true bypass with 1p2t switch?

[searoad]

http://www.kandr.dyndns.org/product/kits/man-q-triper.pdf
found this autowah project from a Japan site.
just take a look at the offboard wiring on 2nd page of the pdf file.
it uses a dpdt switch with a led, wired as we do on a 3pdt, not a millenium bypass or any kinds of led trick.
and the audio switch section only uses spdt:
throw- to input jack and fx input
pole  - to output jack
throw- to fx output

the brown wire(input from jack) and the yellow one(to effect board input) is always connected!
has anyone ever tried this before?

[heyniceguy]

well the problem is that THAT is not true bypass, because the input signal is not "bypassing" the effect circuitry when off. if you hooked it up like that, the fet buffer would load the input signal when in bypass mode and you would have some high end cut. even worse, if the battery went dead, youd likely lose all sound when in bypass. the ONLY way to achieve true bypass AND an LED with a SPDT stomp switch is to have the stomper switch trigger a 3PDT relay. and just hook up the normally closed contacts of the relay in BYPASS mode so if the battery dies, it will stay in bypass mode.

[Mark Hammer]

We've had endless threads/debates about bypassing schemes here.  There are advantages to use of an all-electronic switching scheme, and some advantages to use of a mechanical "true" bypass.  There are disadvantages to each as well.

The presence of a high input-impedance FET buffer in this circuit is partly intended to eliminate the need for switching BOTH the input and output.  The 1M resistor on the input will result in minimal loading of the guitar signal, such that if you simply alternate between taking the output signal from the input jack OR the output of the circuit, the circuit will not constitute much of a "dead weight" on the signal, the way it might if it had a lower input impedance than it does.

Think of it like going shopping downtown with a sibling under age 10, vs an adult sibling.  The one is an ongoing obligation that will rigidly constrain what you attemt to do or where you can go.  Fun to be with while you're in the toy section, but growing VERY bored and agitated while you sift through parts bins at the electronics surplus place, and a royal PITA.  The other is independent enough that you can split up and meet again later.  Mechanical "true bypass" switches that separate both the input and output were intended to fulfill the function of something like an on-demand babysitter for the young sibling, so that it would not pose a constant challenge to what you were trying to do, even in effect-off mode.

[searoad]

thanks for sharing the knowledge!!
i just thought too less before posting.
so if i use the 3pdt switch as usual, should i take off the 1M resistor(R5) or even the whole input buffer?

ps.the autowah got a nice wah-sound instead of quack-sound