Glossary

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Glossary

Ciaran Haslett
This post was updated on .
Beginning in this hobby can be tough.  You'll come across many things that are new to you, not least the terms/acronyms we tend to use on layouts and during discussions.  Here is a list that should clear up some of the "Boys Club" language and at least give you an idea of what we are referring to.  As always, we encourage you to learn as much as you can on your own (this is DIY after all) but we all remember what it was like starting out so here's a little push in the right direction.


Schematic = The "road map" of a circuit.  These are how circuit designs are presented.  They display all the components and their connections in a basic graphical outlay.  They show the direction of current, how current is steered, amplified etc through a circuit from input to output.  We use them to draw the layouts you use to clone pedals.

Layout = The nice colour images showing all the components as they appear in real life on a piece of strip board.  They are not schematics.  They are the authors arrangement of components on strip board that matches the connections shown on a schematic.  NOTE:  2 different people can come up with 2 different layouts for the same schematic.  As long as the component connections match the schematic, the layout is correct.

CLR = Current Limiting Resistor.  You'll need to add one (if it's not on the layout already) to your indicator LED to stop it burning out.  Usually in the 1K to 10K range.  The higher the resistance, the dimmer the LED will be.

LDR = Light Dependent Resistor.  A variable resistor controlled by how much light it can see.  You will find these often accompanied by an LED in optical compressors and modulation effects (tremolo, phasers etc).  The brighter the light it sees, the less resistant it becomes.

Vactrol = Resistive Opto-Isolator.  They are an LDR and an LED in one sealed, convenient package.  Found in the same types of circuits as LDRs.  NOTE:  It is possible to "roll your own" vactrol by placing the face of an LDR up against the top on an LED and taping/heat shrinking them together to block out all ambient light.

IC = Integrated Circuit.  Usually a small rectangular chip with 8 or more pins (legs).  You'll find them in many layouts doing many different jobs.  The important thing is to recognise what kind of IC is being used (dual opamp, comparator, OTA etc) and trust that you can use a different model IC in place of the one specified as long as they have like for like functions.  EG you can usually replace a TL072 with a JRC4558 as both are dual opamps.  

NOTE: All ICs will have an indent or a semicircle on their face that denotes where Pin 1 is.  This is especially important as some layout authors place the ICs upside down for a more compact drawing.  So take note of the shaded semicircle you see in all these layouts.  Never take for granted that they are always Pin 1 north.  There is also a standard numbering convention for IC pins.  Anti-clockwise from Pin 1.  So a JRC4580 (8 pin dual opamp) will be labelled as...

1 - 8
2 - 7
3 - 6
4 - 5



Transistor = Usually small 3 pinned devices.  Found in many of the fuzz layouts as amplifiers but also used for signal switching.  Like ICs, they come with a variety of different internals relating to their function.  UJT, BJT, JFET, MOSFET, Regulator etc.

    UJT = Unijunction Transistor.  A type of 3 pin transistor with only one juction. Legs are labelled as Emitter, B1 and B2.  Acts only as a switch and usually used in tremolo pedals.

    BJT = Bipolar Junction Transistor.  The kind you'll see most often on these layouts.  2N2222, BC550, 2N5088 and hundreds more.  BJTs come with 2 different operating requirements, NPN and PNP.  All you need to know now is that NPN and PNP are not interchangeable.  If a layout calls for a 2N5087, you cannot replace it with a 2N5088.  Always search the components data sheet online.  It will show you things like gain, pinout, operational parameters etc.  BJTs have 3 pins...

    CBE = Collector, Base, Emitter.  NOTE: Not all BJTs follow the same pinout.  The BC range is the opposite of the 2N range for example.  Again, always check the data sheet.

    JFET = Junction Gate Field Effect Transistor.  Another type of transistor used for voltage control/switching.  Like BJTs, they come in N channel and P channel types that are not interchangeable.  They also have 3 pins...

    DGS = Drain, Gate, Source.  NOTE:  These too come with different pinouts.  Always check the data sheet.

    Voltage Regulator = Transistor like package that takes a high voltage input and provides a lower constant voltage output, e.g., 78L05.  It has 3 pins...

    IGO = Voltage In, Ground, Voltage Out



Switch Types

You will find many different types of switches in this hobby with labels such as 3PDT,  2P6T,  SPST and yet further labels as ON/ON, ON/OFF/ON etc.  We'll start with the poles and throws.

