Audio applications

The first audio chain element is the preamplifier. It is used to increase the amplitude of the very small audio signal. They are complexes signals and combine several sinusoidal parts for different frequencies. The audio frequency band is between 100Hz and 20.000 Hz. The small frequencies correspond to bass sounds. The medium sounds are near 1kHz. And the upper limit is occupied by high tons. To become a good additive quality of the relocated signal you have to use high perform ant components, especially for this part of your home designed amplifier, because at small signals, the smallest perturbation will be amplified form the next module together with the utile signal.

The next module is the ton correction. Different people like different types of audio frequency. Also different melodies have a predilection for different frequency bands. Here is presented a very easy ton correction module, which offers an acceptable ton controlling.

The third module is the amplifier it self. For 100 W reported to a 4 Ohm Speaker you need to use a 63V/5A power source. There are 2 “pre-regler” necessities: there are 2 fix-pontentiometers resistors the 10 kOhm to fix the middle (between the 0.33 Ohm resistors) Voltage to ½ from the source voltage; the second (250 Ohm) is for the “offline” current. It will be set to aprox. 50 mA with Input in short. Take care to the final transistor radiator. You have to calculate it from the transistor data sheet.

In order to protect your speakers to the “ON” switch. You know that normally the “On” switch is coming with a powerful “punch” in your speaker, just because the inductive energy preserved in the output system. To avoid a permanent destruction of the speakers you just have to switch the speaker to the system a little bit later. That means to temporise the amplifier output. You can also destroy you speakers by setting a bigger power as they can take. Or sometimes, some melodies have only for small time very high amplitude. You can avoid these inconveniences simply by setting maximal amplitude for the output signal. If the current amplitude is higher this module simply disconnect the speakers.

Here is presented another useful application. You have already seen that after a while the mechanical potentiometers make unpleasant noise. You can avoid them by getting out the mechanical part from the utile signal. This schematic uses a secondary current control to set the utile signal level. And you don’t have to use 2 double potentiometer for volume and balance; you just have to use 2 simple.

For a precise frequency controlling, with not so much components and a complicated schematic you can use the following module with good results.

For small necessities you can use a simple schematic with an Ic and a few condensators.

Instead transistors you can use an IC.

For three frequency bands you can use the following schematic.

If you are planning to make a recording studio you will have to make several records from a single source. For that you have to separate the outputs signals and also to increase the recorder input signal.

If you are living in a small room and you want to listen music as you are in a theatre or in a very big hall, you can obtain a good result with the next proposal.