CLASSIC HI-FI EQUIPMENT

The remembered fever of voluminous and heavy Hi-Fi equipment seems to be back. The suspected reason is its special quality of electronic design and high quality materials, in contrast to the present equipment where plastic and other similar materials are not as resistant to the test of time. The golden age of Hi-Fi equipment is particularly remembered in the 70's and 80's. Automation in electronic design took its first steps and designers...

Functions as important as recording require for their perfect execution, some kind of indication more precise than the operator's own ear, so almost all the devices on the market incorporate some kind of modulation indicator. The most common are: A) The meter This is simply a galvanometer equipped with a bridge rectifier; Therefore its indication is only valid for average signal values. They are usually provided with graduated scales. One from 0 to 100 and the other from -20 to +3 VU. The zero of the VU scale corresponds to...

Noise reduction systems.  Most high fidelity cassette decks incorporate a noise reduction system, of which the most common is the Dolby B version that uses a huge percentage of devices on the market. This electronic noise reduction system appreciates the level of signal reaching the recording head; If it is very high, it does not act; If on the other hand its value is weak, it increases its amplitude and later allows the recording to take place.  When reproducing this signal along with the tape noise is reduced its value...

A) Heads and number of tracks.  The width of the standard cassette tape is 3.8 mm instead of the 6.35 mm of the reel to reel tape or open reel tape; therefore, the recorded tape width is also smaller. As a direct consequence of the reduced track width, it is possible to deduce that the achievement of authentic high-fidelity decks to the cassette is a goal that has been widely achieved today and has always been a task that required time and enormous research effort.  One of the topics that has occupied the laboratories of the main manufacturers...

To obtain maximum performance in its function, the magnetic head must be correctly positioned with respect to the magnetic tape in both height and azimuth. It is called azimuth to the angle that the air gap forms with the perpendicular to the direction of advance of the tape. The position of the head must be so precise that the azimuth is zero...

The demands of this head are much less critical than the others of recording or reproduction, since its function is to record on tape a high fixed frequency. The magnetic circuit is made in two similar halves.  As magnetic material is generally used ferroxcube, the air gap usually has a length of 0.3 mm while the winding is manufactured in a single winding. ...

It must have medium characteristics between the requirements of recording and reproduction, although more importance is given to the reproduction function, therefore, air gap length, winding impedance and shielding must be approximated to those required for reproduction.  The mixed recording-reproduction head is used in most of the equipment on the market and its latest quality levels ensure a completely satisfactory result...

The length of the air gap acquires in this type of heads a paramount importance, since it must be very small to be able to "read" the high frequencies contained in the tape.  On the other hand, in order to obtain a good signal-to-noise ratio it is necessary to increase the surface of the air gap and therefore its length. A middle ground must therefore be adopted.  Usually a reproduction head has air gaps between 3 and 5 μm. The winding is of low impedance and the shielding system must offer a very effective protection...

The magnetic heads of recording, reproduction or erasure it is possible to distinguish two main components:  A) Magnetic nucleus.  B) Winding.  The magnetic circuit is usually composed with very small remnant induction. Hysteresis losses should be minimal as well as those produced by eddy currents.  The winding is distributed in two windings each located in a seminore. This arrangement is preferable because it reduces the sensitivity of the head to disturbing external fields.   The entire core-coil assembly is encapsulated...

>The device which performs the function of recording and reproducing the audio signal on a magnetic tape is commonly called a tape deck. The elements related to the recording-reproduction process common to any tape deck are as follows: 1) Magnetic heads. 2) Recording-reproduction amplifiers 3) Polarization current generator. ...

As much as greater be the surface of the engraved trail will also be greater the quantity of particles of flux-producing and therefore the output voltage will be increased at the terminals of the reproduction head. Increasing the air gap length increases the output voltage, but, in return, the response at high frequencies will be reduced. In practice, the design of the reproduction heads will always be made taking into account the compromise between the signal level and the frequency response. ...

This factor of great importance in all the systems of transmission of information is of singular importance in the case of the recording tape, since unfortunately there are always some noises that inevitably are inherent to the magnetic heads or the magnetic support (tape).  Because the magnetic head of reproduction is sensitive to variations in magnetic flux, it is necessary to take into account that there is no magnetic field around the stereo deck, as well as insulate (with good shielding) power transformers and the motors...

The main elements of a magnetic head are the coils and the gaps (two sets, each one corresponding to a stereo channel). These gaps end up on the surface of the head, on which the tape passes at a certain speed, and are separated by a space of very small size filled with non-magnetic material that separates both poles; the dimensions of the gap are expressed in microns and their definitive value depends on the type of application of the head and the investment (time and money) that the manufacturer has destined for its production.  The...

