Friday, November 27, 2009

Boosting the AN214 – How to do it Right

The heyday of the boosted AN214 DIY amp may be over, but has this iconic hobbyist audio engineering design ever been properly implemented for ultimate sound quality?

By: Vanessa Uy

During the past few weeks, I’ve received some disused but still functional “homemade” AN214 IC amplifier paired with its MJ2955 transistor-based transformer-coupled booster amplifier soulmate for possible tweaking to improve their sound quality. Sadly, I’ve found that an overwhelming number of them – though can function as intended – have been insufficiently designed from an audiophile perspective. Either on the basis of saving money as most electronic DIY-ers are not particularly rich anyway, or following the sway of fashion based on audio electronic myths centered on the AN214. Especially concepts that had been perpetrated by very influential – if rather misinformed – self-styled electronic engineering gurus who are to afraid to be adventurous when it comes to spending a bit more to create a more realistic and natural sounding audio amplifier through over-engineering. Despite of money-saving necessity to skimp on better parts and layout hanging like the Sword of Damocles on the prospective hobbyist, is there a better way to design a boosted AN214 amp without breaking the bank?

I’ve mused before on the virtues of using oversized input and output transformers – to the dismay of electronic and electrical engineering degree holders – for the MJ2955 transistor-based transformer-coupled booster amp design to improve its bass output and quality. But the units I received for tweaking not only have standard sized input and output transformers hindering them from achieving their sound quality potential. Some not only have even smaller than standard transformers in order to save money, but their cost-saving measures can only prove to be expensive in the long run due to the potential damage they might inflict to the loudspeakers connected to them. Fortunately, I have two ways of tweaking the boosted AN214 design not only for better sound quality but also to maintain loudspeaker longevity as well. By avoiding – make that not doing the following if funds allow – when constructing your very own boosted AN214 amp design.

The first is you should not ground the primary / input side of the input transformer of the MJ2955 transistor-based transformer-coupled booster amp. Just because in an overwhelming number of applications of the AN214 IC audio amplifier is in its single-ended output configuration, where the minus side of the speaker output terminal is connected to the ground of its power supply. Does not mean one should ground the input side of the input transformer of the booster amp. Some DIY-ers usually ground the input transformer either to minimize – with the emphasis on minimize – the hum of the AN214 stage. Which is probably either caused by insufficient size of filter capacitors in the AC / DC power supply or just a bad circuit layout. Floating the input side of the booster amp not only makes it sound more dynamic, but also allow you to experiment other IC amplifiers other than the AN214 – especially those in bridge configuration where grounding the negative terminal could destroy the IC amp and the booster amp.

The second is please use separate power supplies for the AN214 section and the MJ2955 transformer-coupled booster amp section. Just because these two sections share the same 12-volt battery in automotive applications doesn’t mean you should use a common AC / DC power supply for both. Some farsighted DIY electronic enthusiasts who care about speaker longevity have even configured a power on delay for the boosted AN214 design by allowing the booster amp to turn on several seconds after the AN214 section turns on in automotive applications to prolong loudspeaker life. Those turn-on thumps heard on the partnering loudspeaker produced by simultaneously turning on both the AN214 and the booster amp section does not exactly bode well to the longevity of the connected loudspeaker.

A significant number of boosted AN214 designs have been paired with the venerable budget wonder of the 1990s, the Mission 731 LE speakers. These types of loudspeakers and their ilk are not exactly as indestructible as their raunchy sounding concert public address speaker system brethren. And those DIY electronic enthusiasts fortunate enough not married to bitch wives from hell who have the ideal set up of a domestic listening room for their hi-fi, a separate power supply for the AN214 section and the MJ2955 transformer-coupled booster amp is the perfect way to go. Favorably if equipped with high-speed Schottky Diode / Schottky Barrier Diode rectifiers and Rubycon Black Gate capacitors for the best possible – and tube amp-like dynamics – sound quality.

Saturday, October 24, 2009

Can the AN214 IC Amplifier Work as an Electric Guitar Amplifier?

Even though guitar players on a shoestring budget with a good enough electronic DIY skills know that it works, but are there any limitations in using the AN214 IC as an electric guitar amp?

By: Vanessa Uy

It is probably the worst kept secret in the DIY hi-fi hobbyist’s world. The AN214 IC-based audio amplifier – especially when partnered with it’s famed transformer-coupled MJ2955 PNP transistor-based booster amp – does work beautifully as an electric guitar amplifier up to a point. But by being probably the cheapest electric guitar amplifier in the world that still has a “decent” tone doesn’t mean that it is set out to be every guitarist’s trusty amp. After all, Liz Phair had not yet endorsed one given her “lo-fi” credentials. But given a much improved access to vacuum tubes via the Internet, why should a typical electric guitar player with a sufficient knowledge of DIY electronics even bother with a 1970s solid-state relic like the AN214 audio amplifier IC?

