Saturday, 18 July 2015

Most Hazarai

Deriving a Beat clock and End of Loop pulse from the Electro-Harmonix ‘Stereo Memory Man with Hazarai’. An update to these previous posts.


I recently attended a talk with Charles Cohen, a musician who has improvised with a Buchla Music Easel for several decades. The Easel is a monophonic instrument but Cohen’s music is multi-layered. To achieve this, he uses long, looping delays to record in a ‘sound-on-sound’ fashion. In Berlin, he used an Electro-Harmonix ’16 Second Delay’, a vintage pedal that’s long out-of-production. A modern equivalent which is also capable of looping is the SMMH.

A stock SMMH will record loops and allow the user to over-dub. It’s fine for guitarists or other manual players, who can keep time with the previously recorded ‘template’ loop. But what if you want to record a clocked sequence from a modular? Laying down the first loop is simply a matter of starting and stopping the recording in time. The problem arises when you want to add a second layer. Although it may be at the same speed, it will probably be out of sync.

I didn’t realize this limitation until I tried Charles Cohen’s layering technique at home. He didn’t seem to have this problem, so what to do? I found a solution that requires a simple modification to the SMMH and - from watching Cohen improvise - a change in playing approach.

Here's what's possible: ehx-smmh-looper-mod.mp3


Unlike the ’16 Second Delay’, the SMMH does not have a clock output. However, its Beat and Loop LEDs do keep time, so this gives us the possibility to derive a clock and, importantly, a reset pulse from the logic signals that drive them.

If we unscrew the base of the SMMH and then compare the positions of these two LEDs with the PCB, we can see where their legs protrude (see above JPEG). If we locate the current limiting resistor R27 + R30 we see that each is linked to a ‘via’, or tiny hole in the PCB. This is where I chose to extract the signal by inserting and soldering a slim solid-core hook-up wire. You could use stranded, but solid gave me an easy, snug fit. A 1K output protection resistor could also be inserted here. I later added mine to the connection at the output jack.

As with the previous SMMH mod, I chose to drill holes in the enclosure with the PCB still mounted as it’s difficult to remove. I protected the PCB with paper and, fortunately, it survived.

In Use:

So, what do we have? The Beat clock is as we expect, but the Loop pulse goes high at the end of the loop. To use it as a reset signal for a sequencer we need to condition it. I use an A-162 Trigger Delay to stretch the pulse just long enough for it to overlap with one of the Beat pulses. This allows me to 'AND-combine' them in an A-166 Logic module. This gives a pulse on the first beat of the bar/ loop. I may find other workarounds or a fix, but for the moment this patch works well.

There’s one last mod I could envisage: a switch carrying 5V to hold the SMMH in perpetual record mode, like the 16 Second Delay. As I already have a trigger input, I just feed it a gate from one of the A-166’s inverters. New material can be added by opening a mixer’s Aux send.

Playing Technique:

Charles Cohen seemed to meditate before playing, taking a moment to consider his next performance. Having done this modification, I now wonder whether this artistic reflection might also have had a technical reason. On the SMMH, the Beat LED does not start pulsing until after the first, template, loop has been recorded. This gives us the opportunity to set the loop length and tap tempo before recording properly: just activate the loop with no signal and ‘record’ a blank template. Yes, that means we also gain a tap-tempo clock!

This modification is a ‘hack’: it’s quick and simple and opens up new possibilities. The great thing about the SMMH is that we can also record the effects in loop mode. Using the SMMH’s looper, I’ve been surprised by how little equipment I need to make interesting music - many of the quick ditties in the above demo were recorded with just one VCO, a set-up not too dissimilar to the Easel used by Cohen.