Author Topic: Switching of effects or subcircuits  (Read 339 times)

Vivek

Switching of effects or subcircuits
« on: June 06, 2021, 01:10:40 PM »
I am working on a circuit that has following modes

A) Bypass

B) One and only one out of 4 possible modes
eg Clean, Crunch 1, Crunch 2, Heavy

C) when one of the (B) modes is chosen, I need the options of

Chorus on or off
Delay on of off

All these circuits are inside the same enclosure.

I need to design footswitches that allow me to choose the above options

I found RG Keen's circuit here: http://www.geofex.com/article_folders/fxswitchr/fxswitchr.htm   See Image 7

Also ESR page https://sound-au.com/project163.htm . See figure 9




Question 1 : What happens in case the guitarist stamps 2 footswitches at the same time ?

Question 2 : How to alter the circuit to define a startup mode ? Suppose I want bypass mode/ no chorus/ no delay to always be the active mode on startup. The ESR schematic has D5 to define the power on default. Can something similar be done for the RG Keen circuit as well ?

Question 3 : Please help me to decide between relays or FET or audio switch CD4066 or other for the actual switching of audio and also some low current DC for bias voltages. What are the pros and cons of each approach ?

Thank you !!!!


« Last Edit: June 06, 2021, 02:40:56 PM by Vivek »

Rob Strand

Re: Switching of effects or subcircuits
« Reply #1 on: June 06, 2021, 07:58:39 PM »
Go here,

https://pdf1.alldatasheet.com/datasheet-pdf/view/50857/FAIRCHILD/CD4043.html
https://www.homemade-circuits.com/ic-4043-datasheet-pinouts-explained/

Quote
Question 1 : What happens in case the guitarist stamps 2 footswitches at the same time ?

For the 4043: The way the chip works is Set overrides Reset.   The idea behind the circuit design is a button press issues both Set and Reset but Set overrides the reset for the selected switch.     Any button resets all inputs so that leaves only the output for the pressed button set.  However, if a one button is held down it's out will go high and all is normal.   However, if now you press another button the Set of this second button will also go high.   The thing is when you release one of the buttons the other button is still issuing Reset so it kills the output of the released button.  So in short multiple outputs can go high while multiple buttons are held down but when all buttons are released only one output will remain.

For the 74C373:   It looks similar.  While one button is pressed all current the button states go through to the output, that means any combination of multiple buttons.  When the last button is released it will grab only that button (it grabs all others as well but  they are released so those outputs will be zero).

Quote
Question 2 : How to alter the circuit to define a startup mode ? Suppose I want bypass mode/ no chorus/ no delay to always be the active mode on startup. The ESR schematic has D5 to define the power on default. Can something similar be done for the RG Keen circuit as well ?

For the 4043.  For a single initialzed output it's no different to what is there.  Just choose a different output or move D5.   However can initialized multiple outputs by wiring multiple diodes to D5 to whatever Set pins you want to come on.   Realize though in operation you can never get back to a multiple output state by using the buttons.

For the 74C373 you need to set-up the inputs then fake a low to high transition on the LE pin.   A bit more mucking about.  Again you can't get back to this state with the buttons.

Quote
Question 3 : Please help me to decide between relays or FET or audio switch CD4066 or other for the actual switching of audio and also some low current DC for bias voltages. What are the pros and cons of each approach ?
Well you can always get both to work.   The 4066 has a loss less circuit but you can't guarantee the switching is quiet.  The JFETs have a whole lot of baggage for shaping the gate signal with RC networks in order to have smooth on/off transitions.   
« Last Edit: June 06, 2021, 10:14:20 PM by Rob Strand »
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ElectricDruid

Re: Switching of effects or subcircuits
« Reply #2 on: June 07, 2021, 04:43:33 AM »
Question 1 : What happens in case the guitarist stamps 2 footswitches at the same time ?

Question 2 : How to alter the circuit to define a startup mode ? Suppose I want bypass mode/ no chorus/ no delay to always be the active mode on startup. The ESR schematic has D5 to define the power on default. Can something similar be done for the RG Keen circuit as well ?

For both of these, you've got a choice: Glue logic or a small microprocessor. No prizes for guessing which I'd recommend.

ThermionicScott

Re: Switching of effects or subcircuits
« Reply #3 on: June 07, 2021, 09:38:38 AM »
I am working on a circuit that has following modes

A) Bypass

B) One and only one out of 4 possible modes
eg Clean, Crunch 1, Crunch 2, Heavy

C) when one of the (B) modes is chosen, I need the options of

Chorus on or off
Delay on of off

All these circuits are inside the same enclosure.

Since "clean" is a possible mode of (B), what would be the state if one of the modes of (B) is not chosen?  It would seem simpler to make the selection of chorus/delay not dependent on (B).

...unless I'm misunderstanding how you've defined things, and (B) is just what happens when you are not bypassing everything via (A).  I usually just think of "bypass" as a blanket cancel on everything. :)
« Last Edit: June 07, 2021, 09:41:16 AM by ThermionicScott »
"...the IMD products will multiply like bacteria..." -- teemuk

Vivek

Re: Switching of effects or subcircuits
« Reply #4 on: June 07, 2021, 10:28:00 AM »
Bypass is everything true bypassed

If not bypassed, one (and only one) of the B states has to be active

"Clean" is treble boost and compressor

I need options on "Clean" for

Treble boost and compressor + (chorus is on or off) + (delay is on or off)




How to decide on relays or FET or Audio switching IC ?

« Last Edit: June 07, 2021, 10:33:06 AM by Vivek »

FiveseveN

Re: Switching of effects or subcircuits
« Reply #5 on: June 07, 2021, 10:41:13 AM »
That's how I read it, although the particular wording

Quote
I am working on a circuit that has following modes

A) ...
B) ...
C) ...
Makes it sound like there should be 3 distinct operating modes where there are more like 17.
So should all the available options look like this?

1) bypassed
2.1.0) clean
2.1.1) clean + chorus
2.1.2) clean + delay
2.1.3) clean + chorus + delay
2.2.0) crunch1
2.2.1) crunch1 + chorus
...
2.4.3) heavy + chorus + delay

Since this sounds like a 4 channel preamp plus post effects, I'm finding the need for global bypass questionable: if it's meant to plug into a poweramp or cabsim, how useful is the bypassed signal? Or if it's going into another preamp, what is the "clean" option adding that you don't already have?
If you use a microcontroller you can offer both a "pedalboard" operating mode (each effect has its own bypass switch) and a preset recall one (switches select a preset, then effect state is set from memory), as many multieffects do. Otherwise you're not saving the user any tap dancing and I'd wager they'd rather have the choice of which chorus and delay to use.

L.E. (replied in the meantime):
How to decide on relays or FET or Audio switching IC ?
You compile a list of all the options from wherever you source your parts, then you sort them by your priorities: performance, price, availability, board space etc.
« Last Edit: June 07, 2021, 10:46:16 AM by FiveseveN »
Does the circuit sound better when oriented to magnetic north under a pyramid?