What’s not going for it? Well, the AN214 IC audio amp when used as an electric guitar amp - even with the addition of the transformer-coupled MJ2955 PNP transistor-based booster amp - can never replicate an authentic sounding rendition – i.e. same guitar tone as that on the record. Especially of Can’t Get Enough by Bad Company or Red Light Fever by Liz Phair. You’ll probably need tubes for that like the venerable 1965 Fender Twin or a 1970s-era Quad-Verb - or a custom tweaked Fender Black Face Champ equipped with Mullard or the even rarer “Record By Mullard” EL84 tubes. But what you’ll get though is a very viable foundation for a guitar tone so unique and so uncontrived – yet still sounds like a tweaked overdriven Marshall-style set-up. If you’ll work at it skillfully enough, critical acclaim will be more than a dead certainty.

On my actual usage of an AN214 IC amp as an electric guitar amp with it’s famed MJ2955 transformer-coupled booster amp – which I built myself – it does have a way better tone than those extremely dry sounding Carlsbo solid-state electric guitar amps from the early to mid 1990s. Although some contemporary Physical Modeling-capable electric guitar amps equipped with audiophile-grade 24-bit 192-KHz digital signal processing offers much, much more tonal flexibility. Although they can be easily many times as expensive as the AN214-based electric guitar amp.

On getting as much a good electric guitar tone from your AN214 amp, I used a DIY discrete component based – i.e. using JFETS, transistors and op-amps – cassette tape hiss reducer with an older audio-buddy no longer uses. It provides a 3dB per octave roll-off above 1-KHz when set at its maximum hiss filtering setting. You can use a dedicated noise gate or a Wah pedal for the same effect. Filters like these should be placed after the distortion / fuzz pedal to make the AN214 sound as if it is a tube amp. I tried 12-inch, 15-inch whizzer-equipped Leslie-type organ speakers / musical instrument speakers with great results. But if you want an authentic Marshall-like tone, use an 18-inch whizzer-equipped musical instrument / organ speaker. Mine was a Japanese-made OEM replacement for a Leslie mounted on an open baffle.

When doing my own renditions of various epic and iconic electric guitar performances of the past, the AN214 IC audio amplifier-based electric guitar amp can actually be used with some skill on Iron Maiden’s 2 Minutes to Midnight. Thanks in part to the skillful super bit mapping technology mastering of Murray Harris and Simon Heyworth of West London CD mastering specialists Chop Em Out - Which (inadvertently?) revealed the germanium transistor and germanium clipping signal diode-equipped Arbiter Fuzz Face pedal being used in the intro of 2 Minutes to Midnight. Probably due to the “extreme” noise-shaping of the Super Bit Mapping / SBM process which inadvertently boosted the signature residual noise of the effects pedal being used on this particular Iron Maiden track. I wonder if it shows on the vinyl version of this track if Mobile Fidelity Sound Lab ever manages to press Iron Maiden’s Powerslave album.

The AN214 also works extremely well in replicating mid-1980s Bay Area Bangers-period Thrash and Death Metal style electric guitar tones. It is probably the cheapest way for an authentic sounding rendition of those old Metallica, Testament, and Death Angel guitar passages that you can have. By the way, I even managed to perform a very convincing rendition of the guitar passages found on the latest Tokio Hotel single titled Automatic from their Humanoid album on my AN214-based electric guitar rig.

In short, it is probably the most cost-effective electric guitar rig that you can find that will run on a 12-volt car / automotive battery. My own AN214 IC audio amplifier-based amplifier works so well that it was good enough to be used in my band’s own rendition of The Gathering’s Liberty Bell. Although this version is a 20-minute long Nusrat Fateh Ali Khan meets Central Asian Bardic Divas with a Gibson Les Paul and Marshall Amplifier full-tilt high decibel Heavy Metal fest - Which could be a nightmare scenario for Ann Coulter and the Bush Administration-era Homeland Security if a hard rock version of the Qawwali or Islamic Devotional Music ever becomes mainstream in the psyche of American teens. Maybe Junoon has been doing this for sometime now.

As an aside, I even played my tweaked Gibson Les Paul wearing a Soviet-era water-cooled partial-pressure suit similar to the one used by Yuri Gagarin and Valentina Tereshkova on their extreme high-altitude cosmonaut training flights. And we played our version of Liberty Bell on the backdrop of a wooden one-to-one scale mock-up of an XB-70 Valkyrie. We might even upload the video on You Tube anytime soon.

Can the AN214 IC Audio Amplifier Be Used to Pickup Ghost Voices?

After dabbling into the mysteries of Electronic Voice Phenomena, can one use the AN214 IC-based audio amplifier to “listen” to “ghost voices”?

