A Look At Zweikanalton Stereo Audio And Comparison With NICAM

With how we take stereo sound for granted, there was a very long period where broadcast audio and television with accompanying audio track were in mono. Over the decades, multiple standards were developed that provide a way to transmit and receive two mono tracks, as a proper stereo transmission. In a recent video, [Matt] over at [Matt’s Tech Barn] takes a look at the German Zweikanalton (also known as A2 Stereo) standard, and compares it with the NICAM standard that was used elsewhere in the world.

Zweikanalton is quite simple compared to NICAM (which we covered previously), being purely analog with a second channel transmitted alongside the first. Since it didn’t really make much of a splash outside of the German-speaking countries, equipment for it is more limited. In this video [Matt] looks at the Philips PM 5588 and Rohde & Schwarz 392, analyzing the different modulations for FM, Zweikanalton and NICAM transmissions and the basic operation of the modulator and demodulator equipment.

An interesting aspect of these modulations are the visible sidebands, and the detection of which modulation is used. Ultimately NICAM’s only disadvantage compared to Zweikanalton was the higher cost of the hardware, but with increased technological development single-chip NICAM solutions like the Philips SAA7283 (1995) began to reduce total system cost and by the early 2000s NICAM was a standard feature of TV chipsets, just in time for analog broadcast television to essentially become irrelevant.

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How To Make A Larger Air-Cored Inductor

Radio amateurs often have a love-hate relationship with home-made inductors, sharing all kinds of tips and tricks as to how the most stable nanohenry inductor can be wound. But there’s another group in the world of electronics with an interest in high-quality inductors, namely the audio enthusiasts. They need good quality inductors with a values in the millihenries, to use in loudspeaker crossover networks. [Homemade Audio] takes us through their manufacturing process for these coils, and the result is a watchable video resulting in some very well-made components.

The adjustable former is a machined aluminium affair of which we’re treated to the full manufacture. It’s likely the same results could be achieved with a 3D printed reel. The free-as-in-beer Coil64 on Windows is used to calculate the dimensions and number of turns, and it’s set up on a jig with a cordless screwdriver doing the winding. The best technique for flat layers of turns is explained, and a coat of varnish is put on each completed layer. We’re guessing this is to stop the coil “singing” at audio frequencies.

With a set of cable ties holding it together the result is a very tidy component. It’s adjusted a few turns to get the right value with an LCR meter, however experience tells us that a tiny percentage either way won’t harm the resulting network too much. If you make your own speakers, the video below the break could be extremely useful.

Need a loudspeaker primer? We have just the article for you.

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A CRT Audio Visualiser For When LEDs Just Won’t Do

It has been a recurring feature of consumer audio gear since the first magic eye tube blinked into life, to have some kind of visualization of the sound being played. Most recently this has meant an LED array or an OLED screen, but [Thomas] has gone one better than this with a CRT television converted to perform as a rudimentary oscilloscope.

The last generation of commonly available monochrome televisions were small 5″ CRT models made in China. They never received digital tuners, so as digital TV has become the norm they are now useless to most people. Thus they can often be found for pennies on the second-hand market.

[Thomas]’s hack involves gutting such a TV and retaining its circuitry, but disconnecting the line driver from the deflection yoke. This would normally leave a vertical line on the screen as it would then be moved only by the frame driver at 50 Hz for PAL or 60 Hz for NTSC. By connecting an audio loudspeaker amplifier to the line deflection yoke he gets that low quality oscilloscope. It would be of limited use as an instrument, but few others will have such a cool audio visualizer. He’s viewing the screen in a portrait orientation, we’d be tempted to rotate the yoke for a landscape view.

It’s worth pointing out as always that CRT TVs contain high voltages, so we’d suggest reading up on how to treat them with respect.

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What’s Old Is New Again: A Linux PC From A Set Top Box

There was a time around two decades ago, when the new hotness was taking control of home routers to use as small Linux computers. An echo of this era lives on in the name of the OpenWrt minimal Linux distribution, in reference to the Linksys WRT54G router which started it all. Routers as small computers were displaced by small cheap Linux machines from the likes of Raspberry Pi, and the promise of discarded home network gear doing interesting stuff receded. Now it might just be back, as [Jasper Devreker] shows us an Android TV set-top box from a mobile carrier repurposed as a Linux computer that can even run a desktop environment.

The method starts as you might expect, by identifying a mystery connector as a debug serial port. This outputs all sorts of interesting boot information, but can be dropped into a uBoot shell. From here with a bit of effort the eMMC storage could be dumped, and from that the nature of the machine could be deduced. The CPU is an Amlogic quad core ARM Cortex-A53 SoC, which by a stroke of luck is a target for which an Armbian build is available. From there a Linux installation could be assembled, and even an AFCE desktop.

These boxes are handed out in the hundreds of thousands by home connectivity providers, so there’s value in this type of hack as they become available for experimenters. Perhaps it’s more useful as a small headless Linux machine than as a desktop, but we sense there are more machines to come in this line.

If you’d like a little bit of history on hackable Linux devices, have a read of one of our earliest posts featuring the Linksys WRT54G.

Classic Video Chip Drives A Modern TFT

A lot of us have a soft spot for retrocomputers, and there’s nothing quite like running original hardware. Unfortunately if you’re after the truly original touch then that means carrying along the family TV from 1982, and that’s where life becomes annoying. What if there were a way you could easily drive an LCD panel from a classic video controller? Help is at hand for owners of TI TMS9928A video chips, courtesy of [umaker], with a clever interface board that drives an SPI or parallel TFT.

At its heart is not the FPGA you might expect, but an STM32G4 microcontroller on an STM Nucleo board. This digitizes the R-Y and Y components from the TMS chip which would originally have been destined for an NSC or PAL encoder, does the color conversion through its algorithm, and transfers the result to the screen. This is a task which would back in the day when NTSC or PAL were king have been seen as extremely computationally intensive, so it’s a mark of just how capable an STM can be that a few dollar microcontroller can do it.

We can see this technique proving to be extremely useful across a lot of different retro color graphic applications. We’re not sure whether its lag would be too much for a light gun game, but it would be nice to think that it would result in handheld retro machines.

We encountered this project previously, when as part of its development he needed a sync separator.

A Single Ended Vacuum Tube Amplifier With A Modern Twist

Despite the oldest solid state audio circuitry now qualifying for a pension and a bus pass where this is being written, the thermionic tube retains a foothold in the world of audio — cherished by enthusiasts for the warm sound it is claimed to impart. ForĀ  the electronics enthusiast a tube audio amplifier makes for an interesting and unusual project, and for that reason it’s one tackled by many. [Keri Szafir] is no exception, and she’s produced a stereo tube amp with a few modern features.

Electrically it’s a relatively conventional single-ended design using a double triode and a power pentode for each channel. It follows a so-called ultra-linear circuit, with a tap on the output transformer feeding one of the pentode’s grids. The modern features come via a switched Bluetooth input and a motorized volume control, something that would have never been found on such an amp when they were the cutting edge.

We have to admit a soft spot for this type of amp, and we particularly like this one for its very period construction style using cable lacing to keep the wiring under control. We more often see these amps using the cheaper integrated triode-pentode tubes which makes them especially easy to build, so the separate preamp is a little different. We’re not sure we’d have spent extra on the fancy E88cc tubes though. Continue reading “A Single Ended Vacuum Tube Amplifier With A Modern Twist”

Tube Audio Amplifiers Needn’t Be Complex

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.