Tuesday, September 17, 2013

Remembering Ray Dolby – Father of Tape Noise Reduction

Though his iconic invention made him a very wealthy man, could the world of hi-fi and music be very different today if Ray Dolby hasn’t bequeathed his invention to the public for almost nothing? 

By: Ringo Bones   

Sadly, Ray Dolby passed away Friday, September 13, 2013 aged 80. Forever remembered after the iconic noise reduction system that bears his name, the music and hi-fi world would probably not exist as we know it today without his inventive solution in tackling the perennial problem of magnetic recording tape hiss.
Ever since the US Armed Forces introduced working samples of World War II era German analog open-reel tape recordings and their associated tape recording and playback equipment near the end of the 1940s in various trade expos, many American audio engineers suddenly got an epiphany that tape hiss or noise is not going to be an easy problem to solve. This is so because tape noise results mainly from the lack of homogeneity of the magnetic coating. Even with existing technology – then and now – the ferrous particles can never be distributed absolutely uniformly throughout the coating and the resulting aggregations of these particles create discrete magnetic fields which – during replay – manifests itself as noise e.m.f. or tape hiss at the playback head and thus amplified along with the desired audio signal. 

Luckily, a then young electronics engineer named Ray Dolby managed to formulate – i.e. engineered - a very cost effective solution that became a noise reduction system that is named after him. Thanks to Ray Dolby, the lowly cassette tape that was primarily created by Philips as an office dictation medium was raised to high fidelity status and became a very cost effective analog tape based music recording medium since the latter half of the 1970s and even displacing vinyl LP in popularity as a domestic hi-fi playback medium during the 1980s. 

In 1967, Henry Kloss heard about Ray Dolby’s noise reduction system – i.e. the Dolby A which was intended for professional studio recording noise reduction applications during the Rock N’ Roll era. It was Kloss who pushed for a consumer version of the Dolby A noise reduction system which is now known as the Dolby B, which Kloss originally saw as a boon to home/domestic open-reel tape users. Somewhat later, Kloss linked the Dolby B noise reduction system with a previously unsuccessful Du Pont product – the chromium dioxide tape. And thanks to the magical midwifery at which Henry Kloss excels, made the Philips cassette tape a runaway commercial success and Ray Dolby a very wealthy man, though Ray Dolby’s almost philanthropic like gesture of never asking for much for the royalties of his iconic noise reduction had only served to popularize his noise reduction system to the masses. 

Thanks to his financial success, Ray Dolby also paved the way for various inventions and inventors to make domestic high fidelity a much more affordable hobby. Using the same Peter Scheiber patents of the old quadraphonic sound systems that expired with barely a whimper back in 1975, Dolby Laboratories managed to create Dolby Pro Logic – a surround sound system that made possible those relatively affordable surround sound capable home cinemas during the early 1980s that also made low-cost mediums like the VHS or Betamax video cassette tapes – and even cassette tapes – capable of life-like surround sound reproduction when used with a designated Dolby Pro Logic decoding box. 

Unbeknown to most of us, Ray Dolby first cut his teeth in the field of radio astronomy. In fact, his Dolby Noise Reduction System came from his earlier work in trying to extract very weak cosmic radio signals from background radiation noise mainly caused by our very own radio telecommunications traffic. 

Tuesday, September 3, 2013

Cathode Poisoning: Death Knell Of Thermionic Devices?

 Though largely forgotten when virtually all consumer electronic devices turned solid state at the start of the 1970s, is cathode poisoning still a concern for those who still use thermionic vacuum tube based electronic devices? 

By: Ringo Bones 

Though now virtually forgotten when virtually every consumer electronic devices we have are solid state based – including the now “affordable” organic light emitting diode (OLED) video display monitors, there was a time when cathode poisoning was of grave concern – like back in the days when the first programmable digital computers still use thermionic vacuum tubes. But as thermionic vacuum tubes returned in the high end audiophile scene, could the concept of cathode poisoning – in a strange twist of fate – inspire consumer electronic companies to design longer lasting thermionic vacuum tubes, even ones rivaling the longevity of solid state transistors and integrated circuits? 

