The Tetra hosts four Mopho voices in an extremely compact housing, meaning you get an analog polyphonic, programmable and a very affordable synth. A closer look…
In 2002, Dave Smith decided to embark on a new hardware synth adventure in order to create instruments that would be pleasant to touch, program, play and hear… In those early days, he launched the Evolver: a small hybrid module that included digital waveforms from the Prophet-VS, as well as analog oscillators and low-pass filters. When it came out, nobody payed attention to a small integrated circuit in the unit: the DSI-120, which was developed together with Curtis — well-known for the VCOs, VCAs, VCFs, envelopes, and other integrated circuits he developed from the late 70’s to the late 80’s, and which glorified analog synths, transforming them into polyphonic and giving them more stability. It was this same DSI-120 that was used for every voice of the Prophet-08 in 2007, making “modern” analog polyphonic synths affordable back then. In 2008, the Mopho extended the already long career of the integrated circuit that provides no less than two DCOs, a low-pass VCF and a stereo VCA. By the end of 2009, DSI presented the Tetra — a Mopho on steroids including four DSI-120 circuits!
The Tetra is a bluish-gray compact module made out of rugged metal and fitted in the same housing as the Mopho. The housing is covered with a layer of Lexan (a printed, soft PVC sheet): the manufacturer says this solution is more expensive than standard silkscreen but adds features like higher printing definition, waterproof LCD and longer durability. The rotary controls have black “deluxe” knobs with chrome binding that remind us of the Prophet-5, but smaller. The Tetra features eight incremental encoders (pitch, attack, decay/release, select + four freely assignable encoders) as well as three potentiometers (volume, cutoff, resonance). All encoders have plastic axes, while all potentiometers are top quality and firmly mounted on the device. The choice of encoders or potentiometers for filter parameter control could certainly be discussed; some will prefer to edit signals accurately and without value drops or threshold effects, while others will prefer to get an immediate response over a short editing range. Dave Smith explains that customer feedback shows that most users choose the second option. Anyway, the potentiometers have three different responses: Jump (the edited parameter jumps to the value matching the physical position of the potentiometer as soon as you turn it), relative (the parameter changes smoothly according to the physical range still available) and passthru (the parameter changes only when the physical position of the potentiometer passes through the stored value). In the middle of the front panel you’ll find an easily readable, blue backlit LCD with 2 x 16 digits. The rest of the front panel is scattered with small selectors: playing mode, navigation (programs/banks), memory save, encoders’ assignment mode, editing layer, and note triggering (“Push It!” with activated LEDs when the Tetra plays back tones).
Ergonomics were no highlight of the Mopho… and given the number of parameters of the Tetra, they didn’t really improve that much considering that editing possibilities are now fourfold! cTo edit a sound, you can use either the row of five encoders/pots with hard assignment or the four freely assignable encoders. To assign a parameter, press the “Assign” button and turn one of the four encoders until you reach the desired parameter. Afterwards, push the “Assign” button again to exit assignment mode and go back to sound editing. Luckily, the assignment is saved with each program! When a program has two layers, push the Edit B / Combo button to access the second layer. In Combo mode, editing can be quite exasperating: it is impossible to access the four sound layers because each assignable encoder is dedicated to one of the voices (so you don’t have direct access to the three other parameters anymore) and the other pots/encoders control all layers simultaneously. Some of the first users have already asked for an OS update. Until then, you’ll have to use Sound Tower’s editor for Mac/PC (either the free “lite” version or the commercial “pro” version)…
Now, let’s take a look at the rear connection panel: separate phones output, four unbalanced audio outputs (including one stereo pair), Midi in + out + polychain connector (to chain up to four Tetras, or two Tetras and a Prophet-08), USB2 port (Midi over USB but no audio), external power supply (standard power supply with auto voltage detection and exchangeable connector). And that’s it? Yes, that’s it! No on/off power switch and, most importantly, no audio input to process external signals! An excellent solution to protect the Mopho… The Tetra holds two small PCBs: an analog board (for the four voices) connected to the motherboard that includes the digital circuitry (processor) and connections. Several remarks: the layout of the surface mounted components (SMC) and the assembly quality of the product are impressive (see picture). From the connection design between the boards we can easily envision several possibilities in other configurations. To be continued…
Now let’s get in deeper into the machine…
As a summary, the Tetra is a powerful polyphonic, multitimbral analog synth. Its price is very reasonable considering that this compact unit hosts a real sound synthesis monster with only a few direct controls. This, however, is also its main limitation because the design doesn’t allow direct and easy editing. Thus, the Sound Tower editor is indispensable. If you consider the Tetra’s outstanding sound quality and the lack of serious competitors, it ought to take you no time to understand that it is the perfect live instrument to complement digital synths and other cold-sounding workstations. So, when is the keyboard version coming out?
- Value for money
- Sound quality
- Compact and rugged housing
- Polyphony and multitimbrality
- Modulation possibilities
- Arpeggiators and sequencers
- Separate outputs
- USB2 interface
- Editing ease
- Limited Combo mode
- No audio input
- No on/off power switch
- External power supply
To read the full detailed article with sound samples please see: Tetra Review