Resistor
Limits current, and sets voltages when two are used together.
Read the colour bands. 10k is brown, black, black, red, brown. The last band is the tolerance.
Breadboard Bench
Breadboard basics
From reading a schematic to a circuit that works, without getting hurt.
Stay safe
A 9V battery on a breadboard is low-risk. The real dangers are the gear around it, so start here.
- Never open an amp, or anything that plugs into the wall. Tube amps hold lethal voltage in their capacitors, even after they're unplugged. This is the one mistake on this page that can kill you. Take amp repairs to a technician.
- Never wire a circuit to mains power, and never open a wall adapter. Everything here runs on a 9V battery. Keep it that way.
- Never plug a pedal into an amp's speaker output. Use the amp's instrument input only. A speaker output carries far more power than a pedal can take, and it can burn out the circuit and the amp.
Every session
- Disconnect the battery before changing wiring. It takes seconds, and it prevents most shorts.
- If anything gets warm, smells or smokes, disconnect the battery and wait. A shorted 9V battery gets hot fast, and so can its wires. Let it cool before you touch it, then find the fault.
- Don't carry a loose 9V battery with keys or coins. Metal across the two terminals is a short circuit in your pocket.
- Follow the stripe on electrolytic capacitors. Fitted backwards, or run above their voltage rating, they can burst and spray. Keep your face away when you first power up.
- Protect your ears. Keep the amp at zero when you power up, then bring it up slowly. Fuzz and unfinished circuits can shriek without warning.
- Wear glasses when clipping legs. Clipped leads fly further than you'd expect, usually toward your face.
- Don't use a wall adapter of unknown polarity. Arduino-style adapters are usually centre-positive and pedal supplies centre-negative. Stick to the battery on the breadboard.
- Be careful with old or ungrounded gear. Avoid holding your guitar while touching a second amp or a microphone on it: a fault can put voltage on the strings.
- If you solder, respect the iron. It's hot enough to burn you instantly and looks the same as a cold one. Ventilate, wash your hands after leaded solder, and keep it away from kids.
Reading a schematic
A schematic shows what connects to what. It doesn’t show where anything sits. Two parts drawn side by side can be far apart on a real board, and two far apart on paper can be neighbours.
Tap a symbol.
- Lines are connections. A line has no length as far as the circuit is concerned.
- A dot where lines meet means they’re joined. Lines that cross with no dot usually aren’t.
- Ground is the set of stacked bars. Every ground symbol is the same point, even with no line between them.
- Names like R1 and C2 identify a part. The value, like 10k, says what it is.
The components
Each part shown as its symbol and as it sits on the board.
Ceramic capacitor
Passes signal and blocks DC. Small values also filter high-frequency noise.
A small disc with a code in picofarads: 104 means 10 and four zeros, so 100,000 pF or 0.1µF.
Film capacitor
The same job as a ceramic, with better sound in the signal path.
A rectangular box, usually with the same three-digit code: 473 is 47 nF.
Electrolytic capacitor
Stores more charge. It steadies the power supply.
A can with a light stripe on the − side. The longer leg is +.
It has a polarity. Fit it the right way round.
Diode
Lets current through one way. In a pedal, a pair clips the signal into distortion.
The band marks the cathode, where the symbol's arrow points.
It has a direction.
LED
A diode that gives off light.
The long leg is the anode. The flat edge on the rim marks the cathode.
Always use a series resistor. Connected straight to 9V, it burns out.
Transistor
A small current at the base controls a larger one, so it can amplify.
A black half-round package called TO-92. Its leg order varies by part number, so check the datasheet.
Looking at the flat face with the legs down, a PN2222 or 2N5088 reads E-B-C. Other parts differ.
Op-amp chip
A high-gain amplifier in a chip. The 4558 holds two of them.
The notch marks the pin 1 end. Pins count down one side and back up the other.
Fitted backwards it can overheat. Power goes on pins 8 and 4.
Potentiometer
A variable resistor with a sliding middle contact, called the wiper. Volume, tone and drive knobs are pots.
A knob with three lugs. The kit pots have a triangle footprint, not a line.
Jumper wire
Joins two holes. It's the same as a line on the schematic.
By custom, black goes to ground and red to +.
Jack
Where the guitar and amp connect. The tip carries the signal and the sleeve is ground.
On a schematic it's often a small circle or a labelled line. Here it reaches the board by clip leads.
Battery
The 9V supply. The big line in its symbol is +.
On a schematic it's often replaced by named labels such as VCC and a ground symbol.
Add a series diode so that connecting it backwards does no harm.
Two drawings, one circuit
These are the same fuzz circuit. The hand drawing is arranged by a person to show how the signal flows. The Bench generates the other one from a parts-and-connections list, so it looks different, but every connection matches.
Published schematics vary in the same way. Compare the original TS-808 drawing with General Guitar Gadgets’ version: different names and layouts, nearly the same circuit.
Nets
A net is everything joined together electrically. It has one name, however many wires it takes. The whole list of nets is the netlist, and it’s the real circuit: the schematic and the board are two pictures of it.
Pick a net to light it on both sides. Everything lit must end up connected on the board.
The breadboard
Tap any hole to see everything joined to it inside the board.
- Strips. In each row, holes a to e are joined inside the board. So are f to j. Different rows aren't joined.
- The centre channel. It separates the two sides of each row, and it's exactly as wide as a chip's legs, which is why chips straddle it.
- Rails. The long lines at each side, red for + and blue for −, run down the whole board. The gaps between groups of five are only spacing.
- Split rails. Some 830-point boards break each rail halfway down. Check yours with a meter.
From schematic to board
The method: give each net its own strip, then push each part’s legs into the strips of the nets they belong to. Here it is with a battery, a resistor and an LED.
Step 1 of 4: Find the nets
The schematic has three nets: VCC, LED_A and GND. Each one needs a place on the board. VCC and GND go to the rails. LED_A gets row 6. Nothing is connected yet.
When that makes sense, try the fuzz on the Bench.
Measuring and fixing
- Set up. Black probe on ground, usually the − rail. Set the meter to DC volts.
- Battery first. A healthy 9V reads about 8.4 to 9.6V.
- Vr. Circuits with an op-amp need a half-supply reference. Expect about half the battery, not exactly 4.5V.
- Continuity. This tests whether two points are joined. Use it only with the power off.
- Current mode. Never touch the probes across a battery in current mode. That's a short circuit through the meter.
Common mistakes
- Reading the board from the wrong side. Row 1 at the top, rails on the left: match the drawing to the board in front of you.
- Saying "flat face toward you". On a board on a table that means nothing. Use "toward the rails" instead.
- Assuming every pot has its lugs in a line. The kit's are a triangle.
- Reading a meter upside down from a photo. Write down what the display says at the bench.
- Putting both legs of a part in the same row. That shorts it out.