) would be connected to the 1st and 4th (from top).  When a headphone is plugged in, those arrow connections would be broken to the speaker and the audio would go to the headphone.

Keep in mind this is only one type of switching jack, and there are a ton out there.  You have to refer to the datasheet/schematic to make sense of exactly how it is designed to work.

[ziggy]

Thanks for all your help folks.

Zig

[dwmorrin]

Ziggy,
The jack you're looking for is probably this one: http://www.allparts.com/EP-4163-001-4-Conductor-End-Pin-jack_p_1381.html  Allparts part number #EP-4163-001
Seems like most of the replies here thought you wanted to know about pedal and amp jacks.
While the pedal world usually uses the "short the ring" trick for the battery, the acoustic guitar world generally does not use that trick.  Open up any Fishman or LR Baggs on board preamp jack, and you'll see something like what I linked to above from allparts.
This avoids a "no output" problem from a TRS cable, and allow for dual signals on one cable (magnetic pickup on tip, piezo pickup on ring).

There are 3 solder lugs on the EP-4163.  Shortest one is for tip connection (main output), middle one is for ring (aux output), and the one closest to the sleeve connection is for the battery negative, and it will switch to ground while keeping the tip and ring isolated.  (Double check the operation of the 3rd lug, as it's been a few months since I had to mess with one of these... but I can't think of any other way it would work. And they do work!)