KiCad Learning - feedback on my Electra?

[Toy Sun]

Hi all,
Trying to learn KiCad with an eye to fabbing my first board. This is my Electra variant - some diode switching, a gain pot. I've built this on perfboard and my daughter absolutely loves it with her strat going into a Vox. Didn't specify the diodes as we will play with some different ones.

Some KiCad challenges: I/O pads, wasn't sure how to do that. And didn't know how to get a micro "u" for caps. And just in general, lots to learn... Thought I'd ask for some feedback and get the schematic right before jumping into the board layout.

Many thanks in advance,
John

[bartimaeus]

looks good to me. i'd just add some extra pads for ground connections (the same way you added i/o).

nearly everyone uses the regular "u" for cap values (for example 10uF), but it you really want a greek "mu" you can type option+u on mac (not sure of the PC hotkey). fwiw, remember you're writing the values for your own reference, or to show others. so don't be too worried, since they have no effect on the PCB you generate.

[antonis]

Thought I'd ask for some feedback and get the schematic right before jumping into the board layout.

P2 looks more like the resistive part of P2/C3 LPF rather than "Gain" pot..
(C3 is set there as a diode knee softener but it also interacts with any former resistance..)
Of course, R2 could bev considered in parallel with R3 (via C2 & Diode pair) but it could only halve Q1 stage gain..
Actually, it can't lower gain less than 2/3 or so 'cause Q1 stage gain is a combination of "open loop" one (R3/R2 - R1 disconnected) and R1 divided by IN signal impedance..

A better approach should be the R2 replacement with a 1k pot with its wiper connectef to GND via a cap..
(it should raise "open loop" gain making Q1 stage gain more close to R1/IN impedance..)

[bluelagoon]

Like antonis mentioned it makes better sense for the Gain Control to replace R2, see attached image of an Electra circuit that works well for me.
Also the added volume control on the output is a bit of overkill you ask me, doesn't add much and and can be made redundant.
I have some prefab circuit boards for the attached image circuit if you were interested, I may never use them all. let me know and I can fish one out and put in the post to you. Either way good luck with your build and your results. It really is a nice sounding fuzz for such a simple circuit.

Cheers, Trevor

[bluelagoon]

There are a couple good previous threads on the Electra, for some extra insight -

https://www.diystompboxes.com/smfforum/index.php?topic=123535.20

https://www.diystompboxes.com/smfforum/index.php?topic=123341.0

You can even purchase a prefab board from Tayda if you want. It covers the Electra as well as a few other effect types possible from the one PCB

https://www.taydakits.com/instructions/electra-distortion/pages/designators-and-components--14

[Kevin Mitchell]

Schematic is lookin' nice and clean 
Flip those pots around. It helps if you think of pin 1 as fully CCW and pin 3 fully CW.
We're too lazy to do that alt-keyboard trick for the "micro u". Either copy this "µ" for the rest of your endeavors or use lowercase like all the cool cats do.

Good luck!

[Toy Sun]

Thanks for the great feedback, all.
This is really more about my KiCad journey than the Electra, though I'm not turning down any of the advice. I know having that gain pot in my V1 above is strange, but it's been the version that sounds best. To that end, I've created a V2 shown below that moves it as as suggested. Should that gain pot be 10k or 1k? Have to try...
I'll breadboard (or more likely go all the way to perfboard) for V2 and hear how it sounds.

That said, this is only phase I of me trying to finally do my own PCB with a fab house. So I think the adventure will continue when I shift to layout, where I want to have board mounted pots and the diode switch offboard by design. So that will be pads and stuff, all new to me to design in KiCad.

Appreciate the note about flipping the pots - that's exactly the kind of mistake I could make and only find out when I get my boards back... 

How does this look?

Thanks again,
John

[Kevin Mitchell]

Better!
I don't believe the transistor you had used is the generic kicad 2N3904 - I can tell by the double collector.
Just make sure the pinout is EBC (123) on whatever footprint you choose. It may default to a different package & lead style.

