The impedance war

The impedance war (5)

13. IT IS A GAIN CHANGE, NOT TONE SUCK

Buffer → Fuzz Face — Fuzz into a cranked amp, The rack rig and buffered loop switching

• Mechanisms: Shunt-feedback input gain, Low input impedance, Buffer, Transistor saturation, Cascaded clipping
• The move: A low-impedance source placed in front of a circuit whose first stage takes its gain from that impedance.
• The friction: The usual explanation is wrong. Q1 is a shunt-feedback stage whose gain is roughly the feedback resistance over the source impedance, so dropping the source from a pickup's few kΩ to a buffer's few hundred ohms raises the gain substantially and flattens its frequency dependence. Nothing is being sucked out; something is being added.
• The recipe: Put the fuzz first on the board, before any buffer, or use a switcher that routes it that way. If a buffer is unavoidable, some fuzzes offer an input impedance control that restores the interaction. And note the limit: this applies to Fuzz Face, Tone Bender and Rangemaster-type circuits, not to a Big Muff, whose four cascaded stages swamp any difference in what drives them.

Fuzz guitar recorded twice in the same piece with the same pedal, sounding like two different circuits, four minutes, 120 BPM, instructive and raw. In the first half the guitar runs straight into the fuzz with nothing in between, so the pedal's input stage sees the pickup's own rising impedance: the tone is thick, slightly soft at the top, wonderfully touch-sensitive, and rolling the guitar volume back cleans it almost completely to a glassy near-clean sound with the fuzz still engaged. In the second half a low-impedance buffered stage is inserted immediately before the same pedal, and the character changes audibly: louder, noticeably brighter, harder-edged, more even across the frequency range, and the volume-knob cleanup is gone entirely — turning down now only reduces level. Both halves play the same riff over the same backing so the difference is unmistakable. The amplifier is a loud valve head into a four-by-twelve, unchanged throughout. Bass and drums are simple, live and constant. Recording is dry, close and mono. It ends by switching the buffer out mid-phrase, so the tone drops back to the first sound on the last chord.

14. THE FIRST TONE CONTROL

Long cable → Bright single coil — The blackface clean rig, The jazz archtop rig

• Mechanisms: Cable capacitance, Pickup resonant peak, Capacitive vs resistive loading, True bypass, Buffer
• The move: Cable capacitance loading a pickup, which is a filter you have already installed whether you meant to or not.
• The friction: A measured Strat single coil self-resonates at 8,500 Hz unloaded. Eighteen feet of cable takes that to about 4.6 kHz; thirty-five feet to about 3.6 kHz. The guitar becomes duller and more mid-peaky at the same time, and every true-bypass pedal adds roughly 15 pF even when it is switched off.
• The recipe: One good buffer early, and keep the cable before it short. That is the whole answer, and the “about five true-bypass pedals” rule of thumb has no measured basis — its own source concedes there is no magic number. Also note that lower capacitance is not automatically better: plenty of canonical tones were made through thirty feet of ordinary cable, and a peak pushed above 5 kHz can be shrill.

Bright, glassy clean electric guitar recorded through a deliberately short signal path, four minutes, 92 BPM, sparkling and immediate. The instrument is a single-coil guitar whose pickup resonance sits high — up around 5 kHz — because almost nothing is loading it: a short cable, a single buffered stage early, and then a low-impedance path to the amplifier. The result is an unusually open, detailed top end with real air above the notes and a fast, precise attack, rather than the duller and more mid-peaky sound of the same guitar through a long cable run. Chords are played with a light touch near the bridge for a nasal, harmonically dense attack, with a lot of ringing open strings where consecutive scale notes fall on different strings and overlap into each other. The amplifier is a clean valve combo with high headroom and a spring reverb tank, open-backed and airy, so nothing compresses. There is no distortion anywhere. Dynamics are wide — the difference between a light stroke and a hard one is dramatic. Bass and drums are quiet, brushed and understated. It ends on an open chord left to ring all the way out.

15. THE CIRCUIT CANNOT HEAR THE GUITAR

Active pickups → Vintage fuzz — The djent direct rig, Fuzz into a cranked amp

• Mechanisms: Active pickup preamp, Low input impedance, Shunt-feedback input gain, Pickup inductance
• The move: A pickup with its own onboard preamp driving a circuit whose entire character depends on hearing a passive pickup.
• The friction: An active pickup presents a fixed low output impedance — a measured EMG81 is 10 kΩ out with its resonance locked at 2.25 kHz regardless of what follows. That is precisely the condition a Fuzz Face-type circuit cannot work with, and it is a permanent buffer you cannot remove from the chain.
• The recipe: Either accept the buffered fuzz behaviour, or use a fuzz that does not care — a Muff-type or op-amp circuit. Do not try to fix it with a passive volume pedal or a resistor in line, which only attenuates. If the fuzz is essential, the answer is a different guitar rather than a different pedal.

