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The OB-6 from Dave Smith Instruments and Tom Oberheim seems to have assumed the mantle of "most desirable analog poly" available. Together with the Prophet 6 which also uses true VCOs and analog filter. Both use the Curtis CEM chipset at their core. The OB-6 however differs from the P-6 in both the VCO waves available and the filter type, which is the classic CEM State Variable 2-pole filter.
We took advantage of the availability of the OB-6 desktop to get one in for review. In all respects it's exactly the same as the keyboard version, but with no keyboard.
What you get is a 2 analog VCO (+sub) analog 6-voice poly synth.
Starting with the VCOs - VCO 1 has Sawtooth through Square with a variable waveshape. Pulse width mod affects the wave in all positions apart from direct Saw. With a range of 5 octave tuning it is stable as you like (you can add detune to mess with that). The sub is a Square wave at -1 Oct - the P6 has a Tri wave sub.
VCO 2 starts at Triangle, through SAW then into Square -with PW taking hold after about the 12 o'clock position. It also has non keyboard tracking and LFO modes for additional modulations.
They sound pretty good - not up with sheer wight of some of new analog mono synths, but that's down to the Curtis SEM voice chip - which I have to confess never blew me away with it's VCO girth.
But that sounds like I'm dissing the sound, very far from it. It sounds lovely.
Unison lets you dial in up to 6 voices to mono with a detune and pan control adding plenty of extra width to the sound. Additionally there's a chord mode - hold a chord and press unison and that chord will sound on each note trigger - stored with each patch.
VCF - this is where the magic happens (or some of it) as an SEM filter you get "that" sound - the variable mode through Low Pass through Notch and into High Pass is a thing of beauty. Theres also a switch to take the filter into Band Pass mode. Resonance adds some lovely colour and familiarity to the sound, but remember, it's not self resonant. You don't appear to be able to drive the level into the filter - but again, thats not what this is about. The SEM filter just sounds great, a really specific smooth phasey sound you just can't get anywhere else. Modulating the Mode parameter is just wonderful.
First up there's a single global LFO syncable, with a wide range - well into audio rates, though there's no delay feature and it is only one LFO, not one per voice. Routing allows you to do plenty - PWM, VCO1, VCO2, Filter Freq, Filter Mode and Amp are the destinations.
The waves are either Uni Polar or bipolar depending on the wave:
Sine= Bi-Polar, Saw = Uni Polar, Rev Saw = Uni, Square = Uni, Random = Bi
Particularly effective when modulating pitch and requiring fixed intervals while still using the base pitch of the VCO.
Two ADSR Envelopes - one hard wired to VCA, one to VCF, though you can route other parameters to it via the poly mod section. This is something that is common to the P6 architecture and really opens up the potential.
Poly mod takes VCO 2 and routes it to 6 possible destinations (both +/- depth). VCO 1 pitch - for some great Xmod sounds, Shape VCO 1, PW 1, Filter Freq, Filter Mode, Norm-BP mode. This section really takes the synth into some beautiful and esoteric places, it also allows you to have effectively 1 LFO per voice allowing for separate modulations per voice. You can also route these destinations via the VCF envelope.
With a wide range of clock divisions of the master tempo, you should be able to find the clock type you want. With 4 Oct range, the usual patterns, you can get some great riffs going especially when combined with a clock linked delay via the FX section.
Sequencer is polyphonic and lets you record up to 64 steps, again stored per patch. Recording is only in step time, with rests and ties input via the inc/dec buttons either side of the LED display.
Transposing the sequencer - hold the REC button and play the note.
Sequences are also stored with each program.
With two DSP engines (A+B), you have a decent amount of algorithms:
BBD, DDL, Chorus, Flanger 1, Flanger 2, Phaser 1, Phaser 2, Phaser 3 - model of Tom Oberheim's 6 stage phaser, Ring Mod - another of Tom's original designs modelled, Hall, Room, Plate and Spring.
A good selection with some nice sounding algorithms, though I would have liked to have seen a more extreme reverb - you know epic...
Delay times can be tempo locked too.
Additionally there's a stereo analog distortion - which lets you get pretty gnarly and extreme if you want it.
Connections: Stereo Out, Phones out, Sustain pedal, Seq start/stop, expression pedal inputs for Filter and Volume too. Nice to see MIDI In, out and through, plus a USB connection for MIDI to DAW.
Memories - there are a whopping 999 patch locations here with 10 banks of 99 patches - selected by the old-school led tab style buttons.
On the face of it the OB-6 might seem lacking in a few modern features, split keyboard, LFO per voice, LFO delay, but honestly I'm not sure that matters. As an instrument it's very compelling, with a great range of highly usable sounds. It's an instrument you can really connect with. It's sound is so familiar, evocative of an entire era of synth sounds, but also perfectly able to take you into other territory. I know it's an expensive item, I mean $2,299 / £1999 is just a LOT of money. But it's the real deal.