By: Vanessa Uy

As an “objectivist” when it comes to the science and art of audio electronics, I am often reminded why I am still fascinated by this hobby. Especially when it comes to the still “unexplained” portions of this hobby that tends to crop up when Halloween season comes along. I’m talking about Electronic Voice Phenomena or EVP that’s more commonly referred to as “ghost voices” by the layperson. Which fortunately gained my interest as of late after examining a rainwater-damaged AN214 IC Audio Amplifier that had turned not only into an ad hoc white-noise generator, but also managed to pickup “unexplained” voices that on rare moments of clarity imply that the voices originate from the “other side”. But before going further, here’s a primer on the very fascinating paranormal phenomena scientifically known as Electronic Voice Phenomena or EVP.

Ever since a large number of ordinary folks gained unlimited access to a tape recorder (probably a few years after World War II) and began doing a wide range of do-it-yourself musical performance and field / nature sound recordings. They began to capture “phantom sounds” or “phantom voices” that couldn’t be easily explained away by the scientific principles governing the working processes of these tape recorders. These phantom voices were often referred to as ghost voices since an overwhelming number of them – especially during the 1960s and 1970s - were captured or recorded in an apparent séance sessions when the spirit of a specific dearly departed were contacted to answer questions regarding life after death.

The first person most popularly credited for capturing EVP on tape was a documentary producer named Friedrich Jurgenson when during a summer day in 1959 as he was recording bird-songs in the Swedish countryside managed to record something unexpected. When Jurgenson played back his tapes later, he was surprised to find a mysterious voice speaking in Norwegian who was also surprisingly narrating along the recorded bird-song sounds rather expertly. After investigating the radio programs airing during the same time of the bird-song field recordings to rule out possible RF rectification, Jurgenson came up empty in his search which only deepened the mystery behind Electronic Voice Phenomena.

By 1965, Jurgenson’s research into EVP gained the attention of a psychologist named Dr. Konstantin Raudive. Later, Dr. Raudive teamed up with a physicist named Alex Schneider, which the two of them became very instrumental in devising ways and set-ups to capture EVPs to augment the tape recorder. Like using white-noise generators, germanium diode-based crystal sets, unused frequencies on the FM dial, and the use of sensitive microphones in apparently silent venues with known paranormal activity – especially very late at night. Dr. Konstantin Raudive’s research into EVPs eventually resulted in the publication of a very influential book on ghost voices / paranormal voice research titled “ Breakthrough: An Amazing Experiment in Electronic Communication with the Dead” in 1971.

Even though Friedrich Jurgenson’s recorded “phantom voice” on the bird-song tape was believed to be the first EVP recording due to its overwhelming popularity. Thanks to the popularity of Dr. Raudive’s Breakthrough - in the newly established EVP research community, there were two American paranormal researchers who were recording and documenting EVPs several years before Jurgenson’s 1959 bird-song recording. Psychical investigators Raymond Bayless and Attila von Szalay had published a paper in the Journal of the American Society for Psychical Research documenting the results of their three-year experiment in investigating EVPs. Bayless and von Szalay’s EVP research started in the investigation of a local psychic in their area named Sophia Williams who was allegedly able to make a disembodied voice appear on tape. To their first ever recording of a confirmed EVP on December 5, 1956. Raymond Bayless and Attila von Szalay may be the first to investigate EVPs, but Dr. Konstantin Raudive was the most prolific cataloger of EVPs - which numbered over 70,000 voices before his death in 1974. Given extensive scientific research and investigation, can it be proven that Electronic Voice Phenomena are really voices of the souls of the dearly departed that speaks to us from the “other side”?

As with the confusion behind UFOs - which officially means Unidentified Flying Objects – as opposed to an overwhelmingly popular prevailing belief that they are highly advanced spacecraft piloted by an extra-terrestrial biological being capable of traversing vast interstellar distances by travelling faster-than light. UFOs are just unidentified flying objects – unless of course you’re part and parcel into those wild conspiracy theories I suppose. Sadly, as it is with our eyes, our ears can also be fooled – especially when it comes to Electronic Voice Phenomena.

It has been well established that our eye-brain system consciously searches out meaningful patterns in apparently chaotic and random places. Like the “Man on the Moon” where the craters and the large “seas” on the Lunar surface roughly resembles a human face. Patterns often crop up in tea leaves another popular medium used to foretell the future. Most EVPs that are heard clearly without extensive signal processing can be easily explained away as RF rectification – i.e. radio signals received in improperly shielded and constructed audio equipment. While ones requiring very advanced digital signal processing – especially on equipment often used by the American FBI or other big-ticket law-enforcement agencies – like EVPs from white-nose can often sound like the auditory equivalent of seeing patterns in a snow bank or tea leaves. It is just too reliant on subjectivity to pass muster as a truly intelligible human speech. Although some psychoactive drugs and herbs when recreationally taken tend to make the sound of white-noise sound as if the Voice of God in Her Infinite Wisdom talking directly to you.