The most simple mechanical switch is the SPST (Single Pole, Single Throw) toggle.  This has just 2 lugs arranged in 1 column (a single pole) and contact (throw) between the bottom lug and the top can be either made or broken (ON/OFF)

A SPDT (Single Pole, Double Throw) switch still only has 1 pole (single column of lugs) but this time has 2 throws, a lug above and a lug below a centre lug.  So now contact with the centre lug can be made (thrown) with either the top lug OR the bottom lug.  If the switch lever has only 2 positions, up and down, then this must be an ON/ON switch, where the centre lug can only be connected to the top lug or bottom lug.  If the lever has 3 positions, Up/Centre/Down then it must be an ON/OFF/ON (where the centre position does not connect the middle lug to the top or bottom)

A DPDT (Double Pole, Double Throw) switch is the equivalent of 2 SPDT switches in 1.  So instead of 1 column of lugs we have 2.  It works the same way as an SPDT switch except you have another operational state, ON/ON/ON, where the up and down lever positions still connect the centre lugs to the top lug or bottom lug but the centre position does something different this time.  Instead of breaking contact with the throw lugs (ON/OFF/ON) it will connect Pole 1 to the top lug and Pole 2 to the bottom lug (ON/ON/ON).  NOTE: You can buy switches that make these centre contacts opposite of what I just described.  Always check your switch before wiring.  Most layouts assume an ON/ON/ON will make contact like the above.

A 3PDT is, you guessed it, 3 SPDT switches in one and work identical to the DPDT.

Important note about toggle switches. As well as what I've described above, you can also get momentary toggles.  This means that one of their lever positions spring back to centre (it doesn't stay up or down without you physically holding it in place).  These can be identified with brackets.  For example, an (ON)/OFF/(ON) switch will have a momentary top throw and bottom throw and will rest in the centre position when not being touched.  We don't tend to use momentary toggles here as we operate our pedals with our feet as our hands are busy rocking out.  But we do use momentary foot switches...tap tempo, dry kill, feedback etc.  You will find all this labelling on the side of the switch itself.

Just like ICs, switches have their own numbering convention.  Start top left and count down, then top of next pole and count down etc.  So a 3PDT will be numbered as follows...

1 - 4 - 7
2 - 5 - 8
3 - 6 - 9


Any additions welcome.  When you've been doing this hobby long enough its easy to overlook terms that newcomers may struggle with.  Cheers folks.
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Re: Glossary

Beaker
Nice one Ciaran.

"Schematic = The "road map" of a circuit.  These are how circuit designs are presented.  They display all the components and their connections in a basic graphical outlay.  We use them to draw the layouts you use to clone pedals."

You could add that it shows the direction of current flow through the circuit, from input to output?

Also:

UJT : Unijunction transistor. A type of 3 pin transistor with only one juction. Legs are labelled as emitter, B1 and B2. Acts only as a switch and usually used in tremolo pedals.

Switch types : The most commonly used switches in pedals are SPST (single pole single throw), DPDT (double pole double throw) and 3PDT (three pole double throw).

SPST are usually on/off or on/on. DPDT are usually on/off, on/on, on/on/on or on/off/on.
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Re: Glossary

Ciaran Haslett
Cheers Beaker.  More info added.

Keep em coming folks
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Re: Glossary

Silver Blues
What about LDR (Light dependent resistor) aka photoresistor? Handy for the modulation effects and compressors.

Also "pampas" in your ICs description
I stand watching the steam-liners roll by...
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Re: Glossary

Ciaran Haslett
You mean you don't have any dual pampas?

Adding LDRs, vactrols next. Cheers Silver
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Re: Glossary

Ciaran Haslett
In reply to this post by Silver Blues
LDRs and vactrols up.  Anyone think of something else thats asked frequently?  Cheers
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Re: Glossary

Suzukiscottie
Pots and trimmers?

Jacks, stereo and mono?

Wire types, solid, stranded, guages?

And then for those with OCD, reorganise it all alphabetically.

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Re: Glossary

Ciaran Haslett
Cheers Suzuki.  I might make separate topics that explain pots/jacks etc but I'll include some terms regarding them here, mono/stereo e.g..  I want to keep this thread pretty direct (thinking of editing down the switch info).  I never noticed before you mentioned it about alphabetical order...now it annoys me lol.  I sort it all out later.  Good man
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Re: Glossary

induction
In reply to this post by Beaker
Beaker wrote
"Schematic = The "road map" of a circuit.  These are how circuit designs are presented.  They display all the components and their connections in a basic graphical outlay.  We use them to draw the layouts you use to clone pedals."

You could add that it shows the direction of current flow through the circuit, from input to output?
Not exactly. Replace 'current flow' with 'signal path' and you've got it.

DC current flows from the high voltage rail to the low voltage rail. The AC current in the signal path doesn't flow only from input to output, it constantly reverses itself (it's AC remember). First it flows one way (input -> output) then it immediately flows the opposite way (output -> input). Back and forth in accordance with the instantaneous signal voltage relative to signal ground (Vref, usually).

</nitpick>
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Re: Glossary

Beaker
You are, of course correct Induction. My bad.

You can't nitpick when it's the truth!