Sunday, March 29, 2015

The 6V6 Vacuum Tube: For Guitarists Only?

Have you ever wondered why there are no commercially produced hi-fi audio power amplifiers using the 6V6 output vacuum tubes despite its widespread use in electric guitar amplifiers? 

By: Ringo Bones 

Despite its widespread use in the “guitar world”, the 6V6 vacuum tube is probably the only widely available vacuum tube – there’s even an excellent sounding version in current production by Electro-Harmonix – that no commercially produced hi-fi audio power amplifier uses as its output power tube. While its closest equivalent – the older venerable 6L6 is widely used in both electric guitar and hi-fi amps, the 6V6 seems to have stuck in the “guitar world” despite the existence of DIY hi-fi literature dating from the 1950s - i.e. 1950s era RCA application notes - with circuit diagrams of audio power amps using the 6V6 vacuum tube. 

The 6V6 is a beam power tetrode that was introduced by RCA back in mid 1937 and still in current use, especially in electric guitar amplifiers. Similar to its predecessor – the 6L6 which was introduced back in 1936 – the 6V6 was far more widely used during its heyday – i.e. from 1945 to the early 1970s when solid-state transistor became reliable and commercially viable enough for household audio amplification purposes. In comparison, the 6L6 produced more output power than required by general use consumer electronic devices right after World War II with corresponding power and circuit requirements. 

The lower powered 6V6 was better suited for the average home use and became common in the audio output stage of “farmhouse” table top radios (Stromberg Carlson?) where power pentodes such as the 6F6 had previously been used. The 6V6 requires less heater power and produced less distortion than the 6F6 while yielding a higher output in both single-ended and push-pull configurations. Additionally, before the transistor era, the 6V6 has applications in the automotive and portable radio market. In an audio output stage, a single 6V6 can be used to produce 5-watts continuous power and a push-pull pair for about 14-watts with the higher output requiring a larger, more expensive output power transformer with grain oriented core laminations for better efficiency.  

The 6V6 was first introduced in both metal and shouldered glass tubes. RCA was promoting the superiority of their metal tube designs during the second half of the 1930s and this tube having been introduced during that period was produced in large quantities in this format. Other vacuum tube manufacturers also produced the 6V6 in glass tubes which were commonly found in radios not made by RCA. By 1940, the 6V6 was mostly being produced in smaller “GT” glass envelope and later the 6V6GTA was introduced which has a controlled warm-up period. 

Generally speaking, 6V6 output power vacuum tubes are sturdy and can be operated beyond their published specifications. The 6P6S – which has poor tolerance for out-of-spec operation versus most American and Western European made 6V6 variants – is an exception. Because of this, the 6V became very popular for use in consumer market musical instrument amplifiers particularly combo style electric guitar amps such as the Fender Champ which uses the 6V6 in a single-ended configuration. While the Gibson GA-40 and the Fender Princeton Reverb and the Fender Deluxe Reverb amps which run a push-pull pair of 6V6s at 410-VDC plus on the plates. This market allows Mainland Chinese, Slovak and Russian vacuum tube factories to keep the 6V6 in production to this day. Because of the relative similarity in voltage and other characteristics between the 6V6 and the popular EL84 / 6BQ5 power pentode vacuum tube, several electronics and musical instrument companies have developed adapters to allow an amplifier with 6V6 octal sockets to accept the miniature noval pinned EL84. However no reverse adapter has been made or developed to be commercially available to allow an EL84 tubed amp to accept 6V6 output power vacuum tubes. 

Cryogenics: A Very Effective Audiophile Tweak?

From vacuum tubes to interconnect cables, does cryogenics prove to be the most effective audiophile / high fidelity tweak of the last 25 years? 

