Friday, August 10, 2012

Are Piezoelectric Ceramic Cartridges Hi-Fi?

Even though its innards are composed of a piezoelectric material that’s only been mass produced after World War II, why are piezoelectric ceramic cartridges still not considered audiophile enough for high fidelity stereo vinyl LP playback? 

By: Ringo Bones 

From a scientific / engineering standpoint, it seems that the “lowly” piezoelectric ceramic cartridge appears to be more advanced than your typical mainstream moving coil and/or moving magnet cartridge for high fidelity playback of stereo vinyl LPs. And yet in this day and age well into the 21st Century, it is the moving coil and moving magnet types that dominate the now esoteric – yet so hip – scene of the vinyl LP playback niche of the audio world. But why is it that a diamond stylus sculpted to almost nano-engineering precision will only be viable for high end high fidelity vinyl LP playback when its mechanical undulations after reading the vinyl LP’s microgrooves are connected to a mechanical actuator/pickup composed of a coil of wire or magnet instead of a Bimorph Rochelle Salt, ammonium dihydrogen phosphate or a barium titanate / combination lead titanate-lead zirconate piezoelectric ceramic cartridge? But first, let’s briefly examine how LP became the dominant Post World War II high fidelity music playback medium. 

Modern vinyl LP playback for the home can trace its origins back to June 1948 when Columbia Records introduced the microgroove 33 and 1/3 rpm long-playing (LP) record as a better sounding and longer playing time alternative to the 78 rpm shellacs. Thanks to the work of Hungarian-born Peter Goldmark who, with the help of William S. Bachman, invented the LP disc in a laboratory set up by Columbia a few years before. Goldmark’s new record was cut in hair-width grooves, utilized a new electronic equalization system – i.e. the now standard for LP called the RIAA playback equalization where all of the music recording industry eventually all adopted back in 1953 – to balance the tone along all portions of the groove, was pressed in non-breakable vinylite plastic, and was played in a new turntable that recorded steadily at a new speed of 33 and 1/3 revolutions per minute. 

Not to be outdone, rival music recording industry bigwig RCA Victor thereupon issued their 45-rpm “donut” discs – and eventually the “hi-fi world” adopted both 33 1/3 and 45-rpm speeds as standard for post WWII vinyl record playback. Eventually, RCA Victor also produced its very own version of 33 1/3-rpm vinyl long-playing records from their burgeoning Classical Music catalogue – and thus paving the way for the Golden Age of Stereo of the 1950s onwards. 

Till this day, piezoelectric ceramic cartridges have a very glaring advantage over their moving coil and moving magnet cartridge counterparts, they can produce and output signal that can reach a peak of 1 volt – as opposed to high end moving coil cartridge that are as expensive as a South Korean made 4-door sedan whose signal output measures only around 5-microvolts or so. This allows ceramic cartridges to be connected directly to the line-level / AUX input of your preamplifier with only a passive RIAA circuit for tone shaping / tonal compensation. 

But sadly, ceramic cartridge design seems to be stuck in the 1950s because the stylus compliance of a typical piezoelectric ceramic cartridge is poor compared to either moving coil or moving magnet cartridge, so greater tracking force is necessary in using ceramic cartridges – which will inevitably exacerbate record wear. Ceramic cartridges also require about 1-megaohm load resistance – whereas most line-level / auxiliary / AUX inputs have far less – typically about 50-kilohms and even less for some solid-state preamps – which means bass output will be drastically cut. Though vacuum tube preamps and power amps in the 1950s with an EF86 tube input stage usually has input impedance greater than 1-megaohm – like Peter Walker’s famed Quad II power amp for example. 

And as a reminder for those folks way too young to remember – Bimorph Rochelle Salt Crystals used in some very high output piezoelectric ceramic cartridges are very sensitive to environmental conditions and should not be kept and used in places where the temperature exceeds 125 degrees Fahrenheit. But if top high end vinyl LP playback cartridge manufacturers try to develop this very instant their own line of high-end piezoelectric ceramic cartridges with the advantage of a really high signal output with much improved mechanical stylus compliance so that tracking force is equal to that of most moving coil and moving magnet cartridges – who knows where vinyl LP will be a few years hence. By the way, despite of the drastically cut low-frequencies, those cheap and cheerful piezoelectric ceramic cartridges can replicate a well-recorded well-thwacked snare drum better than similarly priced moving coil or moving magnet cartridges.    


Letiche said...

Even though I've yet to audition one first hand, have you ever heard the Micro-Acoustics System II stereo cartridge? According to their advert in the January 1981 edition of Stereo Review magazine, the Micro-Acoustics System II stereo cartridge is more than just a new cartridge design - it is a new cartridge technology. The Micro-Acoustics System II - like the best solid state power amplifiers at the time - is direct coupled. Supposedly providing a transient response up to 10 times faster than either moving coil or moving magnet stereo cartridges for vinyl LP playback at that period.

Ringo said...

The Micro-Acoustics System II supposedly has a patented electret transducing system that is supposedly up to ten times faster than conventional moving coil and moving magnet stereo cartridges. In some of their adverts, the Micro-Acoustics System II is supposedly capable of very good transient response by being able to produce a perfect square wave.