Modulate That Pulse!

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Modulate That Pulse!

This month's pedals of old are the Pulse Modulator and its Siamese twin brother, the Stereo Pulse Modulator. These are very similar to the Harelip Microphone Echo we looked at several months back in that they provide a tremolo effect. These 2, however, took the effect several steps further.

The Pulse Modulator, at first glance, looks like a Big Muff on steroids (fig 1). The first thing you notice are the 8 knobs on the top. Then you see the giant Big Muff style box (8 1/8" x 6" vs the Big Muff's 6 7/8" x 5 1/2"). As if that's not enough, there are 3 jacks on the end! Left to right, the jacks are labeled INPUT, BOOSTED OUTPUT, and PULSE OUTPUT.


Now, here's what the Pulse Modulator does. It is THREE tremolos in one box! Not only that, but it has a control to boost your sgnal as well. The upper three knobs are PULSE SPEED, which sets the speed of the effect. The second row of knobs are labeled PULSE VOLUME. These set the relative volume of each tremolo. The knob at lower left is the BOOST VOLUME, with the on/off switch on it as well. This controls the level of the boosted signal. The last knob, at lower right, is the PULSE ATTACK, which sets the strength of the pulses. Your amp is connected to the appropriate output jack, depending on which effect you're using.

You'd think that with all these knobs, this would be one versatile pedal. The fact of the matter is: It's not the greatest thing in the world. The tremolos are "clicky", like the Harelip and when you hit the footswitch, your entire signal is turned off. This could be easily fixed with a minor rewiring job. The boost feature is always on, but your output must be connected to the BOOST OUTPUT to use this feature. What it boils down to is this:

1) You can have tremolo
2) You can have boost
3) You can't have both at once (unless you use 2 amps)
4) You can't bypass the effects (except for turning your entire signal off in the tremolo section)

I've seen some Pulse Modulators with circuit boards and some older ones with the circuit laid out on perfboard.

The Stereo Pulse Modulator (fig. 2) was similar in concept. This pedal was actually designed to be used with your stereo! The jacks on the rear are RCA jacks, perfect for hooking up your 8-track player to it. The pedal (or effect, since it doesn't really qualify as a pedal) has 9 knobs and an on/off switch. You have a MASTER VOLUME, which of course controls the overall volume of the effect. There are also 2 groups of 4 knobs, 2 PULSE VOLUME and 2 PULSE SPEED for each channel of your stereo. Here's what EH claimed in its literature:
"WE GUARANTEE YOU'LL GET STONED!!!.... Two pulses of existing music are continuously re-generated per channel, each with a separately adjustable speed and volume control. It is the mix of these 4 pulses with their intermittent beat frequencies that will give you a new high or reinforce one you already have....... Every object and sub-object has a resonant frequency. The high achieved by the Stereo Pulse Modulator is a result of tuning in to your own resonant frequency."
All I can get it to do is make my stereo sound weird.


The Stereo Pulse Modulator is a technician's nightmare. All the parts are hard-wired together and crammed into a small space. I had to replace the electrolytics on each PULSE SPEED control and nearly went mad in the process. Why couldn't they use a circuit board? Who can tell?

If these were your thing, you could have bought them new in the early '70's for $49.95 for the Stereo Pulse Modulator and $59.95 for the Pulse Modulator. Prices now seem to be $200 and up for either of them. The Stereo one seems to be a little rarer.

Thanks to Kevin Macy for his help in procuring both these effects.