About

Arithmetics is an utility module, mainly focused on different add/subtract operation combinations. It consists of 2 coefficient setters (read: one attenuator and one attenuverter, but with +12v normalized into the input so you could use it as an offset voltage generator) and 4 independent operations - that take some input and process them somehow. First 3 ones are summators of one sort of another, the last one is a comparator at its core, but if one treats it as a literally broken-out op amp, they can build interesting feedback patches with it.

You can see a fifth operation on my build down below - it was supposed to be a 4-quadrant multiplier, but both AD633s (one-chip 4-quadrant multipliers) that came in some days ago were damaged/faulty, so it has a very strange transistor circuit behind it instead. It kind of multiplies, too, but one day i will make an actual preciese four quadrant multuplier module... as a RETALIATION move for this one!

Anyhoo, the top operation is the inverse sum of two signals. It adds them togethers and inverts the sum, as simple as that. If only one signal is patched in - it's just an inverter.

Below is the second operation, which is a sum of normal first input and inverted second input. Patch the first coefficient out in the first input of this operation as an offset, some CV into the inverted in, and you get an offseted inverter! Or use it for harmonic subtraction of filtered sound from clean sound, for example.

Next is the third operation. This one is mainly meant to be used as a mini audio mixer, since it (virtually) divides all incoming signals by 3 before summing, so even at top voltages at the same time, the mix will never clip against power supply rails. So you can just throw your sounds together into it and get a clean equal-power mixdown. But it, of course, is DC-coupled, and you can use it whichever other way with CV and audio.

Finally, the fourth operation with the infinity sign! It's basically an op amp that is kind of.. free to use? In its raw form, it will act as a comparator. Of course we can't get infinite voltage here, it will clip against the power supply voltages, but if the difference of the two inputs is just a bit positive - the output will skyrocket to +12v. Likewise, if the difference is a bit negative, so - the second (B) input voltage is a tad bit more than the first (A), it will instantly drop to -12v. This one is also a crazy feedback experiment gem.

Generally, Arithmetics is a nice multifunctional utility that's easy to build for a beginner. As a bonus, you get one excess op amp and can show some creativity and think of your own fifth operation around it, instead of my failed multiplier attempt! Another comparator? Three-channel inverting mixer? Or maybe a half-wave rectifier? Up to you!

Schematic

Not much to talk about here, very generic op-amp stuff going on! First two blocks are the coefficient setters, first one is passive and basically is an attenuator. Second is a generic attenuverters built around an op-amp, and has two 47K resistors to make it have a bit more precise responce in the middle, as suggested by Cassutronic's article on attenuverters. Big up for a nice hint, Cassutronics! Both coefficient setters have +12v normalized to their inputs through 1K resistors (weird patch safety!), so they can be used as a 0...12v and a -12..12v offset source respectively.

First operation is an inverting summator. As simple as this. Second is a bit more tricky: we invert signal A, and then pass it to the inverting summator - same as in first operation - to sum it with signal B and invert again. So on its path, A is inverted twice, so, not inverted at all. We get a sum of A and B*-1. Third operation is an ivnerting summer with a feedback resistor 3 times lower than the summing network ones, so we get a gain of 1/3 for each signals: this way even at peak positive or negative voltage all at the same time, the sum won't exceed the power supply rails voltages. Then it gets inverted again to 'uninvert' the sum. Finally, the fourth, comparator operation, is just a broken out op amp, as i said before. Only auxillary stuff are the two 10K input resistors (some devices are having troubles of direct op-amp interfacing), and two 1M pulldowns to stabilize it in a way. Otherwise - feel free to exploit its op-ampy nature in some weird as hell feedback loop.

I'm not providing neither the planned AD633 multiplier schematic, nor the actual "for fun" transistor one, of the 5th operation. Not worth it. See that last unused op-amp? Do something fun with it. Express yourself!

That's pretty much it about this fun and useful little pile of subcircuits.

Media

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