3 channel footswitch

[frusciante89]

Hi everyone, I'm trying to design the footswitch for my new three channels amp, but I'm not sure how to pull this off. The amp has three channels: I have two relays that takes care of the channel switching. When they are activated, they will switch to clean or lead. When these two relays are not connected (i.e. the GND is lifted), the amp is in the crunch channel. Channel switching is currently controlled by a three position panel switch and this works just fine.
In addition, I also added a post FX loop additional master volume which is controlled by its own dedicated relay to GND. I would like to have all this switching in an external pedal: normally I make two channels amp, so I can get away with a simple stereo jack. This time, however, I want to be able to switch between the three channels (clean/crunch/lead) and turn the loop on/off as well. I figured I could use a 5 pin DIN port to transport all the signals I need, but have no idea what's the easiest way to wire this up without using microcontrollers or PICs... Do you guys have any suggestions? I'm a bit lost

[Jazz P Bass]

What you need is a double pole switch to select between Clean or Crunch/ Lead.
In Clean mode the Crunch/ Lead switches will do nothing.
When Crunch/ Lead is selected each of those switches will work.
I do not recall the amp model but Peavey had a way of making the Crunch/ Lead LEDs activate (even when not selected) so you new where you where at.

[frusciante89]

What you need is a double pole switch to select between Clean or Crunch/ Lead.
In Clean mode the Crunch/ Lead switches will do nothing.
When Crunch/ Lead is selected each of those switches will work.
I do not recall the amp model but Peavey had a way of making the Crunch/ Lead LEDs activate (even when not selected) so you new where you where at.

Will something like this work?

[Jazz P Bass]

I guess you could go that route.
It still will not light the Crunch or Lead leds when not selected.
I was thinking a of a dumbed down version with simple footswitch contacts.
My previous post stated "I do not recall the amp model but Peavey had a way of making the Crunch/ Lead LEDs activate (even when not selected) so you new where you where at.".
The leds could be lit if a separate contact on the switch was used. (double pole)

[loudthud]

What happens when you step on more than one switch at a time ?

[frusciante89]

What happens when you step on more than one switch at a time ?

That is an exception and it shouldn't happen. If you step on two switches, both input will be latched and turned high. Still not sure how to solve this.

[loudthud]

I posted a schematic that should only allow one switch to latch in.

Link: https://music-electronics-forum.com/...hing-xor-logic

[frusciante89]

I posted a schematic that should only allow one switch to latch in.

Link: https://music-electronics-forum.com/...hing-xor-logic

Thanks a lot for the answer. Is the mod you suggested something that could be added to the schematics I've posted?

[Gregg]

CD4028 can do 3 and 4 channel switching.

And another one with 4011.

[frusciante89]

Hey everyone! quick update! I tried the solutions I've posted, and it worked. However, the relays in the footswitch were inducing some delay in the switching and when moving from the clean to lead channel, the crunch led on the amplifier panel was switching on for a fraction of a second and then switching off.
Since I didn't like this, I moved to NPN (BC546). The goal is to bring the clean and lead wires (coming from the DIN port) to ground, hence activating the relays inside the amp and switching the channels.
The channel switching works, but the LEDs in the footswitch don't. I also have some doubts about the NPN operation.
Sorry if these are noob questions, but I have a very limited experience with solid state devices:
- the CD4017 outputs 12V, but at the NPN, I measure a voltage drop of 0.8/0.9 between the base and ground. Is this normal? I'm using a base resistor R1 of 1k.
- everything works apart from the lead and clean LEDs: they are not turning on: in the beginning I added a limiting R2 resistor (thinking I had 12V at the base), and the LEDs wasn't working. I then removed the limiting resistor it but still nothing (I assume the 0.8V is of course not enough for the LED to turn on). I also tried to remove the voltage divider (R3=330R and R4=220R), but still nothing.

Am I doing something terribly wrong? I tried to test the CD40174 outputs (Q0, Q1 Q2) without the NPN and it correctly shows 12V. Maybe the CD40174 output current is not enough and the voltage gets dropped from 12V to 0.8?

Thanks for your help

[Jazz P Bass]

I would suggest that you move the LED off of the base pin of the NPN.
With a suitable current resistor you could simply go from the IC output pin to circuit ground.

[The Dude]

...... the CD4017 outputs 12V, but at the NPN, I measure a voltage drop of 0.8/0.9 between the base and ground. Is this normal?......

^^^^^^What Jazz said. I'll add to your question quoted above: Yes, that is normal. Think of the B-E transistor junction as a diode. It will always drop around .7V if forward biased.

[Gingertube]

Channel switching becomes complicated when you want to switch relays and JFET switches etc.
Sometimes "old school" DTL (diode transistor logic) works for you. See Hughes and Ketner Triamp, 6 Channel switching here:
https://el34world.com/charts/Schemat.../HK_triamp.pdf

See page 9 for switching circuit and page 13 for footswitch circuit.

Advantages are:
Default to Channel 1A at power up by smaller cap on the Channel 1A transistor base (Change this to "standby" channel if desired). Standby Channel then terminated by added "delay on" timer (555 or similar).
Expandable/reducable as far as number of channels.

Channel selection by momentary action switches to 0V - either footswitch or front panel or both (either).

Channel indication (LED) on both front panel and footswitch

Looks complicated but it does everything you could contemplate.

I like its flexibility.

ASIDE: A local guitar "god" had one of these amps and wanted a different footswitch. Instead of a 6 switch unit (7 switches if you count the effects on/off switch) he wanted two rotary switches to dial up a an A channel selection and a B channel selection, with a single footswitch to toggle between the two selections. He is 6ft 4inches with feet to match and had trouble hitting the desired switch. I designed a fairly simple Unijunction transistor (UJT) based circuit to give him what he wanted. Yell if you want that circuit and I'll see if I can find it,

You will note that a "garden variety" 9 pin D connector is used for the footswitch (or user modified version of the footswitch).

Cheers,.
Ian