Techno-Babble

Why Ortofon, and why moving coil?

I feel inclined to apologise in advance for what follows, since the hard engineering data which could justify one particular pickup cartridge over another are not consistently available from all manufacturers. As a result of that partial vacuum and the typically large amounts of semi-technical hype which usually replace it, descriptions of (and comparisons for) different cartridges are usually versed in subjective terms. Phrases such as "sonic accuracy", "sweetness of sound", "detail" and so on abound. These are great for a sales blurb, or even for a review in a "Hi-Fi" magazine, but are of no use at all when it comes to making an accurate, informed choice from an audio-engineering viewpoint.

Relatively complete data, including distortion figures, are available for Ortofon. However, other well known brands such as Shure and Stanton seem to regard this parameter as unworthy of inclusion in their specifications. (I would have thought that this sort of omission would worry most people - but obviously not.)

Anyway - in light of this dearth of data, some of what follows (especially my comments re variable reluctance cartridges) is thus only semi-technical.

Some history (my awakening)

As a teenager who was fascinated by electronics and the art of music reproduction when vinyl was still dominant, I tried a variety of different vinyl pickup cartridges. These included units such as the Decca Deram (claimed to be a "Hi-Fi" ceramic), a well known "high trackability" variable reluctance unit, and a couple of other widely advertised brands. And of course I also listened critically to other people's systems (often with far more expensive cartridges, amplifiers and speakers than I could afford at that stage). But throughout this period, something kept bugging me: the disc replay quality I was hearing via ordinary TV test transmissions (*) was noticeably better than any of these domestic Hi-Fi systems. It was so clean and transparent that one might have been listening to a live performance.

  * Off the discriminator, through an emitter-follower, and off into a good quality 10 watt "ultra-linear" (partial triode) class AB valve amplifier.

So I contacted a few radio (and TV) stations to arrange tours, and that was where I discovered (almost without exception) that all were using Ortofon moving-coil cartridges. I also discovered a lot of other names such as Neumann, AKG, Sennhieser, Western Electric (microphones), Goodmans, Altec Lansing, Leak, B&W (loudspeakers), AWA, RCA, Gates, Marconi, General Radio (audio processing, modulation monitoring, and distortion analysis) and several others which I'd similarly only heard of vaguely until then.

Looking around their control rooms, production booths, and studios - I was hit suddenly with the quiet reality of "professional audio engineering" (ie: the real thing), as opposed to all I'd known before. Or to put it another way ... I suppose that I started to realise the true meaning of the phrase "broadcast quality". It was all so matter-of-fact to these people - they worked with nothing else but the real thing every day. $2000 Neumann capacitor microphones with field-switchable patterns, Leak monitors, Ortofons, big consoles with stud-faders and illuminated VU meters all over the place. And the sound quality everywhere was - spectacular. Needless to say, I was rather stunned at the sight (and sound).

Mind you - I had no idea why they all seemed to be stuck on Ortofon for disc replay, although a little later on I came across some interesting figures that did cast some light on this: Vinyl singles (7 inch 45 RPM discs) are typically cut with a modulation level of around 10 to 20 cm/sec, which is quite high compared with LPs. Ortofon cartridges have a specified distortion at these levels (FIM and THD) of less than 1%. This may sound very high to some people, but playing such singles with an Ortofon nevertheless yielded a very clean sound. And from my experience, playing highly modulated 45's with a Shure sounded ... well, muddy, somehow (high trackability and low tip-masses nonwithstanding).

After these tours (and later, an 18 month stint working at one station as a "panel operator" before going off to university), the meaning of the term Hi Fi became obvious to me. I realise that this will probably sound cynical, but much of the equipment marketed as Hi Fi is no more than super hyped, over-priced, inferior quality junk - aimed at the naive part of the market. The specifications generally look fantastic, of course. In fact, this whole area of audio equipment specifications (another digression if you really want it :-) is fraught with misleading information (but that's hardly news to most people of course).

Ortofon's long established history and reputation in the production of professional film soundtrack and record cutting equipment - also unknown to me at the time - probably also had something to do with their selection by the professionals.

I subsequently read in various places that:

  • Variable reluctance cartridges usually suffer from subtle magnetic-linearity distortion problems unless the manufacturer does 'this or that' ..."
  • Moving coil cartridges generally exhibit the widest frequency response
  • Crystal and ceramic transducers are inherently non-linear and suffer from mechanical compliance problems ...", and
  • Moving coil designs are inherently linear, although generally expensive to manufacture ...

