Wednesday, April 21, 2010

New Large-Format Modules and Manufacturers

A while back in this blog, I wrote a post lamenting the lack of modular manufacturers getting involved in large-format (specifically, the "5U" formats -- MOTM, Dotcom, and Modcan-A) modules. All of the action seemed to be happening in the Euro format, and I was getting a bit concerned for the future of large format.

But since then, there have been quite a few new makers jump into the "large market": Curetronic, Rob Hordijk, Moon Modular, MOS-Lab, and STG Soundlabs are all building to the 5U format. And what's encouraging is that most of them are not just building "me too" modules, but are actually applying original thinking to the format. Although, so far I'm not seeing the variety of out-there designs that one sees in Euro... but that might not be a bad thing. At least there haven't been any major scandals involving any 5U makers. (And guys, let's try to keep it that way, please?)

I'll take a look here at two of the most recent entrants. The first of the new contenders is Megaohm Audio, and first up is their Delta VCF. Megaohm advertises this as being a new design and not a clone of an existing filter, which is certainly welcome -- I think the synth world has just about all of the Moog-ladder clones it needs. From the block diagram and the board layout, it appears that this is a 4-pole OTA-based design. Also on board is an auxiliary VCA, going along with a recent trend to include VCAs on modules whose primary function is something else. It often seems as if modulars never have enough VCAs when doing complex routing, so I don't think anyone will complain.

Delta VCA -- photo from Megaohm Audio's Web site

The module is packaged in a 2U width Dotcom format. The panel layout is attractive and fairly well organized, if somewhat busy. The filter has a two-input mixer for audio in, and the input level controls, instead of the usual setup of unity gain at full clockwise, have unity gain at the 2 o'clock position and full CW is a gain of 2. That can be a useful feature when you are doing severe filtering and you are having problems with low output level, or if you want to overdrive the filter. The FM 1 input jack has an attenuator that can select inverted or non-inverted input. The FM 2 input is designed expressly for audio frequency modulation of the cutoff; it is AC coupled and switchable for linear response. The filter also has a 1 V/octave output; the manual notes that it is calibrated over about four octaves.

There's an interesting normalling loop. The filter's output is normalled to the VCA input. The VCA's output, in turn, is normalled to the FM 2 input. This means that if you feed the VCA a control voltage, and nothing is plugged into the normalled jacks, the filter's output is fed back to the FM 2 input. You can of course use the VCA for other purposes, although the normalling creates the oddity that if you are doing so, and you aren't using the FM 2 input, you need to insert a dummy plug into the FM 2 jack.

The filter is switchable between lowpass and bandpass response. There is no voltage control over resonance. However, you could use the VCA to create it: patch the VCA's output back into one of the filter inputs, and then apply control voltage to the filter to control the feedback.

It appears that quite a few large-format users are building Frankensynths these days, accommodating more than one format. Accordingly, you find a variety of power distribution schemes. Megaohm realized this and provides both Dotcom-style and MOTM-style power connectors. Very perceptive on their part! They ship the module with a cable that connects to a Dotcom octopus cable, but for a few bucks extra, they will provide a cable that connects to a MOTM 4-pin power distribution board.

The other module Megaohm is currently offering is the LFO Two. This is a slightly odd combination of two dissimilar LFOs in a 1U-width Dotcom format module. Like the Delta VCF, it has both Dotcom and MOTM power connectors.

LFO Two -- photo from Megaohm Audio's Web site

The top LFO is based on a Korg MS20 design. It outputs square/pulse and triangle/ramp signals, through separate jacks (there are actually two jacks for the tri/ramp output). A shape control affects both the pulse width of the pulse output, and the shift between up ramp, triange, and down ramp on the tri/ramp outputs. Shape is not voltage controllable. This LFO is designed to run slowly; in the "hi" position of the three-range switch, range is from "just below audio" (presumably around 20 Hz) to one cycle every 30 seconds. There isn't much apparent difference between the "medium" and "low" range positions; both provide maximum cycle times of a few minutes.

The top LFO is hard-syncable via a reset jack. The bottom LFO can also be synced to this jack, if a circuit board jumper is moved; more about this in a moment. The bottom LFO is said to be based of that of the ARP Odyssey. Its outputs are square and, oddly, sine -- no triangle or ramp. There is no shape or pulse width control for this LFO.

An interesting feature of the LFO Two is the extensive set of options controlled by moveable jumpers on the circuit board. By moving them, one can, for example, select the peak-to-peak output voltages, what phase the top LFO advances to on reset, and whether or not the bottom LFO responds to reset. One useful option makes the pulse output of the top LFO a positive-going-only signal, which is what you want when you are using it as a trigger, gate, or clock. There's also a range selection for the bottom LFO. It would be a fairly simple matter to DIY an auxiliary panel and patch many of these options out.

The other recent arrival on the large-format scene that I want to discuss is Grove Audio. This is a company that has been known in the pro audio area for a while, but they are now taking the plunge into modular synthesis. Their two current offerings are the GMS-782 Dual LFO/VCA and the GMS-725 four-channel mixer. Both are packaged as 2U width Dotcom format modules.

GMS-782 -- photo from Grove Audio's Web site

The GMS-782 has two halves, each consisting of an LFO and a VCA. Both halves are identical. The panel layout is visually pretty clean, considering how much is going on. The LFOs are voltage controllable, and have sine, square, and triangle outputs on separate jacks. There is a high range and a low range; with the switch in high, frequency range is from 100 Hz to about one cycle per minute. The low range divides the rate setting by 10, which didn't seem that useful until I thought about it some; that's a low end of about one cycle per 10 minutes! And on the high end, I admit to having a preference for LFOs that can go at least a little ways into the audio range; I like to use these to drive VCAs for AM effects. However, there is no pulse width or shape control; hence no ramps. Each half has a trigger (reset) jack for hard sync.

The VCAs can be used to have voltage control over the level of the LFO output. Each LFO has its output wired into a VCA; a three-position rotary switch selects which waveform is fed to the VCA. The problem here is that the VCA input is not patchable, so the VCA is not usable for other purposes, which decreases the utility of this module some. The rotary switch takes up a lot of room on the panel, and if I were DIY hacking this, I'd take it out, put in a normalled VCA input jack, and put in a three-position toggle switch for selecting the waveform normalled to the VCA input.

The other Grove Audio module is the GMS-725 mixer. This is pretty straightforward; it contains a four-input mixer with each input having its own attenuator.

GMS-725 -- photo from Grove Audio's Web site

The nice thing here is that there is also a master gain control. Also, there is a DC offset control that can add or subtract up to 5 volts to/from the output. And there are inverted and non-inverted output jacks. Very neat. Further, there is a separate attenuator with its own input and output, and its own DC offset control. This looks very useful as a control voltage adder/mixer, and the default configuration comes with linear pots on the attenuators for that purpose, although you can optionally order it with audio-taper pots.

It's good to see new manufacturers entering the large-format arena with fresh ideas. It will be even better if these fresh ideas can be implemented while maintaining the quality standards that have become expected in the large-format community. These appear to be a good start.

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