DOD 250 cap question?

[davepedals]

is there a good work-a-round for the .05uf (C3) cap in MarkM's layout?  perhaps .047uf?

[jonny]

yip, go with .047u capacitors mostly have a tolerance of +/-20%! Resistor about 5% usually.

[Mark Hammer]

Those new to this hobby/obsession will regularly infer that .047 is not .05, or that 470k is not 500k, and so on.

As jonny rightly points out, when tolerances are taken into consideration, the differences between the numbers printed on the component are essentially meaningless.  That is, the actual value of the part you can get may well be closer to the value the circuit calls for than the actual value of the part you order in because it has the "right number" printed on it.

I have no idea whether this is a historical pattern (i.e., a shift over time from values with '5' in them), or a difference between countries and regional standards (.047 in one continent and .05in another), or a shift in standards for particular families of components (e.g., pots are generally designated as 50k, 100k, 250k, 500k, and rarely as 47k, 470k or 220k), but if the nearest common value is within 10% or so of the part value you think you are supposed to use, you'll be fine.

There are plenty of times where the value of the component you have in your parts bin/s may actually be an improvement on what the schematic calls for.

Learn the simple formulae for calculating rolloff frequency, and op-amp gain, and you'll be very pleasantly surprised at how much it will liberate you to make very viable and useful choices from what you have on hand.

[davepedals]

thanks for the great info!

[petemoore]

  Whether intended this way or not: Throws 'em off.
   I studied to be an electronics assembler, and could not find the components...probably a good thing since...not knowing that it doesn't
matter for me equated pretty much directly with knot knowing when it DOES matter [like high voltage !], or how to get 'the thing' [wanted to builda amp back in 70's geuss it was] to work.
  Kinda cool...was just enough to throw me off building, or be close enough if I got past the 'tolerance matters'.
   Regardless of the application, I doubt 'they' could hear any difference between .047uf and .05 than I can now..takes less space on the schematic if rounded up, afaiktell the digit position the 7 in .047 is in won't make any difference in a schematic, therefore can be eliminated...simple is always better/except in cases where slightly overcomplicated introduction to a complicated matter may thward unwary casual visitors.

[CoolJohnny]

having built the 250 or versions of it several times i can tell you that .047 works just fine. i use it all the time. just for future reference, its always good to breadboard anything you are about to commit to PCB just to make sure there will be no ill-effect with a part swap. and quite often, i've been able to perfect circuits to my liking this way. best of luck. its a great pedal!

[davepedals]

i've been building electronic projects most of my life, but most of them were kits - not requiring me to think too much.  always hated bread boarding but since i'm starting to enjoy experimenting more...i need to learn to love it!

[CoolJohnny]

i cannot reccomend it highly enough. just get a decent breadboard (radio shack will do but they are not very durable and some say they have some inherent capacitance which will affect your tone in the end) and some jumper wires and go nuts. those boards with hard points where you can attach permanent power supply are especially useful.

breadboarding is most helpful in deciding if you REALLY like a certain design by being able to play through it without all the effort and expense of actually building the thing. once you get it on there and working, just start saying "what if?" start swapping values and see what happens. since you are building the DOD 250 you have several different versions to try out, or some combination of them, or something entirely new. it's a very versatile circuit. keep a notebook at your workspace and keep notes of how the sound changes as you swap stuff out. not only does this keep track of things so you don't have to remember what exactly sounded best, but it may help you learn things that might work on future circuits.

i even went so far once as to breadboard a jordan bosstone and take it to a session to use on a friend's recording project. i don't like the pedal enough to spend the time and money to build it but it was a useful sound for one afternoon. 

[jonny]

Funnily enough I was just opening up my '65 mustang as it had some issues and it has a .05u cap. They just must've been a real old school value.