Ken Yap Brings 50-Year-Old Motorola Amplifier Chips Out of Retirement — for KiCad Practice
Unusually-packaged 50-year-old amplifier chips provide a key opportunity for experimenting with KiCad footprint creation.
Engineer Ken Yap has built an amplifier circuit, designed using the cutting-edge KiCad electronics design automation (EDA) package — but using chips built by Motorola 50 years ago.
"I found 4 of these [Motorola] MFC9020 [chips, never used, in my spares box," Yap explains of his project. "The datasheet appears in Motorola's 1972 edition of linear ICs [Integrated Circuits], so that makes them around 50 years old. I decided to put these ICs and a bunch of THT [Through-Hole Technology] parts to work as four amplifiers and get practice in KiCad."
Motorola's MFC9020, a single-chip two-watt audio amplifier, was, to quote the company's documentation at launch, "designed to provide the complete audio system in television, radio, and photograph equipment." "This was designed before high current transistors were common in linear ICs," Yap notes, "so they used higher voltages of up to 24V to get the needed output power."
The component's package features an unusual layout, with staggered spacing for its legs and a pair of large copper tabs designed to bleed heat off into the copper PCB on which it's installed — a key selling point for the chips, which boasted "minimal heat-sinking required." This required Yap to design a custom KiCad component footprint to accommodate the part, before setting about replicating Motorola's reference schematic as a functional PCB.
"I picked yellow soldermask for novelty," Yap says of the finished boards. "Generally I prefer blue or green. After the board was sent off for fabrication I realised that I should have put silkscreen legends on the input, speaker, and power ports. But no matter, this is a once-only design for myself only."
This is far from Yap's first experiment with vintage hardware. Back in October 2020 he unveiled the Irreproducible Clock, a protoboarded clock and display powered by an STMicroelectronic sSTM8 microcontroller and using primarily salvaged components — including its display, formerly used to display the current clock speed of a PC from the era of "Turbo" buttons to slow down its operation for backwards compatibility purposes.
More information is available on Yap's Hackaday.io page.