Guitar Effects Pedals - Part Two - Effects Explained

Effects Pedals Explained -

Welcome to part two of Phosphene Productions Guitar Effects Pedals blog.  This time around I'll show you the different types of effects guitarists use in their tone arsenal, a little bit on how the pedals themselves are made, even a little history and some brand favorites.
In today's world of guitar pedals we have so many choices; analog or digital, tubes or solid-state, even choices in minor variations of capacitors, transistors, circuits, etc... And things get even hairier when you start throwing in variations in effects types or tone!  For these reasons (and others) we can attempt to separate these effect types into several categories, though some pedals use similar technology, and in some cases are considered one in the same.  The hazy area in-between is negligible (getting even blurrier when we bring in digital technology). We have done our best to separate the categories as best we can, though some variations we felt didn't need a whole dedicated section.  In these cases you can find a short description towards the bottom.



Boost

The boost pedal is probably the first step away from a clean guitar sound, intended to boost the guitar's signal just before reaching the amplifier. These pedals are often branded as “distortion-free” or “clean”, “linear”, and though this can be true the general result is anything but entirely clean. Many boost pedals have a tendency to enhance treble frequencies, flatten the guitar sound and/or increase level transparently. Though these pedals can be used as a sort of 'clean-lift', the guitar's tone is almost always thickened by a degree of distortion.

Electro-Harmonix LPB-1

Over time the boost pedal was found to be of great use when attempting to 'drive' a tube-based amplifier into distortion. By using a lower volume setting on your amplifier, you can actually find the 'sweet-spot' of your tube amp's distortion by “boosting” your guitar's signal -- a task that could be completed on a comfortable volume setting of 4 rather than 7 or 8.

From an engineering task these pedals are quite simple compared to a distortion or fuzz pedal.  However, when it comes to engineering transparency, things can get tricky.
Electro-Harmonix LPB1 (Linear Power Booster) was the first widely available and commercially produced boost pedal, arriving only a few years after the fuzz pedal explosion on society, offering clean level increases at the front of a long chain of effects to act as a buffer and line driver, or at the end of a similar chain to boost levels again after signal drain of six or ten pedals.

Chorus

Chorus is a type of delay.  However, the sonic result and the way these short delays are transformed puts this effect in the modulation series.
Chorus pedals as we know them today were not widely available until the 1970s when affordable short-delay chops became available. The idea was to achieve a sound of a group of singers or strings playing together, where some voices or strings inevitably waver slightly from those beside them. When done right, chorus can produce a quivering meld of harmonies that evokes space and dimension, not to mention amazing sound when used in stereo.

A vintage Boss CE-1

Chorus pedals use short delays to create harmonically spaced notches and peaks in the frequency spectrum that are manipulated to modulate more tightly above and below specific frequency ranges.
However, digital chorus pedals work differently than its analog sibling by doubling the signal and adding delay and pitch modulation to one path, the latter wobbling below and above the pitch of the unadulterated signal, which produces an audible out-of-tuneness when the paths are blended back together.
Boss's CE-1 Chorus Ensemble was the first of these types to become commercially available in 1976.

Compression

Designed as a compact version of its larger studio predecessor, a compressor is a leveling device that, simply put, smooths out the attack and decay of an audio signal by softening the front end of a note and amplifying its tail. Compressors in the recording studio are usually used in a much more refined manner than that of the guitar pedal, though the effect is mostly the same.
Part of the compressor's original appeal was its ability to replicate the natural compression, or sag, of a tube amplifier running at medium to high volume levels. Because compression is about audio dynamics, the pedal lent itself as a 'feeling' adjustment, making the guitar feel more tactile or touch-sensitive and playable. Many players favor compressors as sustainers, and some guitarists also use them as booster pedals, by turning down the compression or sustain control and winding up the gain or volume. Guitarists often think a compressor pedal is a tool that increases the dynamics in their playing and tone; in reality, extreme use of compression from a pedal will inevitably level out the peaks of a guitar part, and thus literally decrease its dynamic range.
Recording studio compressors were made with fairly complex tube circuits in the early days, or using equally intricate solid-state circuits based around an opto-cell, as in many classic designs of the 1960s.
Most guitar pedals are comprised of far simpler circuits based around relatively basic op-amps, or sometimes slightly more complex ICs, and the usual handful of transistors, resistors and capacitors that enables them to function in the desired manner. (An op-amp – short for Operational Amplifier – is a compact form of integrated circuit (IC) that squeezes amplification duties into a small eight-pin chip. Other than the tiny resistors and capacitors that link them, these are the most common ingredients in most types of analog effects pedals.)
More complex, and of course, more expensive units often talk about their ability to color the signal very little, if at all, while other more basic models make a virtue of the way they liven up and enrich the guitar's clean tone.

