UMZCH Akulinicheva with broadband os. Circuit diagram of a transistor UMZCH with deep OOS and unipolar power supply (24W)

SOUND ENGINEERING

To implement the linearizing capabilities of broadband OOS, it was decided to abandon the multi-stage UMZCH and limit the number of its stages to only the absolutely necessary ones. In addition, it was necessary to abandon the use of elements that create a delay in the amplified signal, which made it possible to use OOS in the frequency spectrum of switching distortions. As a result, with the help of OOS operating in the range of 40...60 kHz, it was possible to achieve a reduction in the nonlinear distortion coefficient at a frequency of 20 kHz up to 005.Д01% when using the output stage operating mode with zero quiescent current.

This amplifier was used for a long time as a control amplifier in comparative tests of non-inverting versions of the UMZCH. It was repeated by designers who were interested in its circuit and currently works reliably in several stereo complexes

A schematic diagram of a UMZCH with broadband OOS is shown in Fig. 1.

The pre-terminal voltage amplifier is built on two transistors VT1 and VT2. Through capacitor C1, an input signal is supplied to the base of transistor VT1, and through resistors R3, R4, the balancing voltage of the power supply is supplied. To ensure stable operation of the capacitor amplifier Cl. C6 and C8 should not differ from those indicated on the circuit diagram by more than +50%. In order to protect against accidental current overloads, resistor R7 is included in the collector circuit of transistor VT1.

The cascade on transistor VT2 provides the main signal amplification. The resistor chain R11R12 with a traditional voltage boost through capacitor C8 gives an increase in the amplitude of the amplified signal by 10...12%. The synchronization of functional processes in the amplifier arms is ensured by capacitor C5.

The final amplifier of the gel current is built on a complementary pair of transistors VT5-VT8, connected according to a circuit with a common collector. Transistors VT3, VT4 connected by emitters are connected by their bases to the bases of transistors VT7, VT8, and by their collectors to the bases of transistors VT5, VT6 With the help of a current feedback included in the circuit connection of the variable resistor R13 adjusts the voltage at the bases of transistors VT3, VT4 and thus ensures that the voltage at the bases of transistors VT7, VT8 is set 0.1...0.2 V lower than usual and the operation of the terminal transistors in amplification mode with zero current peace

The UMZCH is powered by an autonomous rectifier without galvanic connection with a common wire. Thanks to this, it was possible to reliably protect the speakers from the direct current component of the terminal transistors, without introducing complex relay-transistor protection devices into the amplifier.

The UMZCH is made in a single unit with a rectifier. Its dimensions (135x90x60 mm) are determined by the dimensions of the heat sinks and filter capacitors. The mass of the block is 560 g. The block is mounted on two plates measuring 130x58, between which the heat sinks and filter capacitors are sandwiched. On one of the plates there are rectifiers

with broadband OOS

“At one time, I tested many UMZCHs described in the Radio magazine. Currently I listen to music through UMZCH, proposed by I. Akulinichev. I didn’t make any selection of parts (transistors), I only reduced the capacitance of capacitor C2 from 5 to 1 µF._ Honestly, I was “stunned” by this UMZCH - it has very great advantages, if you do not take into account the 24-watt output power. But it suits me. Many thanks to Ivan Timofeevich.”

The letter of gratitude from G. Khamatnurov, a radio amateur from the city of Revda, Sverdlovsk region, given here is not the only one after the publication of the article by a member of the editorial board of the magazine I. Akulinichev “UMZCH with deep environmental protection” (“Radio”, 1989, No. 10, pp. 56-58). Currently, on the basis of this amplifier, Ivan Timofeevich has developed an even simpler UMZCH, the parameters of which are no worse than the prototype. He used this amplifier for a long time as a control amplifier during comparative tests of various versions of the UMZCH. The article published below provides readers with a description of it.

