# 124 Footswitch Logic and Question

[Lycoming360]

I recently wired up a #124 using a PCB and related schematics. The amp sounds great , and of course is so much different than my Fender amps that I am in the process of learning how to use it.

However, the footswitch did not work as I thought it should. In an ideal world, no matter the position of the cabinet mounted switch, if the footswitch LED is lit, then its associated relay is energized. Much like the light over my basement stairway.

But, if I have the logic correct, that is not how it is . . . The attached shows a simplified version of the logic for the # 124 footswitch/relay circuit. I've deleted the caps for simplicity.

Is this correct?

Is there a (practical) way to have the LED correctly identify the state of the relay, however the switches are flipped? Just thinking it through, I think if I added several more conductors to place the LED in line with the relay, it is possible -- though with a thick cable.

I'm curious how others have approached this problem.

[Lycoming360]

"Alternative Footswitch Logic" shows how a 5 conductor wire can be used to wire a footswitch for both PAB and OD relays. When the footswitch LED is lit, the relay is energized.

I may use this scheme. HOWEVER, the footswitch becomes mandatory and overrides the cabinet switches. Of course, this is NOT optimal, but OK for me as I plan to operate the amp always with the pedal in place. I will probably deactivate the cabinet switches if I do use this idea.

Is there a method to use the cab switches with or w/o the footswitch, and have the LEDs and the relays align?

EDIT: The "Alternative Footswitch Logic" attachment does not work as advertised . . . See Martin's comment and recommendation below.

[Lycoming360]

I think this will work with Mogami W2789 cable -- 8 conductor with spiral copper shielding as ground. Use whatever 8 conductor DIN connector you have around (these always have a path to ground, therefore "9 conductors" is possible).

It would be nice if there is a way to allow each switch to operate, with the corresponding LED to show the correct state of the relay, using a smaller (eg a 5 conductor) cable. I can't figure it out, but maybe some of the gurus here have already done so.

[dorrisant]

The chassis mounted footswitches may be the thing that will keep you from the joy you are after. Check out this diagram for some understanding. After you stare at it long enough, you will probably figure out how to incorporate those switches.

Cliff Drawing.GIF

[martin manning]

It would be nice if there is a way to allow each switch to operate, with the corresponding LED to show the correct state of the relay, using a smaller (eg a 5 conductor) cable. I can't figure it out, but maybe some of the gurus here have already done so.

You might consider this arrangement, just added to the ODS eyelet boards thread in the files section: https://ampgarage.com/forum/viewtopic.p ... 08#p365408
The standard (original) wiring is shown in black, with an option where the foot switch LED will be on if the back panel switch is set to "manual" (indicating the relay state). The foot switch button will be disabled, and that tells you that the back panel switch is set to manual. Setting the switch to "pedal" restores the foot switch functionality with the LED indicating the relay state. Of course the panel switch will work without the foot switch, same as the original, and a 5-conductor cable can handle three relays.

BTW, in your alternative foot switch logic diagram, the second case from the top will not work since the LED is reverse biased. Back-to-back LED's would fix that, but then you'd need two LED's per switch. A two-pin bicolor LED would work, but then you'd have a color change depending on which on state is in use. Either solution is messy IMO, and as you noted you need to have the foot switch plugged in for the relays to work.

[Lycoming360]

The chassis mounted footswitches may be the thing that will keep you from the joy you are after. Check out this diagram for some understanding. After you stare at it long enough, you will probably figure out how to incorporate those switches.

Thank you. I had not considered using latching relays. You are correct that it takes a bit of staring to understand . . . though I think I do.

You might consider this arrangement, just added to the ODS eyelet boards thread in the files section: https://ampgarage.com/forum/viewtopic.p ... 08#p365408

Thank you. I had come to the conclusion that I would live with using the pedal switches as the primary control -- since I do plan to switch in and out of the OD channel while playing. Your diagram makes it all very clear.

And yup, you're quite right about my "alternative footswitch logic" which is in fact illogical. I will edit the post to point this out to future users who may be as hapless as I am.

[dorrisant]

Don't worry about the lack of understanding. Most all of us are or were in the same boat at one time. I've been hanging out here for a over a decade and will never claim to know it all, although, maybe Martin does. Your posts will help others shed light in the proper way. You posted intelligently and clearly. We understand you. Keep going, your on your way.

[martin manning]

I had come to the conclusion that I would live with using the pedal switches as the primary control -- since I do plan to switch in and out of the OD channel while playing.

So, if you must have the foot switch plugged in for the relays to work, why have switches mounted in the chassis at all? That was Fender's approach. The best reason I can think of is that you might decide to rewire it later ;^)

Oh no, Tony, I will never claim to know everything- still learning something every day!

[Lycoming360]

So, final plan with schematic, with some context.

As mentioned above, I built an adapted version of a #124 with just 2 6V6 tubes in the output section. Since I had no prior experience with D-style amps, I chose to use an available PCB with its associated schematic.

The amp sounds great!

However, I was unhappy with the provided "layout" of the footswitch and explored various options.

With advice from Martin and Dorrisant, I've concluded that the best option for this completed build is to adapt the footswitch wiring to a "good enough" configuration. See Adapted Footswitch Logic for details.

Using this schematic, a 5 conductor connector will service two relays. (As Martin points out, more is possible with a different wiring scheme).

INSTRUCTIONS:
1. When the pedal switch (the footswitch) IS NOT mounted, the cabinet switch controls the relay function.
2. When the pedal switch IS MOUNTED, the cabinet switch should be placed in the PEDAL position for correct operation. In this case,
the relay and the GREEN LED are energized when the footswitch is in the "ON" position.
3. When the footswitch is in the "OFF" position, the relay is not energized, the RED LED is lit, and the GREEN LED is off.
4. IF the pedal is mounted AND the cabinet switch is in the "Manual" position, the relay will always be energized. However, neither LED
will be lit, and thus will tell the player to operate the cabinet switch for correct display. A FEATURE, not a bug.

Cheers. Happy soldering!