Help - Adding DC Filtering / Polarity protection to a Big Muff schematic?

[FuzzJourney50]

hi everyone

I've built a big muff schematic from bigmuffpage.com on a breadboard and all sounds great, so now I want to go to the next stage and make a professional pcb for it, but whilst learning Eagle I've come up with a few design questions.

1. For a professional result, do I need to add DC filtering and polarity protection to the circuit I'm cloning below??



2. If yes, could some one help me design that section? I've had a go at adding a polarity protection diode, and some filtering caps, but I suspect it's not right. I'd be really grateful if someone could appraise what I've done. See attached schematic I drew in eagle (forgive the lack of tidiness, it was my first attempt).



All the best
Jon

[idy]

Welcome to the forum.

For best practice people add a small series resistor. See
http://www.muzique.com/news/reverse-voltage-protection/

I tripped for a minute on the schematic at the link showing both a series diode like yours and a shunt diode, then read the explanation that this is depicting a mod to an existing pedal, and there is no harm in leaving an original shunt diode in place but a risk of damaging the board removing it.

[antonis]

Hi & Welcome..

The value of series resistor ( between D5 Cathode & C14 positive leg) depends both on circuit total current consumption (PSU affortable voltage drop) and C14 value..
e.g. for 5mA circuit current (excluding LED), voltage drop across 100R series resistor is 500mV..
That voltage drop should be added to D5 forward drop (300mV for Shottky or 650mV for Si - typical..) to find out total voltage drop from PSU to +9V point..
Also, its value together with C14 value set LPF cut-off frequency (f=1/2πRC), which f should be much lower than rectified AC (100 for 50Hz or 120 for 60Hz mains frequency)

It is clear both for low voltage drop and for resistor power rating (W=I²XR) that the lower the series resistor value the better the result BUT you'll need to raise C14 value..

P.S.
For battery supply, you don't need neither C14 nor series resistor..
(OK, maybe C14 might stay as reservoir cap but then it will also be needed some series resistor for C14 inrush current limitation - but I think this is another story..) 

[ElectricDruid]

There was a good thread about best practice for power inputs a little while back:

https://www.diystompboxes.com/smfforum/index.php?topic=127081.0

I posted my personal favourite solution there, so I won't do it again here.

[FuzzJourney50]

Thanks for everyones comments, it's given me something to think about.