diy stompbox build question

[adamshack]

hi, i am new to this amazing world of building effects. i just had a few questions like, do i need to use all the right values of the components? which ones can i substitute? and why. i would love some help and a kind push in the right direction. thank you R

[Jazz P Bass]

Stompbox

Can you say Electrical Engineer?
Component values are picked according to the criteria of the circuit.

[defaced]

This is like asking how much water to put in a glass. It really is an "it depends" sorta thing. You have to be way more specific to get a meaningful answer. We'll start with what circuit are you working on and what value of component do you want to tweak and why do you want to tweak it?

[Mark Hammer]

It's a fair question, and I have to say it took me several decades to learn what I could slack off on and what needed attention.

There are a couple of things to pay immediate attention to:

1) Ratings (as opposed to value): In many instances, resistors for effects can be the teeny 1/8w size, though in some instances 1/4 and even 1/2 to 1W sizes are called for. Many schematics will simply assume you bought a bunch of 1/4W units, and that's what you'll use. But 4 times out of 5 (or higher) you can use 1/8W with no fear. Capacitors have voltage ratings, with higher voltage ratings generally being larger and costing a little more. The rule of thumb is that the voltage rating on the cap should be at least 1-1/2 times the highest voltage the cap will see. So, for pedals that operate on a 9v battery, you will usually find 16v-rated caps. Higher ratings is fine and has no implications for the appropriateness of the cap. If all you can find are 50v or 250v units, fine.

2) Tolerances: Standard resistors have a 5% tolerance, though you can buy 1% units. Caps often have actual values that are within 10% (+/-) of their stated value. Generally speaking, unless the schematic stipulates 1% values or hand-selected components, assumptions are that it may be a little higher or a little lower.

3) Bandwidth maximizing: In many instances, caps or cap/resistor combinations are used to set the bandwidth of the circuit. That is the range within which the signal is passed in a "flat" unbiased fashion. Depending on where it is inserted in the circuit a capacitor may shave off bass or may shave off treble. I find in a great many instances, manufacturers have used values that seem to assume the joint effect of many pedals doing the same thing. So, an input cap may provide a rolloff that is 3db down at, say 6hz, and an output cap may do the same. That will have no audible effect on your bass signal, but if that same rolloff is applied via 10 pedals in series, it starts to be audible. If your plan is to never have more than 2 pedals on, though, you can certainly afford to replace that cap with something 1/4 or even 1/8 the value stated on the schematic with little or no audible impact. Again, context will be critical, but the bottom line is that a great many circuits can work just fine with what seem to be, on the surface, major changes in component value.

The formula you will be glad to become handy with is F = 1 / [2*pi*R*C], where R = resistance (in megohms), C = capacitance (in microfarads), and F is the resulting frequency where the impact begins. This will enable you to make a LOT of judgment calls about what the circuit can tolerate and still behave reasonably.

[rosssurf]

Mark knows his stuff and is helpfull as allways. He must be a "good egg" as my dad used to say.

[adamshack]

Thanks Mark, I just finished modding my boss cs3 comp. for more bass and a little less squish. I didnt have the exact values at first. Upon reconsideration, I wound up spending the measley 15 bucks or so to get the proper parts lol. But i didnt want to put it together, plug it in and find all the dogs howling in the neighborhood. or have the circuit not work at all. So thats why i wanted to know which parts i could substitute.

Even though i dont have a reference besides my ear, it tells me it sounds much better now, alot less noise too. It seemed almost useless before. Kinda makes me wonder why they didnt just put the pedal out like this. Thanks, Adamshack

[Mark Hammer]

Most pedals produced by larger companies will make somebody happy with all possible settings, and some people happy with some settings. If every such pedal made everybody happy with all settings, then guys like Robert Keeley would be outa business.