If you’ve been following our Flashback Series of Eventide products of the 1970s, you will have noticed that they’re all black boxes. Both literally and figuratively. Black was the studio fashion of the day, and all the boxes had inputs and outputs. At least at the time, what went on inside the box between the ins and outs was something of a mystery to the largely analog-wise world. This Flashback is about an entirely different product. Neither box nor black, it was barely even a product. It was just a circuit board and a pretty specialized one at that. Its input was audio, its output was a computer display, and it made no weird noises at all.
In designing and using audio products, a device called a spectrum analyzer is almost essential. It allows you to see audio waveforms in terms of frequency instead of time, as does the more common oscilloscope. Eventide bought a Hewlett-Packard 3580A to help with designing and troubleshooting our recording and broadcast audio products. We fell in love with it. When eBay made such previously unthinkable extravagance possible, we collected spectrum analyzers, only some of which were included in this “Beauty Pageant” blog of 2006. Today, our “go-to” analyzer is the redoubtable Agilent 89441A, which covers almost-DC up to 2.6GHz with remarkable sensitivity and precision. But we digress…
There’s Something Missing From the Beauty Pageant of Spectrum Analyzers
Although we’ve used all the analyzers mentioned, we also created and designed a unique one from scratch. How unique? So much so that we believe it was the first instrument ever incorporated inside a general-purpose computer. Are we certain? No, of course not. But before this product, instruments were invariably connected to computers, not part of them. This is the story of the “THS224” spectrum analyzer for the Commodore PET.
The Commodore PET, a De-Acronymed Personal Electronic Transactor
The Commodore PET was the first true “personal computer,” pre-dating the Apple II, the Radio Shack TRS80, and the IBM PC. The original version used a cassette tape for program storage and had a so-called “Chicklet” keyboard! But most importantly, it sported very little memory and a yawning chasm of a chassis. You’ll recall from our previous flashbacks that Eventide feasted on memory, and whenever a new generation came out, we found a way to, using today’s jargon, “monetize” it. The PET was too good an opportunity to waste! It sold over 100,000 units and every one of them needed more than the 4k or 8k static memory that came from the factory. We found a way to add the much cheaper dynamic memory to factory units, dubbed the 16k and 24k cards “BIG MEM,” and sold them for what must have been considered a reasonable price in the late ’70s.
The main circuit board of the PET had vastly more space above it than needed for a second board. Unlike today’s compact hardware and flat screens, this computer had a heavy, bulky chassis with a deep CRT display assembly on top. The Big Mem boards, which took little space were the first, obvious addition to the PET.
We had the notion of manufacturing a spectrum analyzer before the PET was introduced, but it would have been a major project for the tiny company we were in the ’70s. It would have required not just the analyzer circuitry, but also the power supply, metalwork, controls, CRT, and cosmetic embellishments that make a product stand out. And we might have had to embed one of the new microprocessor chips in the circuitry, too, if we wanted it to be more than a very simple device. When we got our first PET and saw how much of the spectrum analyzer was already there, we heard the call of the unused space. It whispered “use me!” You don’t hear that a lot nowadays.
The memory board was what is now called a “no-brainer.” Took a few days to design, didn’t require any software beyond a memory test program, and used the same parts we used in some of our other products.
Read the entire blog here: https://www.eventideaudio.com/flashback ... black-box/
