6
So this method is good, and it will work for 10/10 true bypass builds. But, could it be improved? Are there situations where
this particular kind of bypass is not ideal? Turns out there are. Any circuit we are building that is very high gain, or
particularly noisy can benefit from a better bypass. This is because unshielded wire can become microphonic in certain
settings and even push noise into the bypass signal thereby ruining our true bypass efforts altogether.
To construct a better switch-based bypass we will use a technique to ground the circuit input when the effect is bypassed.
This method does not always eliminate potential switching problems, but it gets us there most of the time. When we
ground the circuit input, we’ve eliminated any signal bleed from propagating through the circuit. It also has the advantage
that should our input coupling cap ever fail or become leaky then any DC voltage present at the circuit input will not dump
right back into our guitar.
Here is a schematic drawing of an input grounding bypass
fig.11
A bit more complicated but not too hard to follow. Let’s look.
SW1A and SW1B have been swapped on the input and LED. There’s a good reason for this which you will see in the
wiring illustration below.
Our input is now connected to two places; SW1B lug1 and SW1C lug 3. Why? When our foot-switch is in the up position,
the input connects to the circuit input, just like the previous wiring. Our input is also connected to lug3 of SW1C, but in the
up position it is left open…it doesn’t connect to anything else. When the foot-switch is down, that input is now connected
to lug2 of SW1C and thus the output. But, now the input of the circuit is grounded! Our LED still connects in the same way
as before, just to a different SPDT in the 3PDT foot-switch.