SYN2B – Quadrature Sine
The SYN2B is a wide-ranging and high stability / purity Quadrature Sine-wave Voltage Controlled
Oscillator module. It's main features are:
•
10-turn tuning dial covering a 10 octave range
•
Osc or LFO rates
•
1V/Oct input (0.1% summing resistors) + variable depth FM input switchable between
Exp(onential) DC-coupled or Lin(ear) AC-coupled
•
accurate tracking (less than 0.1% error) over 8 o temperature compensation
•
four bipolar (-5 to +5 V) outputs at 0/90/180/270 degree phases with bipolar LEDs
The module is set up such that one rotation of the tuning dial raises the pitch by 1 octave (ie. Doubles
the frequency) with the zero point of each rotation (see scale on the dial) giving tuning to approximately
A (ie. 440Hz etc.) in VCO mode.
Via the tuning dial, ranges are about 13.75Hz to 14.08kHz in Osc mode and 0.014Hz to 14Hz in LFO
mode. But ranges extend well beyond what is set by the tuning dial – approximately 1V above the
upper range and at least 5 octaves below the low range (thus, by applying a -5V DC signal you could
get the LFO mode to cycle around 30 minutes!).
Typical tuned Osc FM operation can be achieved with the pair of SYN2Bs – both receive the same
1V/Oct signal and then one is used to FM the other in Linear mode. Note that detuning can occur on the
FM'd VCO when the modulation is dialed above about 1 o'clock – the input could have been attenuated
to prevent this, but it was felt that the possibilities of the stronger modulation settings should be kept.
You can also achieve richer waveform timbres by Self-FM – patch an output back to the FM CV input
and adjust Linear FM depth to suit. Using different phase outputs as the self-FM signal will give different
end results – ramp waves or parabolas.
A quasi noise source can be achieved by cross-modulating the two modules – set both to Osc mode,
connect an output from each module to the FM CV input of the other module and set the FM to Exp with
the dial turned up full. Experiment with different rates on each Osc then try turning down the FM depth
to bring back in pitch effects.
Note that in LFO mode it can take a long time for oscillations to get going when the system is first
switched on – this is the nature of the circuit as the oscillations basically reinforce themselves to build
up to full amplitude. The simplest way to get oscillations going is to apply a +10V signal to the 1V/Oct
input until you can see that the LEDs are showing oscillation. Once you have got the oscillations going
you can freely switch between LFO and Osc modes without having to repeat this step.
There are three trimmers on the back of the module for fine-tuning but these have been accurately
adjusted at testing and should only be adjusted when you are sure that they should be.
–
tuning offset
can be used to shift the base range of the tuning dial (eg. It is currently set so that
each 0 rotation point gives an A in Osc mode, but you could adjust it so that C is the zero point)
–
V/Oct Scale
adjusts for accurate tracking but please ensure that your source (eg. External
keyboard or Midi-to-CV) is accurately tuned before adjusting this
–
Hi-Freq Trim
is also used for accurate tracking as the Exponential Converter section will detune
at high frequencies.
An Allen Key is also supplied with each module in case adjustment of the tuning dial is required.
