Stk circuits. Microcircuits - low frequency amplifiers (5)

Sound amplifier 200 watt— I propose for repetition an amplifier circuit with excellent sound quality and minimal noise level. The device is made using the integrated, hybrid properties of the STK4050 microcircuit from the Japanese company Sanyo. In order to have good sound quality and its highest gain, the amplifier needs a power supply that matches the power of this circuit. And also a rectifier with a sufficient total capacitance of capacitors, which creates the necessary conditions for efficient operation of the load.

This amplifier model is perfect for use as part of a home theater or personal computer, as well as in a set of other audio systems. For example, such a sound amplifier is perfect for working with a subwoofer. The STK4050 chip has protection that prevents clicks from occurring when power is applied or turned off. There is also highly effective protection against short circuits in the load and against excess temperature components.

Universal scheme

The circuit of this device is universal in that the circuit itself cannot be changed, but only the installation of microcircuits selected from the list proposed below. This makes it possible to modulate the power you need at the output of the UMZCH in the range from 6 W to 200 W. (All pictures can be enlarged by clicking)

The figure shows the relative placement of electronic elements on the signet:

It is well known that the hybrid microcircuits of the series proposed here guarantee solid output power and low THD. This makes it possible to extract a sound picture from the amplifier with the highest quality reproduction.

The supply voltage of the device is bipolar, which ranges from 20v to 95v and is determined depending on the installed microcircuit (that is, according to the STK marking indicated in the table). The acoustics connected to the amplifier must have a resistance of 4 ohms; the best option is 8 ohms. The output resistance of the UMZCH is 55 kOhm. The quiescent current is within 120 mA. The output current reaches 15A, again depending on the installed STK, according to the table shown in the figure. For reliable operation of the STK4050 hybrid integrated circuit, a heat sink with a cooling area of ​​400 cm2 is required. To ensure efficient heat dissipation, the microcircuit is attached to the radiator through heat-conducting paste KPT-8.

In the early 90s, AIWA music centers were very popular. For a long time, the AIWA ZM-2900 music center served me faithfully. Over time, a laser disc player failed, then a two-cassette tape recorder and a radio receiver. The power amplifier and transformer remained operational.

The electrical circuit of the AIWA ZM-2900 music center can be downloaded from the attachment.

Of the entire electrical circuit, I was interested in the stereo power amplifier on the STK419-150, which provided decent power (about 100 W per channel) and good sound quality.

The connection diagram for integrated amplifiers STK419-110, STK419-130, STK419-140 and STK419-150 is shown below.

Resistances R13 and R14 (with a power dissipation of at least 2 W) determine the level of current limitation through the output transistors of the integrated assembly. Inductors L1 and L2 are made by winding one layer of copper coil wire with a diameter of 0.8 - 0.9 mm onto resistors R12 and R13 (MLT 2W). Resistors R16 and R17 with a power of 0.5 - 1W. The power of all other resistors is up to 0.25W.

The main characteristics of stereo amplifiers STK419-110, STK419-130, STK419-140 and STK419-150 are given in the table.

Integrated amplifier parameters:			STK419-110	STK419-130	STK419-140	STK419-150
Case			H3-20	H3-20	H3-20	H3-20
Output stage supply voltage (Vcc2)	min	V	±25	±27	±30	±33
	max	V	±37	±37	±42	±50
Supply voltage UN (Vcc1)	min	V	±36	±37	±42	±50
	max	V	±53	±57	±65	±70
Quiescent current (Iо)		mA	60	60	60	60
Maximum power output (Poutmax)		W	2x50	2x60	2x80	2x100
Nominal load resistance (Routnom)		Ω	6	6	6	6
Frequency range (Bw)		kHz	0,020-50	0,020-50	0,020-50	0,020-50
Input resistance (Rin)		kΩ	55	55	55	55
Harmonic distortion at Poutmax		%	0,2	0,2	0,2	0,2
Gain (Gv)		dB	32	32	32	32
Manufacturer			Sanyo	Sanyo	Sanyo	Sanyo

To manufacture the power supply of the amplifier, a W-shaped transformer of the music center was used, which has a primary winding of 220 volts, as well as a secondary winding with a common middle terminal (0V), with leads for powering the final stages (20V each) and a voltage amplifier (50V each). The power supply diagram is shown below.

Subjectively, the amplifier sounds more pleasant than the LM3886.

I hope that this information regarding the STK419-110, STK419-130, STK419-140 and STK419-150 integrated circuits will be useful for making your own stereo amplifiers.

Best regards,

In recent years, radio amateurs have increasingly used power amplifiers on microcircuits. For many applications, it becomes impractical to assemble an amplifier using separate elements; such amplifiers in most cases require the establishment of a protection device, setting the quiescent current of the output stage, etc. Integrated amplifiers are actually designed according to the “soldered in and ready” principle. Various versions of such amplifiers have already been repeatedly recommended on the pages of the magazine, however, the maximum (i.e., with nonlinear distortion of 10%) output power of amplifiers on a single chip is usually limited to 100...120 W, at least when using chips from an affordable price category. Even when using two TDA7294 microcircuits in a bridge connection, the load power does not exceed 200 W. But what if you need to assemble a more powerful amplifier, for example, for a disco? An integrated circuit power amplifier is described here that allows output power of up to 300 W per channel.