Delay & Echo

Ray Butts EchoSonic Amplifier.

Delay and Echo is one of the most common effects used among guitarists, pioneered by a loop-based echo system in the 1950's by amplifier builder Ray Butts. First based on recording wire, and then tape (once it was available), Ray built units small enough to be fitted into a combo guitar amplifier.
Stand-alone tube-powered tape units soon followed Ray's idea with models including Fender-distributed EccoFonic, Maestro Echoplex, Watkins/WEM Copicat, Binson Echorec (which used magnetic recording discs rather than tape loops) and the Meazzi Echomatic.
Like an echo in nature, reverberation is a very 'large' sound effect in the terms of physical dimensions required to create a pleasing result. When engineers were finally able to squeeze it into a compact and reliable electromagnetic interpretation of the wash of repeated echoes heard in a large hall, it came to us as an onboard effect built into combo amps, hot on the heels of the new tremolo effect.
Though the term 'echo' was more commonly used in the early days of recording music (particularly early rock & roll), and is sometimes used today to refer to a distinct and distant repeat of a signal, a 'delay' could mean anything from a short repeat of a reverb, to the complex, extended, manipulated repeats of an intricate digital delay line. Regardless, they are basically one in the same.
Analog echo (or delay) pedals transmogrification from a bulky, cumbersome unit into a transistorized analog pedal in the late 1970's and is quite possibly one of the greatest economies a delay-loving guitarist like myself could ever experience. However, though physically manageable, guitarists found the newly invented devices financially unobtainable and sought a more economical solution.
Guitarists found relief when Electro-Harmonix and MXR introduced relatively affordable analog delay pedals in the early 1980s.

Binson Echorec 2

By the late 1980s almost every guitarist on stage had his or her favorite stomp box plugged into their rig. And with almost every pedal manufacturer producing a model or two, its hard to see why not. Though soon guitarists would declare their love for analog counterparts more than the new transistorized alternatives, for convenience sake a majority stuck with the stomp-box for live performances. Where tonal superiority is argued between tape- and tube-based effects, creating high prices for vintage machines, most still find tape impractical when it comes to operation and maintenance.

An old Maestro Echoplex ad.

Analog delay pedals were made possible by a shift in technology in the 1970s, this being the advent of affordable delay chips called 'bucket brigade delay chips'. These chips pass signal along in stages from the input pin to the output pin with anything from 68 to 4096 stages. Simply input the signal, adjust the speed at which it gets passed from stage to stage, tap the output and ta-da! An echo pedal! Obviously then we can understand that the more stages in a chip, the longer the delay the circuit can achieve. However, the longer the delay the greater the potential for distortion in the wet signal, which is why most makers compromise and keep to a maximum setting within acceptable delay-to-noise ratios.

A digital version of the Roland Space Echo

Digital delays came to us in the early 1980s with what seemed to be unlimited capabilities for long, clean signal reproductions and one, two, up to 16 seconds of looping delay. But even with this new technology threatening to defeat its analog counterparts, reproductions were often dirty, harsh or cold sounding, as well as being prone to digital distortion if pushed too hard, or poor resolution on the decay of the signal.
To put the inner workings of a digital delay simply, think of a form of sampler. Achieved by recording a small digital record of your riff and playing it back at a user-selected delay time, with depth and number of repeats is more or less selectable. From this we can understand that the higher the sample rate, the better the sound quality.
Early 8-bit models left a lot to be desired sonically, but once 16-, 20-, and 24-bit designs were developed, the reproductions of the echoes increased dramatically in quality.

Distortion
Possibly one of the most popular incarnations in the world of little stomp boxes is the distortion pedal. By definition a distortion pedal is designed to achieve serious alterations of the guitar's signal. To put it simply, where an overdrive pedal looks to take you anywhere from a Tweed Bassman or a pushed JTM45, distortion pedals aim to do the Mesa/Boogie Triple Rectifier trick, all in a small and portable little box.