  • Ortofon MC15 Super MkII
    So to cut a long story short, I promptly went out and bought my first Ortofon (an S15-T), built myself an RIAA pre-amp, and all of a sudden - my home system suddenly had that same "FM quality" - clean, wide, and transparent. Needless to say, I was very pleasantly surprised, and quite rapt.

    My only concern with this original old S15-T after I'd been using it for a few months was the overall mass of the cartridge due to the built-in stereo matching transformer. When the inevitable (albeit infrequent) "cartridge drop" accident occurred, the stylus survived quite happily by retracting into the stylus guard, but the vinyl often didn't appreciate being clobbered by the massive head assembly! So a couple of years later, I invested in an MC-15 Super and put the S-15T back into its little red jewel-box as a standby.

    Late 1970s - and Ortofon stylus replacement costs start to bite

    In the late 1970's (in Australia at least), a general reaction against the high cost of stylus replacement for Ortofon cartridges arose in the broadcast industry. Most FM and AM radio stations were by this time running without panel operators, meaning that announcers were now cuing their own records. And this ham-fisted brigade were now wrecking several Ortofons a week. At around $150 per stylus replacement, the engineering accounts were starting to look a little sad. The unfortunate result of this, in most cases, was a move across to the (American) Stanton variable reluctance units. These featured reasonably low distortion and user replaceable stylii.

    I must admit that - to my ears at least - the Stanton did sound passable (at least for a VR design). The '600 series was also fairly rugged and it could track highly modulated singles with little obvious distortion. So even though they may have lacked the transparency and extended frequency response of the Ortofon MC units, Stanton nevertheless began to make an impact on the broadcast market here in Australia.

    Still the Rolls Royce

    Cost issues aside, Ortofon moving-coil cartridges remain today the standard to which the others are compared. Their strength is in their simplicity, low moving mass, wide frequency response, and excellent linearity (low IM distortion).


    Postscript

    Under obvious commercial pressure (from Shure, Stanton and others), Ortofon themselves released a range of variable reluctance cartridges with user-replaceable sylus units in 1969 for the mass "Hi-Fi" market, which they continue to market today. However, their moving coil range remains their flagship product for the top end of the market.

    And just in case you're wondering - Bluehaze Solutions has no connection either with Ortofon or any Ortofon distributers.


    What about 78s and Edison cylinders?

    The transcription of wide-groove formats such as 78 RPM discs (or even Edison cylinders) is another issue entirely, of course. There are few organisations these days who would seriously contemplate the once-familiar vision of a drawer full of moving-coil Ortofon cartridges with their green and blue caps fitted out with half a dozen different broad-groove stylii! And in any case, since the distortion levels of broad-groove discs are usually relatively high in comparison with LPs, employing quite reputable units such as the Stanton is probably a reasonable compromise.

    Chris Long's Antiquarian Productions provide an excellent service for transcribing any of these older formats to CD if you do require it - just email your requirements and Chris will look after you.


    Okay, following that rather subtantial diversion on the topic of analogue pickup cartridges, I'd better get on with it and describe the rest of the transcription equipment being used here at Bluehaze for transferring vinyl to CD ...

    The turntable

    There's little that can be said about the Technics SL-D2 turntable. The rumble level is basically inaudible, being limited more by the vinyl itself (ie: cutting lathe rumble). Wow and flutter are also essentially inaudible.

    (Gee - that was easy)


    The RIAA preamplifier

    The pre-amplifier is designed to operate with magnetic replay cartridges and recording curves which follow the RIAA (Recording Industry Association of America) standard. Most of the vinyl that exists was produced to this specification, although some very early LPs were produced according to slightly different standards, such as (eg) AES.

    The engineer who designed this pre-amp (the late J Lindsley Hood - UK) believed that the traditional 3-stage configuration left something to be desired in terms of "transient stability", and this 7-stage design was the result of his research.

    I won't bother giving you the schematic of this particular pre-amp (published in a 1960s Wireless World) because it uses discrete devices and occupies two circuit boards! If you're seriously interested in constructing your own RIAA pre-amp from scratch, you'd probably want to use something like Figure 3 as described in the National Semiconductor LM833 application note these days. (In fact, even just reading this particular Nat Semi App Note is quite interesting in its own right :-)


    Actual record/replay frequency response

    The curve at the left shows the actual frequency response of the Bluehaze transcription system as measured using a Concert Disc PTX-10 RIAA professional test recording (pressed in Australia by W&G). This disc is claimed to be within 1/2db of RIAA standard. The graph shows the final signal levels in the digital audio file (at a reference level of +30db).

