A quick tube (valve) fuzz box

[DrNomis_44]

Depending on what kind of led you use, you might need to use a current-limiting resistor as high as maybe 47k for one of those very bright 3mm blue leds, best thing to do is do some breadboard experimenting with different resistor values first.

[DrNomis_44]

The only downside to the 450V cap (from jaycar at least) is it's size - I'm still pondering how to get my circuit into an enclosure, ha ha

Yeah that's true, I think the 22uF/450V caps are a bit smaller than a 47uF/450V cap, so if you put two in parallel you'll effectively get a 44uF/450V cap.

[jugglindan]

Depending on what kind of led you use, you might need to use a current-limiting resistor as high as maybe 47k for one of those very bright 3mm blue leds, best thing to do is do some breadboard experimenting with different resistor values first.

Yeah, there is a huge variation in available LED brightness. I always breadboard the resistors since my box of LEDs vary quite a bit in brightness by colour, and also to a lesser extent within a colour. Blue tends towards the bright side. I suspect it's due to the complex shenanigans required to get a blue colour.

[Simon Barden]

'True bypass' avoids any connection of the input signal to the circuit, and on this pedal as shown, the signal is still connected when in bypass mode. It may or may not not alter the sound, but for some true bypass freaks, it won't be acceptable.

Take an extreme case of the circuit simply consisting of a capacitor connected to ground (like the tone circuit on a guitar but with the pot set to 0). Then the capacitor would still affect the tone of the signal in both 'in' and 'bypass' switch positions. You'd need the input signal and the output signal to be disconnected for the circuit not to affect the tone.

The circuit as shown doesn't disconnect the input from the circuit, so isn't even the 'basic true bypass' of the linked article. It's just a bypass. Semantics maybe, but still important as you are reliant on the design of the circuit not to noticeably affect the tone in bypass. And there could also be knock-on effects with respect to increased ground loop noise with some circuit designs.

For this circuit, you've got a 1M ohm resistor down to ground that's certainly connected in bypass. This will be in parallel to the amp's input impedance, so assuming that is 1M, you've now got 500 k Ohm. Still pretty much OK. But assume there are several other pedals with a similar bypass design. You can easily drop down to a 250k ohm or below equivalent input impedance, which will start loosing top end if there's no buffered circuit upstream.

So I'd definitely recommend using a 3PDT switch so you can call it true bypass.

[jugglindan]

OK, I see your point and gracefully concede

/me goes back to check my bypass wiring ...

Yeah, the scheme I use connects the effect send (input) to ground, and leaves the effect return (output) disconnected in the bypass state.

[Simon Barden]

A bit of a mental exercise for me as well. I can now see why people insist on either a good buffer or a true bypass switch.

[jugglindan]

I prefer true bypass and separate buffer pedals. That way I avoid the issues caused by too many buffers (I watched a video where they hooked a bunch of Boss pedals together, all buffered - the audio result with all pedals bypassed was not pretty) or not enough, and I get to choose where the buffer goes.

It's also why I use a trusted wiring diagram each time. I don't need to rethink this, just follow the instructions.

[Simon Barden]

Some of the Boss designs haven't changed since they were designed in the 70s/80s, and buffer design has moved on considerably since. There's no reason why a good modern buffered pedal shouldn't be totally transparent in bypass.

[JohnH]

It's embarrassing it's taken so long to finally box this up, but I thought I'd share the final product with you all...

I definitely recommend building one of these - it's a lot of fun to play

[WeirdBits]

Looks great.