Common distortion pedals will generally filth up your tone and slap its own idea of the ideal hard rock or heavy metal EQ all over your tone's backside. Some pedals will boost the guitar's volume as well (depending on your level/volume/output settings), creating a push and pull of tone shaping influenced by the relationship between the guitar, pedal and amplifier.
Most distortion pedals are built around a simple network of transistors and clipping diodes. These components boost the guitar's signal and slightly alter the swaveform of the sound.
Though many units very roughly resemble the standard 'overdrive' pedal, many engineers made heavy work on op-amps, tone-shaping stages and input/output buffers to create the pedals we hear today.
Many distortion pedals are highly adjustable creating tones for anything from classic rock to some serious heavy metal. This is achieved by a tone control that acts more to reduce or accentuate mids rather than the usual high cut/boost, as well as a 'resonance' control to adjust the fullness of the bass end frequencies.

Envelope Filter
Also known as the 'voltage-controlled filter" or "auto-wah", the envelope filter is one seriously funky effect.

Musitronics Mu-Tron III

Envelope filters achieve their funky effect by containing a sweepable peak filter similar to the traditional 'wah-wah'.  However, unlike the 'wah-wah' with an expressive foot rocking mechanism, the envelope filter uses the intensity of the incoming guitar signal to generate a controlled voltage which sends the peak up and down the frequency spectrum.
Most major manufactures began carrying envelope-filter type effects pedals around the early to mid 1970s. Musitronics's Mu-Tron III, introduced in 1972, was likely one of the first widely available, with Eletro-Harmonix close behind with a range of models such as the Doctor Q, Zipper, Bass Balls and the Y Triggered Filter.
Guitarists in the 1970's loved using the natural picking rhythm to induce a sort of 'pumping' or 'pulsating' effect, lending perfectly to funk and disco. Though a massively entertaining effect to play with, after the death of disco the envelope filter was consigned mainly to the novelty shelf.

Equalization

Early MXR 10-Band EQ

Believe it or not, the mini guitar-pedal sized EQ is not so much an effect as it is an inline active tone circuit, most popularly seen in a graphic bandwidth form. The graphic EQ pedal is a multi-band active tone control with sliders rather than potentiometers for graphic style presentation of the EQ settings. The EQ bands are set and logarithmically related to correspond to the way the human ear perceives frequencies, basically meaning the bands are set right in the frequency range most common to a guitar's standard tuning.
Graphic EQ pedals or outboard gear was most popular in the 1970s and 80s where some would argue that guitar amps needed severe EQ to sound like anything.  Fitted with the most common six bands, followed shortly by the 10-band, players commonly used (and still use) these pedals to adjust harsh sounding frequency responses, tailor a rig for consistency in different room acoustics, even to provide a boost in specific frequencies when soloing.

Flanger
Sometimes described as 'swooshing', or a spacey extreme of a soft chorus or phaser sound, the flanger was in use for almost 20 years before the first stomp-box was offered to guitarists.
Accomplished by splitting the guitar's signal and then slowing or speeding up one path, the flanger is a relatively simple effect to achieve.  In the early years this meant having to run identical recording machines in sync on two separate reel-to-reel machines, and then placing a finger against the flange of one to slow it slightly, then releasing it again to let the machine's reel speed up and chase the unadulterated machine.
Even as far back as 1945, Les Paul was pioneering studio trickery of this effect with two disk recorders.  However, the effect was still too cumbersome and labor-intensive for guitarists to use on stage during a performance.  Here again, transistorized circuits worked their magic on a pair of reel-to-reel tape decks and put the dramatic effect of the flanger into its new box-like home that could be used at a moment's notice, which meant it was no longer confined to the world of recording studios.

A/DA Flanger

By the mid 1970's flanger developers from companies like MXR, Electro-Harmonix, and A/DA ushered in a whole new era of psychedelic experimentation, and guitarists sold their old phaser pedals.
The flanger pedal achieves its sonic result by imposing more control over its placement of the notches created by the phase relationship, rather than spacing them evenly as the phaser's sweep does, although this wasn’t possible until larger more complex ICs became available. This extra technology is necessary to harmonically tune the out-of-phase notches and, relative to these notches, its peaks and harmonic spacing can make a genuine flanger pedal sound almost like it is actively participating in the note selection of the sequence being played. Where a phaser design can have from 4 to 10 stages, the individual chips within a proper flanger can carry many hundreds of stages within themselves.
A/DA, though not the first to commercially sell a 'flanger', is probably the first to manufacture and sell a Flanger that worked properly with the full sonic depth of the effect. This was partially due in part to the advent of the SAD1024 chip. Hitting shelves in 1977, the success was short lived being followed by Electro-Harmonix Electric Mistress, and MXR's Gray Flanger. Requiring their own regulated onboard AC power to run, these pedals cost almost $200 new. This, along with being a very 'heavy' sonic effect, led to the flanger being mostly phased out in the early to mid 1980's.

