Op Amps and the stereo jack kill switch

[Electric_Death]

Looks like I stumbled into the wrong forum when I posted this earlier.
My question is, how do I use the stereo jack to switch off the circuit when the battery's ground can only be directly connected to the op amps negative power rail which can't be grounded out?

I've not been overly dedicated to the hobby of building stompboxes and when the bipolar power circuits I built didn't seem to work properly once I started working with op amps, I toughed it out using dual batteries and simply pulled them when I wasn't playing.

After altering my gain set resistor values a bit, it seems reducing the multipliers solved the issues with the bipolar circuit..maybe I was just trying to draw too much power? Dunno and can't say I care because now I'm able to power it with a single battery or a wall supply and it performs exactly as I desired. I couldn't be happier with the results, particularly because I designed the circuit myself based on the basic op amp driven multiplier but it's time I get organized so I can start sticking it in sealed enclosures and etched some boards.

Am I actually supposed to run the "virtual" ground to the ring?

[Mark Hammer]

If the battery has no path to ground then current will not flow.  You COULD do that with an on/off switch, but the stereo input jack can do it for you if using a single battery supply with floating ground (i.e., gnd = +4.5Vdc).

So how do you make and break a ground connection to the battery with the jack?  If the plug inserted into a stereo phone jack is a stereo plu, then the ring contact on the jack will only be in contact with the ring contact on the plug.  But if the plug inserted into the jack is a mono plug, the both the ring and ground contacts of the jack with contact the ground on the plug.

And that's how you can have a ground contact for the battery that is ONLY made when a mono plug is inserted.

[Electric_Death]

Unfortunately, the negative power rail on the op amp can't connect to ground and still work with the current configuration.
I'm using this:



I'm running it as such and it's worked fine:


If I connect the op amps negative rail to the common ground, the circuit of course ceases to function.
Should I be running the common 4.5 to the ring tab of the stereo jack?

[frequencycentral]

Should I be running the common 4.5 to the ring tab of the stereo jack?

No.

Earth is earth. The opamp is getting what it needs from your power configuration, it's getting "what it thinks" is bipolar power. But your 4.5 is not earth, it's vref. Earth is earth. Connect the battery earth to the ring tab of the stereo jack. 

[Electric_Death]

Should I be running the common 4.5 to the ring tab of the stereo jack?

No.

Earth is earth. The opamp is getting what it needs from your power configuration, it's getting "what it thinks" is bipolar power. But your 4.5 is not earth, it's vref. Earth is earth. Connect the battery earth to the ring tab of the stereo jack. 

Uhhhh yeah, so for the third time I will again say.
When I connect the battery's earth to the ring tab, the circuit ceases to function.

Any time I connect the negative voltage rail of the op amp to the "vref" the circuit uses as it's common, it goes dead. Connect it to only the battery's ground and it powers just fine.

[scratch]

one way to deal w/ bipolar powered projects, is to use TRS jacks on both input an output, connect your 'postive' battery to the ring of the input jack, and connect the 'negative' battery to the ring of the output jack, then you have to remember to pull both plugs out to power down.  It's a pain ...

[frequencycentral]

Any time I connect the negative voltage rail of the op amp to the "vref" the circuit uses as it's common, it goes dead. 

Yup - but why would you want to do that? The negative voltage rail of the opamp should be connected to the battery's ground. Vref is not ground - but can be intellectually treated as ground when interpreting some schematics.

Connect it to only the battery's ground and it powers just fine.

Yup - that's where it should be connected - so the problem is?

When I connect the battery's earth to the ring tab, the circuit ceases to function.

Is the sleeve connected to the opamp's negative voltage rail? It should be.

[Boogdish]

Maybe a visual will help you, take a look at this:

http://www.generalguitargadgets.com/pdf/ggg_dist_plus_lo.pdf

it's the wiring diagram for the MXR Dist+ from GGG.  It's a really simple circuit using an opamp.  The negative of the battery is connected to the ring of the jack and the sleeve is connected to ground.  Vref in this circuit is at the junction of R2 and R3 near the bottom of the board.

