Building A Tube-Based Stereo Amp, In Classic Style

July 31, 2022 by Donald Papp 34 Comments

It’s not every day we see the results of someone putting their own spin on a vintage tube amp, but that’s exactly what [lens42] did in creating the McIntosh 217, created as a “mini” version of the McIntosh MC275, a classic piece of audio equipment. Both are pictured next to each other, above.

When it comes to vintage hi-fi stereo amplifiers, two units had particular meaning for [lens42]: the McIntosh MC275 Power Amp, and the Dynaco ST35. The Dynaco was a more budget-friendly amplifier, but looked like a plain box. The McIntosh, however, proudly showed off its tubes and transformers in all their glory. The “McIntosh 217” is design-wise basically a smaller McIntosh MC275, with the innards of a Dynaco ST35.

With so much needing to be designed from the ground up, CAD was invaluable. Component layout, enclosure design, and even wiring and labeling all had to be nailed down as much as possible before so much as heating up the soldering iron. Even so, there were a few hiccups; a vendor had incorrect measurements for a tube socket which meant that the part would not fit. A workaround involved modifying the holes and as luck would have it, the change wasn’t an eyesore. Still, [lens42] reminds us all that whenever you can, have the required parts in-hand for confirmation of dimensions before sending CAD files off for cutting or fabrication.

Many of us can relate to the fact that the whole project was a labor of love and made no real financial sense, but the end result is fantastic, and creating such a thing is something all of us — not just chasers of that elusive “tube sound” — can appreciate.

Upgraded Film Scanner Handles Bigger Formats At No Cost

July 30, 2022 by Donald Papp 2 Comments

Film scanners are a useful tool for digitizing slides and negatives, and the Plustek 8100 that [Christian Chapman] had was capable, but limited to small format film only. Rather than pay for a much more expensive medium format scanner that could handle 120 film, he modified his 8100 to accomplish the same thing with a combination of good old software and hardware tampering.

On the software side, [Christian] modified a driver for the Plustek 8100 so that it sweeps the scan head further than usual. At the application level, to scan medium format frames, it does a total of four scans: one for each quadrant. The results get stitched together in software with a thoughtfully-designed shell script that provides previews and handles failures and restarts gracefully.

Hardware-wise, the scanning carriage needs modification to ensure nothing interferes with the scan head as it moves further than originally designed. Some CAD and 3D printing made short work of this. Incidentally, this hardware mod is an excellent demonstration of one of the core strengths of 3D printing: the ability to make geometrically-straightforward objects that would nevertheless be troublesome or impractical to construct in any other way.

USB Drive Keeps Your Secrets… As Long As Your Fingers Are Wet?

July 30, 2022 by Donald Papp 27 Comments

[Walker] has a very interesting new project: a completely different take on a self-destructing USB drive. Instead of relying on encryption or other “visible” security features, this device looks and works like an utterly normal USB drive. The only difference is this: if an unauthorized person plugs it in, there’s no data. What separates authorized access from unauthorized? Wet fingers.

It sounds weird, but let’s walk through the thinking behind the concept. First, encryption is of course the technologically sound and correct solution to data security. But in some environments, the mere presence of encryption technology can be considered incriminating. In such environments, it is better for the drive to appear completely normal.

Toggling the chip enable (CE) pin will hide the drive’s contents.

The second part is the access control; the “wet fingers” part. [Walker] plans to have hidden electrodes surreptitiously measure the resistance of a user’s finger when it’s being plugged in. He says a dry finger should be around 1.5 MΩ, but wet fingers are more like 500 kΩ.

But why detect a wet finger as part of access control? Well, what’s something no normal person would do right before plugging in a USB drive? Lick their finger. And what’s something a microcontroller should be able to detect easily without a lot of extra parts? A freshly-licked finger.

Of course, detecting wet skin is only half the equation. You still need to implement a USB Mass Storage device, and that’s where things get particularly interesting. Even if you aren’t into the covert aspect of this device, the research [Walker] has done into USB storage controllers and flash chips, combined with the KiCad footprints he’s already put together means this open source project will be a great example for anyone looking to roll their own USB flash drives.

Regular readers may recall that [Walker] was previously working on a very impressive Linux “wall wart” intended for penetration testers, but the chip shortage has put that ambitious project on hold for the time being. As this build looks to utilize less exotic components, hopefully it can avoid a similar fate.

Fix Old Caps, But Keep That “Can Capacitor” Look

July 30, 2022 by Donald Papp 21 Comments

Vintage electronics and capacitor replacements tend to go hand-in-hand. Why? Because electrolytic capacitors just don’t last, not the way most other components do, anyway.

The metal terminal ring and the central plate are kept for re-use, and the metal case re-crimped after the internals of the capacitor are replaced with a modern equivalent.

It’s one thing to swap old caps with modern replacements, but what about electronics where the components are not hidden away, and are an important part of the equipment’s look? [lens42] shares a method for replacing antique can-style capacitors in a way that leaves them looking completely original. All it takes is some careful application of technique.