By: Ringo Bones  

Cryogenics is anything that concerns with temperatures colder than minus 200 degrees Fahrenheit and since the early 1990s, it seems that almost anything from electric bass guitar strings – i.e. Dean Markley’s cryogenically treated bass guitar strings – slide trombones, trumpets, an Olympic trap shooter’s MX8 Perazzi shotgun just to mention a few featured on a Discovery Channel program aired back in 1995 that had improved its performance after these items are cooled as close as economically possible to absolute zero (-459.7 degrees Fahrenheit). With interconnects and vacuum tubes oft marketed as having “improved sound” after they are cryogenically cooled close to absolute zero, does cryogenics proved to be the most effective audiophile tweak out there that is backed by “hard science”?

One widely advertized cryogenic treatment provider online is the “Harma Deep Cryogenic Treatment” or the “Harma Process” in which they can make ordinary vacuum tubes – i.e. modern manufacture vacuum tubes made in Mainland China or Russia that’s less than 20 years old - to sound as good as those NOS (new old stock) vacuum tubes that were manufactured back in the 1930s to the 1950s. According to the company, their “Harma Deep Cryogenic Treated” vacuum tubes offers the immense warmth and smooth distortion characteristics only normally found in very expensive NOS vacuum tubes such as 1950s era manufactured Mullard vacuum tubes. Just imagine what it could do for those already nice-sounding modern manufacture vacuum tubes from Electro-Harmonix.

The “Harma process” involves taking the vacuum tubes and gradually cooling them down during a 12-hour period to minus 312 degrees Fahrenheit and keeping them at that low temperature for a minimum of 24 hours, Then, during the course of a 12-hour period, the vacuum tubes are slowly brought up to room temperature. Metals respond very well to the deep cryogenic process such as these – i.e. brass wind instruments and electric bass guitar strings sounding more sonorous after being subjected to such treatment and even Olympic trap shooting competition shotguns will acquire a smoother action and the barrel lasts longer. 

The reasons for such improvements were as follows: During the cooling or solidification phase of the initial manufacturing process, molecules are trapped in a haphazard pattern. This is down to the stress caused in the bending and welding of the anode plate material. The random placement causes obstacles for electrons and when encountered, this interference can cause noise, slow down electron flow and sound deterioration eventually affecting the sound quality of the vacuum tube. At very cold temperatures below minus 312 degrees Fahrenheit, the molecules will align in a more uniform compact structure through the removal of kinetic energy. When the material is returned to ambient temperature / room temperature, this new uniform compact pattern is maintained, thus changing the molecular structure of the nickel used in the anode and the other bits inside the enclosure of the vacuum tube permanently. 

This process makes a permanent change and the benefits does not deteriorate over time upon the item’s return to the item’s optimal operating temperature, it changes the whole way the vacuum tube performs. The biggest benefit satisfied customers have noticed about the “Harma Process” has been the dramatic improvement in dynamic range. Bass response became clearer and a reduction in microphony and clearer more transparent high frequencies. 

To my ears, cryogenically treated analog line-level interconnects tend to sound twice as loud as their on treated counterparts and offer richer harmonics – especially in the mid range. Back in the early 1990s, I managed to borrow a 150 US dollar cryogenically treated Esoteric Audio USA interconnect and a non-cryogenically treated 500 US dollar Monster Cable interconnect for an “informal” side-by-side comparison. The “cheaper” cryogenically treated Esoteric Audio USA cable has a richer mid range and more “acoustic sounding” low frequencies and sounded a “bit louder” than the more expensive but untreated Monster Cable but the Monster offered cleaner high frequencies and seems to produce very high frequency signals missed by the cryogenically treated Esoteric primarily due to the costlier materials used in the more expensive – but not cryogenically treated Monster Cable. 

Saturday, March 7, 2015

Dolby Atmos: Best Surround Sound Format For Movies Ever?

With relatively good sounding public demonstrations and public appreciations since its launch, will Dolby Atmos become the best surround sound format for movies ever? 