Fuzz
Probably the most popular of the newly invented transistorized guitar effects being built in the early 1960s was the fuzz. Where we can easily describe the components that make up the fuzz pedal, describing the tone your amplifier will spit out with a vintage-style fuzz pedal is nearly impossible to describe. The name truly says it best.
When you turn a tube amplifier's volume just to the point of breaking up, you've achieved gentle overdrive; crank it up to 11 and you've got heavy distortion. Now rip out one of the output tubes, use the wrong-value bias resistor on your preamp tube, or just beat it to a pulp with a crowbar and you might have something close to a fuzz. One thing is for certain, this is not a natural sound.
Though the Dallas-Arbiter Fuzz Face, introduced in 1966, was not the first fuzz box put into production, it is still considered the granddaddy of all fuzz pedals by most guitarists. Part of this is believed to be due in part to the very talented Jimi Hendrix, but can also be attributed to the infamous Germanium Transistor.

Dallas-Arbiter Fuzz Face

Germanium transistors are made from a semi-metallic element of the same name, and were a common component of many solid-state audio devices until more consistent and reliable silicon transistors became widely available in the late 1960s.  Though these transistors are considered by most guitarists to be 'soft', 'round', 'creamy', or 'more musical-sounding' than the 'harder' silicon devices that followed, the Germanium Transistors of the time had a very wide variation of tolerance specifications and were actually relatively unstable and very noisy. Because of these factors, quality between pedals varies widely. Sorting out the good ones was sometimes more work than manufactures could afford to put in, or perhaps knew was necessary.  Over the years manufacturers would attempt to design pedals using silicon transistors only to find their designs met with criticism from musicians begging for their warm, rich tone back.
Contemporary makers from Z. Vex to Fulltone to Roger Mayer himself now take the time and effort to laboriously sort their germanium transistors, and it most definitely pays off in terms of tone and consistency between pedals.
Though the fuzz pedal is by far one of the simplest designs in the world of effects pedals, consisting of fewer than ten components on the board, most will agree two of the ten components are crucial to the design:  The AC128 and the NKT275 transistors.
For the most part, high-end manufacturers have gone back to the classic Germanium Transistor en masse for their fuzz tones, using it in anything from a psychedelic update like the Z. Vex Fuzz Factory, to the vintage-style units like Roger Mayer's Spitfire, or Fulltone's '69, or Frantone's The Sweet.

Looper
A loop is a sample of a performance that has been edited to repeat seamlessly when the audio file is played end to end. The earliest loops were created with reels of tape that were spliced end to end to repeat a section. Some early examples of loops being used in music are The Beatles : “Revolution No. 9” and “Tomorrow Never Knows”. Today loops are created with a wide variety of music technologies including digital samplers, synthesizers, sequencers, drum machines, tape machines, delay units, or they can be programmed using DAW software.

Boss RC-30 Loop Station

In the early 1990s, dedicated digital hardware loopers existing in rack units, effects pedals, or other forms were invented specifically for use in live loop performance. These digital units recreate the looping of tape using an electronic memory to record and store “phrases”. Some of the more popular modern loop pedals may include: Boss RC-300 Loop station, Line 6 JM4 looper, and the Digitech Jam Man.

Noise Reduction
Noise reduction pedals, though not necessarily an 'effect', are intended to reduce 'hum' or 'noise' in your guitar rig. These pedals use a gate to eliminate 'hiss' or 'static' by greatly diminishing the volume of sounds that fall below a set threshold. Noise gates are expanders, meaning that unlike the compressor they will increase the dynamic range of an audio signal in order to make quiet sounds even quieter.