The main feature of the new UMZCH is its use of broadband OOS, the frequency response of which, unlike the OOS of conventional multi-stage UMZCHs, does not have a deep cutoff at higher audio frequencies.

To check the parameters of the assembled amplifier and the effectiveness of the technical solutions used in it, it is recommended to assemble a defect signal selector. Its diagram is shown in Fig. 2. Variable resistors - R1 and R8 provide balancing and compensation for the delay of the controlled signal.

Since the selector was adapted to control the operation of the UMZCH with a gain of 10 and with minimal delay of the output signal, the limits of its adjustment are deliberately limited. Using it to control non-inverting versions of amplifiers with a gain of 15-20 will require connecting in series with resistor R2 a constant or variable resistor with a resistance of 1...2 kOhm. Multistage UMZCHs usually create a significant delay in the output signal and therefore in these cases it may be necessary to increase the capacitance of the SZ capacitor to 350 .500 pF or use a variable capacitor instead.

And in conclusion, I would like to note: if the UMZCH with broadband OOS will be of interest to radio amateurs. then the author will consider his contribution useful in overcoming their fear of the amplification mode with zero quiescent current.

I. AKULINICHEV

With. Arkhangelskoye Moscow regional subdivision

1- se 200 nc che in

diodes and output circuits, and on the other - all the transistors, capacitors and resistors. Most connections are made by their own terminals of the component elements.

Resistor R6, capacitors C11, C12, input circuits and load circuits are connected to a common wire at one point. If the recommendation for a monoblock construction of the UMZCH is not used, then blocking the power circuits with capacitors with a capacity of 0.1 μF will be required.

The amplifier is simple and provides fairly good parameters, primarily due to the introduction of deep OOS.

Particularly noteworthy is its high linearity at higher audio frequencies, low level of quiescent current, the ability to operate without a special device for protecting the loudspeaker from the direct current component, and preservation of functionality when the supply voltage is reduced.

Amplifier parameters:

• The rated output power of the UMZCH at a load of 8 Ohms is 16 W,
• The rated output power of the UMZCH at a load of 4 Ohms is 24 W;
• reproduced frequency range - 20...20000Hz;
• harmonic coefficient measured by the signal defect selector, at a frequency of 1 kHz - 0.005%,
• at a frequency of 20 kHz - 0.008% at the maximum output signal level.

Schematic diagram

Rice. 1. Schematic diagram of a transistor UMZCH with deep OOS and unipolar power supply (24W).

The pre-terminal amplifier UMZCH is a two-stage amplifier with a high-impedance inverting input. Transistors VT1, VT2 of the first stage of the pre-final amplifier are connected according to the circuit of a composite emitter follower.

The final stage of the amplifier is built on complementary pairs of transistors connected in a circuit with a common collector.

To stabilize the current mode and dampen switching processes, a transistor shunt VT7, VT8, controlled by voltage at the bases of the output stage transistors VT11, VT12, is switched on at the input of the final amplifier UMZCH.

This stabilization method ensures the operation of the UMZCH with a threefold decrease in its supply voltage.

Details

The UMZCH is powered by an autonomous rectifier connected to a separate winding of the network transformer. Coil L1 is wound on resistor R15 and contains 30 turns of PEL 0.8 wire. This amplifier is described in detail in.

Literature: Nikolaev A.P., Malkina M.V. - 500 schemes for radio amateurs. 1998, 143 p.

Let me start by saying that I am not a fan of “directional wires and tube amplifiers” and I think that any “sound miracles” can be explained from a scientific point of view. I have been involved in radio electronics for almost 20 years. I never assembled amplifiers professionally, since there were no normal instruments for tuning (the best ones were a Soviet oscilloscope and a Chinese multimeter). Here I will summarize my research on the topic “which amplifier/source is better.” It is “which”, not “which”. Because what will ultimately be evaluated is a complex device designed primarily for listening pleasure. UMZCH with deep environmental protection Akulinicheva I., published in the magazine “Radio”, 1989. No. 10, page 56.

