Beers DAC Transposer/Sequencer
Beers DAC
This module generates 1V/octave CV by summing together different intervals (12ths of a volt) via a simple Digital to Analogue Converter circuit. The resistor values in the digital to analogue converter are weighted to generate reasonably accurate V/oct control voltages. (*I wouldn't dare call this design 'precise' unless you sub in a fancy opamp for U5 and add a bunch more trimmers)
The 'digital' inputs are actually analogue comparators that convert any synthesiser signal that crosses +1V into an either 'ON' or 'OFF' state.
There are no microcontrollers or dedicated ADC or DAC chips involved.
The +12 input adds 12 semitones, or 1V.
+1 input adds 1 semitone, ~83.33mV.
The inputs add together so if +5, +4 are active at the same time the output
will be 9 semitones of CV (750mV).
All inputs active gives ~2.583V, 31 semitones above 0V. This gives DAC the range of a small keyboard, but much trickier to play. Getting the right combination of active inputs sequentially to play a specific melody you have in mind will likely be prohibitively complicated.
On the other hand, feeding it unrelated clock/LFO signals from all over your synthesiser can result in nonsensical phrases you'd never have thought of on your own.
Playing it safe with a clock divider module and just the top three or four inputs generates pleasant arpeggiator-esque sequences.
The inputs for activating each interval can be fed gates or any other signal greater than 1 volt. With a switch down, signal applied to the input will add that interval to the output.
With the switch up the logic is inverted (like a 'NOT' logic gate) and the interval will be added when the input is <1V.
With no signal plugged in you can use the switches as a manual ON/OFF for each interval.
The bottom input IN is summed with the generated CV so the module can be used to transpose up the output of a sequencer, keyboard, or anything else you want to shove in there.
Since DAC only generates positive voltages, negative transposing can only be achieved by tuning your VCO with desired intervals active, then deactivating them to transpose downwards.
6HP. Current draw: +12V: 19mA, -12V: 1.5mA
https://www.modulargrid.net/e/beers-dac
Calibration:
ADJUST TR1 FIRST (on the right, nearest OUT jack)
If you have a multimeter, set all switches down except +12, don't plug anything into any input, adjust TR1 until the voltage on OUT is as near to 1.000 volts as you can measure.
Alternatively, plug OUT into the 1V/O input of your favourite VCO and adjust TR1 until turning on +12 increases pitch by one octave.
+12, +7, and +5 up should add 2 octaves, +4 should be a major 3rd, +7 a 5th ect.
When happy with TR1, adjust TR2 (left, mearest IN jack) until a voltage applied to the bottom IN
jack comes out the same voltage on the OUT jack (with all switches down and nothing else plugged in).
One way to do this is to plug a gate or other stable voltage into V/oct input
of your VCO, tune to a note, then move the patch cable to IN and connect OUT to your VCO. Adjust TR2 until you get the same note you had without DAC in between them. Simpler with a multimeter-make sure the voltage going to IN is the same coming out.
Assembled modules will be shipped calibrated but in some cases you may want to fine tune it with a particular module, or the calibration may drift slightly over time.
These kits and assembled modules are offered on demand, click the link to learn more.
| Module Parameters | |
| Format | Eurorack |
| Panel Size | 8hp |