Only Mechanical Relays Will Do For Automated Hi-Fi Audio Source Switching

March 10, 2018 by Jenny List 54 Comments

If you are a devotee of audiophile-quality analogue hi-fi, switching between sources simply can not be done through a solid-state device. Only physical switches will do because they come without the risk of extra noise or distortion that their silicon equivalents might bring.

That is the philosophy that lies behind [Skrodahl]’s relay-based audio switching board, which boasts 5 high-quality relays each handling a stereo input, with their control passed either to a rotary switch or to an ESP32 module. The ground connections on audio and switching sides are isolated from each other to avoid transient noise finding its way to the speakers.

You might think that an audio switching board is a very simple device indeed and thus not worthy of Hackaday’s attention, but it’s surprisingly easy to make a mess of a module like this one and they have put in some effort to avoid the pitfalls. The metal-can version of the switching transistors seems a little overkill, but fancy audio is a funny business.

If the ESP isn’t your bag, we’ve brought you another relay based audio switcher in the past that used an Atmel chip.

The Best Stereo Valve Amp In The World

August 16, 2017 by Jenny List 83 Comments

There are few greater follies in the world of electronics than that of an electronic engineering student who has just discovered the world of hi-fi audio. I was once that electronic engineering student and here follows a tale of one of my follies. One that incidentally taught me a lot about my craft, and I am thankful to say at least did not cost me much money.

Construction more suited to 1962 than 1992.

It must have been some time in the winter of 1991/92, and being immersed in student radio and sound-and-light I was party to an intense hi-fi arms race among the similarly afflicted. Some of my friends had rich parents or jobs on the side and could thus afford shiny amplifiers and the like, but I had neither of those and an elderly Mini to support. My only option therefore was to get creative and build my own. And since the ultimate object of audio desire a quarter century ago was a valve (tube) amp, that was what I decided to tackle.

Nowadays, building a valve amp is a surprisingly straightforward process, as there are many online suppliers who will sell you a kit of parts from the other side of the world. Transformer manufacturers produce readily available products for your HT supply and your audio output matching, so to a certain extent your choice of amp is simply a case of picking your preferred circuit and assembling it. Back then however the world of electronics had extricated itself from the world of valves a couple of decades earlier, so getting your hands on the components was something of a challenge. I cut out the power supply by using a scrap Dymar Electronics instrument enclosure which had built-in HT and heater rails ready to go, but the choice of transformers and high-voltage capacitors was something of a challenge.

Pulling the amplifier out of storage in 2017, I’m going in blind. I remember roughly what I did, but the details have been obscured by decades of other concerns. So in an odd meeting with my barely-adult self, it’s time to take a look at what I made. Where did I get it right, and just how badly did I get it wrong?

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Retro Teardown: Inside An 8-Track Stereo Player

April 12, 2017 by Jenny List 43 Comments

If you are a connoisseur of analogue audio, it’s probable you might have a turntable and a stack of records at home somewhere. If you are of a certain age you may even have a cassette deck, though you’re more likely to have abandoned that format some time in the 1990s. If you are old enough to have been around in the 1960s or 1970s though, you may have owned another analogue audio format. One of several that you might have found in a well-equipped home of that period was the 8-track stereo cartridge, a self-contained tape cassette format that fit four stereo tracks onto a single quarter-inch tape loop as eight parallel tracks, four each of left and right. A triumph of marketing, really, it should more accurately have been called 4-track stereo.

An 8-track stereo cartridge. Government & Heritage Library, State Library of NC (CC BY 2.0).

8-track cartridges were developed from earlier tape cartridge formats, largely to satisfy the demands of the automotive industry for interchangeable in-car entertainment. Thus if you owned an 8-track player it was most likely to have been found in your car, but it was not uncommon to find them also incorporated into home hi-fi systems. Thus we come to our subject today. Our retrotechtacular series usually highlights a video showing a bygone technology, but today we’re going to get a little more hands-on.

Some time in the early 1990s, I acquired an 8-track player, a BSR McDonald unit manufactured in the UK and dating from the early 1970s. BSR were much more well-known for their turntables, so this is something of an oddity. Where I found it has disappeared into the mists of time, but it was probably at a radio rally or junk sale. I certainly didn’t buy it because I wanted it to play 8-track tapes, instead I wanted a talking point for my hi-fi, something quirky to set it apart from everyone else’s. So every incarnation of listening enjoyment chez List for the last quarter century has had an 8-track player nestling within it, even if it has never played a tape while in my ownership. Thus we have a unique opportunity for this retro teardown.

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Custom Media Center Maintains Look Of 70s Audio Components

April 9, 2017 by Dan Maloney 20 Comments

Slotting a modern media center into an old stereo usually means adding Bluetooth and a Raspberry Pi to an amp or receiver, and maybe adding a few discrete connectors on the back panel. But this media center for a late-70s Braun hi-fi (translated) goes many steps beyond that — it fabricates a component that never existed.

