Monday, December 21, 2015

Are Light Emitting Diodes Too Noisy For High End High Fidelity Use?

Though it has become ubiquitous as a power on indicator of consumer electronics since its introduction back in the 1960s, are light emitting diodes just too noisy for high end hi-fi use? 

By: Ringo Bones 

Ever since I started my audio equipment and musical instrument modifying business back in the early 1990s, I’ve noted that some audio equipment – especially very high gain solid state moving coil cartridge phono preamplifiers – will improve its noise floor when you replace the red or green LED power on indicator or light emitting diode power on indicator with a miniature tungsten filament power on indicator light bulb often used in older audio equipment. In my experience, the main beneficiaries from such moddings are vacuum tube based moving coil phono preamplifiers that use the ECC88 / 6DJ8 / 6922 small-signal vacuum tube and those iconing solid-state moving coil phono preamplifiers that use FETs and transistors or a mix of both like the DNM 3B and the Michell Iso and Michell Argo. 

During the first decade of the 21st Century, I also discovered that organic LEDs are noisier than their plain vanilla LED counterparts. Even though the invention of organic LEDs made possible those relatively affordable and indispensable part of 21st Century home theater unnecessarily large video monitors, blue LEDs that had become fashionable add-ons of power conditioners like the MIT Z-Center, produce an audible buzz when used with critical high gain moving coil phono preamplifiers. 

What’s weird about organic LEDs – even those green ones that emit a more vivid green light than their plain vanilla counterparts is that they can be as noisy as their blue colored counterparts. Weirder still, when viewed through a diffraction grading – either a CD or DVD surface – organic LEDs lack the monotonicity of their plain-vanilla counterparts. Ordinary green and red LEDs produce a pure green or and red light when viewed through a diffraction grating while their organic LED equivalents produced a distinctive rainbow streak. Though it is only noticeable in practice, do LEDs – organic and plain vanilla ones – produce more noise when compared with those tiny tungsten filament power on indicator lamps because LEDs are solid-state semiconductor devices and in the solid-state semiconductor world, noise is directly proportional to operational current? 

Saturday, November 7, 2015

Vinyl Records: An Extraordinary Playback Medium?

Whether LPs or 45s, are vinyl records qualify as an “extraordinary” musical playback medium due to their capacity to “alleviate” screw-ups during the recorded music performance’s mastering stage?

By: Ringo Bones 

Strange how those “wonderful” attributes of the analog vinyl records – whether they be 33 1/3 LPs or 45s - that Stereophile magazine columnist Michael Fremer had been describing about throughout the 1990s still holds true today, well into the second decade of the 21st Century. With the Marantz TT-15 turntable back in 2004 and the more recent Onkyo CP-1050 turntable, one would think that both SACD and 24-bit 192-KHz DVD Audio would have consigned vinyl records to the “dustbin of history” during the first decade of the 21st Century, unfortunately it didn’t. But what is it about vinyl records that managed to raise “more mysticism” than even its own 2-channel analog master tape? 

Chesky Records founder David Chesky once remarked that there was something “magical” and inexplicable about the music generated by a stylus coursing through a record groove. Is the magic we love about vinyl records, whether they be 33 and 1/3 RPM LPs or 45 RPM singles, inherent in the analog nature of record playback, or is it something added by that process that allows vinyl records to create a sense of “reality” better than most commercially available prerecorded music mediums and including its 2-channel analog master tape? Or is it a combination of both? 

In my own listening experience, I suspect it is mostly due to how vinyl record playback cartridges – both moving magnet and moving coil – make the vinyl record playback system like they are very transparent sounding analog “dynamic range expanders” due to the way vinyl records tend to sound “more dynamic” in side by side comparison to the first generation open reel copy of the master tape. Given that some of the master tapes of oft-mentioned classic pop rock studio albums recorded during the mid to late 1970s had been recorded with a little too much compression that even though they are multi-track analog studio recordings they sound as if they have that digital sound that Michael Fremer rails against – i.e. everything gets flattened out – including dynamics. Could the stylus and cantilever structure of a typical vinyl record playback cartridge acting as a “corrective dynamic range expander” that makes some over-compressed studio album recordings sound more natural on their vinyl pressing versions in comparison to either open reel tape and CD, SACD or 24-bit 192-KHz DVD Audio copies? 

Monday, October 26, 2015

The ECF80 Triode-Pentode Vacuum Tube: The Integrated Circuit Vacuum Tube?

Given that it contains two different thermionic amplifiers in a single enclosure, does the ECF80 triode-pentode vacuum tube qualify as an “integrated circuit vacuum tube?

By: Ringo Bones 

Multiunit vacuum tubes may not be able to compete in size and component count with their solid-state integrated circuit counterparts, but if your hankering after that good old robust tone vacuum tube sound, post World War II era subminiature vacuum tubes offer those in a more reasonable sized package. The ECF80 triode-pentode vacuum tube is unusual in that this multiunit vacuum tube can run both its triode and pentode sections at about the same current. The ECF80 makes a great Mu-follower with the pentode strapped as a triode on top and it is often described as a medium Mu triode sharp cut-off pentode. 

