Switch question

[Laudanum]

Been a while since I posted and yes, I'm still less than a whiz kid  ;D

Figure someone can help me with a switch question.  I'm building a more rugged footswitch for guitar amp channel switching.  The original uses a simple SPST latching push/stomp switch.  Fed by a standard patch cable with 1/4 TRS plugs  (two switches).    There is an LED in series with the switch so ... the sleeve is common and connects to one terminal of both switches and ring goes through an LED and then out to one switch and from tip through another LED and out to the second switch.    I want to change this so that I can avoid the potential problem of the relay in the amp not kicking on if the LED fails.

So what I am wanting to do is to wire directly to the switch without going through the LED first.  But I still want an LED indicator for each channel.  What type of switch do I need that would allow me to isolate the LED from the main switching circuit.  Would a DPDT give me two separate sections so that the LED would still come on when I step on the switch yet the two circuits would be separate?      If that makes sense.

 

[Paul Birkeland]

It would probably help to make a drawing of what you have to go along with the description.

 

[Laudanum]

Hi PB.

I'm linking a graphic of how the stock switch is wired.  It only shows one switch with a mono jack with the sleeve connection feeding the switch directly and the tip connection feeding the switch through an LED in series.  For 2 switches,  the connection is through a stereo/TRS cable/jack.  The sleeve would be common to both switches with the connection to the second switch being the ring connection, also through an LED in series.  I'm not sure what type of circuit it's called but basically the switch just shorts the tip (or ring) to the sleeve which activates a relay in the amp and switches channels.  There is about 3V DC present from the amp but in the stock switch, there is no resistor on the LED.  I assume the output current is limited inside the amp? 

With the stock switch wiring, if an LED fails, I lose the ability to switch channels with the footswitch.  I'm wanting to keep the LED's for indication but not have them in series with the connection.    I'm thinking now that I could keep it simpler and use DPST switches.  I think that would allow me to wire one pole of a switch from the tip connection through an LED and the second pole of that switch directly from the tip connection.  Then sleeve would be common.  Same for the second switch but from the ring connection rather than the tip.  If I'm thinking right,  this would work ... clicking the switch on would activate both the channel switching relay in the amp and the LED but if the LED fails the channel switching still works and the two poles aren't connected inside the switch so the LED anode stays isolated from the + voltage on the other switch pole (from the tip or ring).

I'll work on drawing a diagram for the DPST switch.  Have to do it by hand though so it wont be pretty.  :-[

 

[2wo]

Have you had an LED fail? They are pretty reliable...John 

 

[Laudanum]

No, not in something like this but I don't own the stock footswitch.  I figure if I'm gonna build one I'd rather do it this way and I have enough parts on hand that it's cheaper than buying.

 

[Paul Joppa]

... use DPST switches.  I think that would allow me to wire one pole of a switch from the tip connection through an LED and the second pole of that switch directly from the tip connection.  Then sleeve would be common. ...

The second switch will short out the LED so it won't light.

I will suggest using two LEDs in parallel, of slightly different colors - red and orange for instance. Normally the red will light and limit the voltage to where the orange can't take any current, but if the red dies then the orange will take over - and it will tell you that the red has died. As long as the red carries the current, the orange is never subjected to current or eat problems so it should last indefinitely.

 

[Laudanum]

The second switch will short out the LED so it won't light.

I think I get it ...  When the switch is engaged,  + voltage ends up at the cathode because of the common sleeve/ground connection.  Yes?

The two LED's in parallel it is. 

Much thanks.