The article is in German, and the Google translation is a little spotty, but it’s pretty clear what [Sebastian Schwarzmeier] is going for here. The Braun Studio Line of audio components was pretty sleek, and to avoid disturbing the lines of his stack, he decided to create a completely new component and dub it the “M301.”

The gutted chassis of an existing but defunct A301 amplifier became the new home for a Mac Mini, Blu-Ray drive, and external hard drive. An HDMI port added to the back panel blends in with the original connectors seamlessly. But the breathtaking bit is a custom replacement hood that looks like what the Braun designers would have come up with if “media center” had been a term in the 70s.

From the brushed aluminum finish, to the controls, to the logo and lettering, everything about the component that never was shows an attention to detail that really impresses. But if you prefer racks of servers to racks of audio gear, this media center built into a server chassis is sure to please too.

Thanks to [Sascho] and [NoApple4Me] for the nearly simultaneous tips on this one.

Record Players Explained For The Streaming Generation

March 3, 2017 by Jenny List 68 Comments

How do you consume your music, these days? Aside from on the radio, that is. Do you play MP3 or other files on your phone and computer, or perhaps do you stream from an online service? If you’re really at the cutting edge though you’ll do none of those things, because you’ll be playing it on vinyl.

The legendary Technics SL1200 direct-drive turntable, as used by countless DJs. Dydric [CC BY-SA 2.5)], via Wikimedia Commons. — The legendary Technics SL1200 direct-drive turntable, as used by countless DJs. Photo by Dydric CC-BY-SA 2.5

A few years ago reporting on a resurgence of sales of vinyl records was something you would never have expected to see, but consumer tastes are unpredictable. Our red-trousered and extravagantly bearded hipster friends have rediscovered the glories of the format, and as a result it’s popping up everywhere. For those of us who are old enough to have genuinely been into the format before it was cool again, the sight of Sergeant Pepper and Led Zeppelin II on 12″ at outrageous prices on a stand at the local supermarket is a source of amusement. It’s good to see your first love back in vogue again, but is it really the £20($25) per album kind of good?

With the turntable having disappeared as an integral part of the typical hi-fi setup the new vinyl enthusiast is faced with a poor choice of equipment. Often the best available without spending serious money at an audiophile store is a USB device with the cheapest possible manufacture, from which the playback will be mediocre at best. We’ve lost the body of collective knowledge about what makes a good turntable to almost thirty years of CDs and MP3s, so perhaps it’s time for a quick primer.

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Adding Charging Back To Old Apple Accessories

November 9, 2012 by Mike Szczys 6 Comments

From time-to-time we’ve been frustrated by the lack of backwards compatibility for Apple accessories. We have a great Monster FM transmitter that used the screen of the original iPod to select a channel. That was a feature we just loved which it never worked with any future hardware. We may not be able to get that back, but perhaps this hack can help us implement the ability to charge newer Apple devices using older accessories.

Seen above is the mounting dock from the iPod Hi-Fi speakers released back in 2006. Apparently the sound out of this set of speakers is just great, but you won’t be able to charge your modern device while it’s playing music. That is unless you’re not afraid to solder on a few simple components and roll in a switching regulator which can source at least one Amp of current. As we’ve seen in the past, Apple uses a couple of voltage dividers to identify modern chargers. These are installed on the D+ and D- lines of the USB connector and are pretty easy to recreate if you know the voltage levels the device is looking for. In this case a 39K, two 51k, and one 75k surface mount resistors are free-formed right next to the connector on the Hi-Fi’s dock PCB. The regulator on the right supplies the juice for charging. It’ll charge modern devices now, and even work with the iPhone five if you use a simple dock connector adapter.

Resurrecting A Hi-Fi Cabinet

July 7, 2012 by Mike Szczys 25 Comments

[VintagePC] pulled this old stereo out of a barn. It was in pretty shabby shape, but he managed get it running again and make it look great as well.

While it had been protected from the elements, it had not been protected from the rodents. Mice had chewed their way through the fiberboard backing and made a nice home inside. He mentions that they chewed the string which operates the tuning dial, and we’re sure they were the cause of other problems as well. He gives the wise advice of not powering on an old set like this until you have a chance to assess the situation.

The insides of the amplifier were about as disorderly as the last radio repair we looked at. But after carefully working his way through the circuits, replacing capacitors and resistors as needed, he started to make some progress. The receiver coil needed to be rewound and he used wire from an old CRT monitor for this purpose. The loop antenna was remounted and the record player arm was given a new cartridge and balanced using a clever LEGO apparatus. Some veneer work and wood finishing brought the case itself back to its original beauty. We’d say the hard work was well worth it. He’s got a big piece of furniture he can always be proud of!