By: Ringo Bones 

As every high fidelity audio and movie enthusiast knew by now, Dolby Atmos is the name of the latest digital surround sound technology that was announced by Dolby Laboratories back in April 2012. Even though it was first utilized in the Pixar made move Brave, many home cinema buffs associate Dolby Atmos with the movie Gravity that stars Sandra Bullock and George Clooney because it is the one oft use to demo the Dolby Atmos capable home theater audio systems currently on sale. Unlike the DTS encoded Mousehunt release circa 1998, the 2013 era Gravity’s Dolby Atmos surround sound audio tracks managed to produce panned sound effects concurrent to what’s actually happening on screen. 

The first officially authorized Dolby Atmos installation was in the Dolby Theater in Hollywood, California fro the premier of Pixar’s Brave back in June 2012. Throughout 2012, Dolby Atmos saw a limited release of about 25 installations worldwide with an increase to 300 locations in 2013. There are currently 2,000 official Dolby Atmos locations worldwide as of February 2015. 

From the film post production audio engineer’s perspective, Dolby Atmos takes advantage of the now industry standard pro audio digital recording platforms first developed during the late 1990s like a re-recording mixer using a Pro Tools plug-in (available  downloadable from Dolby) or a Dolby Atmos equipped large format audio mixing console such as AMS Neve’s DFC or Harrison’s MPC5 to designate a particular location in the theater as a three dimensional placement where dynamic sound source should seem to be coming from. 

The Dolby Atmos digital surround sound technology allows up to 128 audio tracks plus associated pan meta-data to de distributed to theaters for optimal dynamic rendering to loudspeakers based on the typical commercial or home theater’s capabilities. Dolby Atmos was initially geared towards commercial cinema applications only, but was later adapted to home cinema thus the association with the new surround sound format with the movie Gravity since it was the Dolby Atmos encoded DVD that was often used in demonstrating the Dolby Atmos ready home theater audio systems that recently entered the market. In addition to playing back standard 5.1 or 7.1 Dolby Digital surround sound mix using loudspeakers grouped into arrays, the Dolby Atmos system can also give each loudspeaker its own unique feed based on its exact location, thereby enabling many new front, surround and even ceiling-mounted height channels for the precise panning of select sounds such as helicopter or rain – or even those overhead public address speakers in a supermarket.  

During a recent Audio Engineering Society talk by a one of Dolby Atmos’ senior mixers Chris Goodes, with industry VIPs and a few fortunate enthusiasts took a tour of the facility and some demos of the capabilities of Atmos. This particular demonstration room was intended by Dolby Labs to “officially” demonstrate their latest surround sound system was the size of a small to medium commercial cinema. With Atmos in full flight, everyone noticed a greater “seamless” resolution of movement or pans. Instead of an array of side surrounds that act as a single channel, each one can act as an individual channel. This means there is greater control of movement – at least from a post-production audio engineer’s perspective. 

Dolby Atmos’s “object approach surround sound” means that out of over 100 possible simultaneous objects, each one is assigned a 3D location within the cinema space as well as the object having a size. To my ears at least, it is reminiscent of how a typical zero feedback single-ended triode amp does imaging. In a 5 or 7 channel system, we have 5 or 7 speakers which seek to recreate the sound or acoustic event. With Dolby Atmos, the difference is probably best demonstrated in spaces often found in a typical commercial cinema where you might have 10 side speakers rather than the one or two found in a typical domestic home theater setup. Dolby Atmos in actual practice has the ability to pull the sound further away from the screen. I heard this result, too, but whether it is a good or bad thing is entirely up to you. 

Despite the things that it does right, I still have reservations about Dolby Atmos. If Atmos is not done properly or improperly mixed by post-production “audio-cowboys”, it could result in unnatural use of effects coming from the ceiling that don’t belong there – reminding me of that quirky DTS surround sound demo of Mousehunt back in 1998. But when done correctly, like the audio mix in the movie Gravity, it puts Dolby Atmos in the must-have territory for most home theater enthusiasts given that good sounding entry level systems now cost a little over 200 US dollars. From my perspective at least, Dolby Atmos works best when used subtly rather that a post-production audio engineer trying to recreate what they hear that time when they are high on lysergic acid when mixing a chamber music ensemble or a squad-level firefight.