While my AN214 IC audio amplifier as white-noise generator did receive very interesting EVP “spikes” during the past few weeks. Most of them can easily be explained away as nearby AM transmissions modulating the seemingly constant hiss of the white-noise to produce a rhythmic modulation that’s often mistaken as a ghost voices. But I did managed to pick up a few that can’t be explained away as AM transmissions after I placed the rainwater damaged AN214 in a faraday cage. I even received something that sounded like our long dead Border collie. I just hope that these “ghosts” don’t sue me for copyright infringement because I’ve been hearing one who is a very brilliant singer-songwriter.

Monday, September 28, 2009

Horn Loaded Tweeters: Ideal for Automotive Applications?

Given that the AN214 IC based audio amplifier lives in the 12-volt world of car audio, are those Pioneer horn-loaded tweeters that are often paired with it really good for automotive use?

By: Vanessa Uy

Maybe it was those “old” circa 1993 Lexus adverts that convinced me that there are still those who believe that it is still possible to engineer high-end sound for the acoustically harsh environment of a car’s indoor cabin. Especially that particular advert where Classical guitarist Manuel Barrueco performed and recorded a suite by the 19th Century Spanish composer Isaac Albéniz in the cabin of the “supposedly” recording-studio-quiet 1993 Lexus LS 400 driving at 55 mph. Though it probably work well, given that more recently Lexus had been working with Mark Levinson for a car audio system with a sound quality that is commensurate with the luxury of their famed “entry-level” sports cars.

From the point of view of acoustic science, horn-loaded tweeters are better suited for automotive applications than direct radiators (i.e. ordinary cone speakers) because horn-loaded tweeters have better radiation pattern and smoother off-axis response than their coned counterparts. Horn-loaded tweeters eliminate the problem of upper-frequency dips in a typical car interior. Given that there are a number of horn configurations, which type does suit well in getting as close to a high-end high fidelity sound in an acoustically non-ideal environment of your typical car interior?

Horn tweeters come in three main configurations; one is the round horn, the square horn, and the rectangular horn. Although the Pioneer sourced tweeters that are often used in AN214 IC audio amplifier based systems are typically square and rectangular horn-loaded tweeters. These Pioneer sourced tweeters vary in impedance from 8 ohms to 16 ohms and the type used during the 1980s seldom generate significant acoustic output above 8KHz. The higher impedance types - 16-ohm versions with Alnico magnets - are my preferred choice (if you can still find one since they are virtually extinct) since they provide an easier impedance load for the partnering amplifier. Allowing one to use an AN214 IC audio amplifier configured with reduced negative feedback for better musicality. Even though Pioneer had been recently producing ribbon tweeters that reached out to 120,000 Hz, they are still to gain widespread usage with an AN214 IC-based Pioneer car stereo from the 1970s.

In the audio world, there exists two camps on which type of horn – round or rectangular – provide the optimum sound quality and they’re respective point of views are well defended when it comes to which one sounds best. Audio Note manager Herb Reichert belongs to the camp professing that round horns are the ideal horn shape because – according to him – round horns overcome some of the sonic limitations of traditional horn-loaded speakers. According to Reichert, the more a horn tends toward the rectangular shape of traditional horns, the more it will produce sound with a "honky" or cupped-hands coloration. Public-address (PA system) horns are rectangular because acoustic engineers want to spray the whole auditorium with sound. High-fidelity horns should be round so that they can launch a perfect hemispherical wave front – where the acoustic energy is in phase and of equal amplitude at any point on the acoustic wave-front. Any horn that is not round will sound more colored than an equivalent round horn says Reichert.

While Jean Bernard Gabet and Jean Phillip – designer of the Jadis Eurythmie II horn-loaded loudspeaker – belong to the rectangular horn believers. After examining existing horn-loaded loudspeaker technology, both of them concluded that a properly designed horn system cannot be round but rather must be rectangular in order not to sound too colored.

Given that most tweeters used with the AN214 are either the black-colored Pioneer PT-103F horn-loaded tweeter with a square-shaped horn aperture Alnico magnet equipped with an impedance rating of 8 ohms with a 15-watt power rating. And the much sought after gold-colored Pioneer PT-6 horn-loaded tweeter with a rectangular horn aperture Alnico magnet equipped 16 ohm with a 15 watt power rating and said to be the perfect soul-mate of a tweeter for the AN214 amp. Although there is the black-colored Pioneer PT-205 horn-loaded tweeter with an16 ohm impedance rating which nobody mentions using with the AN214 probably due to its rarity.

Even though most of these tweeters begin to roll-off at 8KHz, they seem to be the primary tweeter of choice for those MJ2955 PNP transistor-based transformer-coupled booster amp for the AN214. Maybe they can tolerate the high frequency parasitic oscillations of interstage and output transformers of such amps that are plagued with stray capacitance and stray inductance due to improper transformer winding.

Wednesday, August 5, 2009

The Great Car Stereo Wars of the 1980s

As a decibel drag race that was formed independent of the American IASCA, does the Great Car Stereo Wars of the 1980s in Cebu City the definitive setting of the AN214 IC amplifier’s “finest hour"?