The amplifier uses a STK4231-II hybrid chip manufactured by SANYO. This chip is a dual-channel chip, so only one chip is required for the bridged connection option. When assembling an amplifier on such a chip, a little more parts are required than for an amplifier on the TDA7294, but it has a number of advantages and, most importantly, allows you to get a significantly more powerful amplifier. The microcircuit is much easier to attach to a heat sink, since its substrate is not connected to the heat-conducting surface of the case and can be directly connected to the heat sink or amplifier case (for the TDA7294 microcircuit, the minus of the power supply is connected to the substrate). This can often be decisive, since isolating the heat sink from the case is sometimes not easy.

Main technical parameters:

Rated output power, W…….250
Maximum output power, W… 320
Load resistance, Ohm………5.3
Reproducible frequency range, kHz… 0.02…20
Harmonic coefficient, no more than, %…….0.4
Input voltage, mV………………….500

Amplifier circuit

The amplifier is powered by an unstabilized bipolar voltage source of 2x(45...55) V. The input signal to one of the amplifiers of the DA2 microcircuit is supplied directly to pin 3, and to the second (pin 20) through an inverting buffer amplifier on op-amp DA1. The op-amp is powered by voltage stabilizers +15 and -15 V, made on DA3, DA4 microcircuits. If necessary, these same stabilizers can also power a pre-amplifier with tone controls or crossover filters. The gain of the power amplifier can be changed by selecting feedback resistors R6 and R11. Their resistance in both arms of the amplifier should be the same.

Transistors VT1 - VT4 have a current protection unit that prevents the microcircuit from failing in the event of an overload. As the current through one of the resistors R18, R28 increases, the voltage drop across it increases, which leads to the opening of transistor VT2 or VT1, respectively. This, in turn, leads to the operation of the thyristor analogue on transistors VT3, VT4, and the microcircuit is blocked. To disable the lock, you must turn the amplifier off and on again. If there is no need for a protection device, then you don’t have to solder transistors VT1 - VT4 and related elements into the board - this will not affect the operation of the amplifier. You can use other types of protection devices with the amplifier, taking into account the fact that when resistors R25, R31 are connected to the common wire, the amplifier is blocked.

The microcircuit has a unit that prevents clicks in the speakers when turning the power on and off. To do this, pin 8 of the DA2 microcircuit receives a constant voltage supplied through the VD2 diode and correction circuits from the winding of the power transformer.

The amplifier is tested in operation with a real load with a resistance of 5.3 Ohms; the output power is slightly less with a load resistance of 8 ohms.

Location of parts on the printed circuit board

In the design, you can use resistors C5-16 with a power of 5 W (R16-R18, R28-R30), MLT-1 (R22, R31, R38, R39), the rest - MLT-0.25 or MLT-0.5. Oxide capacitors - K50-35 or imported for a voltage of 63 V. The remaining capacitors are film (K73 groups) or ceramic (except for the TKE H50 and H90 groups).

Op-amp DA1 can be replaced with K140UD7, KR140UD17, TL071, etc. Transistors KT502E can be replaced with 2SA1207, KT814G, VT3 - with 2SC2911, KT815G, VT4 - with 2SA1209, KT814G. Chokes L1, L2 are wound with a wire with a diameter of 1 mm on resistors R17, R29 turn to turn in one layer along the length of the resistor.
The STK4231 microcircuit has two versions - with indexes II and V. The connection circuit for STK4231-V differs slightly from that recommended for the STK4231-II microcircuit, in which pins 1, 2, 21 and 22 are not used. For STK4231-V, additional elements are connected to them, as shown in Fig. 3; all other terminals are connected in the same way. An amplifier with STK4231-V has a lower harmonic distortion coefficient of 0.08%.

Connection diagram STK4231-V

Such an UMZCH can be powered either from a transformer mains power supply or from a more modern pulsed one. The power of the power supply should be selected 30...40% greater than the maximum power of the amplifier itself. You should also take into account the amendment to this article: pin 12 of DD3.2 (see diagram in Fig. 2 in the article) should be connected to pin 3 of DD3.1, and not as shown in the diagram. In addition, to limit the first inrush current when turning on the UPS, it is useful to introduce a thermistor into the primary rectification circuit.

When using a switching power supply in the amplifier circuit, instead of the KD226A diode (VD2), use KD212, and reduce the capacitance of capacitor C14 to 1000 pF.