MXR SmartGate

This may be a difficult concept to grasp and becomes a little easier to understand once you can get your head around compressors.  It is almost the opposite concept here.
By using a noise gate we can hone in on the 'hiss' and 'hum' in our guitar's signal path to the amplifier and knock it clean out. Some guitarists have found interesting uses for these pedals which varies widely depending upon amplifiers, guitars, and pedals within the chain.

Octave
Not surprisingly, the octave pedal came to us once again from two very well-known names in the effects world, that being Roger Mayer with his custom-built Octavia pedal,  famously heard on 'Purple Haze' and many other Jimi Hendrix recordings. Roger Mayer developed an octave divider with an included fuzz stage for Jimi Hendrix out of his own personal experiments when attempting to double the frequency of a signal in the hope of making the signal appear to add a note an octave up from the original. Though this unit was never offered to the general public as a commercial unit, this new concept opened the door for Tycobrahe to offer its own replication of the Octavia.
The circuitry is fairly simple, consisting of three transistors, a couple diodes and an impedance interstage transformer, as well as the usual caps and resistors.

Roger Mayers Octavia

Roger Mayer once described the effect as “doubling the number of images of the note.  And that, apparently, makes it sound twice the frequency – whereas it really isn't. Because the signal's going up and down twice as much, even though you've changed the relationship of it, the ear perceives it as twice the frequency. It's like holding something up to a mirror, you see two of them, but there's still only one.”
Freaky when used right, or wrong, a simple circuit but a complex sonic effect. Guitarists rave about the use of these pedals when it comes to intervals, declaring fewer harmonics and a firm pick on the neck pickup to be superb.
Though the octave dividers use in music has faded from the heavy rock of the late 1960s and early 1970s, adventurous players still find many uses for these effects in modern music, though not often heard in the Jazz or Country genres.

Overdrive
When it comes to the overdrive pedal, many guitarists find two fantastic reasons to stomp the box: either to provide a gain boost to drive a tube amplifier into distortion, or to approximate the distortion sound of an overdriven tube amp.  And in some respects, these pedals do both.
The general overdrive pedal when cranked toward the max will yield an element of self-generated distortion, and when you generate enough things can get a little fuzzy. Though there are definite distinctions between pedal types, making sense of it all becomes a little more clear when you think in the degree of clipping achieved by the pedal. Overdrive pedals are generally soft-clipping devices and distortions hard-clipping ("clipping" being the term used to describe the way an audio signal is cut off when it hits the point of distortion - eventually the top of the sound wave is entirely cut off and that part of the signal lost, and this is where the clipping device comes in. Once the sound wave approaches full-clipping, the device either smooths out or even adds texture to the peaks of the wave).
The inner workings of these overdrive pedals are based upon the first section of a dual op-amp (purists believe heavily in the JRC4558D chip found in early Ibanez units) and a pair of clipping diodes with transistorized buffer stages at the input and output. Pedals also commonly included a section for tone shaping and output level controls, usually using a second part of the dual op-amp in conjunction with a network of capacitors and resistors.

An Original Ibanez TS808

Pedals made from this type of template offer a sonic quality described as 'tubey', 'warm', or 'rich'. This is partly by achieving smooth and symmetrical clipping, as well as reigning in harsher high harmonics that can result in a sonic image that's described as 'harsh' or 'spikey' in other pedals.
Most guitarists will agree that the Ibanez TS-808 Tube Screamer, and to slightly less extent, the TS9 which followed it, to be the grandfathers of the overdrive effect pedal. In fact, more 'boutique' overdrive pedals are based on the late 70s early 80s Tube Screamer design than any other overdrive pedal in existence! Other early implications of the overdrive effect were designed around discrete transistorized boosting and clipping circuits, and thus leaned a little more towards a distortion unit as properly defined.
It is actually the MXR Distortion +, which preceded the Tube Scream, which is of even simpler design – and, despite its name, is more of an overdrive than a distortion. The pedal is considered to sound a little more 'opaque', or less colored-sounding than the Ibanez counterpart. The MXR pedal uses a 741-type IC and a pair of Germanium Diodes to achieve a soft-clipping sound. Though these components are not the same as the famed 'Germanium Transistor', they are made of the same material and are thus thought to carry many of the same tonal properties.
Most guitarists agree that the overdrive pedal sounds best played through a tube amplifier set at about half-way (since the amp is doing most of the job and the pedal is used mainly as a kick in the pants), the pedal being just enough to boost the amp to break up a little quicker. Its obvious then that the overdrive pedal serves excellently to pre-boost the amplifier to drive the tubes into distortion at a lower volume setting than naturally needed.

