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SYN2A - Utility VCO


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The Rev.2 version SYN2A has been renamed Utility VCO (voltage controlled oscillator) - it is a compact but very capable source of oscillations, both audio rates and low frequencies.

The core circuit of the SYN2A generates Triangle waves and these are then waveshaped to produce Ramp(ish) waves and Pulse waves - these two functions working in tandem via the WaveShape control with CV modulation.

The SYN2A is not focused too heavily on wide tracking (standard 1V/Oct response) but has good tracking over a typical 4 Octave range and it is also temperature compensated. The Range switch offers three ranges - Hi is for typical Audio VCO duties with a frequency range of around 5Hz to 11kHz, the middle setting gives fast LFOs and the Lo setting gives slow LFOs with the longest period being around 90 seconds per cycle (0.011Hz)

There are two CV inputs for Frequency Modulation - one offers standard un-attenuated 1V/Oct Exponential response while the other has a modulation depth control. Via a jumper on the rear of the module, the 2nd input can be set as either Exponential or Linear response.

As mentioned, the Wave Shaping affects both the Saw and Pulse outputs - for the Pulse output this can be seen as Pulse-width modulation (PWM). The effect is interesting on the Ramp wave - see the waveform diagram for an illustration. At either extreme the waveform is a ramp at the same frequency as the triangle, but with the phase shifting so that the clockwise setting is 180deg. out of phase with the counter-clockwise setting. In the middle the frequency is doubled, giving a noticeable sonic shift. It is also possible to push the ramps into squarewaves by modulation 'beyond' the manual Waveshape limits. Note that the waveforms are best described as 'Ramp-ish' because there is amplitude limiting in action to keep the output regular and this results in slightly rounded waveforms - it sounds great though!

The Sync input allows syncronisation of the VCO to any input signal - there is an input comparator so any signal rising above c.+1V will reset the Oscillator.

It should be noted that there is only a coarse tuning dial (Freq), not a fine tuning adjustment - that is why I see this module more as a Utility VCO. An expanded Master VCO (SYN2B) is planned with further features.

Output: -5 to +5 V
Width: 1FW
+40mA / -25mA
User Adjustments:
1V/Oct tracking is set after production, but can be adjusted by the user if required - typically only the V/Oct trimmer (see image) should be adjusted, not the Hi-Trim one. There is also a jumper to select whether the Freq CV response is Exponential or Linear.

Added on Thursday 17 February, 2011.