Pedalboard order is a set of trade-offs, not one correct chain

Placed early, a compressor tracks a clean, consistent input level and evens out picking dynamics before the drive stage ever sees the signal — the result is a smoother, more sustained tone, because the distortion that follows acts on a more uniform waveform. The cost is that the compressor's own makeup gain raises the noise floor slightly, and the drive stage downstream amplifies that noise right along with the signal.

Placed after drive instead, the calculation flips. Distortion itself already behaves like a brutal compressor — hard clipping pins the waveform at a fixed ceiling — so a compressor placed after it does very little classic "dynamics processing." What it does instead is act as a sustain leveller and a clean-signal boost, which is the reason pick attack tends to survive better with this ordering: the compressor is riding the tail of an already-shaped note rather than flattening the transient before distortion gets to it.

A wah or envelope filter follows the same logic for a different reason. Swept ahead of a clipping stage, the frequency band the filter boosts gets distorted hardest — a genuinely frequency-selective distortion, since the rest of the spectrum is comparatively quieter going into the clipper at that instant. Run the same filter after drive and it is sweeping a filter over an already-fixed harmonic spectrum instead — more predictable, but it is no longer shaping what gets distorted, only what survives afterward.

This is the single cleanest illustration of the whole page's premise. A wah swept ahead of a clipping stage boosts one moving frequency band, and that boosted band is what hits the drive stage hardest an instant later — a genuinely frequency-selective distortion, where the harmonic content actually changes shape as the filter sweeps, because different parts of the spectrum are being handed to the clipper at different relative levels. It also tends to sound less harsh, because the full spectrum is not arriving at the clipper simultaneously at full level — only the swept band is hot at any given moment, which reduces the harsher intermodulation products that a wide, unfiltered signal produces under heavy clipping.

Run the same wah after drive and it is doing something categorically different: sweeping a filter over a spectrum whose harmonic content is already fixed by the clipper. Still musically useful — often described as a wider, more dramatic sweep — but it is reshaping a finished waveform rather than deciding what gets distorted in the first place. Neither placement is "correct." They are different tools, and which one you want depends entirely on whether you want the wah to shape the distortion or shape what is left after it.

A pedal placed in front of the amp is shaped by both gain stages in sequence — the preamp's distortion, then whatever the power amp adds on top. A pedal patched into the effects loop instead sits after the preamp and is coloured only by the power amp stage from that point on. That is the entire reason modulation, delay and reverb are conventionally run in the loop: a phaser or chorus creates notches in the frequency response, and distorting that notched signal (by running it in front of an overdriven amp) re-fills some of those notches rather than preserving the sweep cleanly; a delay or reverb in front of the amp has every repeat and every tail re-distorted along with the dry signal, which is what makes echoes progressively blur into each other instead of decaying as distinct, clean events.

None of this requires an effects loop to be "better" in general — it requires deciding whether you want an effect shaping raw string signal (front of amp) or shaping an already-distorted, harmonically fixed tone (the loop). A handful of rigs deliberately run modulation in front of the amp for exactly the re-filled-notch texture that would be considered a flaw in most other contexts.