AJH Synth MiniMod VCO User Manual

Page 4

Square wave output. It has a level of +/-5 volts centred around 0v. The duty cycle

(amount of time the waveform is “high” against “low”) can be varied with the Manual

PWM control (15) or under voltage control (16). The output impedance is 1Kohm.

A control voltage can be applied to the PWM CV Input to vary the PWM duty cycle. The

control voltage range should be between +/- 5volts and the intensity can be controlled

between 0% to 100% with the PWM CV rotary control knob. A low frequency triangle

wave to the PWM CV Input will give the classic sweeping PWM effect. The PWM Shape

Control is still effective when using PWM CV and it changes the offset level.

Power Cable

A Tune Adjust :

Sets the default frequency for the VCO. This is a multi-turn trimmer that should be

adjusted with a fine jeweller’s screwdriver. Turn counter clockwise to increase VCO pitch

and clockwise to reduce the pitch. Adjusting this trimmer will not affect the scaling.

B Scale Adjust :

Sets the volts per octave scaling for the VCO. We do not recommend adjusting this

trimmer unless you have access to a very accurtate voltmeter and frequency counter or

chromatic tuner so that you can observe the effects of adjustment. Rotating counter

clockwise widens the scale and turning clockwise reduces the scale, only minute (less

than 1/4 turn) adjustments should be tried unless the scaling is badly out of adjustment.

C Octave Adjust :

Sets the volts per octave scaling for the Octave Selector Switch. The scaling and

frequency should be correctly adjusted before attempting to adjust the Octave scaling.

Set the Octave Switch to 8’ and note the VCO frequency, then set the switch to 2’ and turn

the Octave Adjust until pitch is exactly 2 octaves higher than 8’ setting. Rotating counter

clockwise increases the span and turning clockwise reduces the span.

D HFT Adjust :

FOR MANUFACTURER ADJUSTMENT ONLY. Specialist test equipment is needed to

calibrate this trimmer correctly.

E Shape Adjust :

FOR MANUFACTURER ADJUSTMENT ONLY. This sets the current level through the

P-FET transistor buffer and incorrect adjustment can halt the Oscillator completely, so

NO ATTEMPT should be made to adjust this trimmer.

Note:

This information is given for completeness, the MiniMod VCO is calibrated after manufacture

and under normal circumstances should not require any user adjustment.

Adjustment and Calibration

C Octave Adjust

HFT Adjust D

Shape Adjust E

Red Stripe aligns with -12V as shown

Scale Adjust B

A Tune Adjust

If you need any help using this module or have any technical questions please feel free to