July 2017 ~ CLASSIC HI-FI EQUIPMENT

2017-07-08

NOISE IN STEREO TURNTABLES.

The noise (rumble) is the sum of all disturbances that accompany the signal provided by the cartridge and that do not belong to the musical message. It is caused by all kinds of vibrations that occur in every movement and are captured by the magnetic cartridge, which is sensitive to vibrations. Hearing these noises fog the music and make a presence as a background purr.

This noise annoys more or less depending on the level of the signal that is recorded on the disc. Thus, it is noticed more in a pianissimo than in a part of great orchestra, for which it is necessary to look for a fixed term for the comparison of the noise.

It is therefore necessary to indicate the signal to noise ratio is measured in dB. That is, how many dB below is the noise relative to a fixed signal recorded at 1000 Hz and with a speed of 10 cm/sec on the disc for the DIN norm. This DIN norm requires between 35 and 55 dB minimum, with values ranging from 40 to 60 dB and the highs reached by high performance turntables between 50 and 70 dB.

Continue

Posted by hifisnecma on 8:08 AM No comments »

2017-07-06

DESVIATION OF SPEED AND FLUCTUATION OF SPEED IN STEREO TURNTABLES.

The speed of rotation of the platter should be as exact as possible equal to the nominal. The DIN standard requires it to be maintained between + 1.5% and -1%. The technology has largely exceeded these values especially in stereo turntables that have fine tuning and even better in those controlled by quartz where the value has reached 0.1%.

Fast speed variations cause a crying-like hearing sensation. Variations up to a 6 Hz rate are classified by whine (wow) and the fastest , from 6 Hz onward, are classified by flutter. Wow is caused by imperfections of the transmission system ( Pulleys, loose or sliding rubber bands) or the turntable itself (eccentricity, low weight, imbalance). The flutter is caused by elements that rotate faster (unequal speed of the motor during a revolution, eccentricity of the motor pulley. A very frequent cause of wow, not attributable to the turntable and that can have a decisive influence is the eccentricity of the central hole of the disc with respect to the furrows.

The DIN standard specifies a maximum wow value of +/- 0.2% in weighted measurement. Currently, values of 0.1% and very high quality stereo turntable are easily reached at values of 0.06% always in weighted measure.

Continue

Posted by hifisnecma on 1:56 PM No comments »

2017-07-05

QUALITY CRITERIA.NORMS.

When in the 50's of the last century the "High Fidelity" apparatuses appeared successfully, the difficulty arose of comparing apparatus of the same functions but of different manufacturers. Each one specified what he thought fit and in the way that best suited it. To put order to this chaos were elaborated norms on the diverse parameters to measure in the reproducers of sound of high fidelity. Some are only measurement standards, they only indicate how it should be done and how to express it so that measurements from different manufacturers can be compared. As an example we have the case of the american norm of measurement IHF (Institute High Fidelity).

Others are quality norms, they specify minimum requirements so that the device can enter the name of high fidelity. The most widely used of these norms was the one written in 1962-63 in West Germany and the German Institute for Standardization (DIN). These standards carry the number 45500 destined to become famous.

Another norm, often used by the Japanese is the JIS that gives in general better values than the DIN, so when comparing values of different devices we must ensure that the norms in which the measurement has been made.

A concept used in the measurements and that should be clarified is that of the weighting specified for some measurements. To weigh in this case is to measure a parameter taking into account the sound sensation produced in the brain each of the audible frequencies. For example, it is not the same to have a certain level of noise on a turntable at 400 Hz frequency than at the frequency of 50 Hz. The second creates a noticeably smaller sensation in the brain.

Continue

Posted by hifisnecma on 8:10 AM No comments »

2017-07-04

MATERIAL AND MECHANICS OF THE TONE ARM TURNTABLE.

The arm should be both rigid and light so it must be necessary to carefully choose the materials and shape to meet this condition. The shape that gives greater rigidity with the minimum section of material is the tube shape. Lately there are versions of carbon fiber arms in the form of a tube that allow them to lighten them even more. The arm must be balanced with respect to its horizontal and vertical axis. When it is in equilibrium, its center of gravity must be at the point where the two axes are crossed. In order to achieve this with respect to the horizontal axis it is necessary to equip it with a counterweight on its back that serves at the same time as a scale in order to obtain the weight necessary for the phono magnetic cartridge.

At this point we must indicate what concerns the shape of the arm, on which has been provoked a polemic between two tendencies: the straight arm and the arm in the form of S.

In the straight arm, the spindle incorporates the angle of elbowing necessary to minimize the reading error; while in the S-shaped arm the angle is incorporated into the bending of the tube, and therefore the head is straight. This represents an advantage and isr />

As for the characteristics of rigidity, weight, accuracy and cost, the straight arm has clear advantages. Perhaps aesthetics favor more curved.

The operation of handling a turntable arm by hand to place it at the beginning of the disc or in any part requires a good pulse, to avoid damage to the needle, which being very hard (diamond),is very fragile and can be broken with a sudden blow. To avoid these risks, the arms are provided with a lifting mechanism that is operated with a lever.

Continue

Posted by hifisnecma on 3:55 PM No comments »

2017-07-02

CENTRIPETAL FORCE OR SKATING IN TONE ARM.

The needle, when traversing the furrow, presents a friction force in the direction of the tangent of the furrow that we can assume is contained in the vertical plane of the pickup cartridge. This centripetal force or lateral thrust is denominated in english language skating. The centripetal force is directly proportional to the working weight of the pickup cartridge and is inversely proportional to the radius of the needle tip.

Continue

Posted by hifisnecma on 9:00 AM No comments »

READING ERRROR IN TONE ARM.

The displacement of the arm on the plane of the disk, the tip of the needle describes a circumference by rotating about its vertical axis so that the vertical projection on the disk to the axis of the needle forms a certain angle (reading error). This angle is not constant and varies according to the distance of the needle to the center of the disk.

The difference in position between the original recording stylus and the reproductive needle is translated into a distortion directly proportional to the reading error and inversely proportional to the radius of the point in question.
The designers went to great lengths trying to minimize this distortion with a careful calculation of the dimensions of the arm; For a given distance between the axis of the vertical axis of the arm, there is an arm geometry (arm length and head angle) that cause the distortion to reach a minimum value along the arm travel.
A well-designed arm should have the values of the maxima and minima of equal absolute value for the distortion.

Continue

Posted by hifisnecma on 8:55 AM No comments »