of a Lifetime
|With vinyl playback enjoying a
renaissance, sources of information about turntables, and what makes one better
than the other, are difficult to find. We hope you find these sections
Turntable Specifications and Feature Definitions
Specifications are important because they give you a baseline for which to compare the engineering competence of individual manufacturers. When basic performance specifications such as speed stability(accuracy, wow & flutter) and internal generated noise(rumble) are absent from a company's sales information, you cannot be sure how well the manufacture of that product is controlled. Will the first unit be the same as the 1000 unit? For if there is no specification, the manufacturer needn't be beholden to one.
Specs are the baseline, demand them.
The Drive System
Speed accuracy will usually be specified in percent %. Broadcast standards accuracy is 0.3% and this is a good figure to expect. to get an idea of the impact of speed accuracy, a 3.3% change in speed will alter pitch one half step. 6% is a full sharp or flat. So, 0.3% is a good margin. Most hi quality turntables will beat this figure
Wow and Flutter
Speed Stability is specified as Wow and Flutter. Wow being slow variations in speed and Flutter being fast variations. The measurement is in % and is an average or weighted value. Good numbers for a belt drive design are less than 0.1% and for a direct drive 0.05%. Inexpensive direct drive systems are more apt to have higher flutter. This can be audible as a shimmering to the sound, most noticeable in piano recordings. A good additional measurement for direct drive systems is a peak wow and flutter measurement. This can reveal the sonically audible variations that don't show in the average measurement. Hi Peak Flutter levels cause a smearing of hi frequency detail.
Only one table that I know of specifies this measurement.
The amount is 0.035% peak W & F and the company is Technics, the model is the SL-1200 MKII.
Speed Drift (Due To Drive System) Never Specified
This is never specified, because a turntable that exhibits drift is not a very good turntable. DC belt drive tables will do this. They will drift several percent over the 20 minutes of an LP side. Usually this drive system is only found in inexpensive DJ systems where only 3 minute singles are played and the drift never becomes a problem. You should always check what kind of drive system the turntable has. Some modified 78 rpm turntables use this system and again, for 3 minute singles it may never pose a problem, but for album sides it will.
Speed Drift (Due To Static Stylus Drag) Never Specified
In a freely rotating system like a turntable, any friction near the outside edge will try to slow the rotational speed. In drive systems without servo control, the turntable truly slows down the moment the stylus enters the groove, some as much as several percent. As the stylus moves towards the center or end of the record, the torque increases and the turntable regains most of its free rotating speed.
To avoid the affects of this static stylus drag, the drive system must have servo control.
Speed drift (Due To Dynamic Stylus Drag) Never Specified
When the stylus encounters a highly modulated groove, it must do extra work in the groove, during this time, friction and drag increases on the drive system. Here we have an affect similar to discharging an electrical capacitor. Based on the duration of the loud passage, and the weight of the spinning platter, there is a time constant that determines how quickly the platter slows down. If the platter is insufficiently heavy (<10 Lbs), the speed can slow sufficiently such that, a moment after the loud passage is over, you become subtly aware of the turntable speeding back up. It can take many years of listening to hear this effect, but like all listening skills, once you attain it, it is with you for life.
Only heavy platter belt drives, or sophisticated direct drive systems can overcome the affects of dynamic stylus drag.
Tonearm Bearing Friction
Rarely if ever specified, this is a measure of manufacturing prowess. Only one table that I know of specifies this measurement. The amount is 0.007 grams and the company is Technics, the model is the SL-1200 MKII.
Tonearm Tracking Accuracy
Also rarely advertised, this is a measure of the tonearm design and how well it is located geometrically. Look for values of about 2 degrees at the outside groove and less than 1/2 degree at the inside groove.
Tonearm Effective Mass
Tonearms will usually be specified as low mass(<12 Grams), medium mass(12 Grams) or high mass(>12 Grams).
The mass of the arm will be specified in grams. This specification determines what cartridges will work best. Low mass arms work best with hi compliance cartridges. Conversely, hi mass arms work best with low compliance cartridges.
The mass of the arm and the compliance of the stylus suspension, create a spring that resonates at a low frequency. This is referred to as the arm cartridge resonance. When this is mis - matched, you either get wild behavior on warped records or poor bass performance.
One observation to make is, if the tonearm uses fluid damping, it will be able to accommodate a wider range of cartridges without problems. The damping all but eliminates the arm-cartridge resonance. (Don't confuse this with fluid damped cueing which only has to do with raising and lowering the tonearm.)
Recently re-introduced, it seems fitting to add the Laser Player to this discussion.
Originally introduced in the early '80's, the laser player failed to take hold. The cost was and still is high > $10,000. Improvements in the laser reading mechanism have greatly reduced the size of the scanning spot. It is much smaller and more adjustable.
From an audiophile perspective, The main advantage of this player is the complete freedom from stylus drag effects since there is no physical contact with the groove.
From a vintage collector or archivist point of view the main advantage is the lack of physical contact and the ability to move the scanning spot up and down the groove wall.
Beyond that however, the player requires powerful electronic processing to eliminate sources of noise that a conventional stylus would never see. Therefore the player requires fulltime rumble and high frequency filters in addition to a defeatable transient noise suppressor. The sonic affects of the filtering is a neccessary consideration here. Stylus drag affects can be overcome with sophisticated drive systems as found in the Technics 1200 and VPI Flywheel Drive turntables.
The counterweight is used to set the tracking force the stylus places on the groove.