Getting ahead here;
If you want to use the popular 16mm alpha pots you'll have to either import a footprint or better, learn how to make them!

Also, it's an easy circuit. Try to stick with single sided layouts until you get the hang of it. Many of us cut out teeth learning how to etch our own boards 

Don't be afraid to ask even the dumbest questions - such as trace widths and how do I do this or that. These learning curves can be a PITA.

[antonis]

Get rid of R2, make P2 1k or so (you'll have to experiment with its actuall value to get a Collector voltage around 4 to 5V) and flip it 180^o (lug 1 to GND..)

[Toy Sun]

Ok, now we are getting somewhere!
Updated per feedback. Thinking about footprints now. I'll start looking at library building for footprints. And about single vs. double sided. I want my pots on the solder side, all other components on the other side - the typical way that project PCBs come in our world. Is that still considered a single sided? Hope so, as that will be easier.

Don't worry, I'll be asking a ton of dumb questions, my specialty. Here is one: after I'm done with the schematic, I understand next step is the netlist and then "dump" the netlist to the PCB layout, correct? Will there be a live connection between the schematic and the PCB layout? For example, if I make a schematic modification, what do I need to do to refresh the PCB layout?

Thanks all,
J

[antonis]

Never dealt with KiCad but I suppose you have to make C4 polarized for PCB transfer..

[FSFX]

Never dealt with KiCad but I suppose you have to make C4 polarized for PCB transfer..

It doesn't matter whether it is represented as polarized or not on the KiCAD schematic as you assign each component a particular footprint for the PCB layout and that is where you define whether it is polarised or not.

[Toy Sun]

Never dealt with KiCad but I suppose you have to make C4 polarized for PCB transfer..

It doesn't matter whether it is represented as polarized or not on the KiCAD schematic as you assign each component a particular footprint for the PCB layout and that is where you define whether it is polarised or not.

My assumption is that happens with the footprint. I've heard there is a KiCAD libary that the stompbox community has developed/shared, does anyone know about that?

Thanks,
J

[FSFX]

It doesn't matter whether it is represented as polarized or not on the KiCAD schematic as you assign each component a particular footprint for the PCB layout

Just to qualify this before others do, it will obviously affect the netlist and the direction of the capacitor in the ratsnest. So having it as polarised will ensure it is seen the correct way around.

[Rob Strand]

Pin 1 on the pot is normally assigned to the counter clockwise rotation.    You want pin 1 to connect to ground.   As is, if you were to translate the schematic to PCB the pot connections would be reversed.   
[I see Kevin already mentioned that.]

You also need to consider if you will be mounting the pots on the top side or the bottom side of the board.   A hack for mounting the pot on the bottom side is to flip pins 1 and pin 3 - it's hack because now the schematic reads incorrectly.  However most modern PCB packages will allow you to select which side of the board the component is on.    ...   and yes it means reading up a lot more about the package and how to do things (properly).

As far as drawing the schematic:  to make the schematic more readable you should rotate the pot on the schematic so the pot resistor symbol is vertical and the OUT signal comes off the wiper to the right.

[Toy Sun]

Not sure which of the pots you were referring to - so here is my guess. That said, I agree that the schematic should be correct with respect to pot pins (not being reversed) and I'll take on the flipping as part of the package/footprint so I can have the pot on the back side of the board. But not going to put the cart before the horse. How does the below look?

Thanks!
J

[Rob Strand]

[Toy Sun]

Thank you!

Ok, next step - breadboard this thing to be sure I'm liking it.
Then I'll do my footprints.
Netlist
PCB Layout.

Been watching a lot of tutorials. There is a learning curve 

[Phend]

Add a color LED with 3k9 +/- resistor in series to indicate on off.
You can add it to your circuit just to just to.
I have been using stereo jacks for the input and using them to connect the ground of the power.
That way when nothing (like guitar) is plugged in then the power is disconnected.
Useful for battery power.