Magnetic cartridge

The cartridge, an electroacoustic transducer (sensor) is called, the mechanical vibrations in solids (acoustic emission ) into an electrical voltage ( the audio or audio signal) converts. This distinguishes the pickup of air transducers ( microphone) and liquid transducers ( hydrophone )

The audio signal is processed sound technology and / or for example made ​​via an audio amplifier to a loudspeaker audible.

Typical examples are pickups of turntables, which receives the vibrations of moving through the record groove needle and cartridge in stringed instruments such as electric guitars.

  • 3.1 Electromagnetic Pickup
  • 3.2 Piezoelectric pickups
  • 3.3 MIDI pickup

Mechanical predecessor

As with the phonograph and the gramophone needle mechanical movements, is transmitted in the straw fiddle the mechanical vibration of the string to a membrane and converted by the horn directly into air vibrations and thus audible. With the stylus, there was a sharp ground steel needle.

Pickups for records

The pickup is mounted on the tone arm assembly with a turntable consisting of stylus, needle carrier and transducer housing. At the end of the needle support a polished diamond is mounted, more rarely, a sapphire or ruby ​​. The shaft of the needle carrier is mounted elastically via a fork construction, the vibrations are transmitted to the transducer. This converts the movement into an electric voltage. At times, the housing for the needle carrier mounted a so-called Besom, which is to remove dust and dirt, especially before the stylus.

With the Kristalltonabnehmer - with a piezoelectric crystal as a transducer - and the Magnettonabnehmer - with a magnetic coil system - the LP was made possible, which was operated only with 33 ⅓ min-1, and thus against the shellac disc ( 78 min -1) significantly longer seasons allow. These pickups needed against gramophone needles significantly lower bearing forces, which increased the life span of plate and needle accordingly.

In order for stereophonic two audio channels scan independently of one another, there are stereo pickup of two converter systems at the still single needle, each inclined at 45 ° to the vertical and transverse to the plate groove, so that they are offset from each other by 90 °. Thus, they are orthogonal and achieve the desired decoupling.

The electromagnetic transducer (MM)

Electromagnetic scanners are the most common Pickups for records. They are relatively inexpensive and the stylus can be replaced on most systems. When the electromagnetic converter is a small piece of iron in the vicinity of the coil is moved by the iron core. The magnetic circuit is energized by a permanent magnet. By the change in distance of the iron parts, a change in magnetic flux is generated in the coils, resulting in an induced voltage. Pickups are with moving magnet as a " moving magnet " (Eng. moving magnet) or "MM " means. They produce higher signal voltages than electrodynamic systems because the coil may be longer. However, in principle, they cause non-linear distortion, especially at large signal levels.

Electromagnetic transducers require an equalizer pre to play and the frequency response of the record corrected ( de-emphasis ). He was (also called " TAMagn " ) provided in previous hi-fi amplifiers by default in the " phono input " is available.

An electrodynamic transducer (MC)

Electrodynamic pickup with moving coils are also called " Moving Coil " (Eng. moving coil) or simply as "MC". In dynamic scanning coils moves in a constant and homogeneous as possible field of a permanent magnet. In the coils due to induction in movement there is a tension. In order to keep the moving mass ( stylus, needle holder, coil carrier and coils) as low as possible, the spool usually only a small number of turns. Wherein the signal voltage is relatively low at electrodynamic scanners. In practice, a distinction here between " Low Output " ( 0.5 mV), " medium output" ( to 1 mV) and " High Output " ( 2 mV and more). Except for High Output all MC systems require a more sensitive preamplifier or a matching transformer ( transformer) before the equalizer pre. The replacement of a worn or damaged stylus is at MC cartridges only when specially constructed types possible because the coils must be securely attached to the vibrating needle carrier. Some manufacturers offer exchange programs for systems with worn needle. Due to the linear relationship between deflection and stress the sound electrodynamic transducer is a particularly clean and transparent.

Piezoelectric transducer

In the piezoelectric scanner piezoelectric ceramic strip generate the signal voltage when they are bent by the stylus. As a piezoelectric material were used earlier, Rochelle salt, barium titanate today / zirconate. Piezo- scanners provide a first electrical charge, which is converted for good bass reproduction by a charge amplifier, a voltage proportional thereto. Due to the necessary bending of the ceramic strips they are quite stiff and require high support pressures. The reproduction is influenced by resonances. Because of these characteristics of this type of transducer is today only in very low -priced appliances.

Piezoelectric transducers require no equalizer pre-amps, since the output voltage is not - depends on the frequency and is high enough to drive standard amp directly - as with electromagnetic pickups.

Differences and other methods

During the Kristalltonabnehmer a deflection of the record groove generates signal voltage proportional, at this Magnettonabnehmer to the speed (fast ) of the needle is proportional. At low frequencies, magnetic pickup therefore produce too low signal level - you would have had to produce different records for both pickups, with a greater track width would have to Magnettonabnehmer due to the higher deflection must be provided with a corresponding reduction of playing time. With the adjustment of the frequency response by the RIAA characteristic, which is compensated in equalizer pre-amps for magnetic systems, the recorded signal is adjusted so that the records can be scanned with both crystal and magnetic pickups.

The development of the pickup reached by establishing a hi-fi standards peaked in the 1980s, as with tracking forces below 10 mN and frequency ranges from 20 Hz to 30 kHz also tentatively quadraphonic ( four-channel ) records were sampled wear.

