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Turn circuit on when another is broken? Answered

I am having a delema on how I should have my preamp that I am assembling turn on. I don't want to use a toggle switch or anything, because I always forget to turn it off, and I end up draining the battery.
So, I was thinking of having some sort of system that involves turning the preamp on when a 1/4 audio cable is plugged into the jack.
However, I don't want to use the common method, having ground and the second pin shorted by the barrel of the audio cable (jack plug switch is the only name I can find associated with it...)
Thing is, some of the cables that will be plugged into it aren't mono, so it wouldn't work. In fact, if I plugged my headphones into it, it would run 9v through one of the drivers... Don't want to do that.
I noticed the jack I purchased has six pins. Three for audio, and three that connect to the other three ONLY WHEN NOTHING IS PLUGGED IN. When something is plugged in, the three metal contacts are lifted off of the other three pins. Since this device will only be mono, I was planning on connecting the left and the right together. This would mean, that when nothing is plugged in, the other set of pins (that aren't connected to anything when something is plugged in) would be connected, but when something is plugged in, the circuit would be broken.
So, is it possible to use those two pins as a switch? Thing is, I need it the other way around: when the circuit is closed, the amp is off. When the circuit is open, the amp is on.
How would I invert it?
And what gate is it called?
Thanks!

EDIT: A NOT gate is what I am looking for. Is there any simple way of making one, for such a situation? The power supply is 9v, and it would be switching it on and off.

Discussions

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Downunder35m

3 years ago

Why not do it quick and dirty?
You need a switch and something to activate it without using power - that's a hard one!
But thankfully someone already solved this problem for watertight flashlights and cameras.
Cut a bit of the plastic off the jack - enough to fit a tiny neodymium magnet in there.
Old hard drives have a tiny one on the arm for the heads and you can get slightly bigger ones in tattoo shops and for jewlery, you know like these earrings without piercing?
Now add a little reed switch where the plug goes in so that the magnet will sit right on it when plugged in.
For greater distance (behind the front panel) you might need a magnet of at least 3mm in diameter.

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RocketPenguinDownunder35m

Reply 3 years ago

Off of the jack- You mean what is on the cable (male)?

I can't modify every single cable I will use... Nor would I want to modify my headphones :P

Thing with modifying the jack to the extent of putting a switch in it (Like a push button, when the 1/4 male jack is plugged in, the tip pushes the button) is that it is bound to break or stop working (IE, button moves out of place)

I wouldn't want that...

(Thing is, I am currently abroad in Europe, and sourcing parts such as reed switches is a lot harder and expensive than if I would be in the US...)

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Downunder35mRocketPenguin

Reply 3 years ago

I said a reed contact and a magnet on the plug to activate it.
Neither see the problem with it, nor how this would be a serious mod....

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RocketPenguinDownunder35m

Reply 3 years ago

Sorry, but I'm confused.

If the magnet and the reed switch are in the jack, then how is the magnet (Or the reed switch) moved??

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Downunder35mRocketPenguin

Reply 3 years ago

You did not read my first on properly or failed to explain it properly.
The reed conatc is located in or at the case of your amp - the magnet is located on the plastic part of your jack.
You insert the jack, magnet closes the reed contact - job's done.
It is only a matter of finding the right size (strenght) magnet for the disatnce you have to bridge.
In my tests I get reliable switching with 2x2x3mm neodymium magnet at a distance of 4mm

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gmoon

3 years ago

Looking at your requirements (and responses), why not use the stompbox trick you've already eliminated (stereo jack, shaft of plug closes the circuit)? No current draw there. Since all your signals are mono, just get a couple new cables with mono plugs.

Otherwise-- and speaking from experience: all my F/X use switching supplies except a positive-ground Fuzzface (battery only), and I still sometimes forget to unplug it. A day or so later, and the battery is dead. The best engineering here depends on you actually unplugging the input cable.

So--how is that any different than having an old-school on/off switch?

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RocketPenguingmoon

Reply 3 years ago

Because will always unplug it when finished (It would be transported a lot, and thus cables would never be left plugged into it. That, or I need my headphones elsewhere.). The main device that will be plugged into it, is my headphones, which aren't mono. Other people will also use it, and I have no idea what type of cable they will use.

I have thought of using the ground pin plus the metal screw collar that is used to mount the jack as my second pin, however, I am afraid of 9v going through my headphones, or possibly the amp it would be plugged into. How great is the likelihood of this? Using a multimeter, I have found that the collar closest to the ground (Can't remember if it is left or right) does in fact make contact with one, while the other makes contact with the ground (Thus causing the 9v to be fed through the driver before getting to the circuit.). Now, I'd rather *not* fry my 150$ headphones because of some irresponsible methods of switching...

Yes, I guess I could get a mono converter for it... But, that would probably be left in it, making the whole "Unplugging will turn it off 100% of the time" false. (The adapter wouldn't be removed from the preamp... Which would leave me at square one.)

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gmoonRocketPenguin

Reply 3 years ago

OK, a question, and another thought:

Are the headphones high-impedance (like 600 ohms)? 9VDC through 600 ohms is like 1.5 mA, which wouldn't cause any problems... Probably wouldn't be the full 9V anyway, as the preamp would be in series with the switch.

The thought: place a push-button switch inline with the jack, where the plug pushes a plastic rod and closes the switch. Maybe a micro-switch...

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RocketPenguingmoon

Reply 3 years ago

38 Ohms (Audio Technica M50)

I was thinking of a push button as well... But that requires modifying the jack... It may be the only option I am left with though.

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dudes

3 years ago

If there is always power available, it would be simple enough to make a not gate with a resistor and a mosfet. While the circuit is closed (amp off), the not gate draws a couple microamps, so it always needs a power supply. Would something like this work, or does it need to not draw any power?

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RocketPenguindudes

Reply 3 years ago

I would *prefer* a solution that doesn't involve any current draw. (It may sit in storage for x weeks, etc. I could always put a toggle switch on it, and have that work as a primary, but then it gets over complicated)

Any other ideas of how to have it turn on and off via the 1/4" audio jack? Doesn't necessarily have to be a NOT gate...

My biggest fear of something that uses the audio plug barrel as a contact is accidentally sending 9v through my headphones...

This is the audio jack I have: http://www.neutrik.us/en-us/plugs-jacks/m-series/nmj6hcd2

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dudesRocketPenguin

Reply 3 years ago

I have no idea how you could do something like that without any power draw. it would have to be purely mechanical, but I haven't a clue how to do that. Also, after drawing up the schematic for my previous idea, I realized that it wouldn't work either, so I really have no ideas. Wish I could be of more help, good luck.