Small stone BOM variations, what's the deal with the RX,RY resistors at Tonepad

[Skruffyhound]

Forgive me if I'm being dense here, I was sort of building this pedal as occupational therapy, so I wasn't really watching were I was going.
At the end of the BOM resistor list for Francisco Pena's version I suddenly had to take notice of the RX and RY resistors, I'd been ignoring them up to this point thinking there must be a logical reason for them, so I began to cast around the net. More mods than you can shake a stick at, but no explanation for this. I went to have a look at the BOM for J.D.'s version at GGG and discovered that I already had four extra resistors compared to his BOM and that's without the ten RX/RY 2k/47k.

Can anyone tell me what's going on here, and while you're at it you could let me in on what cap labels "Ca" and "Cb" should tell me.
Thanks

(I just wanted to solder some stuff at the end of a long days' work/kids, now I'm going to have to go and think and stuff... *grumble*)

[RickL]

If you look at the BOM of the Tonepad layout you will notice that it uses a different chip than the GGG layout. It replaces the more expensive and difficult to find original chip in the GGG layout with a cheaper chip, a couple of transistors and a couple of resistors. Rx and Ry are the resistors. Note the two resistors in the dotted box in the GGG layout. They are a part of the original chip. The extra resistors  in the Tonepad layout are required the make the cheaper chip plus added resistors work the same as the original chip.

Cb is a power supply filtering capacitor that is not in the original circuit. It will help reduce noise if you power the circuit with a less than perfectly regulated power supply. If you run the the Tonepad version only off a battery you can safely leave it out, but for the cost of one capacitor and the 30 seconds it takes to solder it in why bother.

Ca is the 0.1 uF capacitor indicated in red and attached to R16 by a dotted line. I'm not sure of its function but you could probably leave it out and the circuit would still work. Again, for the cost of one capacitor you might as well put it in.

The designators Rx, Ry, Ca and Cb were probably used because these parts are not in the original schematic.

I, and many others, have built the Tonepad version and it works perfectly. Which version you build will probably depend mostly on what chips you bought or intend to buy.

[Skruffyhound]

 

look at the BOM of the Tonepad layout you will notice that it uses a different chip than the GGG layout

Thank God, the world wasn't going mad, just me. Now it all makes perfect sense.
Thanks for the comprehensive answer.