Clíodhna – PCB Version

All the work is done for our Super Screamer, or is it? What if I do a PCB version of this, just for fun? PCBWay said they’d gonna send me some prototyping boards for free right around the time I was finishing the pedal. So I said why not, let’s design a PCB version of the pedal.

You can jump to schematic just below, or the board design notes. There’s also the final bill of material. There’s a bit on what I did for the artwork, it’s still not great 😊 but it’s getting better. I shared all the project files too, so if you feel like it you can play with that.

As usual, if you can’t be bothered to read, just skip to the video. You can always come back for more detail. It’s a relatively short video covering just the interesting bits, and some pedal demo.

Final Schematic

I know I said in the previous two posts that it was the final schematic, but this is final final 😄 … maybe.

All considerations from the previous posts stand, we want all the switches to be on one side when we have Tube Screamer like sound, and flip them to the other side to get slightly (or even dramatically) different sound.

While I was working on the PCB, it became apparent that I won’t be able to fit everything to one board. The height of the components just wasn’t right to fit them on the same board. I would not able to mount them properly to the enclosure.

Split Schematic

I also did not want to use too many wires … a bit of a conundrum. Finally, I settled for a schematic that will have only 4 wires. I split the schematic like this:

I worked from the full schematic. I used hierarchical diagrams to move all input/output components – like power jack, input and output jacks and stomp switch into a separate hierarchical diagram. And I moved the effect part of the schematic to a separate hierarchical diagram:

Splitting Boards

What I actually did was, I designed a PCB from the full schematic, but I created 2 boards. This was so I could run ERC/DRC rules (Electrical Rules Check/Design Rules Check) and make sure everything is fine. It was also easier to create boards to the dimensions of the enclosure I wanted to use and play around with which components to go to which board and see them both on the same 3D view.

Once I was happy with the design, I made a copy of everything – KiCad is just not yet that good in designing multi-board devices. Then I created two hierarchical diagrams as per 2 boards, connected them with 4 traces, each time running ERC.

I duplicated this into 2 folders – InputOutput and Effect. Deleted hierarchical diagrams that I did not need and added a 4 pin connector. On PCB design I just deleted the board I did not need.

A bit of work, but I don’t know a better way of doing this ☹. Despite researching KiCad documentation and forums extensively. Anyway, those diagrams above are the final version … or are they?

Board Layout

As mentioned before, I use KiCad for my schematic and PCBs. It’s a great tool. And I upgraded to version 6 … finally … woohoo!!! KiCad is awesome when you have all the necessary pieces. Here are the 3D renders of my boards:

That looks neat 😎. If you wonder how good is the 3D render compared to the real world, well, wonder no more:

Granted, the 3D render is more colourful 😁 but other than that, looks spot on. Oh, yes, I had to bend electrolytic capacitors … they were too tall for mounting.

Project Files

As I mentioned above, I got the boards from PCBWay. I used PCBWay plugin for KiCad, ordering took just a couple of clicks.

You can download all the project files and even order the boards from:

• The Input/Output Board
• The effect board

All the KiCad project files are there, Gerber files are there, so you can do your own version of it, or submit to your favourite manufacturer.

Bill of Material

Below is the final BOM used for this pedal with dip switches and all. I spent some time figuring out what I want, chasing dip switches that I could use on the top of the pedal.

Also, I went for Neutrik NMJ6HCD2, I call it screw-on, but proper terminology is probably ferrule (I have no idea what that means, just read it on their product page 😇). This also means that PCB needs to fit tightly, and it will only fit 1590B type enclosure:

I have a feeling that it’s a bad idea to use dip switches on top of the board. They are awkward to work with, fiddly to use the switches. I’m still on the outlook for a better option, but this is as close as I got to good (not great, but good).

