25W Class-A Hifi Audio Amplifier Circuit with MOSFET

25W ClassA Audio Amplifier circuit

This circuit is a simple class A audio amplifiers. But with zero distortion, Q1 is a switch is in operation or shut down, so that no load current through the resistor R2. In the best case, the tension in Q1 and the load resistance equal to the Class A operation.

A 100K potentiometer (R3) and a 1-meg resistor (R1), and a simple tea-Variable Bias Circuit. Plase voltmeter between drain (D) of the 1 Quarter and the dissemination of soil and adjust R3 for a meter to half the supply voltage.
Applications IRF511 project much as it is pupola build the electronic circuit.
Nearly everyone will be resistance value for R2 used, as maximum power and the FET are not exceeded.
A resistor value of 22 to 100 Ohms is a good choice for experimentation. For high flows, adapted to be used on a radiator.

Description
   The amp is “El Cheapo 2-30, and was valued at a maximum of 30 watts per channel into 16 ohms. It uses a single power supply regulated power and a capacitor connected speakers. Having had the original, I can now reproduce the scanline detailed information. It was a very simple amplifier, used for almost complementary symmetry power amplifier. For those who are younger than me who had no idea what I am talking about quasi-complementary symmetry system used in time when the PNP power transistors were expensive and silicon devices have been pretty useless. If you want a kind of voltage and current rating, it was necessary to use NPN devices. The quasi-complementary output stage uses a (discrete) from Darlington to the positive side and a complementary pair to the negative (or a rider to a PNP-NPN power transistor coupled).

Meanwhile, in these days when you high gain and the current capacity adequate, germanium transistors would still ruled supreme. Provided they have been used in applications where the leak was not a big problem, germanium devices very well – it’s not entirely the amplifier output stages are, however. Even then, the majority of speakers were 16 ohms, with only a few dare to 8 ohms. All that was less than the almost unknown in 1964.

Figure 1 shows the circuit – it was an amp cheap compared to most offerings of the day. In addition, it was possible to sound respectable – built again in comparison – and me and my many friends from the date of this amplifier with a passion – guitar amps, Hi-Fi, you name it, El-Cheapo went !

Note that the types of transistors are referred to the original equipment. Most are now outdated, but it will be shown a list of skills below.

Those were the days when the transistor is the 2N3055 power of choice (NPN course), and there was no PNP devices remotely equivalent to less than 5 times the price, and even these were much lower. Consequently, almost complementary output very common, and even this is still the case with most IC power amps. The quasi-complementary output stage is the most popular until recently a fairly PNP power devices still available. Immediately, almost everyone started with Darlington NPN and PNP devices connected to the output stage (such as T3 and T4) – The funny thing is that it demonstrated back in the mid-1970 that the full connection Darlington sounds made (or at least measures ) worse than the quasi-complementary phases. Is not progress a wonderful thing?

The input stage of the El-Cheapo is not subject to phase problems of the long-tailed pair, because the class a driver (or SAV – Voltage Amplification stage) is used as the entry. Ampere led in this way often inherently stable. There is a big problem with DC offset of course – the item refers to the negative supply. If the earth (ground), it is no problem, but it precludes the use of this design with a dual supply. The DC is not a problem with capacitor connected speakers.

As shown, the gain for the audio frequency is 18 (25dB), a sensitivity of 1V for an input power of 40W means. The closed loop gain is set by R4 and R7. Since the score is taken after the output coupling cap, the latter does not affect the low frequency response – but this provision creates a network of underdamped filter that causes a 4.5dB peak at about 5 Hz. Increasing C7 4700UF eliminates this problem all respects.

In the original article, there were several variations of the design, but I do this amp based 40W form here. The variations were mainly based on lower voltages, but also a parallel (dual) output stage for the odd low impedance.

Note that the amplifier is great, and the input impedance of the amplifier itself is 1k (R4). For this reason there is an emitter follower (Q1) before the amplifier impedance to the right to convert into something useful. The described system has been far from ideal – a better solution would be to leave everything to the left of C2 and the drive circuit of a DAC (C2 should be reversed if the ADC supplies used alternately remove).

Regulated Power Supply

Power Supply Circuit For 25W hifi

The circuit is prepared as specified, and simple power amplifier with a low open-loop gain is a good idea to maintain a buzzing low. Using a regulated power Desirable Not usually but in this case is probably justified. Germanium transistors were used as shown in Figure 2 (all medium and high power transistors and germanium / PNP).

Because the amp PSRR (Power Supply Rejection Ratio will), only 36 dB, it will provide a noise problem with a non-regulated supply. It is noted Note that step emitter follower (Q1) contributed the bulk of the supply noise – LEAD good for the floor of the DAC amplifier.
The controller is easy, BUT would have worked well enough as indicated. 62V 1W zener Normally the unit, a power for the 60V amplifier gain (similar to the use of ± 30V with power over conventional split). Compared to today’s standards, hoods Probably the filter are too small (like Bouchon The loudspeaker coupling), but I’ll present it as it was originally described.