To improve the sound quality by reducing the noise in addition to the usual Trockenabtastverfahren and wet methods were tested in which the stylus moves in a Abtastflüssigkeit. In addition, the reduced friction and improved cooling results in less wear on the plate and of the needle. However, this method has the disadvantage that the particles stick together after drying, dissolved in the groove, and the plates are practically only wet played or must be expensively cleaned.

As an alternative to this it was also commercially feasibility studies for contactless detection by means of laser or infrared diodes. The sampling is indeed free of wear, but these devices react much more sensitive than Nadelabtaster to dust and scratches.

Certain non-contact optical method, the regeneration of damaged ( cracked or broken ) plates is possible. Because these procedures are very expensive, they are only applied to historically valuable recordings.

Pickups for Musical Instruments

In musical instruments pickups are used to convert the vibration of the sound generator ( string, tongue ) of the instrument into electrical AC voltage which can be supplied to a mixer or amplifier.

This concerns mainly stringed instruments and especially guitars and basses, as well as keyboard instruments ( electric piano, Hammond organ ). In wind instruments, however, it is customary to include the generated anyway airborne sound via microphones.

After the operation, a distinction is electromagnetic and piezoelectric pickups.

Electromagnetic pickups

By means of an electromagnetic pickup (german pickup) is converted to the string vibration in an electric guitar, with electric bass or electro-mechanical electric pianos into electrical signals ( AC). It consists in the simplest case of a permanent magnet around which a coil is wound. The movement of the strings ( they must be made of a ferromagnetic material ) in the magnetic field changes its field strength. Thus, an AC voltage with the frequency of vibration of the string is generated in the coil by electromagnetic induction. This voltage is about 0.1 V, which, however, the thickness of the string and of its direction of vibration and amplitude depends on the thicker is a string, the greater the voltage induced by them. Vibrations in the direction of the magnetic pole lead to higher voltage induction as vibrations laterally to the pole. The voltage generated in this way is then (possibly by effects devices processed) fed to an audio amplifier. To reduce the sensitivity of the pickup for acoustic waves, and thus the possibility of feedback, the coils are often fixed with paraffin and 20% beeswax addition.

The pickups for electric guitars and basses the designs single coil (single coil) and humbucker ( dual coil ) can be distinguished, which are characterized by two very different sound characteristics. Single-coil pickups have often (but not always) the clearer, overtone-rich sound, while humbuckers sound rather soft and center-weighted. In addition humbucking pickups provide the special wiring of its two coils provide better protection from noise generated by the electromagnetic radiation of network devices and others. Of importance for the sound continues to be the position of the pickup. In the vicinity of the bridge produces a hard, more treble sound, while a pickup near the guitar neck features a softer, tiefenlastigeren tone. Since electric guitars and basses are often up to five coils, and three separate pickups, fitted, these can be combined to the desired sound.

A distinction is commonly used for guitar pickups between

  • Passive, which provide the raw sound signal for further processing, and
  • Active pickups: in these, an electronic pre-amplifier in the instrument is integrated, which is fed by a small battery. He often possesses sound and volume control.

Piezoelectric pickups

Piezoelectric pickups are made of piezoelectric ceramics: Mechanical pressure or body sound of the ensemble creates an electrical voltage.

Since no magnetic effect is based on the piezo pickup work for string instruments with all kinds of strings, even with nylon or gut strings.

Piezo pickups are suitable for use on all those acoustic instruments, which resonates the body. You are on acoustic guitars ( Acoustic Guitars, Classical Guitars ), double basses and other plucked instruments, such as mandolins used. Also, violins and electric violins use predominantly these customers. In probe range made ​​guitars piezo transducers are used to remove an acoustic guitar -like sound instead of the magnetic pick. They are useful for pieces of music, in which alternate " acoustic " and other passages - the musician does not then need to change the guitar, but to reallocate only a switch.

Most of the pickup is installed in the web or clamped between the bridge and body. He then receives directly the pressure differences. If it is glued to the body of the instrument, it works like a bone microphone: the vibration of the string, which carries over to the ceiling over the web is converted from the pickup by its inertia in a pressure fluctuation and an AC voltage. It is not only a position transferred from the fast of the vibration as much as possible to the purchaser is ( significant electrical voltage ), but also the desired sound character that is very different in different places.

Since piezo pickups have a high output impedance, belongs to the system almost always a battery-powered preamplifier, which is built into the instrument, and usually has a volume control and a simple tone control.

The disadvantage is that they implement each captured from the body structure-borne noise (knocking / scratching, background noise ) in signals and therefore annoying feedback (feedback) may occur if these sound signals of the speaker receives.

Another use find piezo pickup with tuners. Tones of a musical instrument are included in a vibrating body and is supplied to the device. The pickup is usually designed as " terminal". This clamp can be securely attached to the tuner, but is also available as a remote part.

MIDI pickup

MIDI pickups take on the strings vibrations of the individual strings of a guitar or other instrument. In this case, either the piezoelectric or electromagnetic acceptance of the string vibration for use. The converted vibrations to electrical signals are digitized (A / D) converter with an additional electronic unit and converted by a microprocessor into MIDI signals (see, guitar synthesizer). Early systems analyzed the time interval between the zero crossings of the string vibration. This lead, particularly at low frequencies to significant latencies while MIDI signal. Modern systems use the characteristic transient (English " attack" ) a string for frequency analysis. By this method, the latencies under 1 move to 5 ms, a barely perceptible delay.

Other applications

The pickups are also popular with secret laser microphone, as well as used for communication in noisy environments throat microphone and the bone conduction microphone. All these converters use structure-borne sound for voice transmission.

A special case of the cartridge represents the geophone, an instrument for the detection of mechanical vibrations in the earth.

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