Tube Audio Amplifiers Needn’t Be Complex

December 26, 2022 by Jenny List 25 Comments

There’s a mystique in audiophile circles about tube amplifiers. They can have a very nice sound which is attributed to their even-harmonic distortion, but they are often portrayed as requiring rare and expensive components. You don’t need matched gold-plated tubes and special transformers wound by Japanese monks with oxygen-free silver wire when the tube you’d have found in a TV back in the day paired with a repurposed mains transformer will do. [Mikremk] demonstrates this with a simple but effective amplifier using a PCL82 triode-pentode.

It’s a conventional tube amplifier circuit in which the triode is a preamplifier for the pentode power output stage. The pentode is running in class A mode, and the high impedance of its output is brought down to speaker impedance with that mains transformer. Best of all it doesn’t need a particularly high voltage, with the 40 V DC power coming from a DC-to-DC converter module.

These amplifiers could be found back in the day in some form in most consumer electronics, and remain a spectacularly cheap way to boast a tube amp in your hi-fi even if it might not always be the best possible amp.

Photo of the back of a slingbox appliance, with ports shown and arrows going to them describing what each of the ports does.

Slingbox Getting Bricked – You Have Less Than 24 Hours

November 8, 2022 by Arya Voronova 41 Comments

The Slingbox devices used to let you catch up with the programming on your TV when you weren’t near it, using your Internet-connected mobile device. As cable TV became less popular, their business model faded away, and in 2020, they scheduled a service shutdown for November 9th, 2022. If you own a Slingbox, it’s getting bricked tomorrow – for those reading this in EU, that’ll be today, even. Do you have a Slingbox? You might still be able to repurpose it, let’s say, for local media streaming – but only if you waste no time.

[Gerry Dubois] has been developing the “Slinger” software for the past few months, a small app you run locally that proxies commands and video for your Slingbox, thanks to reverse-engineering communications with Slingbox servers. However, it needs a “hardware password” alphanumeric string, that you need to get from the Slingbox service web interface – which is to be promptly shut down. If you think you might have a use for what’s essentially a network-connected analog/digital video capture card with decent hardware, the GitHub repo has a lively discussion tab for any questions you might have.

One one hand, Slingbox shouldn’t be bricking the devices in a way that requires you act fast – perhaps, releasing a final update that makes the device hacker-friendly, like O2 did with their Joggler appliance back in the day, publishing the hardware documentation, or at least setting up a service up that lets anyone retrieve their hardware password indefinitely. On the other hand, at least they gave us two years’ notice, something less than usual – the amount of time between bricking and an announcement can even be a negative number. For those of us stuck with no operational device, a hardware exploration might be in order – for instance, we’ve torn down the Sling Adapter and even ran simple custom code on it!

A terminal window with a search for "Guineau Pig Olympics" is inset on a photo of an ortholinear keyboard attached by a yellow USB cable to a 70s aluminum and plastic Super 8 film editor/viewer. The device has a large screen on the right hand side, a silver grate on the left, and a tray at the bottom for slotting in film.

Super 8 Film Editor Reborn As A YouTube Terminal

October 30, 2022 by Navarre Bartz 14 Comments

We love hacks that give new life to old gadgets, and [edwardianpug]’s YouTube Terminal certainly fits the bill by putting new hardware inside a Super 8 film editor.

[edwardianpug] could have relegated this classy-looking piece of A/V history to a shelf for display, but instead she decided to refresh its components so it could display any YouTube video instead of just one strip of film at a time. The Boost-Box keeps the retrofuturistic theme going by using the terminal to search for and play videos via Ytfzf.

The original screen has been replaced by an 800×600 LCD, and the yellow USB cord gives a nice splash of color to connect the ortholinear keyboard to the device. Lest you think that this “ruined” a working piece of retro-tech, [edwardianpug] says that 20 minutes would get this device back to watching old movies.

Are you looking for more modern and retro mashups? Check out these Dice Towers Built In Beautiful Retro Cases, a Vacuum Tube and Microcontroller Ham Transmitter, or this Cyberdeck in a Retro Speaker.

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Know Audio: Stereo

September 21, 2022 by Jenny List 16 Comments

In our occasional series charting audio and Hi-Fi technology we have passed at a technical level the main components of a home audio set-up. In our last outing when we looked at cabling we left you with a promise of covering instrumentation, but now it’s time instead for a short digression into another topic: stereo. It’s a word so tied-in with Hi-Fi that “a stereo” is an alternative word for almost any music system, but what does it really mean? What makes a stereo recording, and how does it arrive at your ears?

From West London Trains, To 3D Audio

A steam train passing through a station, from a distance in black and white — The driver of this Great Western Railway train had no idea that he was making audio history.