Back in the 1950s, when vacuum tube technicians were still concerned with their tubes developing “sleeping sickness” whenever it was kept in soft-start mode for a prolonged period of time in radar and digital computer applications, cathode poisoning was of a grave concern on how to prolong the life of their banks upon banks of vacuum tubes when they are mostly switched to low current mode in switching applications. In short, cathode poisoning is the failure mode of a thermionic vacuum tube where the emissive layers degrade slowly with time and much more quickly when the cathode is overloaded with too high a current – which usually results in weakened emission and diminished power of the vacuum tubes or brightness of the cathode ray tubes – i.e. CRTs. Given what every “thermionic vacuum tube experts” had learned through such first hand events, were there any progress made in prolonging vacuum tube life and making cathode poisoning less of a concern? 

Even though there are various rare earth and halogen compound based cathode coatings that prolong thermionic vacuum tube life that make cathode poisoning much less of a concern, in the rather conservative world of thermionic vacuum tubes primarily designed for audio applications, manufacturers are choosing the tried-and-true from a sound quality perspective but older thoriated tungsten filaments which was discovered in 1914 and made practical by Irving Langmuir in 1923. A small amount of thorium is added to the tungsten filament. The filament is heated white hot at about 2,400 degrees Celsius and thorium atoms migrate to the surface of the filament and form the emissive layer. Heating the filament in a hydrocarbon atmosphere carburizes the surface and stabilizes the emissive layer. Thoriated tungsten filaments can have very long lifetimes and are resistant to high voltages. They are used in nearly all big high power vacuum tubes for radio transmitters and in some tubes for hi-fi audio amplifiers. Their lifetimes tend to be longer than those of oxide cathodes. 

Due to concerns about thorium ionizing radiation emission – i.e. radioactivity – and toxicity, efforts had been made to find alternatives. One of them is zirconated tungsten where zirconium dioxide is used instead of thorium dioxide. Other replacement materials include various rare earth oxides like lanthanum (III) oxide, yttrium (III) oxide, cerium (IV) oxide and other mixtures. 

Various rare earth borides had been used to prolong the life of thermionic vacuum tubes but there’s no news yet on how they affect sound quality of vacuum tubes when used in audio applications. Like boride cathode vacuum tubes that use lanthanum hexaboride and cerium hexaboride as coating of some high-current cathodes. Hexaborides show low work function around 2.5 eV. They are also resistant to cathode poisoning. Cerium hexaboride cathodes show low evaporation rate at 1,700 Kelvin than lanthanum hexaboride, but becomes equal at 8,800 Kelvin and higher. Cerium hexaboride cathodes have one and one half times the lifetime of lanthanum hexaboride cathodes due to its higher resistance to carbon contamination. Hexaboride cathodes are about 10 times as bright as the tungsten ones and have lifetimes up to 10 to 15 times longer. They are used in electron microscopes, microwave vacuum tubes, electron lithography, electron beam welding, X-Ray vacuum tubes and free electron lasers. However, these materials tend to be expensive. Other useful rare earth based hexabordes with long lives are yttrium hexaboride, gadolinium hexaboride and samarium hexaboride. 

Even though rare earth based hexaboride cathode coatings for thermionic vacuum tube devices may not yet be a hit in the hi-fi audio world, but I think these might have contributed in making extra long life CRTs or cathode ray tubes in television sets. Back in 1995, I’ve bought a 14-inch GoldStar color TV manufactured by LG Collins Electronics Manila, Inc. It’s a model CN-14A146 with serial number 60524212 which I bought for around 150 US dollars and it is still running until this very day. I wonder if this particular GoldStar 14-inch color TV uses a rare earth based hexaboride cathode coated CRT? 

The 7591 Vacuum Tube: Return of the Prodigal Vacuum Tube?

It became virtually extinct by the time Ronald Reagan ruled the free world, but did the relatively recent reintroduction of the 7591 vacuum tube manage to save our much loved vintage audio gear?

By: Ringo Bones 

From the1966 Ampeg GS-12R electric guitar amp prized by Jazz guitarists for its clean Jazzy timbres to the famed Fisher and Hermon Hosmer Scott receivers from the Golden Age of Stereo, the reintroduction of the 7591 pentode output vacuum tube by Russian vacuum tube manufacturer Sovtek via their Electro Harmonix arm had made every vintage audio gear enthusiast and Jazz guitarist eternally grateful. The reintroduction even makes me wonder if the 1966 Ampeg GS-12 R guitar amp and the famed Fisher and H.H. Scott receivers were even popular in Soviet era Russia and the rest of the East-Block countries during the height of the Cold War. 