[R.G.]

The answer is at GEO.

See the power switching here: http://geofex.com/FX_images/splitter.gif the three transistor circuit in the dotted line lets you use the ring of the input jack to turn on a transistor which then turns on the + and - voltages.

[slacker]

What are you using as you signal ground? What I mean by that is where are you connecting the sleeves of your in and out jacks?

If you're using the 4.5volts as your signal ground then that would explain why the circuit wont work with the battery negative connected to "ground" because then you're shorting the 4.5 volts to the battery negative.

Could you post the schematic you're using that would make it much easier to see what the problem was.

[Electric_Death]

What are you using as you signal ground? What I mean by that is where are you connecting the sleeves of your in and out jacks?

If you're using the 4.5volts as your signal ground then that would explain why the circuit wont work with the battery negative connected to "ground" because then you're shorting the 4.5 volts to the battery negative.

Could you post the schematic you're using that would make it much easier to see what the problem was.

That is exactly what I'm doing, the 4.5 serves as the common of the entire circuit. The pots ground out to it, the input/output jacks ground out to it etc.
There is unfortunately no schematic as I have utilized the basic multiplier as the core then built my own design from there.

[d95err]

Looks like there are two solutions:
a) Use the circuit R.G pointed to
b) Redesign the circuit to use the negative battery pole as ground and 4.5V as just a voltage reference. I.e ground the pots to the negative battery pole etc. You may need some extra coupling caps at some places to handle this. If you at some point want to use the circuit with a battery eliminator this is probably a good idea.

[Electric_Death]

Thanks for all the responses.
With this build the obvious answer is just throw a kill switch in there and make the necessary changes to the design for the day I decide to etch some boards. As it is I find myself fine tuning it, adding switches, extra components and soon an internal thumb wheel so if I don't wrap this fiasco up, I'll end up compromising what is already perfection imo and having the chassis bursting at the seems.
Ultimately I need to get it portable since I detest the sound of store bought pedals and it's the only overdrive I'll use but, it's not going to kill me to slap a power toggle in there when I'll be primarily powering it with a wall wart anyway.
I've made the commitment to rechargeables and have a great habit of keeping them juiced at all times but currently it's a bit senseless when I never take it outside the home and even if I do, I'll still wart the bastard.

The options of commercial pedals has simply made me a greedy perfectionist

[frequencycentral]

That is exactly what I'm doing, the 4.5 serves as the common of the entire circuit. The pots ground out to it, the input/output jacks ground out to it etc.

That's not going to work out with the TRS jack, as you will be grounding the 4.5 volts - short circuit.

4.5 volts is not ground.

There is unfortunately no schematic as I have utilized the basic multiplier as the core then built my own design from there.

Can you work up a schematic yourself?

[slacker]

4.5 volts is not ground.

Can be sort of if you make it have a look at the  GGG 6 band EQ Using a single battery that is basically the same as what Electric Death is doing. It uses the middle of the resistor divider between the battery + and - as ground giving a +4.5,0,-4.5 supply.  This works fine if you use a battery or if you use only that pedal and a wallwart, it won't play nice with other wallwart powered pedals though.

Reconfiguring the circuit like d95err suggested is the easiest solution to the problem though.

[Electric_Death]

Actually the easiest solution at this stage of the build is a kill switch

I've connected it to a half dozen other pedals, no problem due to the common or anything so I'll worry about the grounding situation as I revamp it and canibalize the core circuit to build new things.
So far it's served as a killer overdrive, a fuzz and a horn synth.
I'm hoping to evolve it into a full blown preamp with active EQ to use for my own brand of amps.

I'm not sure if it's a good thing but, it's performance and versatility has me frowning at tubes more than every.