Lofi-nator and capacitors

[ValentinWFP]

Hi there,

I've recently started building a lofi-nator and got the PCB and materials together as a kit. The problem I've got is that the capacitors C11 and C13 I received in the kit are electrolytic rather than non-polarised. Based on the docs (here) and the PCB, I'm under the impression that it's not a problem so long as I solder them with the right orientation; ie. with the - of C11 going to R30 and the - of C13 going to Q1 and R39. For both capacitors, that'd be with the - on the right when facing the PCB.
Is that correct? And if so, how much influence would this have on the signal/sound?

Thanks a lot

Val

 

[Chuck D. Bones]

Both caps have close to zero DC voltage across them, so polarity doesn't much matter here. C13 is way oversize at 1uF. If you have a 470nF or even 220nF film for C13, that will work fine.

 

[ValentinWFP]

Oh wow, I had not realised this. Thanks a lot for your answer!
So I'm left wondering, what's the purpose of those two caps in processing the signal?

 

[Chuck D. Bones]

Honestly, pedal designers have a habit of putting in parts that don't do much of anything. I have built clones and replaced useless coupling caps with jumpers and deleted unneeded bias resistors. Those caps are intended to block DC, and in the case of C13, there is enough DC to block that it makes a difference being there.
The output of IC3 is within 100mV of Vref. Probably within 10mV. C11 could be replaced with a jumper and the circuit performance would be the same.
The bottom end of R34 is within 10mV of Vref. You could leave out R34 and it would sound the same.
C13 actually does something: it prevents the "crackle" you might hear when you turn the LEVEL control. Same sound you hear when you turn a FF FUZZ pot or a Rangemaster pot. The pedal would still work with C13 shorted.

 

[ValentinWFP]

Thank you so much for your detailed answer. I've been working on improving my understanding of schematics/which parts do what and your answer was amazingly instructive, so I can hardly thank you enough!

Once the lofi-nator (hopefully) works, I think the next steps for me will be to build more straight-forward effects on a breadboard and experiment with the parts.

 

[Chuck D. Bones]

My best advice for building experimental circuits is to keep it simple and use quality parts. Build it to a known good schematic first, get it running and checked out thoroughly before changing anything. That way, you have a know good circuit you can go back to when things go sideways. Change only one thing at a time. Take lots of notes. It's really easy to get lost if you are not systematic. I'd skip germanium transistors until you gain some experience because they can be particularly temperamental.