When assembling the described amplifier, special attention must be paid to attaching the microcircuits to the heat sink. The introduction of mica spacers for insulation at such an amplifier power is unacceptable. Microcircuits can heat up to 70 °C during normal operation, but it is advisable not to exceed this temperature. It is advisable to use forced cooling with a fan. The heat sink can be installed pin (needle-shaped), or, in extreme cases, ribbed, acting as the rear or side walls of the amplifier housing. It is possible to fasten the microcircuit with screws using heat-conducting paste to a copper plate 3...5 mm thick, and then a plate with the same paste to a dissipating heat sink. The dimensions of the plate should be 2...4 times larger than the dimensions of the microcircuit used. In this case, the efficiency of heat transfer will be maximum.

With proper assembly and use of known-good parts, the described amplifier does not require adjustment. When powering the pre-amplifier from stabilizers DA3, DA4, you only need to select resistors R38, R39 so that the voltage at the input of stabilizers DA3, DA4 is within 20...30 V.

Original Sanyo microcircuits, STK402 series, are hybrid microcircuits and are made using thick-film technology on unpackaged transistors. Another feature is laser adjustment of resistance values.

These amplifiers have excellent sound and characteristics, and many amateurs put them in first place over amplifiers assembled on TDA and LM chips, although sometimes opinions differ.

Below is a table of some parameters of some of the most popular microcircuits in the STK402 line.

STK402-070 and other microcircuits in this series have quite large, even huge cases. All microcircuits indicated in the table are complete analogs and are completely interchangeable, but, as you may have noticed, they have different supply voltages, as well as different housing sizes.

The load resistance should not be less than 6 Ohms, this is a feature of these microcircuits.

Schematic elements

Resistors of 0.22 Ohm and 4.7 Ohm should be 2W, the rest 0.25W.

Electrolytic capacitors (all) must be designed for a voltage greater than the supply voltage by one and a half times. I used electrolytes at 50V.

I used polypropylene non-polar capacitors with a capacity of 0.1 µF, although this is not necessary (I installed it for beauty), so we put in ceramics. We also install ceramic capacitors for all other non-polar capacitors.

The chokes are wound on a mandrel (drill) with a diameter of 6-8 mm and have 25-30 turns, wires with a diameter of 0.6-1.2 mm. I wound it with 1.2mm wire, it is more convenient to wind it, the choke does not unwind, and it will also hold high currents well at maximum power. The chokes are wound in two layers of 15+15 turns.

When listening to the amplifier on the STK402-070, I really liked it, especially at maximum volume, very little distortion can be heard, the sound is clear and rich. After some listening, I decided to increase the power of the amplifier and installed the STK402-120, and also increased the supply voltage, while the power increased significantly, and the sound remained just as excellent.

Amplifier on a chip STK4048II This is a cheaper analogue of the chip from SANYO - STK4048V.
STK4048II is a microcircuit on which even a novice radio amateur can assemble a professional high-quality amplifier that is not inferior to high-quality industrial transistor amplifiers.

Once, an amplifier with a power of about 100 W was required to “drive” a loudspeaker with a resistance of 8 ohms. After studying the reference books, the choice fell on the microcircuit STK4048II. I am a curious radio amateur and don’t like to repeat myself, but here is a new series of microcircuits for me. STK is criticized for its lack of protection, and praised for its “good sound.” The reference data turned out to be quite scanty, and there are errors in the diagrams. To “not be excruciatingly painful” for a burnt-out microcircuit and wasted money, I advise you to use my recommendations.

The Roman numeral “II” in the designation reflects the harmonic coefficient, in this case - 0.4%. Microcircuits with the number “XI” have a harmonic coefficient of 0.007% in the frequency band 20 Hz...50 kHz. Output power at a load of 8 ohms is 120 W. I haven’t tested the microcircuit at a 4 Ohm load, but, according to reviews on the Internet, it turns out to be 60 W, and it gets very hot. The IC power supply is bipolar, from ±55 to ±75 V. If you look at the structure of the microcircuit (Fig. 1), then, taking into account the external “piping” of parts, we will see a classic UMZCH 80-90s.

Fig.1 Structure of the STK4048II chip

Now about the typical errors in using STK:
1. The gain of the original circuit is 100. This is a lot, and there is a possibility of self-excitation. This is what happened to me, but I was ready for this and reduced the resistance of R7 from 68 kOhm to 20 kOhm (Fig. 2). The amplifier immediately stopped energizing. Some radio amateurs recommend reducing the resistance of R7 to 13 kOhm.

Rice. 2

2. The original circuit uses 5-watt wirewound resistors R10...R13 with a resistance of 0.22 Ohms. Such resistors have high inductance, and the consequences of this for the “sound” are unpredictable. Moreover, the power of these resistors is clearly overestimated. 2-watt metal film ones are quite suitable here.

As my experience shows, the fewer inductances in the audio path, the better the sound! The only exception is the LR filter L1-R14 at the amplifier output, which is necessary to compensate for load reactivity. Coil L1 is wound on a mandrel Ф10 mm and contains 18 turns in one layer. Wire diameter - 0.8 mm. There is a resistor R14 inside the coil. All capacitors in the UMZCH circuit and in the power supply are with an operating voltage of 100 V.

The amplifier is additionally equipped with a protection circuit against constant voltage at the output of the amplifier and a delay in connecting the speaker system (Fig. 3).