Footswitch for Hoffman relay switching circuit

[johnfv]

Please forgive me for the total noob question here. I bought and assembled the Hoffman power supply and relay boards. I'm in the process of installing in my 18W TMB amp for a solo boost on the TMB channel. I never paid close attention to the foot pedal schematic until now. I was assuming I could use a standard 2 conductor 1/4" cable for the footswitch but after reviewing it appears I must have 3 conductor (+5V, "send and return" for ground) to the switch. Can someone sanity check me on this?

[PRR]

If you need the LED on the pedal, then yes you need more wires or more cleverness (possibly more voltage).

I've assumed that LED goes on the _amp_.

[sluckey]

Wire it like the attached pic and you can use a two conductor cable. The LED will be illuminated when the relay is de-energized. The 180Ω resistor 'may' need to be larger, ie, 270, 330, or 470. You also may need to float the power supply and use an isolated jack. Read this thread for more info...

http://www.el34world.com/Forum/index.php?topic=14348.msg135594#msg135594

[PRR]

> Wire it like....

Nice.

> You also may need to float the power supply and use an isolated jack. Read this thread for more info...

If the "-" terminal of the supply is (or can be) grounded, no need for isolated jack.

If the supply is "stolen" from a heater supply which probably swings both ways around ground (CT or 2-100r), then it must be isolated.

[johnfv]

Thanks for the replies. I ended up using Doug's PS but used a relay board from Granger (http://www.grangeramp.com/images/switch_board_docs/3_relay_board_full_wiring_diagram.pdf). This relay board made the footswitch dead simple (2 conductor cable, SPST and LED only) and the LED is on when energized (which is what I want). I'm using it for a solo boost in my 18W TMB amp.

[PRR]

> the LED is on when energized

If you use 2-throw relays, then on/off is in how you wire the contacts. Get the LED on, then figure which relay contacts do the thing which makes your effect "on". The fact that the relay coil is off when the LED is on is meaningless.

That's the part I overlooked before and that Steve's plan incorporates.

[johnfv]

...The fact that the relay coil is off when the LED is on is meaningless...

In my case I want a specific behavior from NC on the relay - I want the boost to be off. That way, if no footswitch is connected (or for that matter, something goes wrong with the relay or supply) the amp will be "stock". There are a variety of ways to address switching the LED vs. function but having a simple circuit where the LED is ON when relay is energized works best for me. YMMV...

[Willabe]

Very nice job John! Looks real good!


              Brad