Very high-gain modern guitar with an extremely low noise floor and completely consistent tone, five minutes, 152 BPM, clinical and heavy. The instrument has active pickups with an onboard preamp, so its output impedance is low and fixed and its resonant peak sits locked around 2.25 kHz no matter what cable or pedals follow — the tone is identical from the first bar to the last, and the noise floor is far below anything a passive instrument would give. The distortion is a fuzz circuit driven by that fixed source, which makes it behave as a fixed, stable, rather bright and hard-edged wall with no touch sensitivity and no cleanup from the guitar's volume control. The amplifier is loud and already saturated. Playing is fast, precise and mechanical: rapid alternate-picked single-note lines and tightly muted chord stabs, all at a constant dynamic level. The mix is dense, close and dry with very little ambience. Bass follows the guitar exactly. Drums are fast and heavily gated. Between phrases the silence is genuinely silent, with no hiss at all. It ends on a single palm-muted note cut short.

16. EIGHTEEN VOLTS INTO A CONVERTER

Analogue drive board → Modeller input — The profiler and modeller rig, The four cable method rig

• Mechanisms: Bridging ratio, Buffer, High input impedance drive, Profiling vs modelling, Impulse response
• The move: Analogue pedals in front of a digital modelling unit, which is documented common practice rather than a workaround.
• The friction: The real gain-staging problem is not impedance and not tone. It is that an 18 V pedal can push hot enough to clip the converter, and converter clipping does not sound like anything else in the chain. Flagship units ship with adjustable input impedance settings precisely because this combination is normal.
• The recipe: Set the unit's input impedance to suit what is in front of it, then set the pedal's output level so the unit's input meter never approaches full scale. Most op-amp drives already act as their own input buffer and do not care what impedance they see. And treat any specific latency figure you read as unverified unless it cites an oscilloscope — conversion accounts for over half of round-trip latency, not the modelling.

Modern hybrid guitar tone with analogue grit in front of a digital amplifier and cabinet, five minutes, 116 BPM, warm but perfectly repeatable. The drive stage is genuinely analogue — a soft-clipping circuit rounding the waveform, with the slightly irregular character of real components — and everything after it is digital: amplifier modelling, cabinet impulse response, and stereo time effects. The tone is therefore consistent from take to take with no drift at all, while still having the slightly uneven, hand-built quality of the pedal in front. Levels are set carefully so the drive never overloads the input, and the result is clean-edged rather than harsh. The cabinet response is a fixed snapshot: it never changes with playing intensity the way a real speaker would, so hard passages sound louder rather than more broken up. Playing is melodic and rhythmically tight over a repeating chord cycle. The stereo image is wide, with delay and reverb spread hard left and right while the drive itself stays firmly centred and mono. Bass and drums are programmed and precise. It ends cleanly on a stereo reverb tail that decays for several seconds.

17. TEN KILOHMS IS NOT ENOUGH

Passive pickup → Mixer line input — The silent rig, The profiler and modeller rig

• Mechanisms: Bridging ratio, Pickup resonant peak, Buffer, Capacitive vs resistive loading
• The move: A guitar plugged directly into an input that was never designed to receive one.
• The friction: A passive pickup's output impedance is 5–20 kΩ and rises with frequency; a guitar amp's input is about 1 MΩ, a deliberate bridging ratio of more than ten to one. A mixer line input at 10–50 kΩ is, per Sound On Sound, “way too low to allow a guitar's pickups to work properly.” That single mismatch is the entire reason DI boxes exist.
• The recipe: Use a DI box or any buffered pedal as the first thing in the chain. An instrument-level input on an interface is usually around 1 MΩ and is fine; a line input is not. If the guitar sounds thin and lifeless before you have added anything, this is almost always why.

Thin, weak, lifeless direct guitar as a deliberate texture, three and a half minutes, 108 BPM, dry and small. The instrument is a passive-pickup guitar whose output is being loaded far too heavily, so its resonant peak is both flattened and pushed down: there is no sparkle at the top, no body in the middle, and the whole signal sounds several sizes smaller than it should, as though heard through a wall. Nothing is distorted and nothing is added — the sound is simply diminished, with a dull, papery attack and very little sustain. That thinness is used as the character of the piece rather than corrected: the guitar sits low and small in the mix while a full, warm bass and a close-miked drum kit carry the weight around it. Playing is clean, repetitive and rhythmic, chords struck on the offbeats and choked off immediately. Later in the piece the same part is doubled by a properly buffered version of the same guitar, full and bright, and the contrast between the two is the arrangement. It ends with the thin version alone, fading out.