NOR logic with two switched 1/8" jacks

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FAP
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NOR logic with two switched 1/8" jacks

Post by FAP »

I'm working on a circuit bending project and I'm wondering if anyone had advice as to how to approach this problem:
There's two switched jacks on this unit, let's just say L for left and R for right. Each one is hooked up to a respective L/R speaker.
The way it functions now is, at least one speaker is active as long as one jack remains free (nothing plugged in); both speakers are deactivated ONLY when both jacks are occupied (something plugged in).
In short, the speakers operate on NAND logic. I'm not discriminating between L & R speakers because I ultimately want both of them to essentially function the same i.e. not operating independently from each other
I want to change this configuration, preferably just through wiring/hardware without the use of logic ICs, so that the speakers ONLY turn on when BOTH jacks are UNoccupied: NOR logic, in short.
See attached image.
I'm trying to do this without adding additional switches: just working with the six lugs I'm given (3 lugs x 2 jacks = 6).
Each jack has a +, a -, and a switch lug. When nothing is plugged in, the switch and + lugs are connected; when something (like an audio cable) is plugged in, the + lug is disconnected from the switch lug.
Now I think the best way to do this (aide from logic ICs, of course) would be to buy some kind of special dual-mono 1/8" jack setup that would allow for NOR logic, because I have thus far not been able to do with with just the six lugs I'm given...
Any ideas?
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Re: NOR logic with two switched 1/8" jacks

Post by crochambeau »

In order for your wants to work, each jack must affect both speakers. I assume these speakers are separate channels, and that tying them together in any way will result in crosstalk, which is to be avoided. Doing this in a completely passive manner would necessitate prohibitively complex jacks.

Can we add a couple of relays into the mix?

You could swap out the example jacks for some TRS jacks, both sides. Connect both of the relay positive coil power to the rail, and tie the coil negative together. This results in a single wire that will actuate the relays when grounded. Tie that wire to the ring of BOTH TRS jacks, sleeve to ground, and then tip to whatever signal output you're working with.

This way, when you plug a TS cable into the TRS jack, it activates the relays which switch over.

Now it's just a matter of connecting the "native" amplifier output to the common leg of the relay, and connecting the speaker + to the NORMALLY CLOSED leg (which will pass signal while the relay is unpowered), returning the speaker - to (assumed) ground as normal.

Flyback diode on the relay coil is recommended, and this will make racket on the output wire when you plug and unplug due to relay current being switched through your audio wire (the tip of which will pass by the coil winding). For low noise you 'd need to insert more circuitry, I would use low level CMOS driving a transistor to pull the coil...

But we're a noisy lot so the main example should work.
When in doubt, add resistance.

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Re: NOR logic with two switched 1/8" jacks

Post by FAP »

I assume these speakers are separate channels, and that tying them together in any way will result in crosstalk, which is to be avoided.
Partially correct: they are separate channels, but they output the exact same signal, so no risk of crosstalk per se...
Relays aren't really in my roundhouse, though the TRS idea may be the seed of something I can work with.
That or I'll just repurpose the 1/8" jacks for something else (e.g. external LDR or CV) and slap a single 1/4" mono jack on there, becasue I rarely use 1/8" cables nowadays anyhow.

For reference, here's what I'm bending (unfortunately this is the highest resolution, relevant image I can find):
114794512714.jpg
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It's an """ultrasonic""" pest repeller; note the jacks on either side.
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Re: NOR logic with two switched 1/8" jacks

Post by crochambeau »

If the signal is the same on both speakers, why do you need two jacks? Are the two speakers fed from the same amplifier output, or are they hanging on separate circuits?

I'd just designate one of the jacks as an INPUT and then do the bog standard normalling on the other jack so it cuts both speakers when an output cable is plugged in. That assumes a bunch of things, the big on being that your intended output is coming from the same source as what feeds the speakers (and that source is ONE channel, not two being fed from one osc).

Then split the signal as needed if multiple feeds are desired.

No experience inside one of those, wouldn't surprize me if they have two circuits that set up intermodulation between the transducers, then you're back to the stereophonic end of the puzzle.
When in doubt, add resistance.

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