This review page is supported in part by the sponsor whose ad is displayed above
Tom Micccolis is a NASA parts engineer who, for personal use and friends, has begun work on a prototype step-up transformer that may or may not turn into a commercial project. Discovering Jeff Day's Garrard Project on 6moons, he submitted the following article to help readers better understand the MC cartridge/step-up transformer interface. Tom also performs vintage audio repairs and modifications for friends out of a garage workshop.
This addendum article to the Garrard 301 Project is intended as a pragmatic primer for those audiophile enthusiast who are presently using, thinking of using -- or may even have used in the past -- a moving coil (MC) phono cartridge in order to enhance their stereo LP vinyl playback performance. I decided to prepare this technical screed based on my review of readily available information on this topic and finding only scattered fragments of truly salient facts. Although the primary focus here is on proper selection and use of step-up devices, a brief overview of stereo vinyl playback was necessary in order to maintain proper context.
This article is not intended as a selection guide or as a "cookbook" type of paper on what cartridges sound best with what step-up device and/or tonearm. Such literature would simply serve to "run up the market" on particular MC cartridges, tonearms, transformers and head amps and quite possibly leave the reader more perplexed, angry and confused than ever. The truth of the matter is that, due to listener system differences, there is no "one size fits all" solution for even the same model MC cartridge. The intention of this article is to enable the reader to ascertain what MC cartridge and step-up devices would best suit their needs and how to make informed decisions regarding audiophile-level vinyl playback in both the short-term and long-term. This article is also not intended to pontificate about the superiority of MC phono cartridges (there are various sites and user groups for that) or to appear overly didactic. It also does not intend, by way of examples, to steer the reader towards any manufacturer or group of products - so no such direction should be inferred.
When it comes to vinyl playback at the demanding audiophile level, the old adage the devil is in the details is more appropriate than ever. Once the listener wants more detail in the resultant sound from vinyl playback and makes the decision to use an MC phono cartridge, old El Diablo rears his mercurial head. If not implemented properly, an unknowing user's step into the world of MC cartridges can be fraught with hum, feedback, imbalance and ultimately poor sonic results. Couple this hassle with the outside world demands of job, home, family etc. and it conjures up the simile of the average audiophile being busier than a beaver trying to build a dam during a downpour! If this has happened to you or seems as if it would, please read on for how to properly navigate this seemingly overwhelming labyrinth.
The Loricraft gang gathers at Tom's after each CES , including here Frank Schroeder, Pierre Sprey and others
Moving coil cartridges are decades old and not a new concept for phono cartridges. However, 30-45+ years ago audiophile preamplifiers were, at best, only capable of properly handling the signal from moving magnet cartridges. Therefore manufacturers of MC cartridges were forced to provide step-up devices in order for them to even be considered (marketed) for use by the average audio consumer. Either placing a step-up transformer in the head shell with the cartridge or one just prior to the MM input of the preamp accomplished this. There is some debate (some love the cartridges but state that the matching transformers were less than optimum) about the performance of all of these early devices so manufacturers subsequently parlayed that into separating the two, thereby being able to charge the consumer for the cartridge and the matching or step-up device (if so desired). Manufacturer's argued that the advent of preamps with MC phono stages as well as a myriad of non-OEM step-up device offerings necessitated that they do this in order to remain competitive. They further marketed that their step-up devices were designed to optimize performance from their cartridges. As an ironic twist, today some manufacturers of high quality MC cartridges offer no companion step-up devices.
My point in mentioning all of this is that this "evolution" of the MC phono cartridge and step-up device is what has contributed to a lot of unnecessary apprehension, confusion and mystique regarding the use of MC cartridges nowadays.
MC cartridge selection
In order to get down to the practical side of all of this, let's start at the beginning - how to select a suitable MC cartridge. After all, a step-up device needs to be selected based on what MC cartridge it is to be used with.This is a somewhat difficult task but certainly not impossible once it is dealt with objectively instead of emotionally. The first piece of information needed is the effective mass or even relative effective mass of the tonearm that you intend to use. Bear in mind that, due to manufacturer's ambiguity, sometimes the latter term is the best that you will be able to ascertain. This appears as something in the form of "this tonearm is considered to be of medium mass". Please do not fret this somewhat ambiguous information. Rather, simply be aware of it and learn from it when selecting a tonearm in the future and utilize it (as best as possible) when selecting a cartridge.
So what does this mean in reality? A medium mass tonearm is an attempt to have a tonearm that is compatible with a wide range of cartridges. Why is this important? A heavy mass (a.k.a. bludgeon a burglar to death) tonearm is intended for use with heavy (high mass) cartridges that require high tracking forces (5+ grams) and generally produce high outputs (5-15 mV). These were popular with ceramic cartridges; early variable reluctance cartridges; and early moving coil cartridges (with the step-up transformers mounted in the head shell). Most of these cartridge types are considered to be low compliance cartridges.
