Arachnid 2019 Board, "using all 16 effects" mod

I Love Music

New member
So I'm sure it's been discussed somewhere, that pin 13 of the FV-1 chip can be grounded to use the 8 internal programs on the FV-1. I'm sure folks here have added a toggle switch to ground for switching "banks" of eeprom using this pin 13 trick.

So, the MOD I'm actually bringing up is …. that R5 on the Arachnid board is only 10K. If you ground this, you are adding more load to the 3.3v regulator IC and turning more power into useless heat, which is bad, m'kay ? So I've been using 100K resistors for R5, copying what the other three switch inputs (for the 8-way switch) are doing.

This way, grounding R5 at pin 13 will not tax the 3.3v power regulator.

Suggestions or Comments ?


P.S. for Arachnid, solder your toggle switch (to ground) at the pad under R5, do not try to solder near the FV-1 chip itself !
 

phi1

Well-known member
Nice idea. I like it. I did the switch mod you are describing and left the resistor as 10k. By my math it's only drawing 0.3mA, which doesn't concern me. Just saying for the benefit of anyone who may have done this and might now be concerned now about their mod. But, your way is technically better.
 

Chuck D. Bones

Well-known member
I had that same idea about the INT/EXT switch. Can't have enough sounds. My Arachnid's almost done and it's getting that switch plus a 3P4T switch & jack for an expression pedal. 300µA is no biggie, either resistor works. Good advice on where to connect the toggle switch.
 

I Love Music

New member
I had that same idea about the INT/EXT switch. Can't have enough sounds. My Arachnid's almost done and it's getting that switch plus a 3P4T switch & jack for an expression pedal. 300µA is no biggie, either resistor works. Good advice on where to connect the toggle switch.

Chuck, how did you wire the expression pedal onto the arachnid ? Is it part of one of the three effect knobs ? I've thought about doing this, and would like to hear your ideas.
 

Chuck D. Bones

Well-known member
It's straightforward from a schematic perspective, takes a little doing to wire it up. I added a 3P4T rotary switch to select which of the three CONTROL knobs (or none of them) is replaced by an external expression pedal. You'll need a stereo 1/4" jack, the rotary switch and a compatible external expression pedal. The center lead (pin 2) of each Control pot is cut short and wired to the rotary switch. The pads where the pot leads would have connected are also wired to the rotary switch. +3.3V and ground are wired from the board to the stereo jack tip and sleeve, respectively. The rotary switch is wired to the stereo jack ring. Here's a schematic of the off-board wiring:

PedalPCB Aracnid Expression Pedal mod v1.1 sch.PNG

The terminals marked U3 do not physically connect to U3, they connect to the CONTROL pot's pin 2 pads. R32 is there to protect IC6 in case someone plugs the wrong thing into the Expression Pedal jack. I'm still wiring it up. When I'm done, I'll post pix in the Build Reports forum.
 
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