As most of you will know, a mono recording uses a single microphone and a single channel while a stereo one uses two microphones recording simultaneously a left and right channel. These are then played back through a pair of speakers, and the result is a sense of spatial field for the listener. Instruments appear to come from their relative positions when recorded, and the sense of being in the performance is enhanced.

Stereo recording as we know it was first perfected as one of the many inventions credited to Alan Blumlein, then working for EMI in London. We have one of his stereo demonstration films in “Trains at Hayes“, filmed from the EMI laboratories overlooking the Great Western Railway, and featuring a series of steam-hauled trains crossing the field of view with a corresponding stereo sound field. His work laid down the fundamentals of stereo recording, including microphone configurations and what would become the standard for stereo audio recording on disk with the channels on the opposite sides of a 45 degree groove. Continue reading “Know Audio: Stereo” →

Equalize Your Listening With HiFiScan

September 12, 2022 by Jenny List 28 Comments

Audiophiles will go to such extents to optimize the quality of their audio chain that they sometimes defy parody. But even though the law of diminishing returns eventually becomes a factor there is something in maintaining a good set of equipment. But what if your audio gear is a little flawed, can you fix it electronically? Enter HiFiScan, a piece of Python software to analyse audio performance by emitting a range of frequencies and measuring the result with a microphone.

This is hardly a new technique, and it’s one which PA engineers have used for a long time to tune out feedback resonances, but an easy tool bringing it to the domestic arena is well worth a look. HiFiScan is a measuring tool so it won’t magically correct any imperfections in your system, however it can export data in a format suitable for digital effects packages.

Naturally its utility is dependent on the quality of the hardware it’s used with, but the decent quality USB microphone used in the examples seems to give good enough results. We see it used in a variety of situations, of which perhaps the most surprising is a set of headphones that have completely different characteristics via Bluetooth as when wired.

If audio engineering interests you, remember we have an ongoing series: Know Audio.

Hackaday Prize 2022: A Plasma Tweeter For Ultimate Clarity

August 8, 2022 by Jenny List 18 Comments

In the world of audio there are a huge variety of esoteric technologies which are rarely seen. One such is the plasma tweeter, a type of loudspeaker which generates sound by modulating a small electrical discharge. The benefit of this design comes in its delivering the closest possible to a point audio source, in effect the theoretical ideal speaker for treble frequencies. They’re a little hazardous due to the voltage but aren’t too difficult to make, as demonstrated by [Mircemk] whose version uses a recycled power pentode tube — which is how it showed up in the Hack it Back round of the Hackaday Prize.

It can be thought of as a cousin of the Tesla coil, with the same resonant oscillator but no capacity hat. Instead the top of the coil ends in a point, from which in the perfect speaker a ball of plasma replaces the Tesla’s impressive sparks. In this case the pentode is joined by a high-voltage TV line output transistor as a bias supply, which is in turn modulated with the audio through a small amplifier. It sometimes needs the plasma teasing out of it through discharge to a screwdriver, but the result is a very effective and clear plasma tweeter.

If plasma tweeters interest you, we’ve featured them before.

50-Year-Old 8-Track Changer Repair And Hack

July 25, 2022 by Chris Lott 28 Comments

For reasons still unclear, [Techmoan] has procured an RCA 8-track changer that holds five tape cartridges in a custom carrier. It somewhat works, but had a bit of mechanical issues here and there which needed some maintenance. Additionally, the player is designed for the US market and 60 Hz mains, but [Techmoan] is in the UK with 50 Hz.

Although electronics are used for the basic tape player portion, everything else is operated by mechanical gears, levers, and motors. The system plays both sides of each tape cartridge through to completion, and then switches automatically to the next one in the stack. Cartridges could be up to 90 minutes each, making for over seven hours of playing time. Oddly, the system does not repeat automatically after the fifth tape ends –operator intervention is required. It’s not entirely clear whether these carousels were primarily intended to play background music inside businesses, or built for niche consumer applications.

After discovering there was no setting to adjust the tape’s speed for 50/60 Hz operation, [Techmoan] could have ordered or fabricated a larger-diameter pulley for the motor drive shaft. But in true hacker style, he instead solves the problem with cellophane packing tape. By trial and error, he builds up the pulley diameter by winding lengths of tape until the music sounds just “good enough” to his ear. Then he pulls out the wow and flutter meter to really zero in — and gets it bang on. He says that this changer is needed for a future video, so we’re looking forward to see how it will be employed.

If you like these old mechanical logic controls, check out the video below the break. If you want dig into the workings of an 8-track player, check out Jenny List’s retro teardown from 2017. Does anyone still use 8-track tapes any more?

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