bypass idea that came in the middle of the night

[Boogdish]

I got up at 11:30 last night (yeah, I'm living the rock and roll lifestyle, in bed by 9:30) and I drew this schematic, it's for an idea for a true bypass that would use a DPDT and no extra parts:


as you can see, the tip of the output is connected to the switch and the output of the effect circuit. In bypass the effect circuit should theoretically not be producing any sound because it isn't receiving 9V+ or any audio input, so there shouldn't be any noise from there.  When not bypassed, the 9V+ lead and the input jack are both connected to the effect circuit and then that goes to the output.  It could also work with the output lead being sent the middle of a side of the switch and having the input jack connected to one end of the switch and the circuit's output connected to the other with the input jack also connected to the input of the effect circuit.

I'm very new to building pedals, so far all I've done is breadboarded other people's circuits and done a couple of GGG kits.  Has this been done before?  Is it a feasible idea?  Does this constitute true bypass?  Is there a very glaring and obvious problem with this that I'm not seeing?  I have some DPDT switches on their way from Pedal Parts plus, but they aren't here yet, so I can't try this out myself for a couple days.

[Morocotopo]

Nice try Boogdish, but there´s a problem: switching the power is a no-no. Each time the circuit powers on or off (each time you step on the switch), you´ll get a BIG pop  and/or other nasty noises circuits make when powered on/off. Also, there´s no status LED... if you wanna do true bypass without a LED, it´s been done. Search theFAQs/wiki.
See "Millenium bypass" at Geofex.com for true bypass switching and status LED with a DPDT.

Morocotopo

[R.G.]

There's another problem as well. The output of the effect is always connected to the output jack. That prevents it from being true bypass, and the output of the jack fights the signal in bypass.

[SmurfJ]

you can prevent the pop with a hight level resistor or so i've been told

[mojo_hand]

Pop or no pop, the connection to the output of the effect is the deal killer.  The whole problem with older sort of unbuffered effects was that the bypass would still leave the very front end of the effect (typically a 100k-500k impedance-setting resistor) in circuit.  Daisy chain a few of those together and you'd end up with massive tone and volume suck from the dividing effect of the parallel resistors.  Leaving the *back* end of the circuit connected does the same thing, but more so, since a solid state effect will usually have a resistor or pot of closer to 10k at that location.  Impedance that low would suck tons of tone and volume even if you were just bypassing the one effect.  So it's time to go back to the drawing board.

[Mark Hammer]

I had an idea in the middle of the night too, only related to work.  Sometimes, they're good ideas, and sometimes it was probably better to stay asleep and think about donuts.   Mmmmmm, nice....greasy......sweeeeeeeeet.....donuts (drool).

The good new is you can always say "Hey, I was hald asleep when I thought of it.  Cut me some slack!"...and people will.

[Boogdish]

thanks for all the responses, y'all!  I knew it seemed too simple to work, but in my sleep addled head I guess I couldn't see why.  Now I kinda want a donut.

[dschwartz]

i think that´s very good that you give a thought about how circuits work and try to find your way to solve problems.. many, or most of the newbies i try to help don´t even bother of trying to understand how a dpdt works and how the signal flows thru the wires..

i earned the fame of "newbie hater" in the chilean forum (plexilandia) cause i just can´t stand those lazy bastards....

[joegagan]

that's what i was gonna say also.

i think it is good that the guy is already thinking like a designer.

welcome, boogdish

[mojo_hand]

i think it is good that the guy is already thinking like a designer.

+1.  Thoughts which don't quite work give way to ones that do.  The only thing to be embarrassed about is if you never come up with any ideas at all.

[Boogdish]

thanks for the kind words guys!

[johngreene]

I had an idea in the middle of the night too, only related to work.  Sometimes, they're good ideas, and sometimes it was probably better to stay asleep and think about donuts.   Mmmmmm, nice....greasy......sweeeeeeeeet.....donuts (drool).

The good new is you can always say "Hey, I was hald asleep when I thought of it.  Cut me some slack!"...and people will.

mmmmmm, donuts.

[mojo_hand]

I had an idea in the middle of the night too, only related to work.

Me too.  Unfortunately, I suspect that my boss' secretary would consider any of them to be highly inappropriate.