The hella rats chronicles

[DailyDovetails]

I think the rat might be my favorite pedal. I want to like all the kooky or fancy pedals but at the end of the day I always go back to the rat. It into a peavy classic 50 was my sound in my 20s. I built a rat with a ton of switching options https://forum.pedalpcb.com/threads/hella-rats.20070/ . From what I learned there I decided my first PCB design would what I liked most from it. Standard rat with extra hard clipping options only.

So far in the process I have received the boards and I like the faceplate a lot but feel like I messed up in the pot and switch footprints. The switches are sub minis and the pots I don’t know what the heck is going on with them. The holes are tiny. I guess that’s what happens when you rely on someone else’s footprints. If you want it done right you have to do it yourself.




I’m going to build one of these out to make sure it works and then I will fix what I don’t like about the design and reorder V2 boards.

 

[Nostradoomus]

Those film cap pads are huge!

 

[DailyDovetails]

Those film cap pads are huge!

Yeah I think I may size them down a bit and make the resistor holes a little bigger.

 

[DailyDovetails]

Got my the prototype working. I somehow botched the volume knob layout and it works opposite the direction I intended but other than that it works and sounds fine. The noise floor is decently low for what it is.



I used my new crimpers to make the connections throughout. I think I will build a few more pedals that way.

For the PCB I need to figure out the volume knob, finish drawing new footprints and add the option for an SMD J201. I also realized as I was looking at some schematics last night that there are some differences between Aion, Electrosmash, the multirat by GGBB @ diystompboxes and Robert’s schematic. I need to spend a bit researching to see if they are meaningful and if I want to make any changes.

 

[DailyDovetails]

Today's chapter is research. I found as many Rat schematics as I could. It appears the biggest difference is the order of the capacitor and resistor following the OP amp. Any idea if it makes a difference?

Aside from that I may add one resistor before the volume pot. In case anyone is interested here are all the schematics I was able to find. I also included the one my current board is based on.

 

[rwl]

I just laid out and built a PCB for the stock rat. Hadn't played a rat in a while and was impressed by the tone. Was thinking of trying to combine multiple different rat pedals (I wanted a true replacement for my Joyo Splinter, which has a few additional switches for fat/normal). Multi-RAT looks like a great starting point. Good find!

 

[lowpitch]

Today's chapter is research. I found as many Rat schematics as I could. It appears the biggest difference is the order of the capacitor and resistor following the OP amp. Any idea if it makes a difference?

Nope. Order of series components between two nodes doesn't matter generally.

 

[DailyDovetails]

Nope. Order of series components between two nodes doesn't matter generally.

Not that it matters here as the low pass is set at a pretty high frequency and the filter is there also. Does the order of the resistor and cap affect the following high pass filter. Would I calc it as a 2k5 into 3n3 with a cut off of 19.2Khz if the resistor comes last and a 1k5 into 3n3 with a cut off of 48.2Khz if the caps comes back or is it the same 2k5 into 3n3 either way?

 

[lowpitch]

Not that it matters here as the low pass is set at a pretty high frequency and the filter is there also. Does the order of the resistor and cap affect the following high pass filter. Would I calc it as a 2k5 into 3n3 with a cut off of 19.2Khz if the resistor comes last and a 1k5 into 3n3 with a cut off of 48.2Khz if the caps comes back or is it the same 2k5 into 3n3 either way?

The low pass filter is formed by the combined resistance of the filter pot and the 1.5k resistor, and the 3.3n capacitor to ground. So the cut-off frequency is 32kHz with the filter pot at minimum, and 475Hz at max. The 1k resistor is there to limit the current going to the diodes. But either way, the order of passive components in series - if there are no connections in between them to ground or elsewhere - still doesn't matter. If you look at the currents and voltages only at the output of a series of components, it will be the same regardless. It's kind of weird and I can't really find the right words to explain it, but it is the way it is

 

[DailyDovetails]

The low pass filter is formed by the combined resistance of the filter pot and the 1.5k resistor, and the 3.3n capacitor to ground. So the cut-off frequency is 32kHz with the filter pot at minimum, and 475Hz at max. The 1k resistor is there to limit the current going to the diodes. But either way, the order of passive components in series - if there are no connections in between them to ground or elsewhere - still doesn't matter. If you look at the currents and voltages only at the output of a series of components, it will be the same regardless. It's kind of weird and I can't really find the right words to explain it, but it is the way it is

That makes sense looking at it and with the explanation. I think I want to start to learn some of the simulation software so I can better understand some of the filtering stuff. I appreciate the reply.

 

[DailyDovetails]

I finished redrawing the component foot prints that were bothering me. Added a capacitor and reworked the layout to make it cleaner. While I was at it I also redid my 3PDT bypass board. I'm hoping it works better with the crimped connectors I have been making.


I'm going to sleep on it and send them in tomorrow to JLCPCB.