By comparison, a light mass tonearm is intended for use with very light cartridges and more importantly, high to very high compliance cartridges. These cartridges would tend to track at less than 1.5 grams of Vertical Tracking Force (VTF), sometimes a VTF less than 1.0 gram. This type of tonearm system is based on the "lighter is better" logic resulting in less LP groove wear and better transient response.
Noteworthy here is that, regardless of tonearm mass, the critical parameters for tonearms are pivot bearings and length. The type of bearing is the utmost consideration in evaluating your present and future tonearm. In general, the less friction (mechanical resistance) the bearings have, the better the tonearm and the higher the cost. This is where tonearm manufacturers incur most of their expenses. The length of the tonearm has to do with tracking error across the entire playing surface of the record. In order to have conventional tonearms (as opposed to tangential tonearms) maintain the cartridge stylus at the proper angle relative to the moving groove whizzing by beneath it, a mathematical approximation equation was developed by Loefgren-Baederwald. This amounts to the equivalent of a "best fit curve" using two "playing points" on an LP. The bottom line to all of this is that the higher the effective length of the tonearm (longer), the less the theoretical tracking error at any playing point across the LP.
|The counter-point to this is that the longer the tonearm, the higher the effective mass of the tonearm and the worse the theoretical tracking error can be across the entire record if the tonearm is not precisely calibrated using the 2-point method during set-up. So if you set up a 12" tonearm incorrectly and/or if it has inferior bearings, it can sound worse than a quality 9" tonearm set-up properly (or even set-up 'improperly' by the same amount). Hence you now understand the "great debate" about 9", 10" and 12" tonearms and how to objectively evaluate tonearms.
Now back to our example. If you indeed have a medium mass tonearm, then you can select a wide range of MC cartridges but tend to stay away from anything "ultra-light" and intended to
be "ultra-high compliance" as your tonearm may tend to hamper the overall performance. I suggest a cartridge that requires a VTF in the range of 1.5 to 2.0 grams. Of course this provides a plethora of MC cartridges from which to select. But with that part now figured out, let's further refine our list of candidate MC cartridges.
|The first thing for the MC cartridge user to ascertain, relative to the selection of a suitable step-up device, is the impedance value of your cartridge. The next thing to know is that no standard exists for the MM phono input of preamps. Most folks see a 47K input resistor and think that it is therefore 47K. In vacuum tube circuitry, this acts as a swamping resistor that will tend to dominate the magnitude of the input impedance but the actual input impedance values vary. The input impedance also varies as a function of frequency. Input impedance variations from 40K to 65K ohms have been measured. Also bear in mind that impedance is an AC parameter and therefore not purely resistive. There are reactive components in there as well (vacuum tube inter-electrode capacitances, coupling capacitance [phase shift], cathode bypass capacitance). So assuming that every preamp presents a purely resistive 47K ohm load over the entire audio frequency spectrum is simply not the case but it is a theoretical starting point.
|To add confusion to the mix of all of this is that the term "impedance value" as it relates to commercially made transformer step-up devices is a misnomer. For instance, if you have a 40-ohm impedance MC cartridge (like a Denon or a Signet) and the transformer has a switch or setting for "40 ohms" (the Signet MK-12T is a perfect example), it does not mean that the step-up transformer is actually set at 40 ohms input impedance when connected
|to your preamp. It just means that the setting is for a 40-ohm cartridge. What is really happening is the transformer may actually be presenting 100 to 200 ohms input impedance to your 40-ohm cartridge at that setting when connected to your preamp. While this may appear to make it user-friendly for the consumer, it actually hides the actual step-up ratio of the device. This can be proven. If it were really matching a 47K ohm load to a 40-ohm input, the transformer ratio would be 34.3:1. This means that a 0.2 mV output signal would be approaching 7mV! Empirically we know that this is not the case (7mV to most MM preamp phono inputs is quite a large signal).
The reason for this apparent Wizard of Oz type secrecy is that there is a balancing act between coupling the fragile MC cartridge signal to the preamp and Q (Quality Factor) - the lower the transformer input impedance, the lower the Q (and the more the resultant bandwidth). Therefore the more the voltage steps up, the tighter the coupling and the more it loads the cartridge. In general, the lower the input impedance, the more bass and loudness you get at the sacrifice of the mid and high end (tends to sound rolled off). As you "lighten" the loading, the less voltage step-up and the more the mids and highs increase and the bass decreases. This tends to produce an edgy or brittle sound with tight, lean bass. Now, when you add the actual construction and components used to actually make the step-up transformer to this mix or balancing act (not to mention the actual input impedance of your preamp's phono stage), it seems that cartridge manufacturers all engage in audiophile schadenfreude. Basically you (the user) are left with a complete mess to try to sort out, usually empirically and at your own expense.
Next the manufacturer's specifications compound these problems further by stating information such as "40 ohms with transformer, 100 ohms with amplifier". This is techno-babble for "I (the manufacturer) am really not going to tell you how to properly load my cartridge for optimum results". Instead I am going to give you "setting values" for "complimentary equipment" that we also manufacture.