We imagine a magnetic tape of them utilized currently in the stereo decks. Basically it consists of a plastic film on which a fine layer of magnetic material is deposited. Even when the plastic support and the agglutinating elements are very important for the smooth operation of the tape, the magnetic layer is the medium that allows recording, and therefore must be a ferromagnetic material.  In most cases different varieties of iron oxide are used although in recent years new materials have appeared suitable for that purpose. The...

The location of the turntable with respect to the loudspeakers should be carefully studied, as they often appear coupling or feedbacks that appear in the form of annoying hum that come to completely prevent hearing. This phenomenon is called Larsen effect and is caused when the sound waves generated by the loudspeakers affect the turntable whether traveling through the air or more frequently when propagating the furniture, walls and roofs. When vibrating the entire turntable, the cartridge detects these vibrations and injects them again in...

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,...

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...

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...

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...

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 ti...

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...

The mission of the reading arm is reduced to keeping the tip of the needle in the groove of the disc without giving any distortion or resonance. The arm is a high precision instrument. It basically has a vertical and horizontal movement that is performed around a horizontal and vertical axis respectively. This allows you to follow the groove throughout the length of the disc. As the force that moves the arm comes out of the support and guide that represents the groove, the arm must meet a number of conditions:  1) Maximum rigidity with...

The velocity of the plate depends on parameters external to the turntable, such as the supply voltage, the frequency of the electric network and the greater or less effort involved in the friction of the needle on the disc. For this reason, the speed of rotation of the plate can differ somewhat from the nominal of the disk and to avoid it have been devised devices that allow to adjust the speed of the plate to its exact value, the so-called...

The plate is the mechanical element that physically supports the disk and prints a rotational speed of the highest possible accuracy at each instant and over time at the speeds at which it was recorded. If this does not happen, variations of pitch are produced in the music played with respect to the original. If a 33 rpm disc is played at 34 rpm, all frequencies are shifted to treble. Material of the platter and shape thereof. The platters are made of iron (iron) or antimagnetic materials (zamag, aluminum). The ferrites have...

The movement of the arm with respect to the disc can be radial, as occurs in the majority of the turntables the needle describes an arc of girth) or it can also be linear (the needle describes a radius of the disc). This last system is taking strength in the market, although its prices are quite superior to conventional. Radial or conventional movement arm. It is the most extended system and the arm is equipped with a movement around a vertical axis and a horizontal that allows it to follow the furrows. The force necessary to move...

Belt traction. The movement between the motor shaft and the plate is carried out by means of a rubber strap that hugs on one side a pulley located on the motor shaft and on the other a drum placed under the plate and concentric with it. The displacement is achieved by means of a movable pin. This system is widely used as it provides good filtering of motor vibrations. The rubber band is usually synthetic rubber and its active face is rectified to obtain a high uniformity of movement. Direct drive.  In these record players,...

Definition We understand by turntable, the devices intended to reproduce the acoustic information stored on the records discs, giving a faithful electrical signal reflecting the sound that was recorded on the disc. Its main elements are three: a) Platter intended to support the disc and rotate it around its own axis and on a horizontal plane (there is some exception to this condition of horizontality). Its movement is achieved...

A good quality of reproduction depends, in a very important way, on the perfection of the silences, therefore: 1) Frequently examine the tip of the needle. A powerful magnifying glass, or better, a microscope of about 100 magnifications, can detect harmful wear to the discs or dirt embedded in the needle. 2) Check the vertical support force and the horizontal freedom of the arm. 3) Preserve the needle from the dust, heat and grease. A cartridge in bad condition can destroy the treble of a disc in a single pass, and alter the...

This feature reports the amount of signal the cartridge will provide to succeed the pre-amp. The tension varies with the speed, so it is accustomed to refer it at a certain speed, being common the value of 3.54 cm/sec. In general the minimum value for current high-fidelity equipment that must provide a needle is 3 millivolts; Under that tension it is necessary to use a preamplifier or transformer to adjust the appropriate level of input to the preamplifier stage. Between the limits of 3 and 7 millivolts the output is acceptable, being...

As the separation between channels reports the existing interactions of one channel on another, the balance of channels clarifies how each channel responds to each frequency. Both channels must respond, in the most identical way possible, to the same frequency of a given amplitude. ...

This specification informs about the shape of the needle tip and its size as well as the shape of its assembly. It is customary to express this value in thousandths of an inch. In tapered needles, sizes greater than 0.7 thousand should not be allowed, and between two tapered needles, the smaller radio is better, as it will better read the walls of the furrow, reducing the effect of the tap. Conical needles should not be greater than 0.3 thousand the radius smaller or greater than 0.7 thousand the largest. ...

In musical reproductions there are no pure sounds, but a set of simultaneous vibrations that influence each other, giving rise to intermodulation distortion. New vibrations appear equal to the sums and differences of the originals in the event of intermodulation distortion. Since musical sounds are usually composed of a fundamental vibration and a series of harmonics, and in an orchestra or ensemble there are many instruments playing at...