Thanks to the reintroduction of the famed vacuum tube in the form of the Electro Harmonix 7591A EH, every Fisher 500-C and  HH Scott 345 and related model receiver – or the 1966 Ampeg GS-12R guitar amp - using the tube can now be resurrected with ease – which was very a very daunting task back during the Reagan administration half of the 1980s where modern pentode type vacuum tube based circuits became extinct since they were slowly being phased out by the start of the 1970s due to the fact that every electronics engineer can more or less replace them with solid state parts - if sound quality degradation due to increased levels of overall negative feedback was overlooked. 

Historically, the 7591 pentode vacuum tube was introduced in 1958 and registered with the EIA in 1960 after being developed and produced by Westinghouse’s receiving tube factory in Bath, New York. Given that Dr. Harvey C. Rentschler used to be the Director of Research for the Westinghouse Lamp Division, one could wonder if Dr. Rentschler was instrumental in the development of the 7591 vacuum tube. And by the way, the best NOS type of this tube was the famed 1962 Westinghouse 7591 which has a clearer sound than the new Electro Harmonix 7591.      

Monophonic Music Utilitarianism In The 21st Century

It might be for all intents and purposes an obsolete music format in the age of 6-channel digital music downloads, but are mono music recordings nonetheless still a utilitarian tool for discerning audiophiles? 

By: Ringo Bones 

From the perspective of today’s de rigueur discrete 6-channel digital surround sound, it is quite sobering to reflect on the historical origins of loudspeaker positioning for optimum two-channel stereo presentation. Around the dawn of the Golden Age of Stereo in 1956, F.H. Brittain and D.M. Leakey wrote articles in the Wireless World magazine on the subject, entitled Two Channel Stereophonic Sound Systems. Stereo – as in two-channel stereophonic sound – in the home wasn’t a common and practical reality until way into 1958, yet messrs Brittain and Leakey laid down basic principles that are still being followed slavishly until today. Well, back in the mid 1990s, Brittain and Leakey’s method were followed by the then newly recruited generation of hi-fi enthusiasts / audiophiles without them even actually knowing who Brittain and Leakey were or the two loudspeaker positioning method that they developed. 

Know them by name or not, there are still veteran audiophiles out there who are not using the “tried and tested” Brittain and Leakey arrangement. Brittain and Leakey’s tried and tested method does have a number of advantages – principally in the creation of a solid narrow image when both left and right speakers are fed with an identical mono signal. This is of crucial importance when it comes to creating a wide, stable, precise left-center-right two-channel stereo soundstage. 

If your speakers are optimally set up, you should hear a narrow center image when a mono signal – or a monophonic music recording – is played. Generally, this will only be achieved if the speakers are angled – or toed in – so their axes cross at an imaginary point in or in front of the main listening area, thus the importance of the toe-in of hi-fi loudspeakers in your listening room. 

With speakers flat against a wall and pointing straight down the room, an arrangement often employed in British homes – and typical in cramped apartment block type dwellings in Singapore and Hong Kong resident audiophiles – you won’t be able to achieve a narrow center image with mono recordings, but effectively create a “double mono” effect. As a result, stereo soundstaging will be less pinpoint precise than it could be, resulting with a vague center placement and poor “spread” between left / right channels.
Whether it is wholly desirable to achieve a narrow center image with two speakers is a moot point, as live sound is never so precise. But a narrow center image does ensure that you hear exactly how a recording was actually miked and mixed stereophonically, by allowing one’s home hi-fi speaker set up to recreate the subtle shifts of amplitude and phase that our ears use to locate sounds. 

Try this experiment; With a mono music recording or a mono radio broadcast (this can be often found in the AM radio band) – or if your FM only tuner has one – switch it into mono mode to convert what was once stereophonic FM broadcasts into instant mono. Using such methods, listen to how narrow your phantom center image sounds. You should hear a thin narrow central line of sound and not be aware of the two spaced loudspeakers – only an image between them. But be careful though as some recorded musical instruments – and even certain singers’ voices – can sound quite timbrrally different when converted into mono. A good example is Gloria Estefan – her voice sounds wholly different in mono when compared side-by-side with her full-blown stereo recordings.   

If you don’t get a clear impression of a center image, check for correct speaker phasing then angle each enclosure in or out until the center image snaps into strong focus. If possible, alter the distance between your listening seat and the speakers, moving closer or further away to see what happens.
A narrow center image with two-speaker mono will not necessarily result in a more pleasing overall sound, but things should be more precise – imaging wise. And this should allow you to hear the music exactly as it was recorded – in your listening room and in your own home.