External Switching

[kurtlives]

I am building a effect that will be rack-mounted. Its got a bypass toggle on it (3PDT). I would like the ability to bypass it externally though wiyh a footswitch. When I do this I would like the LED that is on effect to turn on and off as the effect it turned on and off.

How would I go about this? Somehow use relays?

Thanks...Chris

[slideman82]

Right, that would be the most simple thing to do... relays... but you'll need 6V or 12V (I don't know about 9V relays...), or 24V if you have that supply.

[kurtlives]

This would be in a tube pre-amp and I got regulated 12V DC heaters so 12V would work.

Now all I need to know is how the hell do I use a relay for what I am trying to do?

Why are they used in external switching?

[R.G.]

1. Use a DPDT relay's contacts to replace the 3PDT bypass toggle, ignoring whatever the third pole does for LED switching. DPDT relays are much smaller, cheaper and easier to find than 3PDT or 4PDT relays, and you don't need the third pole.
2. Rig an external alternate action footswitch to turn on 12V to the relay coil.
3. Wire a resistor plus LED in parallel with the relay coil to show when it's on.

That's all there is to it... unless you want BOTH a remote footswitch AND a panel mounted switch to do the same job, flipping the bypass/not bypass status of the relay. If you want both, you'll have to either use special XOR switches (and I've never seen these in stomp switches, although they exist for wall switches) or use momentary switches to flip the state of a flipflop inside the unit. It's the "make both switches so they toggle the bypass" that gets logically complicated.

[kurtlives]

1. Use a DPDT relay's contacts to replace the 3PDT bypass toggle, ignoring whatever the third pole does for LED switching. DPDT relays are much smaller, cheaper and easier to find than 3PDT or 4PDT relays, and you don't need the third pole.
2. Rig an external alternate action footswitch to turn on 12V to the relay coil.
3. Wire a resistor plus LED in parallel with the relay coil to show when it's on.

That's all there is to it... unless you want BOTH a remote footswitch AND a panel mounted switch to do the same job, flipping the bypass/not bypass status of the relay. If you want both, you'll have to either use special XOR switches (and I've never seen these in stomp switches, although they exist for wall switches) or use momentary switches to flip the state of a flipflop inside the unit. It's the "make both switches so they toggle the bypass" that gets logically complicated.

Sounds like just having relay switching is the best option for me.

What is I used a 12B stero jack...somehow short the onboard bypass switch to ground so that only the relay is being used?

[R.G.]

Sounds like just having relay switching is the best option for me.
What is I used a 12B stero jack...somehow short the onboard bypass switch to ground so that only the relay is being used?

We're kind of at the place where we're going to use many thousand words because we don't have a picture to refer to, I think.

The relay ...completely... replaces the onboard bypass switch, at least in terms of the functional switching of signals. The 3PDT toggle is removed from any signal switching at all. Only the new relay switches signals.

With that done, what is left to do is the functions of (a) lighting up an LED when the relay is on and (b) telling the relay when to be on.

We take care of (a) by simply connecting a resistor and LED across the relay coil. Now whenever the relay is on, the LED is on.

I had not looked at how to do (b) in detail until this morning. The general case of more than two switches to actuate the relay is harder, but I found an easy way to do it with only two. You can use one of the three sections of your 3PDT toggle and half of a remote DPDT footswitch. You hook the relay coil to +12 on one end. The other end connects to one pole of the 3PDT. The two throws of the pole you've just used go out to the remote footswitch throws. Finally the remote footswitch pole connects to ground. It takes at least three wires going to the remote footswitch: two throws and ground.

The way it works is that the remote footswitch pole is grounded, so one and only one of its throws is grounded at any one time. When the onboard 3PDT connects to that wire, the relay turns on. Flipping the 3PDT back and forth turns the relay on and off. Stomping on the remote footswitch changes which one of the throw wires is ground, so it also turns the relay on and off remotely.

You could, if you want, make the onboard 3PDT work without the remote footswitch plugged in if you do the following:
(a) get a phone jack which has both tip and ring contacts (that is, a stereo jack) with a tip shunt contact. The tip and ring are the two throw wires, the sleeve carries ground to the remote footswitch.
(b) wire up the tip shunt to the sleeve.

Now when the plug is pulled, tip is grounded, and the 3PDT turns the relay on and off. In this setup, the 3PDT is always one direction; that is, one direction of the switch, Up or Down, will be "on" for the relay. When you plug in the remote, the 3PDT is only a "toggle" and either up or down will be on, depending on the setting of the remote footswitch.

Any better?

[Aleksi]

Hi guys,

I'm actually also in the process of doing a rack which will have four effects in it. I actually did just as R.G. suggested, I used relays. Each effect has a DPDT relay (when it's off the effect is bypassed, and when the relay is on, the signal goes into the effect PCB). Each relay is controlled by an external footswitch (connects 9V to the FET). So basically you can use a SPDT foot switch for controlling the relay.

Pic enclosed of the first two relays (for the first two effects). Please ignore the R1 and R3 (1k series resistors), those are not required.




Hope that helps.

BR,
Aleksi

[kurtlives]

Sounds like just having relay switching is the best option for me.
What is I used a 12B stero jack...somehow short the onboard bypass switch to ground so that only the relay is being used?

We're kind of at the place where we're going to use many thousand words because we don't have a picture to refer to, I think.

The relay ...completely... replaces the onboard bypass switch, at least in terms of the functional switching of signals. The 3PDT toggle is removed from any signal switching at all. Only the new relay switches signals.

With that done, what is left to do is the functions of (a) lighting up an LED when the relay is on and (b) telling the relay when to be on.

We take care of (a) by simply connecting a resistor and LED across the relay coil. Now whenever the relay is on, the LED is on.

I had not looked at how to do (b) in detail until this morning. The general case of more than two switches to actuate the relay is harder, but I found an easy way to do it with only two. You can use one of the three sections of your 3PDT toggle and half of a remote DPDT footswitch. You hook the relay coil to +12 on one end. The other end connects to one pole of the 3PDT. The two throws of the pole you've just used go out to the remote footswitch throws. Finally the remote footswitch pole connects to ground. It takes at least three wires going to the remote footswitch: two throws and ground.

The way it works is that the remote footswitch pole is grounded, so one and only one of its throws is grounded at any one time. When the onboard 3PDT connects to that wire, the relay turns on. Flipping the 3PDT back and forth turns the relay on and off. Stomping on the remote footswitch changes which one of the throw wires is ground, so it also turns the relay on and off remotely.

You could, if you want, make the onboard 3PDT work without the remote footswitch plugged in if you do the following:
(a) get a phone jack which has both tip and ring contacts (that is, a stereo jack) with a tip shunt contact. The tip and ring are the two throw wires, the sleeve carries ground to the remote footswitch.
(b) wire up the tip shunt to the sleeve.

Now when the plug is pulled, tip is grounded, and the 3PDT turns the relay on and off. In this setup, the 3PDT is always one direction; that is, one direction of the switch, Up or Down, will be "on" for the relay. When you plug in the remote, the 3PDT is only a "toggle" and either up or down will be on, depending on the setting of the remote footswitch.

Any better?

Ok so your saying I can use 1/3 of my 3PDT onboard bypass switch. Ok that's fine as the LED is not used on the 3PDT, it is dealt with by the relay coil??

Do you have a diagram or picture of any of this? I am still having a hard time wrapping my head around it all.