By: Vanessa Uy

This ad hoc and largely forgotten and unknown “hi-fi” movement of the 1980s probably started when a bunch of hi-fi audio enthusiasts began – maybe independently from each other - reverse-engineering their Pioneer KP-500 FM / cassette tape equipped car stereos in order to find out what makes them tick. Sure enough, this tinkering spawned a hi-fi revolution that probably rivaled the single-ended triode revolution in Japan that began in 1970.

Unlike the present incarnation of decibel drag racing using IASCA approved high-powered (supposedly 160 decibels loud but a Pratt & Whitney F100 afterburning turbofan jet engine in test compliance burns sounds way, way louder while roaring on its static test stand at just 135 decibels) switching-mode power amplifiers of dubious musicality. They sound really gray and really colorless to me! The “audio gear” used in the Great Car Stereo Wars of the 1980s still has a sound quality that those with musically-literate ears and brains can appreciate without prejudice.

Primarily, it was the Pioneer KP-500 that became the audio gear of choice back then. With its now iconic circular tuner display, dinky volume, bass and treble knobs. A then-cassette era mandatory loudness switch and if you cover the old illuminated Pioneer logo with its stylized tuning fork and ohm symbol, an audio enthusiast from the 1990s would honestly mistake it for a 1996 era Musical Fidelity X-A1 integrated amplifier.

Given a lack of Nakamichi tape deck dealership in Cebu – then and now. Cassette tape era audiophiles attempted to replicate – to a degree of success – a “Nakamichi Solution” to make the cassette tape sound “musical” by boosting both the low and high frequency portions of the audio spectrum via tone controls / equalizers. A bloke by the name of Edwin – a.k.a. Big Boss Edwin – with his Kansas Sound, developed a novel equalization method – probably in the late 1970s - to improve the inherent limitations of the stock Pioneer KP-500 car stereo sound. Edwin even extolled the use of Pioneer’s in car PT-6 horn-loaded tweeter in conjunction with his audio system designs despite the Pioneer tweeter’s 8kHz bandwidth limit. Audiophile-grade tweeters today can easily reach 120kHz.

Even though Edwin blacked-out the capacitor and resistor values of his signature design tone control preamplifier to avoid his design from being unlawfully ripped-off noting that it is much coveted back then. After I reversed engineered now “abandoned” units of his famed preamplifier / tone control. I do agree that Edwin’s novel preamplifier / tone control is based on the great studio equalizers / tone controls then in studio use during the “Golden Age of Stereo”, specifically the famed Abbey Road Studios where The Beatles used to record.

I found it of similar design to a vintage tube / valve-based Pultec Model EQP-1R, which was first manufactured by Pulse Technologies Inc. of Englewood, New Jersey back in 1955 and has spawned many derivatives. Amongst which are some of the cream-of-the-crop “vintage” vacuum tube-based studio equalizers of today! The Pultech’s power lies in its ability to independently select the frequency range or frequency band over which boost and cut may be applied to a degree of subtlety way beyond that of a standard Baxandall-based tone control circuit. Although in actuality, the EQP-1R in its original form is so complicated that offers too much of a good thing for domestic use. Edwin’s version uses “blue input captain” – i.e. I.F. transformers that are color coded blue – as the inductors for his tone control circuit while the original Pultec uses dedicated E and I core-based chokes or inductors.

The important detail to notice is that the user may, for instance cut bass frequencies below 100Hz and – at the same time – boost those frequencies below 30Hz. Using the Pultec Model EQP-1R tube studio equalizer or Edwin’s tone control design, it is possible to clean up a “boomy” recording – i.e. excess sound energy in the 100Hz to 200Hz region – without unduly emasculating the bass frequencies. A tone control with this capability can also be very useful for correcting for room resonance effects - which we all suffer, especially in the cramped quarters of our “compact” cars.

The flexibility of this type of tone control can also be used to “tame” the high frequency audio band. For cassette tape users, a conjunction of boost in the 5kHz region and a treble cut above 10kHz can help restore sparkle to cassette tapes recorded with incorrect azimuth or tape head alignment without introducing too much tape noise or tape hiss in the process. Thus bringing the cymbals and other high frequency sounds back to dull cassette tape music.

The only disadvantage of Pultec’s passive approach is that the circuit introduces about 24dB of static attenuation at all frequencies when adjusted for a flat response. In the original circuit, this loss was compensated by the introduction of a push-pull tube amplifier constructed from pre-amp tubes with relatively low output impedance and high anode dissipation (4 to 5 watts) like the 12RX7, 12RU7 tube and a couple of transformers. Whether this is the influence of the transformer-coupled amp booster for the AN214 is still open to speculation though.