The BOM is split by board, here’s the “input/output” board:

Designators	Component	Notes
	Enclosure	1590B or equivalent I used 27134PSLA (Eddystone)
	PCB	Custom designed, fits 1590B or equivalent enclosure only (ca. 60mm width)
J1, J2	Neutrik NMJ6HCD2	In & Out jacks
J3	RAPC722X	DC Jack – Switchcraft RAPC722X, just something I had handy. PCB mount, there are alternatives just check the footprint
S1	SF17020F-0302-21R-L	Taiwan Alpha 3PDT Latching Foot Switch (or equivalent)
C10	100uF	Electrolytic cap 25V
D7	3mm LED	Low Current 3mm Red LED – I used Wurth 151031SS06000, but any colour or manufactured will do
D8	9.1V Zener	I used 1N757A zener diode, but any zener between 5 & 9.1V will do
R19	4.7K	5% carbon resistor – LED current limiting, not critical, depends how bright you want it
R20	100K	1% 250mW metal film (not critical)
BT1		9V battery snap, but I could not fit battery to the enclosure so I did not use it in the end
Q1	TP2104N3-G	This is for reverse polarity protection, P-MOSFET – TO-92 S-G-D pinout, most transistors with that packaging and pinout will work

And now for the effect board:

Designators	Component	Notes
	PCB	Custom designed, fits 1590B or equivalent enclosure (ca. 60mm width). It will fit bigger enclosures but the other board won’t
SW2, SW3	CES-0402MC	Nidec-Copal 4xSPST dip-switch. This one fits nicely and looks nice, this is all about physical dimensions rather than footprint
RV1, RV2, RV3	Alpha 9mm 100K linear pot
C1	10n (0.01uF)	Metal film PET cap
C2, C13	220pF	Ceramic C0G cap
C3, C7	220n (0.22uF)	Metal film PET cap
C5	470n (0.47uF)	Metal film PET cap
C6	4.7uF	Electrolytic cap 25V
C8	47uF	Electrolytic cap 25V
C9	100n (0.1uF)	Ceramic X7R
C11	330nF	Metal film PET cap
C12	2.2nF	Metal film PET cap
D3-D6	1N4148	Small signal diodes for clipping
R1, R3, R16	2.2M	1% 250mW metal film
R2	1K
R4, R10, R11	10K
R5	510 ohm
R6, R12	470 ohm
R7	5.6K
R9	100 ohm
R13	47K
R14, R15, R17, R18	100K
U1	TL072	op-amp

Artwork

I struggled with artwork once again … I did a better job this time around though:

I messed up the labeling of the dip-switches … again! When you watch the video you can probably notice that I hesitate at some stage because I was unsure whether the labeling was correct based on the sound I was getting.

But I’m working on a better design and hopefully I nail that next time. I also got better at drilling and cutting … all the destructive work 😉.

Here are a few more pics:

Video

Have a look how did I build it and how did it end up:

Conclusion

This was fun. I think I got this nicely done. The pedal sounds great … as we’ve seen before. All the components fit great, so I would say this was a great success.

Things that did not work great or might need improvement, and possibly a slight change to the diagram:

• Battery could not be fit … no room in the enclosure (1590B type). There’s a different enclosure, 1590B2 that is slightly deeper, that might work, but I think I’ll just get rid of this connector altogether. Note though that this PCB only works on 60mm width enclosures, so 1590B3 or 1590BB type won’t work.
• I need to double check if grounding the enclosure will improve noise/interference performance. The noise is OK, but I forgot that Neutrik jack does not have chassis connection (I have some other plastic jacks which do). I could’ve connected mounting pins of one of the pots. Anyway, something to think of for v2
• I did not like footprint for 9mm pots. While they are good fit, the mounting pins are causing DRC errors. Not a deal breaker, I just hate that I can’t get the PCB to be without DRC errors
• I need to improve Artwork … and finally label dip switches correctly 🤔
• Maybe get rid of dip-switches altogether and simplify the design a bit
• Nicer knobs?

I’ll probably keep on improving this so if you want to be notified when that happens, subscribe at the bottom of the page.