Phaser
I think its fair to first start with an explanation of what phase is, and what it means in the audio world. At the most basic level phase is referring to sound waves and the relationship between two separate sound waves to be exact. When the human ear percives sound, what we are actually hearing is a change in air pressure created by the sound's source vibration. Think of these sound waves and changes in pressure like water movement, ripples when a stone is dropped in, waves comprised of peaks and dips. These are the waves that cause our eardrums to vibrate and our brains to translate that information into what we perceive as sound.
We call these phase-adjusting pedals “phase-shifters” because of their nature to split a guitar's signal into two paths and shift one of those paths out of phase with the other, varying between 0 and 360 degrees through the range of the frequency spectrum, and then blending it back with the dry signal. This blending of the signal back with the original is crucial to allowing the auditorial effect of the signal to move in and out of phase with itself.

A Vintage Uni-Vibe

When two signals are totally out of phase – meaning any time they are 180 degrees apart from each other in the full cycle of 360 degrees – they cancel each other out, creating what we call a notch.  When we sweep this frequency notch, a dramatic sonic effect is created at the peaks between the notches, where both the paths are completely in phase, and we have a full-strength signal. Leaving this notch to sit in the same spot would thus emphasize the same low-, middle- and high-frequency notes – and remove the same notes at the notches.  Thus the phaser circuit employs an oscillator to continuously move the point at which the notches and peaks occur. This oscillator allows different frequencies to be emphasized and de-emphasized at every pass and by a rate usually determined by the unit's "rate" or "speed" knobs.
Designers look at this and begin to speak in terms of continual shifting of the phase relationship from zero to just about infinity, depending upon how many shifting stages the circuit is designed with. Phase shifts by 180 degrees per stage, and two stages completes the full 360 degree circle.
Most phaser pedals are designed with a four-stage shifter, allowing for a 0 to 720 degree shift with three peaks and two notches along the way. Peaks on these designs are generally occurring at 0, 360, and 720 degrees and notches at 180 and 540 degrees.
The popularity of this design is probably most attributable to an outdated pedal with a two-function switch labeled 'Chorus' and 'Vibrato' named the Univox Uni-Vibe, one of the first transistorized effects of this genre to be widely available. Contrary to its labeling ('chorus'), this pedal is actually creating a phasing effect, and due to its designers' desire to create a Leslie cabinet sort of effect, it was mis-labeled. Though many designers have remained true to the Uni-Vibe's original concept for creating a chorus-like effect, many were re-designed from the ground up with varying sounds and circuits, though still very much a phaser.

Reverb
In today's times reverb is a very common effect, included on almost every amp in production and boasting abilities to reproduce springs, plates, halls and chambers. However, believe it or not, reverb was a fairly difficult monster to crack back in the early days of guitars and effects. The earliest studio reproductions of this seemingly complex sonic quality were simple recreations of the real thing but on a smaller scale. This method was achieved by placing a mic and speaker in a purpose-built sonically reflective room, also known as a reverberation chamber, or something less purpose-built like an empty bathroom or closet.

It wasn’t long before Les Paul advanced the idea of echo in the recording studio when he introduced an electromagnetic solution based around a modified reel-to-reel tape machine. It was this idea that sparked the revolution in recording and effects pedal technology and ideas.
The type of reverb most guitarists are familiar with achieves its sonic quality by driving signal down a set of springs and then tapping the resultant shimmering effect with a small transducer, and blending it back with the dry signal. Tube-powered spring reverb circuits are really just small amplifiers within themselves, with little output transformers (OTs) that drive a signal through a set of long springs much the way any tube amps larger OT does through a speaker. More common in the recording studio before the digital era is the Plate Reverberation, created in roughly the same way, sending signal through thin metal plates suspended in a cabinet.
Tube-based spring reverb units first arrived in amplifiers by brands like Gibson and Premier in the late 1950s, and even later by the more popular Fender, not being seen until the Vibroverb in 1963. Many manufacturers also offered separate reverb boxes as early as the late 1950s, but these boxes were often large, tube-based circuitry and transformers, and nearly the size of the amplifier's head cabinet. Certainly difficult to carry around.

