Notes about some features of audio power amplifiers
Table 1 gives some of the power audio amplifiers (PAAs) that are appropriate for voltage splitters (VSs). We should make short notes about some features of the PAAs and op amps (OAs) used in VSs. That is important in order to understand better the circuits proposed below. In all cases the datasheets and application notes of the involved ICs should be considered carefully.
* - the gain can be or is adjusted with external components
(sometimes wider range that specified in the table is possible).
** - Please see the datasheets and the application notes (in all cases).
The input stage of the PAAs and OAs
The input stage and the parameters associated with that stage are very important to obtain stable and reliable operation of the VSs. Generally speaking there are three types of input stages of the PAAs and OAs:
- differential amplifiers based on PNP transistors,
- differential amplifiers based on NPN transistors,
- input stage based on single transistor (usually NPN) which is comparing the input signal and the signal from the negative feedback from the output.
Each of the inputs mentioned above has some advantages and disadvantages and particularities. For example with the differential amplifiers based on PNP transistors we can go typically to the input ground, which is usually not possible for the second and third type of input stages.
The input stage and the parameters associated with that stage are very important to obtain stable operation of the VS. Some of the inputs of the ICs have effective built-in protection but others are not well protected and should be taken into consideration.
Power supply range
The power supply range of the PAAs and OAs can have a lot of particularities. For example, some of the ICs are specially designed for a single power supply, e.g., LM380, LM386, LM324, etc. Many of these ICs automatically keep the DC output voltage around half of the applied power supply. Care should be taken about the DC levels of the input pins of these ICs.
If these circuits are used with a dual power supply, we should take some precautions in order not to damage them, e.g., the load may have a particular configuration. Other PAAs as TDA2030/40/50 and others can work with single and dual, symmetrical and non-symmetrical power supplies.