The first thing to do is carefully file away the crimp of the metal can until one can release the ring and plate that hold the terminals. Once that is off, the internals can be pulled from the metal can for disposal. Since the insides of the old cap won’t be re-used, [lens42] recommends simply drilling a hole, screwing in a lag bolt to use as a handle, and pulling everything out. There’s now plenty of space inside the old can to hold modern replacements for the capacitor, and one can even re-use the original terminals.

That leaves the job of re-crimping the old can around the terminal ring to restore a factory-made appearance. To best do this, [lens42] created a tapered collar. Gently hammering the can forces the bottom into the taper, and the opening gradually crimps around the terminal ring. It’s also possible to carefully hammer the flange directly, but the finish won’t be as nice. This new crimp job may not look exactly the same as before, but once the cap is re-installed into the original equipment, it won’t be possible to tell it has been modified in any way.

If this sounds a bit intimidating, don’t worry. [lens42] provides plenty of pictures. And if this kind of thing is up your alley, you may want to check out the Caps Wiki, an effort to centralize and share details about tech repair, especially for vintage electronics.

Custom Raspberry Pi Case Shows The Whole Workflow

July 25, 2022 by Donald Papp 29 Comments

If you are a process junkie and love seeing the end-to-end of how a thing is made and with what tools, then watch [Michael Klements] show off his Raspberry Pi case design. His case has quite a few cool-looking elements to it, and incorporates 3D printing as well as laser-cut and clear bent acrylic for a gorgeous three-quarter view.

[Michael]’s write-up (and accompanying video, embedded below) are partly a review of his Creality 3D printer, and partly a showcase of his Raspberry Pi case design (for which he sells the design files for a small fee on his Etsy store.) But the great part is seeing the creation of every piece that goes into the end product. Not everyone is familiar with the way these tools work, or what they can create, so it’s nice to see attention paid to that side of things.

Both the blog post and the video nicely show off what goes into every part. The video opens with unpacking and setting up the 3D printer (skip ahead to 4:58 if you aren’t interested), followed by printing the parts, laser-cutting the acrylic on a K40 laser cutter, bending the acrylic using a small hand tool, and finally, assembling everything. For the curious, there are also links to the exact parts and equipment he uses.

Like we said, it’s part 3D printer review and part showcase of a design he sells, but it’s great to see each of the parts get created, watch the tools get used, and see the results come together in the final product. And should you wish to go in the opposite direction? A one-piece minimalist case for your Raspberry Pi is only a 3D printer away.

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Complex Movements From Simple Inflatables, Thanks To Physics

July 24, 2022 by Donald Papp 5 Comments

Inflatable actuators that change shape based on injected pressure can be strong, but their big limitation is that they always deform in the same way.

The Kresling pattern, which inspired the actuator design.

But by taking structural inspiration from origami, researchers created 3D-printed actuators that show it is possible to get complex movements from actuators fed by only a single source of pressure. How is this done? By making the actuators physically bi-stable, in a way that doesn’t require additional sources of pressure.

The key is a modified design based on the Kresling pattern, with each actuator having a specially-designed section (the colored triangles in the image above) that are designed to pop out under a certain amount of positive pressure, and remain stable after it has done so. This section holds its shape until a certain amount of negative pressure is applied, and the section pops back in.

Whether or not this section is popped out changes the actuator’s shape, therefore changing the way it deforms. This makes a simple actuator bi-stable and capable of different movements, using only a single pressure source. Stack up a bunch of these actuators, and with careful pressure control, complex movements become possible. See it in action in two short videos, embedded just below the page break.

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Digital “Toy” Camera, Made For Tilt-Shift And Other Analog-Like Experimenting

July 23, 2022 by Donald Papp 5 Comments

Like many others, [volzo] loves playing with photography in a playful and experimental way. Oddball lenses, vintage elements, and building from kits is what that world looks like. But that kind of stuff is really the domain of film cameras, or at least it was until [volzo] created his Digital Toy Camera design. The result? A self-built, lomography-friendly digital camera that allows for all kinds of weird and wonderful attachments and photo shenanigans.

3D-printed mounts and magnetic attachment makes swapping parts a breeze.

To make a DIY digital camera that allowed that kind of play, the first problem [volzo] had to solve was deciding on an image sensor. It turns out that sourcing image sensors as an individual is a pretty cumbersome process, and even if successful, one still needs to write a driver and create things from the ground up. So, the guts of [volzo]’s creations use the Raspberry Pi and camera sensor ecosystem and M12 lenses, a decision that allows him to focus on the rest of the camera.

3D printing, a bit of CNC machining, and some clever design yields a “toy” camera: simple, inexpensive, and enabling one to take a playful and experimental approach to photography. The design files are available on GitHub, and there are some neat elements to the design. Magnetic mounts allow for easy swapping of lens assemblies, and a M12 x 0.75 tap cuts perfect threads into 3D-printed pieces for M12 lenses.

Heat-set inserts also provide robust fastening that can hold up to disassembly and re-assembly (and don’t miss that our own [Joshua Vasquez] has shared how best to design for and use heat-set inserts.)

[volzo] has a fantastic video to accompany his project; give it a watch (embedded below, under the page break) and see if you don’t come away with some inspiration of your own.

Continue reading “Digital “Toy” Camera, Made For Tilt-Shift And Other Analog-Like Experimenting” →