D.I. jack insertion relay trigger

[atavacron]

I would have thought this a common circuit, and maybe I’m searching wrong, but what logic method are people using to trigger a mechanical relay to switch between a transformer secondary and a 1/4” instrument input? In my case the load is a tube grid but I think it doesn’t matter. The jack is on the front panel, the transformer and tube are deeper into the PCB, and I don’t want to send signal out to the front panel from the transformer.

The rest of the relays in the system are on a ULN2004, and I have a spare channel. I’m working in through hole, and logic voltage is 6V, though I could add a little 5V regulator if need be.

I’d like to use either the shield normal or ring normal on a regular PCB mount TRS jack. Maybe a little trickle of voltage through the normal, and when the ring goes low it triggers an inverter feeding the spare ULN2004 channel, to pull it high? It’s just not coming together visually for me and I need an example.

[It came together in Post #23]

It would be nice to avoid running any voltage through the jack if possible. I have looked at audio sense circuits (rectifier, smoothing, comparator), but I think the potential for flutter is too great. We don’t just run the cold side of a coil to an open ring contact, do we? That’s like 20mA at 5V that the tip has to pass through…

 

[ruffrecords]

The obvious way is to fit a TRS socket.A regular jack plug will short the ring and screen together when it is inserted. You can use this connection to turn on a transistor which operates the relay.

Alternatively you can used a switched TS jack socket. Use the switch on the S to operate the relay.

Cheers

Ian

 

[Voyager10]

If you'll forgive the back-of-an-envelope-CAD, something like this:



You need a jack with a contact which is connected to the 'sleeve' terminal when the socket is empty, and disconnects when the plug is inserted. Most standard plastic jack sockets do this.

When the socket is empty, the transistor base is grounded, the transistor is 'off' and the relay is off. When a plug is inserted, the transistor is turned on by current through the 100K resistor and the relay turns on.

The point is that the current through the relay coil goes via the transistor's emitter to ground, so you can keep this ground connection separate from the jack socket's ground, and therefore away from the audio path.

 

[atavacron]

If you'll forgive the back-of-an-envelope-CAD, something like this:

View attachment 128303

There it is, thanks so much! I was overcomplicating it.

 

[Brian Roth]

If you'll forgive the back-of-an-envelope-CAD, something like this:

View attachment 128303

You need a jack with a contact which is connected to the 'sleeve' terminal when the socket is empty, and disconnects when the plug is inserted. Most standard plastic jack sockets do this.

Hmmm... in my experience jacks with a "switched" sleeve contact don't seem to be very common. But I could be wrong about what is currently available from Neutrik or Switchcraft.

Bri

 

[Ilya]

Hmmm... in my experience jacks with a "switched" sleeve contact don't seem to be very common. But I could be wrong about what is currently available from Neutrik or Switchcraft.

Bri

Neutriks have jacks with switched sleeves. I use them all the time.

 

[Brian Roth]

Neutriks have jacks with switched sleeves. I use them all the time.

OK...cool! It's not an item I've needed in the past. Rather than digging around on the Neutrik website (I'm lazy...lol), do you have specific models in mind? I need to learn more. Thanks!

Bri

 

[Ilya]

These are just one example:
https://www.neutrik.com/en/product/nmj6hc-s

There’re quite a bit more available with the same switching arrangement.

 

[Brian Roth]

Many possibilities with a switched sleeve.

https://www.neutrik.com/media/8557/download/jacks---circuits.pdf?v=1

https://www.neutrik.com/en/neutrik/products/plugs-jacks/jacks/m-series

https://www.neutrik.com/en/neutrik/products/plugs-jacks/jacks/slim-jacks

Then a matter of finding a supplier with stock of the desired physical configuration.

Bri

 

[nsalis]

There are almost no 1/4" sockets anymore that have one or more additional potential-free contacts. Here is such a TRS socket:

https://guitarelectronics.com/9-pin-1-4-stereo-jack-for-guitar-w-dpdt-battery-switch/

If you google, be careful not to come across a B-gauge (= BPO 316 = PJ 051) socket. These are not compatible with the usual (A-standard) jack connectors used in musician's and consumer electronics (headphones).

Nick Salis

 

[abbey road d enfer]

These are just one example:
https://www.neutrik.com/en/product/nmj6hc-s

There’re quite a bit more available with the same switching arrangement.

