Guitar Amp Effects Loop — Which Pedals Go Where and Why

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Not sure what your amp's effects loop does? 

Learn what it is, how it works, and which pedals belong in it for the best possible guitar tone.

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The effects loop is one of the most screwed up features on guitar amplifiers — and understanding how to use it correctly makes a significant difference in the quality of the effects in your signal chain.

What an Effects Loop Is

An effects loop is a series connection point built into the amplifier circuit that places external effects devices between the preamp stage and the power amp stage. The signal path through an amplifier with an effects loop runs: guitar input → preamp section → effects loop send → external effects → effects loop return → power amp → speaker.

The effects loop send takes the signal after the preamp has amplified and shaped it — including any overdrive or distortion the preamp produces — and sends it to the external effect. The effect processes this signal and returns it to the effects loop return, where it enters the power amp stage.

Why the Effects Loop Exists

The fundamental reason for the effects loop is the interaction between time-based effects — delay and reverb — and gain stages. When delay and reverb are placed in front of an overdriven amplifier — in the guitar's input path rather than the effects loop — the repeats and reverb tails pass through the overdriven gain stage along with the original signal. The gain stage amplifies and distorts the repeats and tails, creating a congested, smeared sound where the echoes feed back on themselves and the reverb washes out the definition of the original signal.

When delay and reverb are placed in the effects loop — after the preamp's overdrive — the time-based effects process the already-overdriven signal. The repeats and tails emerge from the effect clean and defined, decaying naturally without being pushed through additional gain. The result is a cleaner, more defined relationship between the original note and its echoes — each repeat is distinct and the reverb tail decays cleanly.

This is why professional guitar players running overdrive-based amps — almost universally — place their modulation, delay, and reverb in the effects loop while keeping their drive pedals, wah, and compressor in front of the amp.

Effects Loop Types: Series vs Parallel

A series effects loop interrupts the signal path completely — all of the signal goes out to the external effect and all of it returns. The effect is always 100% in the signal path.

A parallel effects loop splits the signal — part goes through the loop to the external effect, part continues directly to the power amp — and blends the two paths before the power amp. The blend control determines how much of the effected signal mixes with the dry signal. A parallel effects loop allows the fundamental dry character of the amp to remain present regardless of the effects in the loop.

Parallel effects loops are less common than series loops but are preferred by engineers who want the ability to use longer reverb tails or dense delay sounds without affecting the dry character of the amplified tone.

Effects Loop Levels: Instrument Level vs Line Level

Effects loops operate at either instrument level — approximately -20dBu — or line level — approximately +4dBu. The operating level of the effects loop must match the operating level of the effects device inserted in it.

Most guitar pedals are designed for instrument level operation — they expect the guitar's low-level signal at their input. Inserting an instrument-level pedal in a line-level effects loop overloads the pedal's input stage, causing distortion and coloration that is typically unpleasant. Inserting an instrument-level pedal in an effects loop without a level pad — an attenuation device — or a mixer with appropriate level matching produces similar problems.

Check your amplifier's specifications and your effects pedals' operating levels before inserting them in the loop. Most modern rack effects units operate at line level. Most floor pedals operate at instrument level. Some amplifiers provide a level switch that accommodates both.

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