Van Amps Reverbamate

Being generally created with large springs or plates, reverb has been lured more into the delay camp of effects in modern times due to its bucket brigade analog technology or digital delay technology used to create long echoes which can be manipulated to produce a reverb sound. When you tap into the multistage analog delay chip with a very short delay, layer it even further with short delays, you've birthed a reverb, sounding similar to a spring reverb common in guitar amplifiers or maybe even an old studio plate, in that both approximate the reverberant sound of a guitar played in an empty, reflective room.
Digital reverbs, like their digital delay counterparts, offer a very powerful variety of settings. In addition to doing some approximations of a spring reverb sound, digital reverbs usually offer a more 'like-like' reverberation when used in anything from a small room to a large concert hall. But when it comes to the classic sound of a plate or spring, look no further than the original.

Synth
Ring Modulators, or synth pedals, come to us from the world of analog synthesizers, and though usually better suited for use with such, they have some interesting sounds for guitarists as well.
The ring modulator takes it name from a transistorized topology, consisting of a ring of four diodes and two transformers. Though most synth pedals can get a lot more complex than this, for our purposes we'll keep it simple. The pedal takes signal from two sources – either two separate inputs, or one input and an internal oscillator called a 'carried frequency' – and multiplies the signal to produce a new signal totally different from the original signals.

Z. Vex Ringtone

The resulting sonic effect is similar to an octave divider, trying to handle two notes at a time rather than one signal note, spitting out a dissonant mess as a result. The pedal is specifically designed to cope with these two different signals, but their multiplication produces a new signal with notes at both the sum and difference of the frequencies of the two source signals.
Early implications of the ring modulator pedal for guitar usually have a single input and generate their own carrier frequency internally, and occasionally with a user-selectable variation. Some more complex models even allow for internal oscillation in selections and add an extra input for use with an external control signal such as a drum machine, microphone, or some other line-level source.

Tremolo
Tremolo is the effect of rapidly modulating a sound signal from the 'On' state to the 'Off” state (or, nearly off). The advent of tremolo was originally an amp-based effect, as described in part one of this blog. In this case the tremolo circuit is acting between the phase inverter and power tubes to cut the signal as it enters the output stage of the amplifier, or when the signal is tapped by the bias circuit to pulsate the 6V6s on and off, neither of which can be properly replicated in a standalone pedal.

Electro-Harmonix Wiggler

However, the circuit used in Fender amplifiers from 1963 and onwards, with its lopsided triangular waveform, can and was adapted to fit into a small box.  This design is based around a photo-coupler made from a small neon lamp and a light-dependent resistor (LDR) coupled together in a small clear tube. An oscillator makes the lamp pulse at a speed determined by the effect's 'speed' control, and the LDR – which is in the signal path – inputs this pulse into the guitar signal with an intensity determined by the 'depth' control.
While most amplifiers of the late 1960's and early 70's carried this effect, they usually used a tube to drive the oscillator.  Pedals use a photo-coupler to convert the drive section to a transistorized stage.
As with the majority of budget tremolo pedals, they use ICs to accomplish all oscillation and modulation tasks, usually with transistorized input and output stage buffers, an even simpler process.
Though tremolo may have dropped out of fashion in the late 1970s, it is still a favored effect put in many amplifiers stock with the reverb.

Vibrato
True vibrato, contrary to popular belief, is the wavering of a note above and below pitch to create a vibrating, warbling sort of effect.

Guitarists can achieve this effect very easily by wiggling their finger against the fretboard of the guitar, or by moving the arm of a vibrato tailpiece. Electronic implications of vibrato were achieved fairly early on with a relatively complex circuit, usually requiring at least two preamp tubes and most oftentimes installed in amplifiers.
Today's vibrato pedals are achieved in solid-state technologies with circuits similar to that of those used in analog chorus units, and even some high-end and fairly complex transistorized designs of modified phasers.
For more information on vibrato, please see Part One of this blog.

Wah-Wah
The wah pedal is probably one of the most recognizable pedals on the market, when not being confused with the simplistic volume pedal. These pedals contain a circuit with a sweepable peaking filter – a bandpass filter that creates a peak in the frequency response which the player can manually sweep up and down the frequency spectrum. When this peak is swept through the frequency spectrum containing the notes being played, the pedal will emphasize the frequencies and produce the well-known 'wah-wah' sound.  The different amounts of resonance produced by this peak sweep contributes to the characteristic sound of the pedal, and can vary considerably model to model.
Because these pedals are designed specifically for guitar use, it is easy to hone in on the frequencies most used by guitar, that being between 400Hz and 2.2kHz. Some pedals even offer control over this bandwidth, as seen on the Dunlop Cry Baby 535Q.

