FUZZBOX PHYSICS — Passive Components Quiz

Question 1 — Identify the component

Which of these schematic symbols represents a component that stores charge and passes high frequencies more easily than low frequencies?

A Resistor — opposes current flow equally at all frequencies

B Capacitor — stores charge, impedance decreases at higher frequencies

C Potentiometer — variable resistor with a wiper, controls level

Question 2 — Where is the filter?

This is an RC low-pass filter. When you play a bright guitar signal through it, does the output sound "brightened" or "darkened"?

A Brightened — the filter boosts high frequencies

B Darkened — it passes lows and cuts highs (low-pass)

How Capacitance Controls the Filter

The cutoff frequency of a first-order RC filter is:

fc = 1 / (2πRC)

Larger C = lower cutoff. Smaller C = higher cutoff. Capacitance sets how quickly the capacitor can charge and discharge relative to the waveform. A bigger capacitor can follow slower (lower-frequency) wiggles, so it starts treating lower frequencies as "high" and routing them along its preferred path.

In a low-pass (cap to ground): high frequencies see a low-impedance path through the capacitor and get shunted to ground, while lows barely move charge on the cap and pass to the output. A bigger C gives that low-impedance path at lower frequencies too, so it absorbs a wider band of highs and upper-mids — the sound gets darker.

In a high-pass (cap in series): low frequencies see a large capacitive impedance and are blocked, while highs see a small impedance and pass through. A bigger C reduces that impedance at any given frequency, so more bass gets through and the cutoff moves downward. A smaller C pushes the cutoff up, absorbing more bass.

Question 3 — Series vs. shunt

In the RC low-pass filter above, the capacitor C shunts high frequencies to ground. If you decrease the capacitor value (smaller C), does the filter cut highs more or less?

fc = 1 / (2πRC) ← smaller C = higher cutoff frequency

A More — smaller cap filters more aggressively

B Less — cutoff frequency goes up, so more treble passes through

Question 3b — Bigger cap, darker sound?

You're building a low-pass tone control for a guitar pedal. The current cap is 1nF and the tone is too bright. You want to darken the sound (cut more treble). Should you increase or decrease the capacitor value?

A Increase it (e.g., to 10nF) — bigger C lowers the cutoff, absorbing more treble

B Decrease it (e.g., to 100pF) — smaller C means less charge, less brightness

Question 3c — Coupling cap and bass loss

A coupling capacitor sits in series between your guitar pickup and the first gain stage (acting as a high-pass filter). You notice the sound is too thin — not enough bass. Should you use a larger or smaller coupling cap to let more bass through?

A Larger — bigger C lowers the HPF cutoff, letting more bass pass through

B Smaller — smaller C has less impedance so more signal gets through

Question 4 — Signal path tracing

Here is a simplified true-bypass pedal wiring diagram. The footswitch toggles between two states. When the pedal is bypassed (off), what happens to the audio signal?

A Signal goes straight from input jack to output jack through the switch, bypassing the circuit entirely

B Signal still passes through the pedal circuit but the effect is muted

C Signal is disconnected — no sound comes out

Question 5 — Protecting the LED

In the pedal wiring diagram above, what passive component protects the LED indicator from burning out?

A A capacitor in parallel with the LED

B A resistor in series with the LED (limits current)

C The footswitch — it only powers the LED briefly

Question 6 — Match function to schematic fragment

Match each circuit fragment to its function. Look at where the component sits relative to the audio signal path and ground.

FRAGMENT 1 — Cap in series with signal

FRAGMENT 2 — Pot + cap to ground

FRAGMENT 3 — Resistor to ground

Question 7 — Coupling capacitor

In a guitar pedal schematic, you often see a capacitor placed in series between two gain stages. What is its primary purpose?

A It amplifies the signal between stages

B It stores energy to power the next stage

C It blocks DC bias voltage while passing the AC audio signal through

D It adds distortion by clipping the waveform

Question 8 — High-pass filter

If you swap the positions of R and C in the low-pass filter from Question 2 — putting the capacitor in series and the resistor to ground — what kind of filter do you get?

A Band-pass — only lets a narrow range through

B High-pass — passes highs, cuts lows (tightens the bass)

C Still a low-pass — swapping R and C doesn't change the filter type

Question 9 — From blocks to schematic

In the Modular Pedalboard lab, a Tube Screamer-style pedal is built as:
HPF 720 Hz → Gain → Soft Clip → LPF 3.5 kHz → Level

In a real TS-808 schematic, which passive components create the input high-pass filter (the first stage)?

A Two resistors in a voltage divider

B A capacitor in series with the signal and a resistor to ground — the cap blocks low frequencies

C An inductor in series — it blocks highs