Everyone’s Talking GPMI, Should You?

April 10, 2025 by Jenny List 75 Comments

The tech press has been full of announcements over the last day or two regarding GPMI. It’s a new standard with the backing of a range of Chinese hardware companies, for a high-speed digital video interface to rival HDMI. The Chinese semiconductor company HiSilicon have a whitepaper on the subject (Chinese language, Google Translate link), promising a tremendously higher data rate than HDMI, power delivery well exceeding that of USB-C, and interestingly, bi-directional data transfer. Is HDMI dead? Probably not, but the next few years will bring us some interesting hardware as they respond to this upstart.

Reading through pages of marketing from all over the web on this topic, it appears to be an early part of the push for 8k video content. There’s a small part of us that wonders just how far we can push display resolution beyond that of our eyes without it becoming just a marketing gimmick, but it is true to say that there is demand for higher-bandwidth interfaces. Reports mention two plug styles: a GPMI-specific one and a USB-C one. We expect the latter to naturally dominate. In terms of adoption, though, and whether users might find themselves left behind with the wrong interface, we would expect that far from needing to buy new equipment, we’ll find that support comes gradually with fallback to existing standards such as DisplayPort over USB-C, such that we hardly notice the transition.

Nearly a decade ago we marked the passing of VGA. We don’t expect to be doing the same for HDMI any time soon in the light of GPMI.

Designing A Tone Control Properly

April 8, 2025 by Jenny List 12 Comments

Many years ago, audio equipment came with a tone control, a simple RC filter that would cut or boost the bass to taste. As time passed, this was split into two controls for bass and treble, and then finally into three for bass, mid, and treble. When audiophile fashion shifted towards graphic equalisers, these tone controls were rebranded as “3-band graphic equalisers”, a misleading term if ever we heard one. [Gabriel Dantas] designed one of these circuits, and unlike the simple passive networks found on cheap music centres of old, he’s doing a proper job with active filters.

The write-up is worth a read even if you are not in the market for a fancy tone control, for the basic primer it gives on designing an audio filter. The design contains, as you might expect, a low-pass, a bandpass, and a high-pass filter. These are built around TL072 FET-input op-amps, and an LM386 output stage is added to drive headphones.

The final project is built on a home-made PCB, complete with mains power supply. Audiophiles might demand more exotic parts, but we’re guessing that even with these proletarian components it will still sound pretty good. Probably better than the headphone amplifier featured in a recent project from a Hackaday writer, at least. There’s a build video, below the break.

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Newspaper clipping with words 'speaking personally' and a photo

A Fast Rewind To The Era Of Tapesponding

March 12, 2025 by Heidi Ulrich 5 Comments

Imagine a time before Discord servers and cheap long-distance calls. Back in the 1950s, a curious and crafty group of enthusiasts invented their own global social network: on reels of magnetic tape. They called it tapesponding (short for tape corresponding), and it was a booming hobby for thousands of radio hams, tinkerers, and audio geeks. Here’s the original video on this analog marvel.

These folks weren’t just swapping mixtapes. They crafted personal audio letters, beamed across the globe on 3-inch reels. DIY clubs emerged everywhere: World Tape Pals (Texas-based, naturally) clocked 5,000 members from “every Free Nation” – which frames it in a world in terms of East vs. West. Some groups even pooled funds to buy shared tape decks in poorer regions – pure hacker spirit. The tech behind it: Speeds of 3¾ IPS, half-track mono, round-robin reels, and rigorous trust networks to avoid ghosters. Honestly, it makes IRC net ops look soft. Tapesponding wasn’t just for chatty types. It fostered deep friendships, even marriages. It was social engineering before that term was coined. The video is below the break.

What are your thoughts on this nostalgic way of long-distance communication? The warm whirring of a spinning tape reel? The waiting time before your echo is returned? Or are have you skipped all the analog mechanics and shouted out into the LoRaWAN void long ago?

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Closeup of a rackmounted custom HiFi setup

Rackmount All The Things, Hi-Fi Edition

March 6, 2025 by Heidi Ulrich 8 Comments

For those who love systems and structure, owning a 19-inch rack with just one slot filled is just not it. But what if the rest of your gear isn’t 19-inch? Well, then you go out and make it so, just like [Cal Bryant] did recently.

The goal was to consolidate multiple devices — DAC, input selector, streamer, and power routing — into a single 2U rackmount unit. His first attempts involved drilling 1U panels to attach gear with removable faceplates. That worked, but not all devices played nice. So his next step became a fully custom enclosure with CAD-modeled brackets and front panels.

