5.3.4 Replay Equipment

5.3.4.1 Optical replay is available for LPs and should be investigated before selecting any transfer equipment, however contact transducers, or styli, are presently more common, perceived as less complicated and preferred by most technicians.When using contact transducers there are so many variables in the reproduction chain that exact repeatability of any particular replay is not possible. Pick-up arm, cartridge, stylus, tracking force, previous groove deformation or wear all contribute to the variability in replay. Even temperature can affect the replay characteristics of a cartridge/stylus combination to some degree. However, if LPs are to be captured for digitisation high quality components in the playback chain from stylus to recording equipment will ensure the most accurate audio capture.

5.3.4.2 Perhaps the most important part of the replay chain is the cartridge/stylus combination. Moving coil pickups, considered by some to be the most sensitive, tend to have a price tag and lack of robustness that precludes their use for anything but very careful domestic use. A good,high compliance,low tracking force (less than 15 mN, commonly quoted as 1.5 grams) variable reluctance (moving magnet) cartridge with a bi-radial (“elliptical”) stylus will be the most practical choice.Replay styli should include a range from 25 µm (1 mil), commonly used on early mono LPs, to 15 µm (0.6 mil), including conical, elliptical and truncated styli depending on the age and condition of discs to be played.

5.3.4.3 Attention should be given to the adjustment of vertical tracking angle (VTA) of the pickup system, which ideally should match the VTA produced in the recording process. The recommended playback VTA during the 1960s was 15±5º, which changed by 1972 to 20º±5º. It is impossible, however, to check the VTA of a given record (unless with test records which permit the evaluation of the intermodulation distortion of a vertical signal). As a basic adjustment, however, attention should be given to the horizontal position of tone arm, parallel to the surface of the record, under the appropriate tracking force. This should ensure the VTA intended by the pick-up system manufacturer. Any deviation from there can be achieved by lifting or lowering the tone arm.

5.3.4.4 Another angle to be adjusted is the tangential tracking angle (TTA).With tangential tone arms it must be insured that the system is mounted to lead the stylus exactly along the radius of the disc. With conventional (pivoted) tone arms a compromise must be made by adjusting the position of the stylus (= effective tone arm length) with the help of gauge, generally supplied by precision equipment manufacturers.

5.3.4.5 A high quality, low noise preamp capable of reproducing the standard RIAA curve as well as reproducing a flat transfer of the audio will be required. If pre-1955 records are being transferred, then a preamp capable of coping with the equalisation variations listed in Table 2 Section 5.3 Equalisation Chart for Pre-1955 LP Records, may be necessary. Multiple setting preamplifiers are not readily available, and it may be preferable to modify the equalisation after the normal preamp output, or applying custom equalisation to a flat transfer in the digital domain.

5.3.4.6 Vital to calibrating the replay chain is a test record cut with the recording characteristics of the records being transferred, and adjusting the frequency band of a graphic or parametric equaliser to achieve the proper output. An accurate RIAA test disc can be used to calibrate the system for non RIAA equalisation providing the characteristics of the replay curve are known. Finding an appropriate test record may prove difficult and even if available, older test records can suffer from wear and no longer give an accurate response, especially at the higher frequencies.

5.3.4.7 The vast range of playback components available in the 1960s and 1970s is no longer offered, and whilst not as difficult to locate as replay equipment for 78s, a much more limited range is now available. Though relatively impervious to damage and decay, LPs can become inaccessible if suitable replay equipment becomes unavailable. Although a good stock of spares and consumables is recommended for medium term access, it is important to note that styli and assemblies do not have an infinite shelf life.