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Showing posts from January, 2023

Eurorack Voltage Detector

 This is a Eurorack Voltage Detector module design. The idea for this comes from combining two previous modules I designed; the Level Display module and the recent Comparator module. This module uses op-amps in the comparator configuration to compare a signal against several reference voltages and display the output of the comparison on an LED.  The voltage levels compared against are approximately: ±9.8V, ±4.9V, ±3.2V, ±0.9V The module has two independent sets of comparators so two different signals can be plugged in at the same time.  The main use for this in my rig is when interfacing modules from various manufacturer's the acceptable input voltages aren't always the same and it's annoying to have to look that up for each module. I usually remember to add the output voltage range in the engraving on my panels so there's no guess work, others don't usually do that. This module will let me quickly see what voltage a signal is at and attenuate/amplify it as needed

Eurorack Comparator Module

 A Eurorack Comparator module in 6HP. Like the Analog Switch  this module comes from my journey to create a noise gate with modules. Most of my attempts to make a monolithic noise gate have required some form of comparator to determine when the signal goes above (or below) the noise floor, so making it an independent module is likely to be useful. The core of this module is a dual comparator LM393. The input signal is rectified by the op-amps that buffer the input so both inputs on the comparator are operating in the positive range but one of them is the negative half of the input and the other is the positive half. This creates a window from -LEVEL to +LEVEL where the comparator outputs GND and if the input goes above/below  ± LEVEL the output is 10V (or 5V if desired). I made several simulations of the circuit to improve idle noise issues and allow adequate adjustability of the desired level to detect. The latest simulation is here . There's a simple RC filter on the signal input

Eurorack Analog Switch Module

This design comes from a long term project/idea to make a noise gate for Eurorack. I've attempted several designs for a noise gate over the last year but haven't been happy with the result (yet). In the latest attempt I used an analog switch and a comparator and had some success. I decided that those two parts of the noise gate would be fine as individual modules so that's where this came from. It's really a very simple module, there's a buffered input and ouput and a gate input to turn the switch on or off. When it's on the audio or whatever input signal is passed through to the output. The schematic calls out the DG418LDJ (normally open) analog switch. The DG417 should work as well for a normally closed version. The gate circuit is using a few generic NPN transistors to turn whatever the gate input is into a sharp 5V logic signal for the analog switch. There's a simulation here . Of course the design started on the bread board. Then I designed and ordered