Repairing The Questionable £25,000 Tom Evans Audiophile Pre-Amp

November 14, 2024 by Maya Posch 123 Comments

One of the power supply boards in the Tom Evans Mastergroove SR MkIII preamplifier. (Credit: Mend it Mark, YouTube)

It’s not much of a secret that in the world of ‘audiophile gear’ there is a lot of snake oil and deception, including many products that are at best of questionable value. The Tom Evans Mastergroove SR mkIII preamplifier is one example of this, as [Mark] from the Mend it Mark YouTube channel found in a recent video when he got one to repair which the manufacturer claimed ‘could not be fixed’. This marvel of audio engineering provides amplification for record players, for the low-low price of only twenty-five thousand quid, or about 29.000 US bucks. So what’s inside one of these expensive marvels?

Claiming to be a high-end unit, with only ten units produced per year, you’d expect a gold-plated PCB with excellent noise isolation. The unit does come with an absolutely massive external power supply that dwarfs the preamplifier itself, but the real surprise came after opening up the unit itself to take a peek at the damage, some of which was caused by transport.

As it turns out, the inside of the preamplifier consists out of four stacks of rather cheap, home-made looking boards with what looks like improvised RF shielding in the form of bare PCBs and filed-off markings on many parts. In between the rat’s nest of wiring running everywhere, [Mark] had to trace the broken channel’s wiring, creating a full repair manual in the process. Along the way one of the opamp boards was found to be defective, courtesy of a single shorted tantalum capacitor.

With the tantalum capacitor replaced, [Mark] had repaired the unit, but even though the preamplifier isn’t terribly designed, the illusion of its price tag has been shattered worse than the contents of a parcel kicked across the parking lot by the Royal Mail.

Thanks to [Jim] for the tip.

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You Wouldn’t Download A Chair…But You Could

November 12, 2024 by Lewin Day 16 Comments

[Morley Kert] had a problem. He’s a big fan of the lovely Fortune Chair from Heller Furniture. Only, he didn’t want to pay $1,175 for a real one. The solution? He printed his own instead!

The basic concept is simple. Capture or recreate the geometry of the fancy expensive designer chair, and then print it out on a 3D printer. That would be easy, except for scale. Chairs have to be both big enough to seat humans, and strong enough to carry their weight. For the average 3D printer owner, meeting the big requirement is difficult, since most printers are quite small compared to chairs.

[Morley] gets around this in the typical fashion—he prints the chair in multiple segments. Indeed, we’ve seen [Morley] tackle a similar project before, too. Only, last time, he had the benefit of a print farm and some easily-accessible geometry for the target object. This time, he’s working very much more from scratch, and chose to print everything at home. That made things quite a bit harder.

Scaling up is never as easy at it seems at first!

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A stack of Activation Locked MacBooks destined for the shredder in refurbisher [John Bumstead]’s workshop.

Apple IOS 18’s New Repair Assistant: Easier Parts Pairing Yet With Many Limitations

October 27, 2024 by Maya Posch 12 Comments

Over the years, Apple has gone all-in on parts pairing. Virtually every component in an iPhone and iPad has a unique ID that’s kept in a big database over at Apple, which limits replacement parts to only those which have their pairing with the host system officially sanctified by Apple. With iOS 18 there seems to be somewhat of a change in how difficult getting a pairing approved, in the form of Apple’s new Repair Assistant. According to early responses by [iFixit] and in a video by [Hugh Jeffreys] the experience is ‘promising but flawed’.

As noted in the official Apple support page, the Repair Assistant is limited to the iPhone 15+, iPad Pro (M4) and iPad Air (M2), which still leaves many devices unable to make use of this feature. For the lucky few, however, this theoretically means that you can forego having to contact Apple directly to approve new parts. Instead the assistant will boot into its own environment, perform the pairing and calibration and allow you to go on your merry way with (theoretically) all functionality fully accessible.

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Simple PCB Repairs Keep Old Vehicle Out Of The Crusher

October 24, 2024 by Dan Maloney 21 Comments

For those of us devoted to keeping an older vehicle on the road, the struggle is real. We know that at some point, a part will go bad and we’ll learn that it’s no longer available from the dealer or in the aftermarket, at least at a reasonable cost. We might get lucky and find a replacement at the boneyard, but if not — well, it was nice knowing ya, faithful chariot.

It doesn’t have to be that way, though, at least if the wonky part is one of the many computer modules found in most cars made in the last few decades. Sometimes they can be repaired, as with this engine control module from a Ford F350 pickup. Admittedly, [jeffescortlx] got pretty lucky with this module, which with its trio of obviously defective electrolytics practically diagnosed itself. He also had the advantage of the module’s mid-90s technology, which still relied heavily on through-hole parts, making the repair easier.