The antiskate force is a correctional force the keeps the stylus pressure equal on both sides of the groove wall. This is important for best stereo reproduction. This is usually set to the same amount as the counterweight. Test records are available for optimizing this setting.
Arm Height (VTA)
If your arm has a height adjustment, set it so that when the stylus is in the groove, the tonearm appears parallel to the record surface when viewed from the side eyes level with the platter. If no height adjustment, you can shim the cartridge if the arm is angles downward. If it is angled upward, perhaps a shorter cartridge design will be the solution.
This is often referred to as setting the Vertical Tracking Angle.
Cartridge Overhang (Offset Angle)
This is the setting of the the cartridge in it's mounting. For as simple an operation as it seems, you are actually setting the alignment of the stylus in the groove. It is important because the stylus must maintain its geometry from the beginning of the record to the end. Many tonearm companies have simplified this process with tools and guides. There are also aftermarket products that will make this process relatively painless.
The Phono Cartridge
The Suspension Compliance
The stylus suspension should be specified with a compliance figure. The number will typically vary from a low compliance of 10 to a high compliance of 30. This figure is important because it will help you select the right cartridge to match the mass of your tonearm.
This is the most common cartridge made. It features a replaceable stylus. The stylus assembly includes the diamond tip, the cantilever, the suspension, the magnet, and the stylus housing. An important point, often overlooked, is that each time you replace the stylus, you replace the entire moving system so that includes the magnet.! These cartridges are designed to work in any modern gear that has a phono input.
This is identical to the moving magnet design above. the difference is the coils are wound on a magnetic structure and the stylus carries a low mass iron piece. This design appeared before rare earth magnets made the scene and at that time it was viewed as the best way to reduce stylus moving mass. The downside of these designs is that they can be overly microphonic. This will give them a fuller sound quality often described as a mid bass bloom. It is not an accurate sound but is very pleasing and as thus the design continues to be a favorite of collectors and audiophiles. These cartridges are designed to work in any modern gear that has a phono input.
Moving coil cartridges, as the name implies, have the coil wound on the stylus cantilever and the magnet structure is stationary. The stylus is not replaceable in these designs, though most companies offer re-tipping or trade in replacement on a new one. The potential advantage of these designs is two fold, they can exhibit very low moving mass, and because they feature a very low coil inductance, they have the best phase response. This is really only true for the low output designs. In these designs the sound has a certain clarity and "hear through" transparency. High output moving coils lose much of that magic because of the higher amounts of wire required. Low output 'coils will require a special phono stage specifically for them. Hi output designs will work into a conventional phono input.
A Word About Mounting Styles
Standard mount cartridges mount with 2 screws from the top 1/2" apart. There are four visible wires on the back of the cartridge. Typically color coded red, green, white, blue. If your turntable terminates in a head with these 4 wires and the two slots 1/2" apart, than a standard mount cartridge is what you need.
P-mount is a coordinated system devised in the '80's by which a standardized tonearm designated T4P was designed, and a standardized cartridge was designed. When a Pmount cartridge is plugged into a T4P tonearm, the alignment is perfect and the tracking force is perfect. The arm requires no adjustments. This was perhaps the best system ever devised to take the problems of tonearm set up out of the hands of the basic consumer. Tonearm set up continues to be one of the most common problems the consumer faces in getting the best sound from his turntable.
The Turntable Base
Sensitivity To Airborne Vibration
There is no current specification for this though it is well known to be responsible for the sonic differences often heard between turntables with similar specs. Ed Long, a reviewer for Audio Magazine, used to run a test where he placed a loudspeaker over a turntable, and, subjected the turntable to a frequency sweep. The stylus rested in a stationary groove and the output was plotted. His reports would show resonant nodes where the body of the turntable was, well, resonant.
Ideally the turntable should be inert to outside vibration. The best known way to do this is a sandwich construction method called constrained layering. One uses materials of dissimilar qualities. Mixing stiff materials like cast aluminum with engineering resins and rubber, can produce a very inert object incapable of sustaining vibration.
A manual turntable means the user places or cues the needle into the groove, and must cue and return the tonearm when the record is over. It is a fully manual operation.
Semi Automatic Turntable
A semi automatic turntable is one in which the user places or cues the needle into the groove, but at the end of the record the tonearm automatically lifts and returns and the turntable shuts off.
Fully Automatic Turntable
A fully automatic turntable will, at the push of a button or lever, start the record and at the end of the record will the tonearm will lift and return and the turntable shuts off.
An automatic changer has the operation of a fully automatic turntable and adds a stacker spindle that lets you play multiple records.
This lever raises and lowers the tonearm. It is usually a lever located near the rear of the tonearm. It is also often designed as a button or lever on the front of the turntable so it can be actuated with the dustcover down. It offers a convenient and safe way to raise and lower the tonearm from the playing surface.
Locating A Turntable
Most turntables made today no longer have the lightly spring suspensions of yesterday. There fore todays tables are more sensitive to foot falls. The best location for a turnable is a wall mounted stand. This will eliminate problems from floor bound vibrations. Home centers have good wall shelf systems that work very well and are adjustable.
Understanding turntables more should help you choose the right turntable for your needs. As always, weigh the needs you have today with the demands you may have in the future. This is probably the last turntable you will purchase. Weigh the features carefully and be sure to understand the retailer's refund policy in case you are unhappy with your purchase.
KAB Electro - Acoustics
P.O. Box 2922
Plainfield, NJ 07062