Tremolo History
I'm not an expert, but these are the things I've picked up while researching.
First, let us define what exactly we are talking about.
Generally when we talk about Tremolo, we are talking about amplitude (VOLUME) modulation. Like turning the volume up and down.
Now there are different types of "Tremolo" that don't exactly fit that definition. But we call it Tremolo anyways.
To add confusion, Fender called their Tremolo circuits, "Vibrato" instead.
Vibrato, just to be clear is modulating the PITCH of a note
Like most guitar effects, Tremolo originated in a keyboard instrument. Not in the guitar world.
There is an excellent article on Tremolo at the below link, if you are interested in more history.
Tremolo first showed up in guitar amplifiers first, not pedals. And there were different ways these circuits were designed that gave different sounding results. Generally when people want a certain type of Tremolo, they are looking for the end result of the sound, and not necessarily HOW the circuit is designed. Purists will be looking for both. Most people wont care, just so long as the pedal is in the ball park.
Pedals get into more complex circuitry, and so they can achieve results in different ways that Amplifiers could not.
Bias Tremolo -
The initial type of Tremolo was created by changing the Bias of either the power or pre-amp tubes in an amplifier. Basically you were cutting power to the tubes and applying it again. This causes a very SMOOTH valley and rise which we refer to as a sine wave. This type of Tremolo is often described as smooth, deep, and swampy.
Examples of types of amps with Bias Modulated Tremolo in them:
Power Tube Bias: Fender Blackface and Silverface Princetons, Black and Brownface Vibro-Verb
Pre-Amp Tube Bias: Blackface & Silverface Vibro Champs, Fender 5E11 Tremolux
Bias shifting Tremolo was generally hard on the tubes when the amp was being pushed, which people with tube amps tend to do ;) So eventually they "graduated" to a method that wasn't as hard on the equipment.
Optical Tremolo - AKA Photocell AKA Signal Shunt also known by other names
Basically it's tremolo that modulates the volume by turning a light on and off.
This was a lot less hard on amplifiers, cheaper to produce, and more reliable. Gotta cut them costs!
In general this tremolo is described as fluttery and choppy. Typically by default, not as deep or rich sounding as Bias Modulated tremolo. There are modifications you can make to make these circuits sound less choppy and more deep.
Examples of Amplifiers with Optical Tremolo:
Fender Twin, Fender Deluxe Reverb
Now between Bias and Optical there was Harmonic.
Harmonic Tremolo
Harmonic Tremolo incorporated a 3rd tube into the circuit, and instead of modulating volume, it modulated between high and low frequency bands. To generalize this is more like turning the tone knob back and forth on your guitar.
It is described typically as lush or phasey. This circuit was more complicated and more expensive to produce, so it did not stick around long.
Examples of Amps with Harmonic Tremolo: Fender Bandmaster, Super, Showman
So those are the 3 basic types of Tremolo. Considering one doesn't strictly modulate volume, there are really only 2 types.
The last "type" i'll mention, simply because Fender calls their circuits "Vibrato" and there was actually a true "Vibrato" circuit at the time, is the Magnatone Vibrato. This was found in Magnatone amplifiers and is different from straight up vibrato because it was a stereo effect and there seemed to be a little something extra in there. Probably some phasing. It sounds wondrous. So go check that out if you are interested.
So that is a brief overview of the circuits you generally have. There are some one offs here and there.
Many times the circuits would not be "perfect". The power shift wouldn't be equal on both sides, there would be a quicker rise than fall etc... Humans tend to like things that aren't perfect.
The thing to keep in mind is that pedals can have more complex circuits, and the end result is what is important, not necessarily the internals. Pedals can get you a lot more complex wave shapes.
While you may want to harken back to the good old days, also understand that pedals typically have A LOT more options than amplifiers, which usually only had speed and intensity controls. A lot of pedals do what the amps did, and then a lot more than that.
Another good source for some more information on the types, which I got a lot of this information from.
Carls Custom Amps - Types of Tremolo in Tube Amplifiers
Fender Twin, Fender Deluxe Reverb
Now between Bias and Optical there was Harmonic.
Harmonic Tremolo
Harmonic Tremolo incorporated a 3rd tube into the circuit, and instead of modulating volume, it modulated between high and low frequency bands. To generalize this is more like turning the tone knob back and forth on your guitar.
It is described typically as lush or phasey. This circuit was more complicated and more expensive to produce, so it did not stick around long.
Examples of Amps with Harmonic Tremolo: Fender Bandmaster, Super, Showman
So those are the 3 basic types of Tremolo. Considering one doesn't strictly modulate volume, there are really only 2 types.
The last "type" i'll mention, simply because Fender calls their circuits "Vibrato" and there was actually a true "Vibrato" circuit at the time, is the Magnatone Vibrato. This was found in Magnatone amplifiers and is different from straight up vibrato because it was a stereo effect and there seemed to be a little something extra in there. Probably some phasing. It sounds wondrous. So go check that out if you are interested.
So that is a brief overview of the circuits you generally have. There are some one offs here and there.
Many times the circuits would not be "perfect". The power shift wouldn't be equal on both sides, there would be a quicker rise than fall etc... Humans tend to like things that aren't perfect.
The thing to keep in mind is that pedals can have more complex circuits, and the end result is what is important, not necessarily the internals. Pedals can get you a lot more complex wave shapes.
While you may want to harken back to the good old days, also understand that pedals typically have A LOT more options than amplifiers, which usually only had speed and intensity controls. A lot of pedals do what the amps did, and then a lot more than that.
Another good source for some more information on the types, which I got a lot of this information from.
Carls Custom Amps - Types of Tremolo in Tube Amplifiers
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