"True" vs. "Non-true bypass" switching

[Calamazoo]

I built a COT out of spare parts the other day and used a dpdt swith instead of a 3pdt. I had planned on wiring it with no LED then I saw these on GGG.

 

http://www.generalguitargadgets.com/how-to-build-it/technical-help/switching-and-wiring/bypass-sw-options/

 

I used the input unbypassed wiring. It seems to work fine and not effect my tone while it's off so my question is if this works why bother with a 3pdt switch? This was eaisier to wire and seems like dpdt switches are cheaper. Sorry if the answer is obvious but I am still an amateur pedal builder.

[JeffB]

I dont know. Just bumping it for you.

[Kuz]

No clue, sorry.

[kbp810]

Easiest answer is the one you've already given yourself - Since it is not effecting your tone, or at least not that you've noticed, then it doesn't matter.

 

If you study the wiring diagrams, you can see that in the non-true bypass with DPDT switch the effects circuit is in parallel with your signal path - so even with the effect off, it is going to technically still have some impact to the signal; with a 3PDT, the signal path is on its own pair of poles, so when the switch is off, it is bypassing everything else in the box.

[duhvoodooman]

You're probably not experiencing any appreciable amount of the dreaded "tone suckage" (i.e. treble frequency loss) because that pedal has a high enough input impedance that it's not loading your pickups down even though the circuit remains in parallel with your signal path when the switch is off. If the pedal had a low input impedance, like the original late '60s wah pedals to use the most famous example, your experience might be much different.

 

While there are several alternatives to consider, as that GGG page shows, probably the most commonly used these days, esp. by DIY pedal builders, is the "True Bypass/LED indicator DC Jack, input grounded" version under the 3PDT category. You are correct that this type of footswitch will cost more (about $4 is typical vs. about a buck for an SPDT) and is more complicated to wire, but this wiring method has several advantages:

• It's a true mechanical bypass of the effect circuit--no connection between the effect circuit and your signal path when in bypass mode--so tone suckage or other undesirable anomalies from the effect circuit becomes a physical impossibility.
• You get the convenience of an LED indicator for the bypassed/engaged switch positions.
• In conjunction with the use of a stereo input jack, your battery power won't engage unless there's a cable inserted into the input jack, since it takes the sleeve of the cable tip to complete the needed battery ground connection. This makes a convenient way to insure that your battery doesn't drain between uses of the pedal--just pull the cable out of the input jack.
• The grounded effect circuit input in bypassed mode is an additional safeguard against potential noise when switching.

To me, this footswitch wiring method is well worth the extra bit of expense for the 3PDT switch and the greater wiring time, compared to the advantages it offers over the life of the pedal.

 

Here's the switch wiring per the above method on one of mine:

 

[ScottNaylor]

Duhvoodooman, you are a treasure!

[Calamazoo]

Thanks for the responses. I usually use 3pdt for my pedal builds but this was made out of spare/RatShack parts and they didn't have any 3pdt. I think I will stick with 3pdt for more complicated pedals.

 

Regards