Unfortunately, his luck stopped there, as the caps had released the schmoo and corroded quite a few traces on the PCB. Complicating the repair was the conformal coating on everything, a common problem on any electronics used in rough environments. It took a bit of probing and poking to locate all the open traces, which included a mystery trace far away from any of the leaky caps. Magnet wire was used to repair the damaged traces, the caps were replaced with new ones, and everything got a fresh coat of brush-on conformal coating.

Simple though they may be, we really enjoy these successful vehicle module repairs because they give us hope that when the day eventually comes, we’ll stand a chance of being able to perform some repair heroics. And it’s nice to know that something as simple as fixing a dead dashboard cluster can keep a car out of the crusher.

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A Wobble Disk Air Motor With One Moving Part

October 22, 2024 by Dan Maloney 17 Comments

In general, the simpler a thing is, the better. That doesn’t appear to apply to engines, though, at least not how we’ve been building them. Pistons, cranks, valves, and seals, all operating in a synchronized mechanical ballet to extract useful work out of some fossilized plankton.

It doesn’t have to be that way, though, if the clever engineering behind this wobbling disk air engine is any indication. [Retsetman] built the engine as a proof-of-concept, and the design seems well suited to 3D printing. The driven element of the engine is a disk attached to the equator of a sphere — think of a model of Saturn — with a shaft running through its axis. The shaft is tilted from the vertical by 20° and attached to arms at the top and bottom, forming a Z shape. The whole assembly lives inside a block with intake and exhaust ports. In operation, compressed air enters the block and pushes down on the upper surface of the disk. This rotates the disc and shaft until the disc moves above the inlet port, at which point the compressed air pushes on the underside of the disc to continue rotation.

[Resetman] went through several iterations before getting everything to work. The main problems were getting proper seals between the disc and the block, and overcoming the friction of all-plastic construction. In addition to the FDM block he also had one printed from clear resin; as you can see in the video below, this gives a nice look at the engine’s innards in motion. We’d imagine a version made from aluminum or steel would work even better.

If [Resetman]’s style seems familiar, it’s with good reason. We’ve featured plenty of his clever mechanisms, like this pericyclic gearbox and his toothless magnetic gearboxes.

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Pac-Man Ghost Helps With Air Quality Sensing

October 21, 2024 by Bryan Cockfield 13 Comments

In the past, building construction methods generally didn’t worry much about air quality. There were enough gaps around windows, doors, siding, and flooring that a house could naturally “breathe” and do a decent enough job of making sure the occupants didn’t suffocate. Modern buildings, on the other hand, are extremely concerned with efficiency and go to great lengths to ensure that no air leaks in or out. This can be a problem for occupants though and generally requires some sort of mechanical ventilation, but to be on the safe side and keep an eye on it a CO2 sensor like this unique Pac-Man-inspired monitor can be helpful.

Although there are some ways to approximate indoor air quality with inexpensive sensors, [Tobias] decided on a dedicated CO2 sensor for accuracy and effectiveness, despite its relatively large cost of around $30. An ESP32 handles the data from the sensor and then outputs the results to an array of LEDs hidden inside a ghost modeled after the ones from the classic arcade game Pac-Man. There are 17 WS2812B LEDs in total installed on a custom PCB, with everything held together in the custom 3D printed ghost-shaped case. The LEDs change from green to red as the air quality gets worse, although a few preserve the ghost’s white eyes even as the colors change.

For anyone looking to recreate this project and keep an eye on their own air quality, [Tobias] has made everything from the code, the PCB, and the 3D printer files open source, and has used accessible hardware in the build as well. Although the CO2 sensors can indeed be pricey, there are a few less expensive ways of keeping an eye on indoor air quality. Some of these methods attempt to approximate CO2 levels indirectly, but current consensus is that there’s no real substitute for taking this measurement directly if that’s the metric targeted for your own air quality.

DIY Air Bearings, No Machining Required

October 20, 2024 by Dan Maloney 26 Comments

Seeing a heavy load slide around on nearly frictionless air bearings is pretty cool; it’s a little like how the puck levitates on an air hockey table. Commercial air bearings are available, of course, but when you can build these open-source air bearings, why bother buying?

One of the nice things about [Diffraction Limited]’s design is that these bearings can be built using only simple tools. No machining is needed past what can be easily accomplished with a hand drill, thanks to some clever 3D-printed jigs that allow you to drill holes with precision into stainless steel discs you can buy on the cheap. An extremely flat surface is added to the underside of these discs thanks to another jig, some JB Weld epoxy, and a sheet of float glass to serve as an ultra-flat reference. Yet more jigs make it easy to scribe air channels into the flat surface and connect them to the air holes through a bit of plaster of Paris, which acts as a flow restriction. The video below shows the whole process and a demo of the bearings in action.

[Diffraction Limited] mentions a few applications for these air bearings, but the one that interests us most is their potential use in linear bearings; a big CNC cutter using these air bearings would be pretty cool. We seen similar budget-friendly DIY air bearings before, including a set made from used graphite EDM electrodes.

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