Even though it is not featured in the 1959 Mullard Tube Circuits For Audio Amplifiers, Mullard says that the ECF80 was designed for operation up to 220-MHz and it was first introduced back in 1954. As 1950s era television receivers tend to use the PCFnn 300-milliampere filament heater vacuum tubes, the production of the ECF80 with a 6.3 volt heater filament suggests that it was aimed at the 1950s era professional VHF communications market. In a typical VHF application of the ECF80, the triode section is often used as a Wien-Bridge oscillator and has to produce a 5-volt peak-to-peak signal which could allow the ECF80 to be used as the active transceiver tube in 1950s era walkie-talkies. The screen pentode is the mixer. The vacuum tube has two cathodes so the two independent amplifiers are enclosed in a single envelope. The twin anode construction is clearly visible with the triode occupying the much smaller anode. The two sections can be used separately if required and thus extending the versatility of this vacuum tube. 

Given that post World War II subminiature vacuum tubes are primarily used as a cost saving preamplifier and phase-splitter sections of power amplifiers that use 1930s era output power tubes, the World Audio Design K6L6 Integrated Amplifier is probably the most famous application of the ECF80 triode-pentode vacuum tube where it was used as a “novel” phase-splitter. The problem with conventional double-triode phase-splitter, like the 12AX7 double-triode phase-splitter section of the ubiquitous Mullard 5-20, is that its high output capacitance caused by the Miller Effect. This causes high frequency loading on the input vacuum tube and reducing bandwidth, making it very difficult to use appreciable amounts of negative feedback without instability due to the phase shifts incurred. A pentode vacuum tube has a very low output capacitance and high gain due to the shielding effect of the screen grid. This means that the loading on the input vacuum tube is greatly reduced, increasing bandwidth and decreasing troublesome phase shifts. And the WAD K6L6 Integrated Amplifier’s use of the ECF80 triode-pentode vacuum tube as a phase-splitter also eliminated the need of an interstage phase-splitting transformer which also kept costs down. 

Sunday, October 25, 2015

The 6AU6 Low Noise RF Pentode: The Retro Vacuum Tube?

Even though modern-manufacture vacuum tube makers have yet to reissue it, does the 6AU6 vacuum tube truly qualify as a “retro preamplifier vacuum tube”?  

By: Ringo Bones 

The NOS or new old stock versions were quite plentiful back in the 1990s when I first got serious into vacuum tube hi-fi as a hobby and even until today modern-manufacture tube makers like Electro-Harmonix, Svetlana and Sovtek still doesn’t have an economically viable need to manufacture their own version of the 6AU6 low-noise RF pentode vacuum tube. And from what I know so far in this hobby, I think the primary raison d’être of those subminiature vacuum tubes manufactured after World War II is to lower the build cost of the preamplifier and phase-splitter stages of power amplifiers that uses output vacuum tubes that date back from the 1930s. 

The 6AU6 low noise radio-frequency pentode vacuum tube was developed by RCA Victor Co. Inc. of New York, New York and it is identical to the EF94. Entered into the Electron Tube Registration List back in October 25, 1945 and entered the Manufacturer’s Literature RCA Datasheet back in October 23, 1945. It has a miniature 7-pin base and was often used as the front end sections of radio and television receivers and it eventually gained widespread use in hi-fi audio towards the end of the 1950s. The 6AU6 is an indirectly heated small signal vacuum tube with a 6.3 volt filament and a 300-milliampere filament heater current. The 6AU6 was described as an RF-IF sharp cutoff amplifier for use in sets with series connected heaters and was eventually superseded by the 6AU6A since November 1956. 

It gained popularity back in the 1990s to keep build costs down when used as first stage preamplifiers of power amplifiers that use power output tubes that dates back from the 1930s – like the 6L6 beam power tetrode – which was first manufactured back in 1936. One of the most popular applications of the 6AU6 low noise RF pentode was in the World Audio Design K6L6 integrated amplifier back in 1995. The WAD K6L6 circuit topology is similar to the ubiquitous Mullard 5-20 amplifier but the 6AU6 low noise RF pentode was configured as a high-gain single-ended amplifier stage. But the relative rarity of the use of the 6AU6 was that the original 1959 Mulalrd Tube Circuits For Audio Applications handbook never used the preamplifier tube in its construction guide of its ubiquitous Mullard 5-20 vacuum tube power amplifier.   

Saturday, October 24, 2015

The Type 85 Vacuum Tube: The Rescued From Obscurity Vacuum Tube?

Even though it dates from the Golden Age of Radio, but did you know that despite it is still in current production, the Type 85 vacuum tube has been languishing in obscurity for almost forever?

