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An Anonymous Coward writes:

https://northcoastsynthesis.com/news/logic-before-ics/

So, you want a simple digital logic function in a synthesizer. Maybe it's an AND gate, or a couple of XORs, maybe as much as a shift register. How will you build it?

Today it often makes sense to just throw in a microcontroller chip. They're cheap and versatile. The same microcontroller can be programmed to serve many different purposes, so you can keep just a few types of them in stock, buy them in huge quantities, and that keeps costs down. If you need more speed, then it may make sense to use FPGAs (field-programmable gate arrays), but very few synthesizer circuits really need that much speed.

Twenty or thirty years ago, before microcontrollers were cheap, the usual way of doing a small amount of digital logic was to throw in a couple of MSI (medium-scale integration) logic chips, such as the 7400 or 74LS00 series based on bipolar transistors or the 4000 series based on CMOS. These were small logic building blocks, typically a few gates on each 14-pin or 16-pin DIP chip. There were dozens of popular chips in these series and a few hundred less-common ones. They first existed in the late 1960s but weren't cost-effective and readily available to hobbyists until the mid-1970s. Such chips still exist and you still see a lot of them in DIY designs, but they're gradually falling out of production as cheaper microcontrollers become more appealing to the large commercial interests that are most of the market.

Even further into the past, integrated circuits of any kind were too expensive to be the first choice for hobbyists, and we had to build things out of one active device (transistor or even tube) at a time. I used this kind of logic in my MSK 012 Transistor ADSR. Logic gates built with the minimum number of transistors are barely digital at all: they may be better understood as analog amplifier circuits that happen to be amplifying digital signals. The chips we usually use today, and the gates inside them, have become more complicated and involve more transistors as transistors have become cheaper, but they can be understood as just evolutionary developments from the simplest possible gates.

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