While Edwin’s method employs the Pioneer KP-500’s built-in AN214 IC-based amplifier as a preamplifier for his tone control design before the signal is amplified again by an another AN214 stage en route for amplification into the MJ2955-based transformer-coupled booster amplifier. I think these types of tone controls - though lossy – are more musical than multi-band graphic equalizers that use solid-state integrated circuits. Or the op-amp based Baxandall tone control – which is plagued by group delay distortion and a high degree of transient inter-modulation distortion due to the relatively high levels of negative feedback. A prime anathema for audiophiles with musically trained ears and brains.

Edwin’s tone control design was effective enough to be used as an ad hoc “vocal eliminator”, since it can be tuned to cut only frequencies in the human voice part of the audio spectrum. The problem with it, however is that the “multiplicity / flexibility” makes it very easy and also very tempting to emphasize the spectacular over the real. To turn the system into a hi-fi “fireworks display – which their users often would in decibel drag races. Some “seasoned veterans” of the “Great Cebu City Car Stereo Wars” often had 8-Track variants of Pioneer circular tuner display car stereos. Probably the older version of the cassette tape-based Pioneer KP-500 playing a special “Bill Laswell-style remix” of Scorpions’ song “China White” for use in "audiophile quality" decibel drag racing back around 1981 to 1982.

I would have liked to have a first-hand experiment on the bass enhancing effects of 8-Track tapes. Sadly, these "Beasts” had become increasingly rare over the years. Pioneer 8-Track car stereos are virtually extinct nowadays, never mind Pioneer 8-Track tape decks that allow you to record from vinyl LPs. I wonder how would those Bill Laswell recorded Motörhead albums, with Lemmy Kilmister’s Rickenbacker bass guitar and Philthy Taylor’s drumming captured in full glory, sound through these systems? Or what about Nina Gordon and Louise Post of Veruca Salt, or Lunachicks, how will they sound through a Pioneer KP-500? We will probably never know because even the Pioneer KP-500 is about as rare as a German EMT 927 broadcast turntable.

Thursday, July 16, 2009

Don’t Forget the Heatsink

Despite of its relatively low power output does the AN214 IC still deserve the tender loving care of adequate heatsinking to achieve better sound quality?

By: Vanessa Uy

During the AN214 IC-based amplifier’s heyday in the early 1980s, heatsinking is usually of little concern due to the device’s relatively low power output that barely reaches 5 watts. Hobbyists back then – especially those that lack adequate knowledge on how semiconductor ICs work – usually bolt the AN214’s metallic tab / backside of it’s 9-pin single inline package to a piece of scrap metal to serve as an ad hoc heatsink. Or maybe to the aluminum chassis of the amplifier’s intended housing, without further concerns on how hot it might get during the AN214 IC’s intended lifetime.

Ideally, when operated under the right conditions, solid state devices tend to last for hundreds of thousands of years. Some of these inadequately heatsinked amps just manage to last up to 8 months at most. As most electronic engineering textbooks – then and now – often states that low-powered applications require minimum thermal mass, a few centimeters of sheet metal, to transfer the small amount of heat generated by a low-power semiconductor device to the ambient air. But is common-sense engineering good enough for the perfectionist audiophile-grade applications for the AN214?

The raison d’être of heatsinking IC-based power amplifiers – even low-powered ones – is to obtain the IC amplifier’s maximum output voltage swing as specified by the manufacturers’ spec sheets. This can easily show up under triangular-wave or sine-wave tests when the inadequately heatsinked IC-based amplifier can’t even output one-tenth of it’s intended maximum output voltage swing - on the cathode ray oscilloscope, the sine and triangular wave peaks would be melting or clipped like crazy.

Non-linear reactive loads like loudspeakers – or the inter-stage transformer of the MJ2955 PNP transistor-based booster amplifier – tend to have some unwanted effects on inter-stage amplifiers (the AN214). The resulting back-EMF of the load may attempt to swing beyond the power supply voltages applied to the amplifier. Thus in order for the IC’s output protection circuitry – assuming it has one – to work, then a heatsink is always a necessity in “controlling” the inductively-generated electromotive force of whatever inductive load that happens to be connected to the AN214 IC-based power amplifier.

To obtain the best theoretically possible sound quality from your AN214 IC-based amplifier, an infinite heatsink – or a realistic equivalent – is a must. To make your intended finned aluminum alloy heatsink approach the heat-dissipating performance of an infinite heatsink, its main body – the point where you bolt-on the IC / semiconductor package – should be thicker than 1/16 of an inch. And this part should be polished to maximize heat transfer. You can also add silicone grease with metal oxide to further boost heat transfer. After bolting-on the IC to the heatsink, you can paint the aluminum alloy heatsink’s surface with a mat black-colored oil paint – preferably thinned a bit with linseed oil – to further boost the heatsinks’ emissivity rating. If done properly, your AN214 IC-based amplifier now has the potential to perform its very best.

Thursday, July 2, 2009

Is the AN214 IC Amplifier Hi-Fi?

Given that it resides in the 12-volt world of car audio, does the AN214 IC amplifier fulfil the tenets of high-fidelity audio reproduction – namely a good to excellent sound quality?