By: Ringo Bones 

Kara Chaffee of deHavilland Electric Amplifier Company has recently become a cause-célèbre in the audiophile world when she designed those keenly packaged and cleverly priced zero negative feedback preamplifiers that became well-loved by both critics and real-world audiophiles. Even though she had been designing zero negative feedback preamplifiers since the mid 1990s as the “gold channel” preamplifier circuit for recording studio and boutique audiophile label mastering establishments, Chaffee had earned the reverence of audiophiles the world over when she used an obscure but still in manufacture small-signal vacuum tube that dates back from the 1930s Golden Age of Radio – the Type 85 vacuum tube - and turned it into an excellent sounding preamplifier, the deHavilland Mercury preamplifier that even managed to regenerate a sense of wonder even to the most jaded high-end audio equipment reviewer. But to those unfamiliar with it, here’s a brief history of the Type 85 vacuum tube. 

The Type 85 is a 6-pin dual-diode triode multiunit vacuum tube with its distinctive top metal cap – that is a vacuum tube containing several independently acting vacuum tubes in one envelope – as it is composed of twin triodes and two radio-frequency detector diodes in a single glass envelope. First manufactured during the 1930s, it was primarily used as a radio-frequency detector, automatic voltage controller and first stage audio amplifier in AC line operated AM receivers. It is also used as the phase inverter in several 1930s era public address amplifiers. The Type 85 is electrically identical to the octal based 6V7. The Type 85S is a spray-shield type made by Majestic. 

The Type 85 has a maximum plate voltage rating of 250 volts though typical operation as an amplifier the plate voltage is around 135 volts, it has a maximum plate current of 8-milliamperes though in typical operation it is around 3.7-milliamperes, it has a maximum grid voltage rating of -20 volts though in typical use this is around -10.5 volts. Typical in its operation, its heater voltage is 6.3 volts and heater current is 300-milliamperes, amplification factor or mu is 8.3, transconductance or gm is 750 and a plate resistance of 11,000-ohms. By way of comparison, an ECC32 has a plate resistance of 14,500-ohms while the 6SN7 has a plate resistance of 7,300-ohms thus making the Type 85 as having higher output impedance that it’s closest rival preamplifier vacuum tubes. As mentioned previously, the Type 85 vacuum tube contains two diodes which are used as radio-frequency detectors like the 1904 era J. Ambrose Fleming’s radio-frequency detector diode. 

Dating back to the 1930s Golden Age of Radio and it is still manufactured in “sufficient” quantities by Russian and Mainland Chinese vacuum tube manufacturing firms and even sold in antique radio hobby suppliers in South-East Asia at around 5 US dollars each, the Type 85 vacuum tube has never received any recognition in high end circles – unlike its audio and radio frequency power transmitter vacuum tube siblings like the Western Electric 300B, the 211, the 845 and the Russian GM70 transmitter vacuum tubes which became famous during the 1990s era hi-fi boom. The Type 85’s humble origins as a 1930s era audio frequency preamplifier tube did not solidify its image as a much coveted exotic vacuum tube back in the 1990s. 

Internally, the Type 85 is composed of two R-F diodes and a single triode section housed in a single envelope. Such a “compaction” certainly facilitated the mass production of “affordable” 1930s era AM radio designs by combining the front-end R-F detector, amplifier and the automatic voltage controller into one stage. Sadly, this topology is not the sort of vacuum tube likely to engender a cult following either back in the 1930s or in the 1990s. It should be noted that the triode section is almost completely independent of the R-F detector diodes, the only shared element being a cathode sleeve. The top metal cap of the Type 85 vacuum tube is electrically connected to the ground and therefore does not represent a high voltage shock hazard and we should be thankful to Kara Chaffee of deHavilland for approaching this vacuum tube with an open mind and thus discovering its hidden sonic potential.    
Sound wise, the Type 85 vacuum tube has a much more gorgeous and creamier midrange than its nearest competition – the 6SN7 vacuum tube – which Kara Chaffee also used in her famed deHavilland UltraVerve preamplifier. And on a side-by-side comparison, the Type 85 even excels the ability of the other famed 1930s era preamplifier tube – the ECC32 – in making modern over-bright over-equalized multi-track 24-bit 192-Khz pop-rock recordings much more pleasing to the typical hardened audiophile’s ears. Even though it is pricier than the ECC88 vacuum tube equipped Musical Fidelity X-Pre, the Type 85 vacuum tube equipped deHavilland Mercury preamplifier sounds much, much better – though the deHavilland Mercury is around 10 times the price of the 250-US dollar Musical Fidelity X-Pre. High cost be damned – or if you have the spare time and the ability to DIY a Type 85 vacuum tube equipped preamplifier – the deHavilland Mercury and its Type 85 ilk can make any reasonably good sounding solid-state power amplifier the ability to create a soundstage as if it is a zero-feedback single-ended triode vacuum tube power amplifier. 

Though most modern vacuum tube reissue manufacturers - like the famed Electro-Harmonix and Svetlana -  has yet to manufacture their own "audiophile grade" Type 85 vacuum tubes, the ones I currently have and used in my preliminary DIY work are from National Union (Made in USA) NOS ones that still register "OK" in my audio-buddy's small-signal vacuum tube checker and a newer Mainland Chinese one whose brand is written in Chinese characters. Both managed to sound great from a vacuum tube perspective and I think the tone produced by a preamplifier using the Type 85 vacuum tube will easily please "tone freaks".