So how does one sort this all out without spending inordinate sums of money? The first rule of thumb is that most (some exceptions exist) MC cartridges like to see a load impedance of 3X to 6X their output impedance value. This is evident in the example above where the specification states "100 ohms with amplifier". This is most likely the rock bottom input impedance value at 2.5X the output impedance of the cartridge. In this example, our 40-ohm cartridge would have a desired input impedance range of 120 ohms to 240 ohms. This translates to a step-up transformer of approximately 20:1 to 14:1 respectively. This now provides a gauge to evaluate step-up transformers by - namely the step-up ratio (ratio of secondary windings/preamp input side to primary/MC cartridge output side). Be advised that the impedance is transformed by the square of the turns ratio. So a 20:1 step-up transformer provides a 400:1 impedance change. Thus for a 47K preamp input, impedance is transformed to approximately 120 ohms.
So now armed with this information, you can start to intelligently maneuver in the labyrinth of step-up transformer devices. Since transformer losses can be a factor, be sure to check the transformer specifications for what voltage and/or power levels it is designed to handle. Also be sure to note if it is shielded (or not) and what type of shielding it has (electrostatic or magnetic - or both).
More visitors chez Tom's, with Sandy Gross of Definitive Technologies in the center seat
Resistor loading or tweaking
The Most Important Part - what to do and what not to do
Now that you know how to intelligently select and/or upgrade your tonearm, MC phono cartridge and MC cartridge step-up device as well as ground the entire system properly, this section is perhaps the most important of all. The real tragedy that I have seen over the decades is the enormous sums of money spent by audiophiles on cartridges and step-up devices while using turntables, plinths, tonearms, stands, preamps, interconnects and even speakers and source material that were all somewhat to seriously limited. In other words, they would band-aid their system by using a cartridge that "sounded better" or "costs more" and call it "synergy" - complete rubbish.
As you know, this article is being offered as an add-on to Jeff's Garrard 301 Project. As such, I cannot stress this section enough no matter what type of equipment you are presently using. The Garrard 301 is a fixed or non-suspended turntable and as such has its own list of ownership demands in order to provide the best results. It is not something to be placed atop a card table or some other shaky structure the way suspended turntables can be. Be sure to use the best interconnects and tonearm that you can reasonably afford. My point here is that there are most likely many areas worthy of judicious improvement before upgrading to any MC cartridge costing over $1000 perhaps even over $500. The reason is that you will be unable to fully appreciate the sonic differences of a higher priced MC cartridge if other areas of your system are in more need of improvement.
|In closing, I would like to see more and more detailed, objective specifications offered by manufacturers of audiophile products and actually have these parameters (and some others) tested in an independent laboratory on a randomly selected unit. Unfortunately, the audiophile community has not progressed towards that goal very far but we now at least have independent reviewers which are not in some way, shape or form paid by manufacturers.
|As an audiophile community, we should demand more from the esoteric manufacturers offering audio products and services. Salient, objective parameter such as MC cartridge output impedance as a function of frequency plots, proper cartridge loading information, turns ratios, shielding methods, type of wire and bobbins used for MC step-up transformers, friction measurements for tonearm bearings and actual MM phono input impedance plots for preamplifiers - to name just a few. In the meantime, hopefully this article (and perhaps others like it) will help to dispel some of the mystery and audiophile voodoo that seems to have pervaded audiophile stereo vinyl playback.
Tom Miccolis' pater familias was a WWII B-24 navigator veteran and a committed audiophile type since the 1950s, exposing his sons to audio their entire life. "Dad made his own huge JBL horn systems and actually bought JBL Hartsfields and tore them apart for the parts (he said they were "limited"). He also had EV Patricians which he eventually sold when he made his big JBL system.
I have a BSEE degree from Drexel University in Philadelphia/PA and have been working in the military and aerospace industry for 25 years. I have an Extra Class Amateur Radio license as well. I grew up just outside Philadelphia in a suburb town where Acrosound and others were literally within walking distance. My dad was a silk screen printer by trade and actually printed some of the labels used for the Dynaco MK II amplifiers. Herb Keroes is buried in the next town to where I grew up. My father knew Julius Futterman ( I have 2 sets of his H3AAA amps), Harvey "Gizmo" Rosenberg and David Hafler. He was a member of the Philadelphia Audio Society (PAS) until his death in 2000.
My next oldest brother (Benjamin Franklin scholar, MSEE, University of Pennsylvania) and I were put into service by my dad fixing and upgrading audio equipment by the time we were teenagers (out of necessity - my dad did not possess electronic skills but we both did due to our acivity in Amateur Radio). I have been exposed to all of the now "classic" sound systems when they were released as I tried to be around my dad as much as possible. So I got to go to HiFi shows, listening salons, HiFi dealers, friend's homes etc. to hear all kinds of sytems and music.