These don't have a SEPARATE switch. It's possible to use them as a separate switch but it puts a constraint that a "stereo" (TRS) plug must be used, which is not the case with a typical guitar lead.
Anyway, it's very easy to use them for switching a relay.

You may want to be a tad creative if you want to avoid the risk of damaging the source when the Tip of the jack meets the Ring of the socket. Hint: use a transistor.

 

[Voyager10]

This sort of thing: https://cpc.farnell.com/cliff-elect...66a/6-35mm-jack-socket-2p-mono-pcb/dp/CN23320

The data sheet shows switched contacts for Tip and Sleeve. Most horizontal PCB mounting ones are similar, if only because they need to be held down at all 4 corners.

As you insert the plug the tip makes contact with the •unswitched* sleeve terminal, and then lifts it off the switched terminal as you push it in. So the tip will be briefly shorted to ground, but it's never exposed to any voltage from the switched terminal.

 

[JohnRoberts]

I have seen people use switching contacts on T-S jack sleeve switches. Some even game TS plugs shorting ring to sleeve with T-S plugs, but be careful about putting DC on audio jacks that could connect to audio paths.

JR

 

[abbey road d enfer]

This sort of thing: https://cpc.farnell.com/cliff-elect...66a/6-35mm-jack-socket-2p-mono-pcb/dp/CN23320

The data sheet shows switched contacts for Tip and Sleeve. Most horizontal PCB mounting ones are similar, if only because they need to be held down at all 4 corners.

As you insert the plug the tip makes contact with the •unswitched* sleeve terminal, and then lifts it off the switched terminal as you push it in. So the tip will be briefly shorted to ground, but it's never exposed to any voltage from the switched terminal.

Indeed, but how would you use the switched contacts to switch a relay, when the cable has a "mono" (TS) plug?

 

[Brian Roth]

I've seen more than a few stomp boxes use a TRS jack. The ring connected to the internal 9V battery's negative lead. A TS phone plug would short the jack's ring to the (grounded) sleeve and complete the battery's minus path and power up the circuit.

I always wondered about some sort of voltage "glitch" being fed back to the instrument as the guitar cord's tip passed across that ring terminal of the jack.

Bri

 

[Voyager10]

Indeed, but how would you use the switched contacts to switch a relay, when the cable has a "mono" (TS) plug?

From the Cliff datasheet -


Pin 4 connects to the plug sleeve when it is inserted. Pin 1 is connected to 4 when there is no plug, and is disconnected when the plug is inserted. Likewise pin 6 and pin 3, for the plug tip.

For my circuit pin 4 is grounded, and pin 1 is connected to the 100K resistor and transistor base. The tip of the plug connects briefly to 4 and then to 6, but it's never connected just to 1 or 3.

Pin 6 is the regular audio input. Normally you'd connect 3 to ground so this input isn't left floating when nothing is plugged in.

This type of switch isn't usable for a stomp box situation, where you need to make a connection when the plug is inserted, which is why people use the nasty 'short R to S' trick.

 

[abbey road d enfer]

I've seen more than a few stomp boxes use a TRS jack.
The ring connected to the internal 9V battery's negative lead. A TS phone plug would short the jack's ring to the (grounded) sleeve and complete the battery's minus path and power up the circuit.

Indeed. It's the most common way of turn on circuit for guitar pedals.

I always wondered about some sort of voltage "glitch" being fed back to the instrument as the guitar cord's tip passed across that ring terminal of the jack.

I've never seen a guitar being damaged by the short 9-12V spike that happens when inserting/disconnecting the jack from the pedal, whatever the type (passive, piezo or active) but some electret mics could suffer.

 

[abbey road d enfer]

From the Cliff datasheet -


Pin 4 connects to the plug sleeve when it is inserted. Pin 1 is connected to 4 when there is no plug, and is disconnected when the plug is inserted. Likewise pin 6 and pin 3, for the plug tip.

For my circuit pin 4 is grounded, and pin 1 is connected to the 100K resistor and transistor base.

OK. Wasn't thinking straight.

This type of switch isn't usable for a stomp box situation, where you need to make a connection when the plug is inserted, which is why people use the nasty 'short R to S' trick.

Why "nasty"?

 

[Voyager10]

Nasty because it briefly connects the battery -ve to the tip of the incoming plug, and battery +ve (via the circuitry) to the sleeve. I'm sure a million guitars survive this treatment every day, so it's probably fine in practice.

 

[atavacron]

Amphenol: