Forgot to add filter cap...

[Joncaster]

Hi,

So I was half way through layout of my Si Rangemaster type boost, and forgot about any filtering on the DC.
Strange i forgot, cause I've been deeply immersed in tube amp filtering research (my on-again long term project)

Wondering if I should take it back to breadboard and test with the DC jack and RC or C filter? (only been testing with batteries), Then redo the perfboard.
Or why not just pop a 47uF across the DC input jack and be done with it?

I'll use a Boss wall wart for now (will upgrade that later to something a bit more isolated, filtered, etc)

I know that best practise dictates I should be conscientious (especially with a single discreet circuit)...so I've answered my own question.

But hey, there is this amazing forum where one can ask.

[antonis]

When we answer our own questions, forum is amazinigly quiet..

[Joncaster]

haha...

[ElectricDruid]

Or why not just pop a 47uF across the DC input jack and be done with it?

Because without the "R", it's not an "RC" filter. There's no such thing as a "C" filter! You need that series resistance too.

Of course, the wiring will have *some* resistance, but it should be very low, so unless your C is *very* large or the frequencies you're trying to filter out are *very* high (and if they're mains hum, they're not) then that resistance won't be enough.

HTH,
Tom

[Joncaster]

Or why not just pop a 47uF across the DC input jack and be done with it?

Because without the "R", it's not an "RC" filter. There's no such thing as a "C" filter! You need that series resistance too.

Of course, the wiring will have *some* resistance, but it should be very low, so unless your C is *very* large or the frequencies you're trying to filter out are *very* high (and if they're mains hum, they're not) then that resistance won't be enough.

HTH,
Tom

Ah yes, I was meaning the C would form an RC with the wire, but your point clears that up for me nicely, thank you.

Back to the breadboard! (while i'm there I can fiddle with the input cap selector some more too, and maybe rework the output stage into an LPB-1 type, so there's no DC on the output Pot. Although I never got any scratching anyway).

[antonis]

Of course, the wiring will have *some* resistance..

Added to *some other* supply source internal resistance.. 

With "bad" source and loooooooong wiring we might not need series resistor at all... 

[EBK]

Of course, the wiring will have *some* resistance..

Added to *some other* supply source internal resistance.. 

With "bad" source and loooooooong wiring we might not need series resistor at all... 

And don't forget there are also the cap's ESR and ESL (and other inductance properties of your source and wires).    
Everything is an RLC filter! 

[ElectricDruid]

Of course, the wiring will have *some* resistance..

Added to *some other* supply source internal resistance.. 

With "bad" source and loooooooong wiring we might not need series resistor at all... 

And don't forget there are also the cap's ESR and ESL (and other inductance properties of your source and wires).    
Everything is an RLC filter! 

This is all true. But we're all good designers around here and we don't go building circuits that make assumptions about what comes before or goes after, do we?! (We can build a FuzzFace for that!) We like all our circuits to be robust and not fussy about what feeds them and what they feed, and we try to design them so they sound the same in a wide range of situations.

Well, it's a nice ideal to aim at, anyway

Tom

[EBK]

To avoid any possible confusion, listen to Tom.  I was merely having a bit of academic fun, and I apologize for any annoyance that this habit of mine causes.  When you need a resistor, use a resistor, not wire or assumptions.  It is good to know the other bits of information exist (ESR, ESL, power supply internal resistance, and other non-ideal properties which more completely model the behavior of components we use at the cost of added complexity), but you shouldn't dwell on them if they are largely irrelevant in a particular situation, as here. 

[Joncaster]

For me, building pedals is about getting into those deeper details of the whole system.
So one aspect of the build will spark a new chapter of learning.
I can then apply that to other things and further myself as a musician and sound guy.

Besides, the whole reason I got into this was on the way to building an amp.
I got sidetracked, but realized I wasn't ready for the amp yet.
I feel it's important to practice good engineering principles (or at least try to understand what they would be). One feeds into the next stage and you develop a way of thought.

It's a good exercise for me to think about what I'm building as being 'robust' in the engineering sense Tom mentions, and it's good to hold myself to certain standards as a life lesson.
It's also good to not dwell too much and move forward, build, play and find out what it is I'm actually trying to do with all this.

So I really appreciate you guys and these kinds of thoughts.