Though the most popular wah-wahs of all time are the Vox Wah and Cry Baby of 1967-68, not to mention the Thomas Organ Clyde McCoy Wah-Wah which preceded these models by a year or two, all achieve their classic sound with a circuit consisting of only a couple of transistors, a coil inductor, a couple of resistors, and a capacitor. And of course, a potentiometer with a gear mechanism on its shaft so a rocking treadle can move.
Many guitarists boast about the early Italian-made Jen Vox Wahs with Fasel inductors in the circuit, and claim that nothing made after them has ever sounded as rich or expressive. However, flaws in these early Fasel inductor designs included an ability to achieve asymmetrical clipping with some even-order harmonic content, as opposed to the spikier-sounding odd-ordered harmonics of other clipping inductors.

Many guitarists over the years have modified their stock wah-wahs to improve or upgrade their tone and playability, commonly seen with the replacement of inducers found in early Cry Baby wahs. Though something of a tricky art, a number of modifications exist – some user-installable – aimed to help players make the most of both new and vintage models. (Look up Roger Mayer's Red Lion Wah kit, which can be fitted into a standard Cry Baby wah.)
While the Cry Baby and Vox wahs remain the classic mark, makers have offered a range of variations on both the circuit and the mechanical operation of the pedal. Morley had an occasionally popular wah which used quiet photo-resistors instead of a potentiometer for sweep control through the frequency spectrum. Roger Mayer's Vision Wah is also a potentiometer-less pedal, with a low-profile housing and a treadle positioned ergonomically for more comfortable action while standing and playing. And for pure insane inventiveness, try the Z.Vex's Wah Probe, which uses a theremin-type antenna in the form of a copper plate mounted to the sloping front face of the pedal for a contact-free wah-wah.

Leslie Cabs
Though the infamous Leslie Cab is not necessarily an 'effects pedal', its creation most definitely sparked a revolution of new guitar pedals attempting to imitate its sound. To this day guitarists and organists alike have lusted and swooned over its beautiful three-dimension choral tones. Introduced in the early 1940s by Don Leslie, originally intended for Hammon organs, Leslie models create their sound by splitting the signal path to both a low-end 15” speaker mounted within a rotating drum at the bottom of the cabinet, and a high-end horn mounted at the top. The spinning effect of each speaker creates a constantly shifting warbling sensation aided by the application of the Doppler effect on two different planes.
This effect is made even more interesting by the Leslie Cab's shift between speeds – slow (originally called 'chorale') and fast ('tremolo') and that the change between speeds is not instantaneous. This lag time while each rotor accelerates at a different rate creates a phasing effect until each speaker finally catches up to each other and pulls everything into synch.
The original Leslie Cab was meant to create a spacious, warbling choral effect, intended to create cavernous cathedral pipe organ acoustics into the small chapel or living room. Though this stood true for the organist, the guitarist sought a way to downsize this effect into a small and portable stomp-box.

Early re-creations of the effect in pedal form ranged from complex tube vibrato circuits, to the first solid state chorus and phaser pedals like the Univox Uni-Vibe and, later, the Maestro Phase Shifter.
In 1967 Fender released its own solution to the guitar-friendly rotating speaker cab by introducing the Vibratone. At the time, CBS owned both Leslie and Fender and was freely able to use Don Leslie's patents and apply them to a cab aimed at the guitarist. The Vibratone design employed a single 10” speaker inside of a drum that rotated on a vertical plane rather than a horizontal, as the rotors do in the Larger Leslie counterpart.
With just one speaker the unit was lighter, easier to carry, and simple to mic up. However, its time in the limelight was short lived, being discontinued in 1973. By the time everyone had heard what transistorized emulations like the Uni-Vibe could sound like in the hands of greats such as Robin Trower and Jimi Hendrix, it hardly seemed worth hauling around such bulky equipment like the Fender Vibratone or the even larger Leslie cab.
Though the love affair for the original sound of a Leslie Cab has never died, most guitarists rely on the dependability of the newer stomp boxes.  Most will agree, however, that to achieve a true Doppler effect... stick with the rotating speaker.