just got an ae modular ( https://www.tangiblewaves.com/ ) and now i am trying to convert grids from eurorack to ae modular. In ae modular, all voltages are between 0 to 5V, there are no negative voltages.
So this is one CV input from Grids. As far as i can tell it is some kind of inverting summing amplifier and it needs a negative 5V at one of it’s inputs to work properly.
The problem is: AE Modular doesn’t know negative voltages. So instead of an inverting summing amplifier i will use a non inverting one and then correct the inverted readings in the code.
So i came up with this (i found it on the internet to be honest) which is a non inverting summing amplifier:
So basically it works as expected. The Problem is: when the CV input is not connected then the summing doesn’t work anymore. So one could just use a switching jack which ties the cv input to ground in case noting is connected, but we can’t use these for ae modular because it uses even smaller connectors (the ones found on an arduino board for example)
So i came up with this solution:
In case there is nothing connected to the input then the whole input is tied to ground via R7. Comparing to R2, R7 is so small that it doesn’t affect the summing that much which should be ok.
But the problem here is: R7 needs to be small to not affect the summing too much, but when it is small it will suck a lot of current from the cv input when there is something connected.
So to solve this issue i came up with this:
Now the pull down resistor R6 is so big that the current it sucks from the input should be small enough and it also doesn’t affect the summing any more because of the buffer.
So this circuit finally works, but at the cost of having another opamp.
The question i now have is:
Is this complete bullshit or does this sound like a reasonable approach?
Is there maybe a better solution which doesn’t need the second opamp, or maybe no opamps at all?