By: Vanessa Uy

Today, we audiophiles – at least the sane ones anyway – judge an audio amplifier’s performance by its ability to realistically reproduce the sound of a recorded musical performance. As opposed to how many watts it can deliver or how low it’s overall total harmonic distortion – i.e. a good to excellent set of measurements, and even the amplifier’s circuit topology / technology.

The practice of using our ears – as opposed to a 10,000 US dollar multi-function audio analyzer – probably gained fashion (again?) back in January 1994. When Stereophile magazine released a correspondingly dated magazine with a riddle posted on the cover that goes “If either of these amplifiers is RIGHT…the other must be WRONG”. An idea probably influenced by James Carville’s book titled “We’re Right, They’re Wrong: A Handbook for Spirited Progressives” – a reactionary idea born out of chronic bullying by Rush Limbaugh and his global warming / climate change denying ilk directed at us liberals. It looks like our too liberal postmodern dictum of everyone’s opinion is right is our own downfall - at least according to Mr. Carville.

Returning to the world of hi-fi, it does seem like sound quality has indeed gained vogue in assessing the pride of ownership potential of audio components, especially audio amplifiers. The circuit topology and technology used seems no longer relevant, probably due to the single-ended triode “revolution” in Japan during the 1970s which made audiophiles around the world reexamine their views about what’s important about their hobby.

Given that the AN214 IC amplifier might be cheap, its hi-fi credentials easily manifest by the overall improvement in sound quality every time you over-engineer one. Use larger than necessary output transformers and the bass quality improves, just like its single-ended triode counterparts. Use larger than necessary heat sinks and the AN214 amplifier rewards you with a more agile pace, rhythm, and timing. In fact if you tweak the AN214 amplifier’s power supply with Rubicon Black Gate capacitors, it could even sound better – from a musical perspective – than a standard Pioneer A400 amplifier. The only way a Pioneer A400 can be more musical than a tricked-out AN214 amplifier is by doing a T. Evans Audio Design-style modification to its power supply.

During the AN214 amplifier’s heyday, many audiophiles – especially absolute beginners – have never been told about the wisdom of trusting their own two ears as the ultimate arbiter of sound quality. This is why back then solid-state high-powered full-complementary output stage direct-coupled power amplifiers were touted as the ultimate in sound quality. Even though most of them sound sluggish in the pace, rhythm, and timing department because their power supply capacitors have not been designed to take advantage of time-constants. Ad given that solid-state full-complementary amplifiers are relatively complex in terms of component count, tweaking one – especially if you are an audiophile on a budget – seldom makes fiscal sense. It is even cheaper – time and labor wise – to buy very expensive solid-state amplifiers from Mark Levinson, Krell, and Spectral.

So, is the AN214 IC-based amplifier hi-fi? If you trust your own two ears, then the answer is a resounding yes. If the music matter’s more to you than the circuit complexity of your audio amplifier, then maybe it is about time you should check out the AN214 amplifier - especially if you can’t afford exotic single-ended triode tube-based amplifiers, or if you live in a place where the 50 caliber Browning Machine-Gun cartridge is way more plentiful than 300B vacuum tubes. During the AN214 IC amplifier’s heyday, it might have the requisite resolution to play out the full beauty of Larry Carlton’s guitar playing on Michael Jackson’s Don’t Stop ‘Till You Get Enough.

Saturday, June 20, 2009

A Transformer-Coupled Booster Amplifier for the AN214

Due to it’s inherently low power output design, does addition of a transformer-coupled booster amplifier to an AN214-based amplifier aid or hinder it’s sound quality?

By: Vanessa Uy

Given it’s inherently low power output – between 4 to 5 watts into an 8-ohm load. It was therefore inevitable to find a way of increasing the “meager” output of the AN214 IC-based audio amplifier without sacrificing it’s inherently good sound quality (on the cheap?). I wonder how many ways were “engineered” during the past 30 + years or so history of this device. Surprisingly, a consensus was reached of choosing a “primitive” transformer-coupled PNP transistor-based design that probably dates from the 1950s.

The design configuration of the transformer-coupled booster amplifier used to increase the 5-watt power output of the AN214 IC-based power amplifier for all intents and purposes resembles that of a transformer-coupled 300B-based push-pull tube power amplifier circuit. Except that the 300B tubes (or valves as they say in Merry Old England) were replaced by MJ2955 PNP power transistors in a TO-3 package. From my point of view, this transistor-based transformer-coupled booster amplifier circuit was probably based on the first transistor-based audio power amplifier designs first published in the US-based audio electronics magazine called AUDIO. Probably those issues dated between January 1960 to December 1961 - i.e. the Golden Age of Stereo.

During my experimentation of the MJ2955-based transformer-coupled booster amplifier – which to all intents and purposes is a continuation of the experiment done by my older audio-buddies during the last 25 years or so – I did optimize the input transformer winding design. By eliminating stray capacitance of the input transformer / driver transformer winding and optimizing it for a near-perfect square wave performance and transfer function characteristics. I did manage to reduce the booster amplifier’s recommended negative feedback level, which only improved the sound quality to no end.

