The modulation oscillator is a sine core design, with auxiliary outputs at double the frequency. For the unfamiliar, Sine and Cosine are the same basic waveform, though separated in the time domain by 90° (1 quarter of the wavelength). If Sin were to be mapped onto the X axis of a graph,and Cos onto Y, the combination of the 2 waves would draw a circle. The outputs of the mod osc are labelled SIN, COS,2SIN and 2COS. Low distortion was the objective of this design, as during FM any distortion in the modulation waveform quickly creates additional sidebands in the carrier output. In some instances these additional sidebands may be perceived to be desirable in harmonic relation to the output signal, but equally they may not be. High waveform accuracy in combination with the auxilliary second harmonic puts the decision into the hands of the user. Measured distortion performance is approximately -90dBc (largest distortion peak is 90dB lower than the fundamental).
The variable harmonic oscillator has 2 outputs, F(X) and ΣF(X)dt, which can be viewed similarly to the 0° and 90° SIN and COS outputs, and likewise would draw circles. The 2 outputs patched on each side of the stereo field gives a pleasing effect.
The variable harmonic circuit is a fully analogue implementation of a wavetable type oscillator, with a multifrequency output of a cluster of sine waves. The Evolve parameter effectively detunes the oscillator against itself giving control over the sines that make up the output signal. Control over specific partials is outside the of the constraints of the design, and unlike typical wavetable oscillators the range of tonalities may seem limited, for example it is not possible to move abruptly between crystalline and abrasive tonalities. The motivation behind the design was to have the musicality that fully analogue computation in known for, with a focus on just a handful of absolutely necessary features, combined with calibrated controls to give access to harmonic relationships. Careful, deliberate playing, especially combined with the use of FM will give good results.
Each oscillator has two 1v/Octave inputs dedicated to it that are summed together, under the row of 4, the 2 on the left are for the Sine oscillator and 2 on the right are for the variable harmonic. The outermost inputs on each side have a switch underneath that can invert the signal (so the values from your sequencer are subtracted instead of added). The Evolve harmonic control also has a calibrated 1v/oct input with switch. Successful FM patches may involve using the on board multiple jack to control several aspects of the voice in parallel, for example applying the output from the sequencer to the carrier and modulator will give the same results that are found in classic FM synths like the DX7 and software based on them. An additional sequencer controlling the carrier or the modulator can dynamically vary the ratio.
The carrier oscillator is relatively limited in it’s range compared to other analogue oscillators, working at a fundamental frequency of 1hz to 6khz . Harmonic control allows output frequencies many octaves above this. Temperature compensation of the exponential converters that determine 1V/oct response and frequency stability is done with active sensors, meaning drift is as low as is possible for an analogue design.
It is not possible to damage the module through ordinary patching, including accidental patching of output to output.
Current consumption is +/-250mA. Operation voltage is +/-15V
For correct operation 0V / signal ground on the power supply must be linked to mains earth. Please ask for advice regarding correct installation if unsure. Hinton Instruments Full Power PSU exceeds the necessary requirements for a low noise, reliable and safe supply.
Output impedances 100 ohm. Input impedances for audio and ordinary control are 10k ohm. 1v/oct are many Gigohm.
Audio output voltages are +/-5V (10V peak to peak).