What ‘s the Application of audio capacitor?
In the audio transmission chain equipment starting with the CD player, record player and tuner, through to the transducer, pre-amplifier, power amplifier and finally in the crossover of the loudspeaker, capacitors with an almost endless variety of different capacitance and voltages are used.
The majority of the applications are directly in the signal path and can have a direct influence on the audio signal. Great care should, consequently, be taken in the choice of suitable capacitors.
Audio applications can be grouped into three basic fields:
- Applications in the signal path
- Functional tasks
- Use in voltage and support
By using optimal capacitors versions in all three fields of application, distinct improvements in the tone can be achieved, or, to be correct, the sound will be less affected.
The capacitors in the signal path certainly have the most direct influence on the audio signal. Consequently, real improvements in the sound can be achieved just by exchanging inferior quality capacitors with high quality capacitors.
Another very important criterion is the functional capacitors, which can be the cause of signal distortions in applications such as CD players, D/A-A/D transducers and pre-amplifiers.
Capacitors for voltage support have less influence on the precise re-production of the music, providing they have sufficiently large capacitance. However, they should not be disregarded in genuine high-end equipment. With qualified optimisation in this field too, ultimate refinements in the conception of the equipment can be achieved.
Self-inductance
In the field of audio application, very precise pulse reproduction is required. This is assessed in the pulse behaviour criteria. In particular, When seeing audio signal dynamic jumps of up to 100 dB occur. This means a voltage of
100 dB → U1 = 1 : 100000
Both the parasitic self-inductance and the ohmic resistance of the capacitor have a de-emphasising effect on such voltage changes. Furthermore, such voltage curves are made up of a high proportion of harmonics of fundamental oscillation. Therefore, the frequency spectrum transmitted exceeds the audible range of f = 20 Hz to 20 kHz considerably. In this case, the transmitting frequency is up to f = 100 kHz.
The tape length of the winding element determines the value of the selfinductance.
The remaining self-inductance is reduced to the smallest resulting conductor loop possible, which is made up of the
- width of the winding element
- remaining length of the leads
Values for practical purposes: L= 1 nH/mm
- Example:
- lead length 2 x 3 mm
- PCM 5 mm
- Lself ≈ 11 nH
Modern radial capacitor technology complies with the efforts being made in audio applications to keep the signal paths as short as possible.
The old axial designs, often still offered as special audio capacitors, have the striking disadvantage of unnecessarily lengthening the conduction paths on the PCBs and, because of the larger structure and longer remaining length of the leads, they have considerably higher self-inductance.
The pulse behaviour of axial constructions is, therefore, much worse than that of modern radial ones.
Further advantage: Low ohmic resistance
With contact over a schoopage layer, the largest possible area of the winding element is contacted and this inevitable results in the lowest ESR.
The structure form of the capacitors electrode also influences the dissipation factor/phase angle and pulse accuracy. In general, there are three different constructions available for use in audio applications.
Double-sided metallized versions
To cover positions with high capacitance values in audio applications, the principle of the double-sided metallized construction used in the GDHY CBB20 is the most suitable.
Here, the capacitor electrode is made of film metallized on both sides. The capacitor is produced with 4 layers of film. Such a construction has a 5-10 times greater
pulse rise time and a much better pulse behaviour due to the double contact of the metallization and also benefits from the improved toothed attachment of the schoopage due to the enlarged spaces in the winding element.
The good contact to the capacitor electrode also has a favourable effect on the dissipation factor. Types which are metallized on both sides have a 30-50% lower dissipation factor than comparable versions metallized on one side only.
Applications in the signal path
Efficient polypropylene capacitors are available for all the fields of audio applications mentioned before.
The field of applications in the signal path covers the greatest capacitance range. Coupling capacitors of C = 100 pF are used, for example, in transducers and pre-amplifiers, as well as values above C = 10 μF in crossover networks.
Functional tasks
Functional capacitors are generally used in the field of small signal processing. Typical for this are applications in pre-amplifiers, D/A-A/D transducers, filters, in tuners, CD-players, record players etc. The capacitance values required here are in the lover capacitance range. Highly precise 1% versions are often demanded for filter, timer and integration applications or as sample and hold capacitors in transducers.
Furthermore film/foil capacitors show the best time constant. They therefore remain within the specified parameter even after many years of use.
Use in voltage support
Reservoir capacitors have the task of storing energy and passing it on as quickly as possible when needed. They are directly connected to the voltage supply of the respective amplifier stage. When high dynamic jumps occur in the audio reproduction, high power demands are suddenly made on the amplifiers which cannot be provided directly from the
central power supply with the electrolytic energy storage capacitor.
Such a power bounce would lead to a drop of the supply voltage and, inevitably, distorsions and unfavourable pulse behaviour.
To avoid this effect, capacitors in the capacitance range of: C = 0.1 μF ... 10 μF are connected against the ground directly at the feeding point of the voltage supply of the respective amplifier stage. When power bounces occur, these capacitors provide the required energy as quickly as possible and effectively avoid voltage drops.
In the subsequent pulse pause, the reservoir capacitors are recharged.
Furthermore, GDHY capacitors have the advantage of very small box sizes, i.e. the designer is in a position to use the largest possible capacitance value within given space requirements.
