AND/OR Switching System\\ Part 1

Part 1: The Gestalt

   The ability to control two different effects is one of the joys of having multiple pedals or multiple effects. To date, I have focused most of my attention on switching between channels in a "parallel" manner. However, while doing research for the DBA sound saw and the Kill Kill Filter, it seems that users were interested in the ability to run one filter into another. The challenge ahead is how to develop a system which could accomplish at least 3 modes of operation (1) A into B, (2) B into A, (3) A or B, and (4) A and B.

    Here's a version of a generalized schematic diagramof the switching systems we're interested in with. It should be noted that (1), (2), and (4) could use different grounding methods depending on your preference. 

    I have left off the LED switching systems at the moment for simplicity. Regardless, moving from (1) to (2) can be accomplished in a simple manner using the Geofex Juggler Effects Reverser.

 

    What we can see from this is that in addition to the Switching system to turn each effect ON and OFF, we require an additional 3 (or 4) SPDT switches to change the effect order.

    So the challenge becomes mostly focused on getting between mode (3) and either mode (1) or (2). As well as getting to mode (4) and making sure that there aren't any phase issues. If we can draw out the paths to get between these modes, then its just a matter of a couple more SPDT switches to change the effect order.

    Herein lies four of the starting challenges I've identified thus far:

A. The number of SPDT switches required.

  We are already at 3 or 4 to just move between modes (1) and (2) NOT including the LED indication. Adding in mode (3), and it should be clear that there is probably not going to be an analog toggle switch or rotary switch which will be able to accomplish this switching. In addition, we will need a way to cycle through states in a relatively easy way.

B. Switch life time.

    Part of the fun of the OR configuration is the ability to switch back and forth between effects/channels to quickly switch between different sounds. This will result in the "Channel Select" switch getting pressed more than the "Bypass" switch. Like everything, mechanical switches have a lifetime, can get worn out, and die on us, which present challenges with replacing them. Normally Open (NO) momentary switches have been used to toggle states of relays for pedals and can be used, but we'll need a way to address the toggled status of effects after power is disconnected. This is notably a problem in the OR mode.

C. CMOS switching and pop.

    To accommodate the anticipated large number of switches, we'll likely need to use CMOS chips for switching. In my experience, there has always been a popping issue for me when I have breadboarded this. We'll need to include a form of muting system to prevent popping from being an issue when switching between the AND/OR modes when the effect is powered up.

D. Method of indicating which MODE we are in.

    Switching between 4 modes, pretty much eliminates a single toggle switch (e.g. ON-ON-ON) to select the mode. I believe the choice is between (i) a rotary switch, and (ii) a push-button switch that cycles through the modes with some additional LEDs to indicate which mode is currently selected. I am leaning toward the pushbutton cycle selection since it is a new area for me to explore and doesn't take up as much space as a rotary switch. In my experience with Alpha Rotary switches (both plastic and metal) is that they stick up higher than the potentiometers, and often times require additional washers or an additional nut to get the right spacing/height with the inside of the enclosure. The issue with LEDs is finding the optimal way to communicate with the user which mode is currently active.

    At the moment, the solution seems to be pointing toward a microcontroller-based solution. I'm pretty sure this switching system could be achieved to a degree without a microcontroller. But one of my goals for 2021 was to push myself in a different direction. I think that incorporating microcontrollers into my effects pedals will push me into uncomfortable territory but ultimately improve my creations.

Switches & channels

Switches, either mechanical or digital, provide opportunities to route different part of the circuits around in some interesting ways.

To start, I have always been a fan of having two channels on pedals, something attracts me to that sort of design. Probably my early exposure in pedals to the DBA soundsaw and kill kill filter.

Recently, there is a Big Muff by Wren and Cuff ("Garbage Face")  that has been released which allows for two different volume settings for a channel.

I can't say for certain how they implement this, but if I had to guess it would be like the old Beavis audio, two pots on a stomp with an LED approach. http://beavisaudio.com/techpages/switches/

Not a bad approach at all! Easy to implement, minimum parts count and greatly expands the sonic pallete of a certain pedal.  In fact the DBA KKF uses this type of control, to change the tone potentiometer. Move this over to the potentiometer for gain, and you can have two channels which allow you to vary the saturation of your dirt circuit. All of this with a 3PDT switch (Stomp or toggle pick your poison)

If you don't care for the LED indicator, you could get by with the DPDT. But wait!!! What about other options.  As far as mechanical switches go, we can move up the the 4PDT. Which depending on how we want to implement it for channel switching, we could get creative and allow changes to be made to 3 controls of a circuit, but would need to isolate components so they don't interact across channels. I.e. the we don't want the volume control for channel one to change the volume of channel two. Digital switching systems are more complicated, but offer a longer life-span and the potential for more parameters of the pedal to be channel switched.  This comes at the cost of more knobs to interact with though. Digital presets are the next evolution which allow you to have the base number of potentiomers and the ability to cycle through "saved" states.  The challenge with this approach is not being able to see what the preset was.

The NEW DBA ROOMS pedal looks to have 3 channels switchable on their "ALT" footswitch. While there are large knobs for Frequency, Depth, and Time, there is also a smaller 9mm potentiometers for F, D, and T which I am going to guess is tied to the ALT footswitch.

This of course depends on how the potentiometer is oriented in the circuit to begin with. This is most ideal for potentiometers set up as voltage dividers.


This is brief post covering aspects of mechanical switches for "multi channel" modifications to your pedal, but also serve as a backdrop to part of the process going into the Sound Saw REMAKE. The pedal toggles back and forth between the boost and the filter sides of the circuit.