# Making a DIY inverter

Hi there,
I made a Shruthi, a Shruthi XT and an Anushri few years ago and I’m very happy with them. Last year I’ve started my eurorack journey and it’s amazing, I got modules from different companies but is mostly Mutable instruments.
I’m not an electronic expert and I just have a problem in making a diy inverter and I need some help, the one I just made is not working.
I got 3 sequencers and I’m using a Vermona qMI2 to sync them to the Octatrack, a sequencer starts and stops with the reset output of the qMI2 but the other two sequencers need an inverted reset signal. I’m inverting it with Maths but I don’t want to sacrifice the two attenuverters for this, I also got an MFB Megazwerg that has an Inverse section that do the job but I’d like to make a DIY small module to put in the rack instead to take the Megazwerg with me to play the modular outside my studio.
I’ve tried to made the inverting amplifier circuit as in the Doepfer DIY page http://www.doepfer.de/DIY/a100_diy.htm and here a picture of what I made:

Anyone can tell me my mistake and how to fix it?

You invert the voltage, so 5V becomes -5V and 0V becomes 0V. That is probably not what you want. I don’t know your gear but I’d guess you need something that spits out 0V on 5V input and 5V on 0V input.
It’s called comparator. You can wire one up with your opamp like this
The 470k resistor acts as a hysteresis. You can leave it out, but its better when its there.

Thank you very much TheSlowGrowth, that’s actually what I need! from the Megazwerg manual it says this about the Inverse section: "Inverse is a voltage-inverter with additional offset function. 5V means “0” becomes “5” and “5” becomes “0” ". In fact the sequencers don’t start/stop just inverting the reset output with an attenuverter, I set up Maths with the reset output going in the first attenuverter applying a positive attenuation and the second attenuverter with a negative attenuation, then I can use the inverted mix output to start/stop the sequencers. I didn’t know that’s called a comparator, I thought it was just an inverter! thanks for the info!
Now I will look for a DIY comparator on the web as I don’t know how to translate that circuit pic you linked to actually wire the thing up. I will test further if my inverter works anyway, my plan is to make a 4hp module with the comparator and two passive attenuators, but maybe I could make another module with another couple of attenuators and an inverter too, I often feel the needs for those utilities .

Try this version. I added some labels so it should be easier to understand

The 40Hz triangle wave in the simulation is simply there to have some sort of input for the simulation. In reality it must be replaced with the input jack.

The gate/clock signals in eurorack are typically between 0V and >5V. Going up to 10V or even 12V is okay for the “on” state, but for the “off” state it should be below 1V to be sure it is read ocrrectly by most gear out there.

To achieve this, you must power your uA741 from +12V and GND, as the comparator crcuit makes it drive its output as high or as low as it can. In this configuration you will get output voltages of 2V for the “off” state (should be fine for most gear, but probably not all) and 10V for the “on” state. That is because the uA741 can only drive its output within 2V of its supply rails.
if you want to be sure that the “off” state is recognized by all gear out there, choose a rail-to-rail capable opamp like the MCP6002/MCP6004. With one of these powered from 12V and GND you will get almost +12V for the “on” state and almost 0V for the “off” state. That should be fine for almost any gear.

Thank you for drawing the circuit, now I understand it better! I will try it and see if it works with the UA741.