    The deviations (relative to 1KHz) show a small rise toward the low end (+1db at 250Hz, and +2db at 30Hz). There is a similar small rise toward the high frequency end, with the response at 16KHz (the upper measurement limit) being +4db relative to 1KHz.

    This slight lift in the high end is deliberate. When comparing given pieces of vinyl to their CD re-releases, the vinyl (to my ears) has generally sounded slightly lacking in the high end. I have no idea why this should be, but including this small degree of high-end lift in the pre-amp equalisation does serve to minimise the effect.

    The nett result is certainly quite satisfactory. One aquaintance recently rang me with the comment that "... I've being listening to those (Madder Lake) albums for years, but I didn't realise how good they were until you dumped them onto those CDs ..."

    I couldn't really comment on this at the time (I haven't really heard his vinyl replay equipment in action), but comments like that are quite satisfying.

    Mind you - I'm fairly sure he uses a variable reluctance cartridge of some sort, and he probably hasn't heard a good moving coil unit at such close range before :-)


    Spectral comparisons - Vinyl versus CD


    Spectrum of a 3 sec section off CD

    Spectrum of same section off vinyl

    The two spectral analyses above are from the same three second portion of "The Logical Song" (Supertramp). The CD sample was analysed off the WAV file obtained via a direct "rip" from the CD. The vinyl sample was analysed off its "recorded" WAV file (via the Ortofon MC15, etc).

    It's interesting to note that the vinyl is actually rolling off more gently than the CD above 15KHz. In particular, the energy content of the vinyl is about 6db higher than the CD version at 20KHz. This could be due to any one or more of the following:

  • Deliberate, steep filtering in the audio chain for the CD recording process,
  • A deteriorating master tape, or
  • The master tape being played with a very slight asimuth error.

    Either way, it is interesting that the vinyl transcription in this particular case actually appears to surpass the CD at the very top end.



    Others media formats


    Minidisk

    For those of you doing your own vinyl transfers - a brief word of warning re the use of high-density (compressed) formats such as MP3 and Sony's Minidisk.

    The proprietary Minidisk format, unlike "normal" audio CDs, employs lossy digital compression (ATRAC). This situation has similarities with lossy image compression formats such as JPEG. A well processed original JPEG can look superb, but since it uses a "lossy" compression format, reprocessing it several times results in obvious degradation by the time you reach the 3rd or 4th "generation". As such, it is obviously unsuitable for serious archiving purposes - it's designed specifically for compact, one-off "end user" media delivery.

    For exactly the same reason, the "Minidisk" format is unsuitable for mastering or archiving. A "one-off" copy will generally sound great, but if you ever need to make a copy, and even later, a copy-of-a-copy, digital compression "artifacts" will become audible.

    Another point to bear in mind with lossy compression systems is that the reconstructed (decompressed) waveforms, although excellent for most of the time, can still go badly wrong on certain signals. And when they do, the effect can be painfully audible.

    For audio CDs, apart from some small translation loss during the initial conversion of the analogue signal into digital (viz: a gradual roll-off in the high-frequency response between 15KHz and 22KHz due to the "anti-alias" filter), there are no such problems - because the normal "Redbook" music CD format does not use digital compression. And since subsequent copying of an audio CD (to another CD) would normally be done digitally (by "ripping"), even a "copy of a copy of a copy of a copy" will be identical to the original.

    So if you do decide to copy your irreplaceable vinyl onto "Minidisk", just beware of this limitation in the format. Sony's Minidisk is very much an "end user" (consumer market) system, and as such, it's not appropriate for archiving.

    Click here for even more in the way of Minidisk information, thoughts and comparisons (from others) if you're interested.

    MP3

    MPEG layer 3 (MP3) is also a "lossy" compression system, but now much more widely accessible than Sony's Minidisk. There are a variety of encoding and decoding programs to choose from for creating and/or replaying MP3s on PCs - each with their own subtle strengths and weaknesses.

    One big plus for the MP3 format is that most of the more recent domestic DVD players will play MP3 audio discs, as will many recent car CD players, and some portable "Walkman" type units. And since stereo music in this format (using the most popular encoding bit rate - 128k/bits per second) creates music files which are about 1/10th the size of an uncompressed WAV file, a nominal 72 minute standard audio CD can hold around 720 minutes in this format. Quite impressive - and very tempting.

    As with Minidisk, however, lossy compression means that the audio is no longer an exact representation of the original, and every time you process it and then re-encode it, you'll lose a bit more quality. So as before - fine for general listening around the flat or in the car, but not appropriate if you want the best possible quality or if you want to leave your options open for reprocessing and cleaning up the tracks more at a later date.


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    Last update: 12-Sep-2004