Analog Synth Modules | Big Sounds in Small Packages

Apr 9, 2010 1:48 PM, By Gino Robair

           
 

FOUR PORTABLE ANALOG SYNTH MODULES THAT WON'T BREAK YOUR BUDGET

Clockwise from top: Tom Oberheim SEM, Patch Panel edition; Dave Smith Instruments Tetra; Doepfer Dark Energy; and Dave Smith Mopho

Photo: Bill Schwob

As interest in analog synthesizers continues to increase, more and more manufacturers are getting into the game. The world of modular systems, in particular, is exploding with new products, especially in the Eurorack format.

But whether it’s a keyboard or a rack of modules, an analog synth can take up a lot of room. Sometimes you just need a simple synth voice—an oscillator or two, an LFO, a filter, an envelope generator, and a VCA—in a portable package to put that fat bass line, searing lead, or space-age burbling where you want it. That’s where a standalone synth module comes in handy.

These modules offer subtractive synthesis in a small footprint, providing the perfect complement to a DJ setup, a laptop rig, digital keyboard workstation, or the digital plug-ins in your DAW. Although all-in-one modules date back to the ’70s, technological advances over the years have allowed manufacturers to make them smaller and more powerful and increase their stability, without sacrificing the vintage tone.

Bonus Material

Dave Smith Instruments Prophet '08 Review

Dave Smith Instruments Mopho Review

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In this article, I examine three single-voice, analog-synth modules released in the past few months, as well as a related 4-voice module, all of which are priced less than $1,000 (some considerably so). I admit that comparing the features of these instruments is very much an apples-to-oranges-to-bananas affair, but this isn’t a shootout to see which synth ranks highest. Rather, I want to show the differences in design philosophy because, on top of the sound quality of an instrument, the voice architecture and feature set inspires each musician differently.

Let’s begin with the instrument that has the longest pedigree.

Tom Oberheim SEM
Designed in the early ’70s to inexpensively augment monosynths by ARP and Moog, as well as support the company’s digital sequencer, Oberheim’s Synthesizer Expander Module (SEM) offered a basic feature set with a distinctive sound that has remained popular over the decades. The instrument’s creator, Tom Oberheim, has finally given in to the pressure of friends and fans by reissuing the SEM, following the original specifications as much as current parts availability would allow. Yet, like any restless developer, he took the design a little further by adding a few welcome features.

FIG. 1: The Tom Oberheim SEM, Patch Panel edition, adds 33 patch points for increased sonic control.

The Tom Oberheim SEM is available in three configurations: the Patch Panel edition ($899; see Fig. 1), the MIDI edition ($899), and the Panel Only edition ($599). I received the Patch Panel edition for this roundup because the MIDI edition wasn’t shipping yet. But that suited me just fine as I prefer to work with patch cords. Because many readers will want to know to what degree the new version resembles the original, I will compare features between the two.

The classic SEM had a straightforward synth-voice architecture, with two VCOs; two 3-stage envelope generators (EGs); a 2-pole (12dB per octave) multimode, resonant filter; a sine-like LFO that goes into the audio range; and a VCA. The audio and CV I/O were on 3.5mm jacks. The new SEM is exactly the same, with a nearly identical front panel in layout and size. The main physical difference is that the new SEM isn’t as tall as the original, but the left panel adds an extra 2.25 inches to the module’s width. Both have rear panel power switches, and the new version has a rear panel ¼-inch output, which means you don’t need a 3.5mm-to-¼-inch adapter to use the module with a mixer or amp.

The SEM’s front panel has a slightly unusual layout. Each VCO can produce a sawtooth or pulse wave, but the waveform is selected in the filter section. The knob is actually a level control: Fully counterclockwise gives you the sawtooth at full volume; at the 12 o’clock setting, you get no signal; and the pulse wave is at full volume when the control is fully clockwise. At full level, the VCOs overdrive the filter in a very musical way. Each pulse wave can have its own duty cycle (10 percent to 90 percent), as well as individual pulse-width modulation or frequency modulation using the LFO or EG.

Another interesting design feature is that the knob that selects the filter type is continuously variable, from lowpass through notch to highpass. In the original version, the control would click into bandpass mode in its full counterclockwise position. The update has a separate bandpass switch.

The filter’s cutoff frequency can be modulated (positive or negative) by the LFO, Envelope 2, or an external source. Thankfully, the new SEM has separate controls for fine- and coarse-tuning of the VCOs. The vintage model had dual-concentric pots that stacked the tuning controls. (Fine-tune was on top of the coarse-tune.) Everyone hated them, including Oberheim, because it was easy to accidentally bump an oscillator out of tune.