Sometimes near enough just isn’t good enough – we have to have precision. Eurorack modular synthesisers use the Volts per Octave standard for pitch control, where a change of exactly one Volt in pitch CV results in an exact one octave change in pitch from the oscillators. Even small inaccuracies in voltage can lead to quite large changes in pitch, so for transposition and control voltage addition it is important to have a very accurate voltage source and adder to keep everything in tune.
The AJH Synth Precision Voltages can be used as a super accurate voltage source, voltage adder or both at the same time. It has two channels to which voltages representing Octaves and Notes can be added or subtracted. If there is no input to a channel then it behaves as is a voltage source, or if an input is added to that channel then it becomes a very accurate voltage summer that can add a precise voltage to the incoming voltage.
Channel A also allows an external Gate signal to be used to turn on and off voltage addition while still passing the input signal to the output unchanged. We also have a useful Combination Mode, where channel B can be added or subtracted from Channel A.
A calibration output is also included which has an accuracy of +/-0.5mV so that it can be used instead of expensive test equipment to calibrate VCO’s and similar modules.
A few uses for the Precision Voltages Module:
The Precision Voltages can generate extremely accurate voltages, and can also add a very accurate voltage to an incoming voltage. It can also add two (or subtract from one another) two incoming voltages and add a fixed voltage too by using the OUT channel.
Typical uses would be:
1) Feeding the output from a sequencer to the IN A, we can then either add or subtract octaves and notes to this control voltage which is routed to OUT A. This way we can very easily transpose the incoming Pitch CV up or down by both octaves and in half note increments too.
2) Adding accurate octave switching to VCO’s that do not have an Octave switch. Many Eurorack VCO’s (excluding the AJHSynth MiniMod VCO) only have Course and Fine Tune controls, and do not have an Octave transpose switch. To add this feature to a VCO simply patch the V/Oct CV pitch voltage to the Precision Voltage IN A and patch the Precision Voltage OUT A to the VCO 1V/Oct input – you will now have both Octave and Chromatic Note adjustment for the VCO.
3) Precision addition or subtraction of two voltages. Connect one voltage source to IN A and the second Voltage source to IN 2. Ensure that the A+/A- and B+/B- switches are centred so that no internal voltage is added to either of the incoming voltages. The COMBINATION MODE switch can be used to accurately add togther the two voltages (A+B position), or subtract one from the other (A-B position) and the resultant voltage is routed to the OUT jack.
4) Calibrating VCO’s – We use the Precision Voltages Module here at AJHSynth to calibrate all of our MiniMod VCO’s – yes, its accurate enough to be used as a piece of test equipment! This is the purpose of the CAL output – it uses a super accurate voltage reference and low tempco resistors to give an astonishing accuracy from 0 to 10V range of +/- 0.1mV, and this level of precision makes it perfect for calibration, or re-calibration of oscillators.
Power: 25mA @+12v / 15mA @-12v