Compared to its 300B tube-based sibling sound quality wise, it was a close match. Although the 300B-based push-pull amplifier did manage to display irreproachable beauty where it excels. Like in the Middle-C region of the musical performance – i.e. upper bass and lower midrange region of the audio spectrum. And even though it was criticized during the 1980s that transistor-based transformer-coupled booster amplifiers are notorious for having high total harmonic distortion (THD) in comparison to a full complementary direct-coupled solid-state power amplifier. But if you wind the transformers properly by eliminating stray capacitance – especially the input / driver transformers, the inherently high THD (total harmonic distortion) of transformer-coupled solid-sate booster amplifiers can be dramatically reduced. Although high-quality audio frequency transformers – driver transformers and output transformers - that are wound at artisan levels to optimize their square-wave performance and optimize their transfer-function characteristics across the audio spectrum are magnitudes more expensive in comparison to matched pairs of high-power output transistors.

The bad news is – from a perfectionist audiophile’s perspective – a lot can go wrong, sound quality wise, in the actual construction of full complementary direct-coupled solid-state power amplifiers. Especially if the “engineer” doesn’t trust their own ears and chose to trust on measuring instruments instead could result in a sluggish sounding power amplifier with unlimited reserves of power - but one that is sorely lacking in the pace, rhythm, and timing department. That's why I really hate musically illiterate audio engineers. Looks like the old-school wisdom gained by audio engineers during the Golden Age of Stereo still applies well into the 21st Century. And it also provides a low-cost route to audio nirvana via the AN214 IC-based audio power amplifier route. Ain’t it fun to be an audio cheapskate?

Wednesday, June 17, 2009

What in the World is an AN214 IC?

In spite of it’s age – and apparent manufacturing extinction – are AN214 IC-based audio power amplifiers still “noteworthy” in our 21st Century hi-fi world?

By: Vanessa Uy

If you asked me – or any of my older audio-buddies – about AN214 IC-based audio amplifiers, they do admit – albeit reluctantly – to have “once upon a time” taken this integrated circuit route to audio nirvana. Given that this low powered audio-amplifier-on-a-chip is about as technologically advanced as a cassette tape when viewed from our 21st Century perspective, does it still deserve serious discussion? Though the short answer by audiophile die-hards lucky enough to stock significant quantities of the AN214 IC is: “you betcha!”

Part of the allure and mystique of the AN214 integrated circuit-based audio power amplifier is that manufacturer authorized and approved – i.e. reliable – spec sheets and application notes are few and far between. In my opinion, it is safe to say that anyone who has seen first hand “proper” AN214 IC spec sheets – especially the device’s slew rate and power output rating – are either: a) had forgotten about it due to illicit drug use during the past 25 years. b) Have gallantly gave their lives during Operation Desert Storm, or more likely c) had joined a technology-rejecting / technology-abhorring religious cult.

But what everyone lucky enough to remember the virtues of the AN214 power amplifier during it’s heyday is that it has always been inexplicably linked with the ubiquitous back in the 1970s and 1980s Pioneer in-car stereo cassette tape deck and FM tuner combo. Which from an electronic engineer’s standpoint is inevitable given that both live in the 12-volt world of car audio. Although I’m lucky enough to have heard first hand Pioneer’s 8-track version of this in-car tape and FM tuner combo that sounds as if it was designed by famed recording engineer Bill Laswell due to it’s legendary ability to reproduce recorded music with tons of electric bass. I f you’re an unabashed reggae music and dub fan lucky enough to demo this legendary Pioneer in-car 8-track tape and FM stereo combo. Buying it would be the next best thing to hanging out with Bill Laswell in the recording studio capturing your favorite bass-based musician on analogue tape.

Although the AN214 IC audio amplifier was famed in its heyday for “heroically” bringing out the musicality of the cassette tape medium despite of it’s “engineering” limitations. This 5 watt (according to bench test measurements, although it sounds apparently more powerful in real life use) integrated circuit-based power amplifier has still so much to give in our wide bandwidth wide dynamic ranged hi-fi world. Even in the era of DVD Audio and SACD whose bandwidth could easily stretch to 100,000 Hz. Compared to CD’s 22,050 Hz Nyquist Frequency criterion limitation – never mind cassette tapes, which have a hard time reaching past 15,000 Hz.

Given that the first decade of the 21st Century is almost over, I find it real surprising than an integrated circuit-based low-power amplifier whose heyday pre-dates the discovery of the AIDS virus can still hold its own in 2009. If any of you out there has something extra to add to my woefully inadequate knowledge to the electronic engineering aspects of the AN214 IC-based power amplifier, please drop me a line. Your help is greatly appreciated. Especially the slew rate part of this venerable device.