OFF-BOARD SWITCH WIRING FOR GUITAR FX
Here's some common options for stomp switch wiring.
3PDT TRUE BYPASS SWITCHING
Make sure you have latching 3PDT switches, or prepare for disappointment. The alternative to latching switches are momentary switches. Momentary switches are only switched while they're held down. There are times when you might want a momentary switch, but the on / off switch for you pedal is generally not one of them.
Like all things, you generally get what you pay for. The cheap bulk buy from China is OK, but when you put them next to a proper switch, they're often noticeably different.
Helpful diagram below care of the good folks at StewMac
The switch alternates between either connecting the upper row pins or the bottom row of pins to the row in the middle (marked as common below). So pin 2 is either connected to pin 1 or pin 3. Pin 5 connects to either pin 4 or 6 and so on.
A Three Pole Double Throw (3PDT) switch, is just three single pole switches in one box.
DPDT TRUE BYPASS SWITCHING (DOUBLE POLE, DOUBLE THROW)
DPDT are normally only seen in vintage effects, that do not have a LED indicator. Quite often DPDT switches are of a more sturdy construction than modern 3PDT switches. Surprisingly, 3PDT stomp switches have not been around that long.
You can use a normal 3PDT switch instead of a DPDT, and just ignore one row - I prefer using DPDT when they're required, due to the better construction.
SWITCH POP
Personally, I always use a bypass wiring method that grounds the input of the circuit when it's not on. Why? because reduces switch pop.
The 1meg pulldown resistor found on a lot of circuits allows any voltage that leaks from the coupling capacitor on the input, to have a path to ground. If the input of the circuit is grounded, that pulldown resistor becomes redundant, as the there is a direct path to ground.
Circuits tend not to need pulldown resistors on the output, as the volume pot normally takes care of this (there's always a path to ground, even with the volume on 100%). There are exceptions to this rule, the Rangemaster being one of them.
If a circuit doesn't normally have a pulldown resistor and you add one, the input impedance of the circuit is lowered. This usually doesn't matter much, but on something with an already low impedance, do you really want it even lower?
If you are having trouble with switch pop, it can be a mechanical issue with the switch, related to the LED, or capacitor leakage. There's no immediate way to tell which one it is. It's just a process of elimination.
Thanks, great info! I was wondering if you could elaborate somewhat on the 5 3PDT wirings, pros and cons?
ReplyDeleteThe main point to note is that some have the circuit input grounded when off / bypassed.
DeleteI always use this method, as you never have to worry about DC leakage from the input cap. It can also help prevent random oscillations in high gain circuits.
Apart from that, it comes down to personal preference.
Hi, sorry for my newbie question, what is "to effect" and "from effect" means?
ReplyDeleteHi Dan - the comment left by Matopotato is right.
DeleteTO EFFECT: connects to whatever is the input of the effect.
FROM EFFECT: connects to the output of the effect. For a lot of layouts here, this will be from a volume pot.
IN / OUT will always be clearly marked on layouts here, and most other people do the same.
For a 3PDT switch, I nearly always use the one shown on the bottom right (with the 4.7k resistor). I like grounding the input of the circuit when it's off. Reduces the chances of weird things happening with oscillations and pops.
To effect should go to the IN of the board. Pcb or tagboard. From effect should connect to the OUT of the Pcb/tagboard. Hope this helps
ReplyDelete