Electronics · 4 min read

Impedance and the First Three Feet

Where to put a buffer pedal — why the first three feet of cable do more to your tone than the rest of your board.

By Jason Colapietro

One common and cheap-to-fix source of tonal degradation is the unbuffered cable run between the instrument and the first pedal.

The Problem

A passive guitar pickup has an output impedance that swings with frequency, typically peaking somewhere between 5 kΩ and 25 kΩ depending on pickup design.[^1] Any capacitance downstream forms a low-pass filter with that source impedance. The cable is the dominant capacitance in the chain. Common instrument cables often sit around 30–80 pF/ft, premium low-capacitance cables often sit around 12–25 pF/ft, and high-capacitance runs can exceed 100 pF/ft.

A 20-foot cheap cable presents roughly 600 pF of shunt capacitance. Combined with a typical humbucker source impedance, this places the rolloff knee in the audible top end, sometimes as low as 4 kHz.

The Math

The treble rolloff frequency is approximately:

f₋₃dB ≈ 1 / (2π · Rₛ · C)

For a 15 kΩ source and 600 pF cable:

f ≈ 1 / (2π · 15,000 · 600e-12) ≈ 17.7 kHz

That looks safe. The trap is that the pickup is not a resistor. It is an LCR resonant network. The audible "sparkle" of a Stratocaster bridge pickup sits on top of a resonant peak somewhere between 3 and 6 kHz. A long cable's capacitance combines with the pickup's own inductance to drop that peak's amplitude and shift it lower in frequency, where it loses the perception of clarity.[^2]

What a Buffer Does

A buffer is a unity-gain amplifier with high input impedance (typically 1 MΩ) and low output impedance (typically under 1 kΩ). Place one early in the chain and:

The pickup sees only the buffer's 1 MΩ load, so there is no audible high-end loss
Downstream cable capacitance now interacts with the buffer's low output impedance instead of the pickup, so the same 600 pF cable now has its rolloff knee well above 100 kHz

In other words: the buffer moves the bottleneck out of the audio band.

When Not to Buffer

Buffers are not universally good. Specific cases where you want the pickup running into the next device directly:

Vintage germanium fuzz: Fuzz Face and friends rely on pickup interaction for their volume-knob cleanup behavior. A buffer flattens this.
Treble-bleed-style volume controls: these are tuned for the specific impedance the pickup presents. Buffering changes the math.
Guitarists who deliberately want darker, woolier top end: sometimes that rolloff is the sound.

Practical Rule of Thumb

Less than 10 ft of cable, premium quality: passive run is fine
10–20 ft, mixed-quality cable: buffer at the front of the board
More than 20 ft, or running into a switcher with long internal paths: buffer at both the pickup end and downstream

Recommended Topology

Tuner pedals often have input buffers that remain active. Placing a tuner first solves the problem incidentally, provided the tuner's buffer is reasonable. Most modern ones are.

Quick Diagnosis

Symptom	Likely cause	First check	Fix
Bright straight into the amp, dull through the board	Cable capacitance loading the pickups	Measure total cable length before the first buffer	Put a good buffer first or shorten the unbuffered run
Fuzz loses cleanup when the tuner is first	Buffer before germanium fuzz	Move the fuzz before the tuner for one test	Put germanium fuzz before the first buffer
Top end returns when the guitar volume is full up	Pickup and volume-pot loading	Compare 250 kΩ vs 500 kΩ guitar behavior	Match pot value, cable length, and first buffer to the pickup