OpenSCAD turned out to be a lifesaver, letting [Cal] design modular mounting solutions. Exporting proper circles for CNC turret punching however appeared to be a nightmare. It was FreeCAD to the rescue for post-processing. After some sanding and auto-shop painting, the final faceplate looked factory-made.

Custom switch boxes for power and audio routing keep things tidy, housing everything from USB to XLR inputs. A 4-pole switch even allows seamless swapping between his DAC and DJ controller, while UV-printed graphics bring the finishing touch to this project. For those looking to clean up their Hi-Fi setup (or just love modding for the sake of it), there’s a lot to learn from this build.

If buying a rack is not within your budget, you could start with well-known IKEA LACK furniture.

A TV With Contrast You Haven’t Seen For Years

March 5, 2025 by Jenny List 42 Comments

It’s something of a surprise, should you own a CRT TV to go with your retrocomputers, when you use it to view a film or a TV show. The resolution may be old-fashioned, but the colors jump out at you, in a way you’d forgotten CRTs could do. You’re seeing black levels that LCD screens can’t match, and which you’ll only find comparable on a modern OLED TVs. Can an LCD screen achieve decent black levels? [DIY Perks] is here with a modified screen that does just that.

LCD screens work by placing a set of electronic polarizing filters in front of a bright light. Bright pixels let through the light, while black pixels, well, they do their best, but a bit of light gets through. As a result, they have washed-out blacks, and their images aren’t as crisp and high contrast as they should be. More modern LCDs use an array of LEDs as the backlight which they illuminate as a low resolution version of the image, an approach which improves matters but leaves a “halo” round bright spots.

The TV in the video below the break is an older LCD set, from which he removes the backlight and places the electronics in a stand. He can show an image on it by placing a lamp behind it, but he does something much cleverer. An old DLP projector with its color wheel removed projects a high-res luminance map onto the back of the screen, resulting in the coveted high contrast image. The final result uses a somewhat unwieldy mirror arrangement to shorten the distance for the projector, but we love this hack. It’s not the first backlight hack we’ve seen, but perhaps it give the best result.

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Is This The Oldest HD Video Online?

March 5, 2025 by Jenny List 35 Comments

Take a look at this video from [Reely Interesting], showing scenes from traditional Japanese festivals. It’s well filmed, and as with any HD video, you can see real detail. But as you watch, you may see something a little out of the ordinary. It’s got noise, a little bit of distortion, and looking closely at the surroundings, it’s clearly from the 1980s. Something doesn’t add up, as surely we’d expect a video like this to be shot in glorious 525 line NTSC. In fact, what we’re seeing is a very rare demo reel from 1985, and it’s showing off the first commercial HDTV system. This is analogue video in 1035i, and its background as listed below the video makes for a very interesting story.

Most of us think of HDTV arriving some time in the 2000s when Blu-ray and digital broadcasting supplanted the NTSC or PAL systems. But in fact the Japanese companies had been experimenting since the 1960s, and these recordings are their first fruits. It’s been digitized from a very rare still-working Sony HDV-1000 reel-to-reel video recorder, and is thus possibly the oldest HD video viewable online. They’re looking for any HDV-1000 parts, should you happen to have one lying around. Meanwhile, the tape represents a fascinating window into a broadcast history very few of us had a chance to see back in the day.

This isn’t the first time we’ve touched on vintage reel-to-reel video.

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Bringing A Current Dumping Amplifier Back To Life

February 27, 2025 by Jenny List 9 Comments

Over the years there have been many different audio amplifier designs which have found favour for a while and then been supplanted by newer ideas. One of them has crossed the bench of [Jazzy Jane], it’s a current dumping amplifier from the mid-1980s. A nicely-done home-made project on stripboard mounted on a wooden base board, it sports a power supply, RIAA pre-amp board, and the amplifier itself.

The current dumping amplifier is one that combines a small class A amplifier with a hefty class B one, and through feedback trickery uses the combination to remove the crossover distortion of the class B stage. It’s a simple yet elegant circuit with fewer parts than an equivalent class AB amplifier, and there was a time back in the day when it was all the rage. This one has an op-amp providing the class A part and a complimentary pair of Darlington pairs as the class B.

The video below the break shows the process of bringing the amp back to life, a process mostly concerned with the power supply. There are a set of tantalum capacitors which have failed, and the replacements she’s using turn out to have problems too. They’re a period part for a project of this age, but we might have been tempted to go for another capacitor type here.

The result is an unusual amplifier, brought back to life. You may have seen [Jane] feature here before, with her 1950s signal generator.

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