Types of Tremolo in Tube Amplifiers

Lot of folks ask me about what the difference is between types of tremolos in amplifiers. There many opinions about the different types and what sounds best. In this article I will briefly cover the basic types of tremolos and how they affect the sound. I will also have a list of on the bottom of the page of some of the amps that use each type of tremolo.

What is Tremolo?

Tremolo is the effect of changing the volume of the sound. It gives the sound nice shimmering ethereal effect.  Fender wrongly used vibrato as the label for tremolo in their amps. Vibrato is actually bending the pitch of a note. Interestingly there are a few vintage amps that have real vibrato. I worked on a Magnatone amp that did. it’s a neat piece of electronics and sounds really strange. However, it’s not really all that usable of a sound.

The Three Major Types of Tremolo in Amplifiers:

Bias Shifting Tremolos: 

How it Works-

These tremolos work by changing the bias to either the power tubes or a pre-amp tube in a amp.   By changing the operating parameters of the tube the signal can be cut off momentarily and the brought back up. This creates the tremolo effect. These tend to have a very rich deep pulsating sound.  There are a couple of important things to know about bias shifting tremolos. First that the signal does not pass through the tremolo circuitry so they do not effect the fidelity of the signal. Secondly, for the tremolo to work properly the amp must be biased correctly.

Types of bias shifting Tremolos-

There are two types of bias shifting tremolos: one that work on the bias of the power tubes and ones that work on the bias of a pre-amp tube.  The power tube kind requires a fixed bias setup so any cathode bias amp that has bias shifting trem uses the pre-amp variety.

Signal oscillating tremolos:

As you might guess these work by cutting on and off the actual signal within the amp. There are a wide variety of kinds of signal oscillation tremolos but the most common uses an opt coupler which is basically a bulb (neon or incandescent) paired with a light dependent resistor. These types of tremolo give a nice fluttering effect however, they are not a deep or rich sounding as the other types.  An important thing to keep in mind with this type is that the signal does pass through the tremolo circuit and thus affects the gain and fidelityof the amp.  A common thing players do with Blackface Fender Amps that do not us their trem (most have this type of tremolo) is remove the tube that runs the tremolo circuit. There is a noticeable increase in fidelity with the tube out!

Harmonic Tremolos:

Very few amps have harmonic tremolos but they are among the wildest and most hypnotic sounding tremolos.   They are found in a handful of Brownface and Blonde Fender Amps. The main trouble with harmonic tremolos is that they take three 12AX7s to run! Many amps do not even have that many pre-amp tubes. While the tremolo is sound is great the signal does pass through the tremolo circuit and because of the size the circuit the tremolo greatly affects the amps total sound quality.

So which is best?

This is mostly a matter of personal opinion. However, I have found that most people find the Harmonic and Bias Shifting  Tremolos sound the best and have the most depth. I prefer the bias shifting variety because they do not affect the quality of the signal. Also as a builder devoting three tubes to a task like tremolo seems a bit excessive.

 Some Common Amps by Tremolo Type:

Power Tube Bias Shifting:

 Fender Blackface, and Silverface Princetons

Fender Black and Brownface Vibro-verb

Fender Brownface Deluxe

Fender 5G9 Tremolux

Carl's Custom Amps Blonde Series Amps

Pre-amp Tube Bias Shifting:

Fender Blackface and Silverface Vibro Champs

Fender 5E11 Tremolux

Signal oscillating tremolo Amps:

Most Fender Blackface and Silverface Amps with tremolo (except the Princeton and Vibro Champ)

Vintage Vox Amps

Most Vintage Gibson Amps with Tremolo

Harmonic Tremolo Amps:

Fender Brownface and Blonde Pro, Bandmaster, Super, Showman