Precision DC

Type: Module

Category: Utility

Updated: Sep 08, 2020

Manufacturer: MRB

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During the development of the Luxury Filter Bundle, I created this very helpful module to aid me in the effort. It saved me so much time and trouble in evaluation and calibration that I decided to make it available to the Voltage Modular community in the hope it will do the same for everyone else. It is primarily aimed at folks who are writing their own modules, but I'm sure it can be of use to anyone. Owners of the MRB Laboratory Bundle will get this free.


The module has 2 sections, a precision DC voltage source and a frequency counter.


Simply dial in each digit of the desired voltage, select either positive or negative polarity and that DC value is output. The range is +/-9.999v and the voltage is remembered in a preset. Since the first digit is integer volts, it will make a VCO do exact octave jumps regardless of the setting of the other digits. If you need a higher voltage for any reason, just use multiple instances of this module plugged into the same jack -- they will add. This technique is also useful for "base and offset" type work.


The frequency counter has 3 modes which require a little explanation. There are 2 main ways of measuring frequency, the time gate method and the calculating counter method. The first mode, labeled 1sec GATE, counts the number of input cycles (actually positive going zero crossings) that occur each second. This count is the frequency, and the numeric readout is updated with a new value every second. This is the way virtually every frequency counter you buy operates.

The next 2 modes, labeled CALC FAST and CALC SLOW use the calculating counter method. This method does not count input cycles directly, but instead counts how many ticks of a high frequency clock fit into each cycle of the input signal. This number is the period of the input which is the reciprocal of frequency (seconds per cycle rather than cycles per second). A simple 1/P calculation (thus the term calculating counter) yields the frequency, and you get a new value every cycle. Since the only high speed clock available is the 48KHz sampling rate, it is used as the clock. This is adequate for low to medium frequency signals and you can watch the readout track frequency changes very quickly. In order to get an accurate reading, the output from the calculation is time averaged with your choice of FAST or SLOW time constants.

Because of the vagaries of frequency counting in general, there may be a 1 or 2 count difference between the modes.

Caution: This module counts zero crossings, so if you want an accurate reading, don't input complex waveforms from things like wavetables or resonant filters that might have an unpredictable number of zero crossings per cycle. If you want to measure a waveform that doesn't cross zero at all, you can bias it up or down a little (maybe with the voltage source in this module or the Cherry DC module) so that it does. Just plug both the wave and the DC bias into the IN jack.

I hope you can put this module to good use and that it helps you as much as it did me.