Capacitors??? HELP!

[Snapey]

Hi guys i'm new to building pedal, and one thing that is confusing me is capacitors!! Which types should i be using in certain areas when builiding, there are so many such as ceramic, poly, electrolitic!
Help!!
Thanks
Ian

[Enzo]

There are ideas out there on why such and such an esoteric cap ouoght to be used in any particular spot, but for the most part it doesn;t matter.

Make up a parts list for your project. Make a grid on a sheet of paper - like a calendar.

Down the left list each cap, and across the top make columns for electrolytic, film, ceramic, tantalum, silver-mica, steam powered, and sodium free.

I think as you look each part up in the catalog of some large supplier like Mouser, you will find out that for a power supply cap like 47uf or 220uf or whatever, the only choice you have is electrolytics. That is anything over a very few ufds.

And fractions of ufs generally won;t come in lytics. Try finding an electrolytic 0.047uf cap. Good luck.

Right around 1uf, you might find a choice, but the elytic will be small and convenient sized, while a 1uf film cap will be the size of your whole footpedal.

Ceramic discs come in sizes mostly up to about 0.1uf and down to the smallest value. I am sure there are larger ones out there, but 0.1 mostly is the top.

SIlver-mica caps are nice caps, but tend to have a much more limited range of values available.

Tantalum caps have certain interesting qualities, but they are also TOTALLY intolerant of voltage and polarity problems. I don;t like them.

You are building pedal, so your circuits run on a 9v battery or a low voltage wall wart, right? As long as the voltage rating on your caps is twice the power supply rating or higher, you are OK. The higher the voltage rating is for a cap, the larger it will be in size. You can use 600v film caps in your circuit, but on a small cramped board, they may crowd themselves out.

Look up a .001uf 50v disc ceramic and a .001uf 1000v disc ceramic and compare the dimensions. Try it with film caps.


Capacitance is capacitance, and 1uf is 1uf. There may be nuances and subtle tonal differences, but your circuit should work with any cap of the wanted value. Once you have your circuits working, and have made a few circuits, then it the time to start wondering what differences in cap type matter, and to what extent.

[Snapey]

Amazing cheers mate that has helped alot i like the grid idea i will employ this while creating circuits!

When building pedals and things do you print your own circuit boards?? Or do you just use normal PCB and use wires to connect the strips etc!

Cheers
Ian

[tubeswell]

When building pedals and things do you print your own circuit boards?? Or do you just use normal PCB and use wires to connect the strips etc!

Cheers
Ian

Hi Ian

This site is good for DIY pedalmen (and wimin) freestompboxes.org • Index page

[BackwardsBoB]

Ceramic caps are very useful for their low ESR, low cost, and small size for low voltage parts, but their capacitance changes as you put voltage on them, with up to 50% capacitance reduction at their rated voltage. A single series ceramic cap can keep you from achieving better than -40 dB THD+N in some cases (large signal, Y5V dielectric, 20 Hz).

Capacitor Type Selection Optimizes PC Sound Quality for Windows Vista Audio Requirements - Maxim

A big application for ceramics is supply filtering in digital circuits. It's not uncommon for these caps to have a +80/-20% capacitance value rating, even measured at 0V DC. You can use them for supply filtering in a pedal with a 9V supply, but you should try for something better in the signal path.

COG dielectric ceramics cause the least problems among ceramics, but they are generally limited to a few hundred pF of capacitance.

For those 0.1uF to 0.001uF caps you'll find attached to the signal path, you're better off with a physically larger cap with "Poly"-something (plastic) in the description.

Of course, for a pedal, the ceramics might "enhance" the "tone".

For most pedals, you can just use a piece of unclad perfboard with 0.1" hole grid, use leaded components stuck through the board, and wire/solder it with maybe 26 AWG wire. Get creative. I've built large circuits on clad PC board blanks using double sticky-tape, 30 AWG wire, PCB strips for power distribution, etc.

You can get PC boards made fairly cheaply, and some vendors have free design software. Here are two random links:

Quality Sunstone Printed Circuit Boards | Sunstone.com
PCB Manufacturer, Advanced Circuits Printed Circuit Boards Production, Annular Ring Boards, Circuit Board Fabrication, PCB's Fabricator and Distributor

You can find others in electronic design magazines.