UMZCH Akulinicheva is the first amplifier I assembled. I don’t remember the exact year of assembly, it was the 90s. “Played” very well on the two 5GDN speakers. A few years later I replaced the output transistors with IRF540/IRF9540 field switches. They cost the same as the rest of the amplifier. The sound became softer. I left it that way. Next was the purchase of better speakers (as I thought then) - Defender Mercury 55A, several sound cards (I settled on Juli@). I bought the book "G. S. Gendin. High quality tube audio amplifiers. 2nd edition"

I assembled a single-ended tube amplifier based on 6P14P/TVZ 1-9. What can I say, after Akulinichev’s amplifier, the tube amplifier pleased me with its detail. There was slightly less bass. This alarmed me, since they write everywhere that the TVZ transformer has bad bass.
It sounded to me for a long time. Next was the purchase of good speakers - Acoustic Energy Aelite Three

You don't need a lot of power for the AE Aelite Three speakers. Sensitivity 89dB(!) in a room of 20 sq.m. Allows you to comfortably (even loudly, if in the evening) listen to 2x2W. And over time - the audio E-MU0404 USB, since I abandoned the computer in favor of an HTPC + laptop. There was no work at work, so I decided to assemble an amplifier on a microcircuit and compare the sound with a tube one.
After much research, the choice fell on the TDA1555Q chip and a bridged circuit.

Despite the relatively low power of 2x22W, for high-quality sound it requires either stabilized power or a powerful transformer in the power supply. In the power supply filter, it is enough to install 2 × 10000 μF capacitors, and shunt the rectifier diodes (or diode assembly) with film capacitors with a capacity of 0.1 μF. As a result of comparing microcircuit and tube amplifiers, the latter retired.
By chance I got a modern broadcast amplifier Show AMP-1600 with a power of 1600W. Having disassembled it, I found 7 pairs of output transistors 2SC5200/2SA1943. After reading the datasheet on them, I wanted to assemble an amplifier and compare it with a microcircuit one. At this time I already had a digital oscilloscope and normal soldering equipment. A long search for information yielded results - it was decided to assemble a single-ended Class A amplifier based on the “John Linsley-Hood Class-A amplifier” circuit using output transistors of the same conductance (NPN). At the same time, compare Soviet KT819G transistors with imported 2SC5200. The JLH-2005 scheme has been changed. The amplifier started working immediately, without excitement. Resistors that set the operating mode of the transistors are soldered in as multi-turn trimmers. Launching the JLH amplifier with the calculated resistor values ​​and the Soviet KT819G immediately knocked out the amplifier on the TDA1555Q chip. And replacing the transistors with 2SC5200 knocked down the Soviet KT819G. This was followed by experiments with supply voltage and quiescent current. Briefly:
1. For KT819G transistors, you should take a quiescent current of 0.3-0.6A - this is the most optimal range. Below there is a noticeable drop in quality. Above this, there is no noticeable increase in quality, only additional capacitors are required for the filter. The supply voltage was from 15 to 30 volts. No difference was noticed, except for heating the transistors and increased power. 2. For 2SC5200 transistors, the supply voltage is important. With a voltage of 30V and a power of 1 W, additional nuances of the phonogram became noticeable compared to a power supply of 15V. A quiescent current of 0.5A at a voltage of 30V and using radiators from a computer (70x75x45) is the most optimal option in terms of temperature/quality ratio. The quality itself stops growing at a quiescent current of more than 1.3A. In this case, the radiators at the point closest to the transistor heat up to 65-70 0C. Accordingly, the transistor crystal is 20 0C larger. The critical temperature is 125 0C. So this mode is undesirable. It is necessary to either increase the area of ​​the radiator or forcefully remove heat from it.
At the moment I am assembling a version of a class A amplifier with complementary transistors. I'll write about the results.