Colorless writings, part 9 – The Switcheroo

Back on the subject of bypass switching are we?

Partially yes. But i think i’d like to say thing or two more about switches in general. Actually. I was sitting on my desk that i use as work bench and killing myself with a build. That’s when the title of today’s Colorless Writings came to me.

As i personally hand-wire everything in my builds, i only use switches with solder lugs. In the time i’ve built and repaired pedals, i must have soldered on way more than 600 switches altogether by today. At first, these mechanical components seem solid. But if you take a closer look of how those are made, you might convince yourself that the first impression isn’t as accurate as you thought.The pins/lugs are held in with plastic housing. Now, those may seem sturdy enough, but when you’re soldering your wires to those lugs and apply just a little too much heat and pressure, you can see and feel the lug moving. Once the lug moves a fraction of a millimetre, the structural integrity is compromised. In a sense, those components are probably the most fragile thing in any build. I don’t want to think how many semiconductors i’ve soldered on in all this time, but never burned any transistors by accident (yet). But have i burned switches? Many. And if we count the ones that have landed back on my desk with them becoming faulty after six months of use, there are a few more. Someone on the mighty interwebs said that firm, decisive and quick is the way to go with all the switches. I couldn’t agree more.

How do the switches work?

The most common toggle and stomp switches we use for pedals are SPST, SPDT, DPDT and 3PDT (of course there are others as well…). Next you might ask what do these initialisms mean. Well:

  • SPST – Single Pole Single Throw
  • SPDT – Single Pole Double Throw
  • DPDT – Dual Pole Double Throw
  • 3PDT – Triple Pole Double Throw

As you might have guessed, the SP/DP/3P part means how many vertical poles the switch has. The second part tells us the effective “throws”, or positions. This may be a bit misleading, since there are different ways the toggle connects the lugs. First, the SPST has only two lugs. The other position has these two lugs connected and the other has them apart. Simple, right? But then we get to the SPDT which has three lugs. There are two different toggle types of this switch. On-On and On-Off-On. Meaning that there’s actually three effective throws on the On-Off-On switch. One position connects the middle lug to the upper lug, other connects the middle lug to the lower lug. Middle position connects nothing to nothing. The DPDT has six lugs and those work exactly like the lugs on the SPDT, except that there are two vertical poles that both respond to the same flick of that switch. Same thing with 3PDT. The nine lugs represent three different poles that all connect or disconnect the same way as SPDT. There are just three of those vertical poles connecting and disconnecting at the same time. 4PDT has four poles, but those too act in the same way. Different poles can be used to connect and disconnect different things on a circuit – for a single flick. I’ve drawn a memory guide for myself a long time ago. It also includes the pot lug numbering convention that i’ve adopted for my use.

Other types of switches you might find on a pedal are tactile or momentary switches, rotary switches and possibly On-On-On types.

The tactile and or momentary switches are very common and usually used in electronic bypass switching circuitry. These come usually in two different configurations. Namely NO and NC. These mean that there is always only one “pole” that is either connected or unconnected when the button isn’t pressed. NO is short for Normally Open (not connected) and NC is short for Normally Closed (connected). Now, when you push a button that is NO, the connection is made for the time you are pushing the button. Once you release your hold, the connection is gone. Momentary switches come in all the variation of different numbers of poles with usual On-On configuration. I haven’t seen this kind of switches on pedals, since the circuitry behind the 3PDT momentary switch is usually complex – unless it is used for momentary feedback or mute control.

The rotary switches are fun. These come in many, many different configurations. For example, 2P6T and 4P12T. First part of the type “code” is for the number of poles. Usual number of poles are one, two and four. Second part tells us how many positions the pole can have. 6T is for six turns and 12T is for 12 turns. Common boutique use for these switches is to place different cap values or different clipping diode arrangements on the turns. For the cap value switching, the simplest example would be the good ‘ol Rangemaster with 1P6T switch. On that configuration, the input of the circuit should be placed on the middle pin. Then the board should have six different values for the input cap. Let’s say 4n7, 10n, 22n, 47n, 120n and 470n. All those caps need to have the other lead at the transistor’s base, while the other leads connect to the six lugs on the switch. This way the Rangemaster can be used from treble booster to bassy wide range booster and everything in the middle. There are, of course, numerous different pole and turn variations of these switches available.

The one type that’s quite rarely used in a pedal is the DPDT On-On-On switch. There are exceptions. You may have come across one of these switches in your time. Most Les Pauls, SGs, 335s and basically any of the guitars with two humbuckers have this type of switch for the pickup selector. The up and down settings work exactly like in On-On switch, but the middle position is different. While down position connects middle lugs to the upper lugs and up position connects the middle lugs to lower lugs, the middle position has fthe first pole’s middle lug connected to upper lug and the second pole’s middle lug is connected to lower lug. This gives out even more switching options than the previous types.

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