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In the 1960s there were plenty of amplifier manufacturers that were clamoring to compete with giants like Leo Fender. Of course, competition breeds creativity, and many companies struggled to find their niche. Silvertone, for example, secured their place as the “budget-friendly” Fender competitor and monopolized the mail-order catalog. Ampeg cornered the bass amplifier market. Vox and Marshall voiced their circuits in a distinctly different way that produced the “British sound.”

Enter, Magnatone. Known for their clean, but not as sparkly as Fender, tones and their stiffer, less-responsive overdrive, there wasn’t a wide-open field for their company to shine. Sure, the Magnatone sound is different and excellent in its own way, but it wasn’t spectacular enough to dethrone the Fender royalty. Except for one special thing; one secret and proprietary effect that would cement Magnatone in the halls of amplifier history: true vibrato.

*Magnatone ended its run in the mid 1970s, but there has been a modern revival. If you are enamored with the sound, you can purchase a brand new reissue of one of the classic circuits. Or, you can always try your luck at finding a vintage one that’s hoping for resurrection. Most fans now lovingly refer to them as “Maggies”.

Vibrato versus Tremolo:

Let’s clear up a confusing detail right away: the difference between tremolo and vibrato. Many vintage and modern amps include onboard effects like reverb. The most common and ancient effect is tremolo. This is a post-amplification effect that modulates, or changes, the instrument signal by rapidly changing the volume. Commonly, you can alter the intensity of the tremolo, or its depth, as well as the speed at which the volume change happens. This allows the player to layer on a slow, rhythmic pulse all the way to a fast, trembling warble. Remember: tremolo is a manipulation of output volume.

Vibrato is a change in pitch. Say, for example, someone sings the musical note “C”. Vibrato happens naturally in healthy singing, and if you were to look at a recording of that singer, you’d see an audio wave that subtly fluctuates around the note “C” by going slightly sharp, then flat, then sharp, then flat, etc. Vibrato sounds organic and is commonly heard in the human voice, orchestral strings like the violin, and even guitars and fretted instruments on longer notes.

In the 1960s world of amplifiers, it was pretty simple to create tremolo, a fluctuation in volume, but extremely difficult to create vibrato, a fluctuation in pitch.

The difference between tremolo and vibrato is easily confused, but it’s further convoluted by the fact that Fender called their effect “vibrato” on many of their amps (and still do!) when in reality, the effect that they were producing and manipulating is tremolo, a fluctuation in volume, not pitch.

Hold Up:

You may be wondering if the difference between tremolo and vibrato is noticeable, or if it even matters. Yes, it is noticeable, and yes, it matters! The two effects are closely related, but they do have distinctly different sounds. Check out this video from one of my favorite technicians of all time, Uncle Doug. Around the 18:30 mark, you can hear a side-by-side comparison of tremolo and vibrato… plus, he’s using a vintage Magnatone amp!

As you’ve probably surmised, Magnatone figured out a way to create real vibrato in their amplifiers. They coined their effect “true vibrato”, and kept the circuit a secret. That didn’t work for long, though, as amp technicians were able to get their hands on the Magnatone true vibrato, trace the circuit, and see how it works under the hood. Speaking of…

How Magnatone Vibrato Works:

Traditional tube tremolo (like the kind found in Fender amps) is pretty straightforward: take a tube that can function as an oscillator, then have it throttle the audio signal before it gets to the output section of the amp. It can also be done by oscillating the signal at the phase inverter, which is technical nerd jargon for “you can have the audio signal cancel itself in rhythm to create the effect”.

Magnatone true vibrato uses a rare and super special component called a varistor. A varistor is a type of semiconductor that is kind of like a common resistor. Instead of being one permanent value, however, the varistor can change its electrical resistance based on how much voltage is applied to it. They are most commonly found in surge protection, so think of it this way: if current is flowing normally through a circuit, the varistor will have very little resistance. If a voltage spike happens and the circuit starts to overload, the varistor will “see” this irregularity and will quickly increase its resistance until the spike has been resolved. This helps protect the rest of the components.

Now, this isn’t helpful for audio. Magnatone realized that a partner circuit had to be employed to make the varistors shine. This is an LFO, which stands for a “Low Frequency Oscillator”.

LFOs are incredibly common with audio. Most modulation guitar pedals, synthesizers, and keyboards use them. They simply generate an audio wave that is too low for human hearing. Then, this wave can be controlled like a common amp tremolo circuit by manipulating the intensity and the rate. Most importantly, other audio signals, effects, or controls can be attached to the LFO and “ride” it to create interesting and novel sounds.

So, in combination, the magic and mystery of Magnatone true vibrato is this:

Instrument audio signal enters an amplification tube. At the same time, an LFO signal is being injected into the same tube. This LFO is strong enough to rhythmically vary the voltage at the tube, meaning that the output signal of the tube also varies accordingly. The tube has a separate varistor attached to both the positive and negative outputs, so the out-of-phase audio signal (which has been juiced with the below-human-hearing varying signal) gets squeezed and “corrected” by each varistor. When the two out-of-phase signals are combined at another amplification tube, the summed sound is the smooth, musical vibrato that we love. If you’d like to see an explanation using a schematic, check out this video at the 34:05 mark.

The Maggie, the Myth, the Legend:

Much to the despair of amp technicians back in the day, Magnatone was one huge step ahead: they kept the values, construction, and technical details of the varistor close to their chest. The actual component doesn’t have any markings on it, and attempts to recreate it have been futile. That is, until the Maggie revival in the 2010s. The current company that produces these amps spent a ton of time, research, and development in reproducing the varistors, and while their construction is still a secret, it’s refreshing to know that the knowledge of how to make them hasn’t been lost to time.

Is It Worth It?

To me, a vintage nerd, technician, and enthusiast, yes. Yes, the Magnatone true vibrato is a completely unique sound unlike any other, especially in comparison to traditional tremolo. It’s a subtle, musical, and organic sound that sits with the music. Tremolo interrupts the music more – it sounds choppier and more abrasive once you’ve tasted the sweetness of vibrato.

That being said, the Magnatone sound is a sum of its parts. An all-tube ensemble, vintage (often sub-par quality speakers), and the ability to jumper channels on the amp give the vibrato a charming grittiness, warmth, and mojo.

If you’re looking for just the sound of the vibrato and don’t need the full amplifier, there are some great modern pedals that try to faithfully emulate the Magnatone vibrato sound. Check out the Equilibrium by Alexander Pedals, Magnavibe by Bigfoot FX, SurfyVibe, and Killer V by Crazy Tube Circuits.

Wrapping Up the Vibes:

Thanks for learning about this unique and magical circuit from the 1960s! Keep in mind that not all Magnatone amps have the true vibrato circuit under the hood, but models that do can still be found in the wild. Keep an eye open for vintage ones at places like the Orlando Guitar Expo, and there’s always Reverb. Stay tuned for more interesting and nerdy offerings, and contact us if you have any questions!