Replacing switching circuit with 3pdt switch

[Nikenzzy]

Hello. I am looking at some DOD pedals and i see that they bypass effects with a circuit rather than 3pdt switch. For example, DOD FX65 chorus. Dry and wet singals mix in the final opamp before output. Transistor that controls the effect signal is placed before that opamp. If it blocks effect, only dry signal goes into final opamp. If i remove entire switching circuit and wire that effect signal path to a 3pdt switch, will i get the same result?

[amptramp]

True bypass has some advantages and disadvantages as listed below:

Advantages

1.   Negligible signal distortion in bypassed mode
2.   Exact unity gain in bypassed mode
3.   Negligible frequency response deterioration, connected or bypassed
4.   Minimal noise addition
5.   Minimal interaction with effect circuit
6.   No power required for switch function
7.   No other circuitry required except switch pop reduction resistors

Disadvantages

1.   Expensive 3PDT alternate-action switch required
2.   Introduction of switch pops unless circuit modified
3.   Different behaviour depending on order of contact transfer
4.   Low reliability and life of switch
5.   Difficulty in adding remote switching capability
6.   Cannot be initialized on turn-on
7.   Advantages not necessarily applicable to delay functions
8.   Gritty feel to switch function unless you buy a big $$$ switch

Most of these comments are self-explanatory but items 3 and 7 of the disadvantages deserve more explanation.  I don't know of any manufacturer who guarantees which contact of the switch transfers first and the answer will generally be different for switching in each direction.  If you connect an output before you connect an input, the results will be different if you connect an input before you connect an output from the point of view of switch pops.  If you put an effect through qualifying tests, a subtle change in switch manufacture may suddenly give you a switch pop you didn't have before.

It is common to ground the input of an effect that is not active.  This can be a problem with delay circuitry where the input has to be connected all the time or you will get a gap in output.  This means the advantage of no connection and no input impedance drop in the inactive state cannot apply here.

So why have major production manufacturers like Boss and Ibanez avoided true bypass?  Check the disadvantage column.  The 3PDT switch is used by some manufacturers and I have seen some with a very smooth feel to the switching – in $400 pedals where they could afford to specify the best and get it – that requires constant SQA (supplier quality assurance) vigilance and a premium price tag.  Otherwise, you get a switch that feels gritty in operation and has the short life and poor reliability of a low-quality item.  The prospect of warranty returns is enough to make the greater complexity of active switching acceptable.

[Mark Hammer]

Ron/amptramp provides a very nice and comprehensive summary of the pros and cons of "e" vs "TB" switching. One of the things he notes as a disadvantage is #5.  Here's a video explaining how to install remote switching on most e-switched pedals (i.e., those that connect a contact to ground for switching; not ALL do).

Note that converting an e-switched pedal to TB can be a bigger chore than one thinks.  At the very least is machining the enclosure to accept a 3PDT switch.  There is also the matter of identifying and disabling the components involved in the normal E-switching.

When it comes to effects that combine a dry signal with some modulated or time-delayed version of the signal, e-switching is normally used to cancel, rather than bypass, the effect.  Although nearly any modulation pedal (phaser, chorus, flanger) can produce a vibrato effect wen the dry signal is cancelled, it is uncommonfor such pedals to be equipped with that capability, unless some design changes are implemented.  The reason is that, if "bypass" simply involves cancelling/blocking the wet signal, then physically lifting the dry signal would leave you with NO signal, in bypass mode.  If the pedal is for noodling around at home, then that's not a big problem - you simply flick the toggle for when you do or don't want vibrato.  For live performance, however, this is problematic.  Some pedals will provide a dry/wet mix control, which solves the challenge.  But if they don't, then sticking the modulation pedal in a loop, preset to vibrato mode, and selecting that loop when you want vibrato,can provide usable vibrato when gigging, without having to bend down and flick a toggle, or risk hearing nothing.  BUt these are choices the user needs to make.