# Harmonic Tremolo



## mhammer (Nov 30, 2007)

Finally built myself a harmonic tremolo today. Where has this been all my life? Hot damn, they sound so nice, and make lush chords sound so much more lush.

For the unfamiliar, where "regular" tremolo, whether photocell-based or power-tube-bias tremolo, or something else, raises and lower the overall volume in throbbing fashion, harmonic tremolo splits the guitar signal into highs and lows, and modulates them in complementary fashion. So when the volume of one gets higher, the other gets lower. The split is not steep/abrupt, since it only uses a single stage of filtering (6db/oct) to separate the highs and lows. That means that there is a reasonable amount of overlap in what's included as "high" and "low". The net result is a certain animation to the sound that is much less distracting than regular tremolo, or Uni-vibes, or phasers. It's the sort of thing you can leave on for a while, without it feeling like a nuisance or any sort of sonic "trap". 

Ry Cooder, Blake Mills, and Joey Landreth are big-time users of harmonic tremolo, though I couldn't tell you which of them is using a pedal and which is using an amp. Some of the early 1960's Fenders used this form of tremolo, and I would imagine some boutique builders have incorporated it in more recent amps, given how sought-out it is. I noticed that some of the recent digital modulation pedals, like the EHX Mod 11, also include Harmonic Tremolo as one of the effects.


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## DaddyDog (Apr 21, 2017)

Cool. Milkman Sound has recently started building them. And the Truth About Vintage Amps podcast talked about it in the episode I heard this morning.


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## vadsy (Dec 2, 2010)

The Strymon Flint does the harmonic trem really well and so does the Swamp Thang from Monster Effects


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## sulphur (Jun 2, 2011)

My Alexander Equillibrium has that type of trem as an option, cool stuff.


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## Merlin (Feb 23, 2009)

My Source Audio Vertigo has a great harmonic trem; it can get into Univibe territory too.


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## mhammer (Nov 30, 2007)

Well there you go, all good recommendations. Nice to see so many are including it.


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## cboutilier (Jan 12, 2016)

The harmonic trem in the blonde Fender amps was surreal. It was just far too complex to continue building with tubes. Photocells were much cheaper and compact.


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## mhammer (Nov 30, 2007)

I'll say! Some of the tremolo circuits only required half of a 12AX7.


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## Frenchy99 (Oct 15, 2016)

Really cool that you can build all your pedals !


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## cboutilier (Jan 12, 2016)

mhammer said:


> I'll say! Some of the tremolo circuits only required half of a 12AX7.


Whereas the harmonic used 2.5 12AX7s, If I remember correctly.


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## mhammer (Nov 30, 2007)

Good call! I just looked at the schematics for the "6G..." Concert and Pro amps. The earlier issue uses 4 triodes (two 12AX7s) and the issues immediately after use 5 sections (2.5 12AX7s).


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## CathodeRay (Jan 12, 2018)

I couldn't find any decent info on this... what's the 'harmonic' aspect of the harmonic tremolo?
Is it a bit of added vibrato? Synced? Unsynced?


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## mhammer (Nov 30, 2007)

Traditional tremolos modulate the amplitude of the_ entire _signal. Harmonic tremolos split the spectrum in two ("half" is probably not accurate), and modulate each part in reciprocal fashion. So, as the lower portion 's volume level is reduced, the upper portion's volume is raised, and vice versa. The net effect is that one perceives an "animated" sound, but it never seems to get quiet-loud-quiet-loud, because something is always at full signal level. I find it to be a less disruptive or distracting effect. Why is it called "_harmonic_ tremolo"? I can't be certain, but I gather it's because the harmonic content (i.e., upper band) is modulated separately from the fundamental (lower band).

In some respects, it is analogous to the Boss Dimension C pedal, which also countersweeps, although the DC-2 sweeps the delay time of two delay chips in complementary fashion. For the DC-2, the benefit is that the resulting sound is never identifiably sharp or flat the way a standard chorus pedal can be. Similarly, with the split/counterswept amplitude modulation of a harmonic tremolo, the result is never audibly louder or softer; it just seems to wiggle in place. Here's some nice illustrations from Winnipeg boy Joey Landreth, beginning around the 18:00 mark.


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## Hammerhands (Dec 19, 2016)

I was trying an experiment to see if I could get an effects unit to do harmonic tremolo.

I did get it to work! Then I tried modulating the lower and upper parts at different frequencies. I set the lower part to 120bpm quarter notes and the upper to quarter note triplets. So if you played the 6th string then the upper strings, they would pulse in time but at different speeds. The depth wasn't very deep.

This was very good.


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## mhammer (Nov 30, 2007)

I'm curious. What were you doing this with? It sounds, from your description that you might be doing it with a plug-in.


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## mhammer (Nov 30, 2007)

My bad for forgetting the Korora Merlo. Walt Jones, who makes them, is a terrific guy, and a quiet innovator. He had a small unassuming booth at Summer NAMM when I visited. We've kept in touch since. He needs a better distribution system.

The Merlo is an all digital harmonic tremolo that allows for a wide range of custom configurations, in addition to more traditional sounds.


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## Hammerhands (Dec 19, 2016)

mhammer said:


> l9
> I'm curious. What were you doing this with? It sounds, from your description that you might be doing it with a plug-in.


Boss GT-001, it is sort of a desktop version of the GT-100.

Weirdly, I had just been reading the Pedal Crush book, I'm sure I looked up if the GT-001 had a harmonic tremolo setting and I thought it did. Then I saw a post somewhere on Joey Landreth's video, and I looked again and it doesn't have that setting.

So I set both amps the same (Clean Twin), set the divider to dual so they run in parallel, split A with a low-pass filter, B with a high-pass filter, I tried the crossover at 800hz, I should try 400hz. Then assigned a wave pedal, I chose triangle shaped yesterday, to preamp A level, changing the level from about 35 through 60, then assigned another wave pedal to preamp B level, changing the level from 60 through 35. You have to adjust the depth to taste...I ended up with 42-67 for the high side and 77-16 for the low side.
The mixer is confusing, setting it stereo with a spread of 0 mixes the two channels to mono.

The sweet spot seems to be 630hz. 25-67 on the high side.


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## mhammer (Nov 30, 2007)

A whole lot easier when someone has done all of that for you with a circuit, eh? I made mine using this schematic: http://www.geofex.com/FX_images/FakeFenderVib3.pdf

How do you like the book?


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## Hammerhands (Dec 19, 2016)

mhammer said:


> How do you like the book?


Mostly I really liked the book. I liked the tips, those and the descriptions of the pedals gave me ideas about combining pedals that I would like to try. I now have a strong desire for a delay pedal with a feedback loop.

I should have read the book in my own preferred order. I would have enjoyed it more if I had started with the modulation section, read the utility section later and read the interviews as a separate book.

I did conclude that I'm not as interested in the subject as I thought.

Another experiment partly inspired by the book I tried was running two phasers, adding a second oscillator to the one phaser with a wave pedal and controlling the other with an expression pedal. It was very muddy.


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## mhammer (Nov 30, 2007)

I actually spent a lot of time working with Scott on the modulation section.

I have the Dave Hunter Guitar Pedal Handbook, and while a lot of it is a big disappointment, the interviews with the pedalmakers pull it out of the fire and are the highlights of the book.


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