The DIY kit presented is a AB class audio amplifier using the BA5406 integrated circuit produced by ROHM. Easy to make, with only a few electronic components, the audio signal amplifier based on the BA5406 circuit can be easily connected to most signal preamplifiers or to the output of sound cards from the PC, its input impedance being high.
The power obtained is maximum if the assembly is supplied from a direct voltage source, well filtered, which can discharge in load, without problems, more than 1.5A and if a 4 Ohm impedance speaker is used. A minimum electrolytic capacitor is recommended when filtering the power supply 2 x 4700pF / 16V.
Technical instructions for mounting
As noted in the electronic diagram, no filter element is used on the supply bar (terminal 1 of the BA5406 integrated circuit), which makes, as in order to have a low low frequency mist, the voltage source must be well filtered.
Definitely, if you prefer power from a 6 or 12V battery, high capacity (in the car), filtering is no longer necessary. The maximum supply voltage is 15Vdc.
The integrated circuit will be mounted on a aluminum cooling radiator. The connections from the installation to the power supply and from the installation to the speakers must be made with insulated copper conductor, two-wire, of the shortest possible length.
The conductor section must be over 1 - 1.5mm square. To avoid reverse connection to the power supply and / or to the speakers (if they are polarized) it is recommended to use differently colored two-wire conductors. Advice for beginner builders!
What type of capacitors should we use?
C1 and C2 they are input capacitors and block the continuous component of the audio signal from reaching the inputs of the integrated circuit.
These two capacitors must not be of the ceramic type, but of the MKT type with polyester or multistart. C9 and C10 they have the same function, but on the output side, preventing the component from continuing to pass to the speakers; they will be electrolytic with aluminum. Groups C4-R1 and C7-R2 perform the negative reaction in alternating current, R1 and R2 determining the level of this reaction.
How do I calculate the assembly gain?
Thus, the gain is equal to 1 + (24 KOhm / R1) = 201 (or 46 dB), with R1 and R2 = 120 Ohm or 25 (28 dB) if R1 and R2 = 1 KOhm.
Groups R3-C11 or R4-C12 ensure stability at high frequencies, if the loudspeakers or loudspeakers used have a much higher inductive reactance, otherwise these elements can be omitted. R3 and R4 are 1W power resistors. R1 and R2 must have a power dissipation of 2W.
- Supply voltage: 5 - 15Vdc, 1-2A;
- Output power: 3W RMS / channel, 4 Ohm load, at 12Vdc (2W RMS / ch, on 8 Ohm, at 12V or 2W RMS / ch, on 4 Ohm at 9Vdc);
- Signal to noise ratio, S / N> 85dB for G gain = 28dB or S / N> 68dB for G = 46dB;
- Distortions: THD <0,5% at 1W;
- Frequency band, at -3dB, 40Hz..100kHz;
- Input signal level: <200mV for G = 28dB or 20 mV for G = 46dB;
- Input impedance: 100 KOhm.
List of required components
R1, R2 = 120 Ohm / 2W (or 1 KOhm);
C1, C2 = 220 nF;
C3, C4, C5, C6, C7, C8 = 47 uF;
C9, C10 = 470uF;
2 x speakers (see details in the article);
IC1 = BA5406 + radiator;
5 x terminal contacts for two audio inputs, two outputs and power supply.