Electro Harmonix Pulse Modulator (1970)

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After a year and half of releasing plug-in style effects, Electro Harmonix came out with their first true stompboxes in the Spring of 1970. These were the Big Muff π, the Low Frequency Compressor, and the massive Pulse Modulator. Obviously the most popular of this trio is far and away the Big Muff, but unfortunately to the point that people tend to overlook the ingenuity and technical wizardry that went into creating the other two.

And because of this, most people are not aware that in addition to the now legendary Perfboard Big Muff, both the v1 Low Frequency Compressor and the v1 Pulse Modulator also featured circuits built on perfboard!

In the ocean of wild and ridiculous effects that Electro Harmonix has produced in the last 50+ years, the Pulse Modulator is right up there with craziest...

So what is it?

Well in a simple explanation, it's a pedal with 3 separate tremolos that allow you to control the speed and volume of each individually. It also features a boost circuit, that I assume is somewhat similar to the LPB-1(?). 

When it comes to the tremolo, it's considered a pulsewave, which is essentially a non-linear squarewave (on/off) style. And if you engage all three at different speeds, you can imagine how chaotic this would get; with cascading pulses creating mind-melting patterns and wild polyrhythms!

So the design itself was a bit ahead of its time (or maybe it was perfectly OF its psychedelic time), because in just two short years the Pulse Mod was no longer being sold by ehx.

Even though it didn't do well, the Pulse Mod surprisingly saw two brief spin-offs with the Stereo Pulse Modulator and wildly misnamed Hare Lip Microphone Echo.

All three of these effects were super weird, and would essentially set the stage for the type of experimentation that Electro Harmonix and Mike Matthews would become known for.

While it hasn't been 100% confirmed, I do believe the Pulse Mod was conceptualized by Matthews and designed by Bob Myer (who also invented the Big Muff).

When looking inside, it seems very likely that the two pedals were created around the same time. And you even see some of the same exact parts that were used in both; certain very specific capacitors and resistors can be found.

And while they both have the same 1966 date codes that you typically find in all early ehx pedals, the real clue lies in the CTS brand on/off potentiometer that's dated to the 22nd week of 1970 (which again you will find in many perfboard Muffs).

For vintage pedal nerds the Pulse Modulator wasn't seen as very collectible for a long period of time. More often it was simply a cheap(ish) way to harvest a stash of  knobs for Triangle Muffs!

But the rarity of these, and the fact that they were made for a very short (and very early) period in Electro Harmonix history, is finally starting to be realized.

So while you may have a hard time finding a perfboard version, I do recommend tracking down a Pulse Mod for history-sake, as they signal the beginning of Electro Harmonix' legacy of innovative boldness.

thanks for reading!

-ed