High fidelity amplifier. UMZCH VV with a microcontroller control system. Operation of the AC cable resistance compensator

UMZCH BB-2010 is a new development from the well-known line of UMZCH BB (high fidelity) amplifiers. A number of technical solutions used were influenced by Ageev’s work.

Specifications:

Harmonic distortion at 20000 Hz: 0.001% (150 W/8 ohms)

Small signal bandwidth -3 dB: 0 – 800000 Hz

Output voltage slew rate: 100 V/µs

Signal-to-noise and signal-to-background ratio: 120 dB

Electrical diagram of VVS-2010

Thanks to the use of an op-amp operating in a lightweight mode, as well as the use in the voltage amplifier of only cascades with OK and OB, covered by deep local OOS, the UMZCH BB is characterized by high linearity even before the general OOS is covered. In the very first high-fidelity amplifier back in 1985, solutions were used that until then were used only in measuring technology: DC modes are supported by a separate service unit, to reduce the level of interface distortion, the transition resistance of the contact group of the AC switching relay is covered by a common negative feedback, and a special unit effectively compensates for the influence of the resistance of speaker cables on these distortions. The tradition has been preserved in the UMZCH BB-2010, however, the general OOS also covers the resistance of the output low-pass filter.

In the vast majority of designs of other UMZCHs, both professional and amateur, many of these solutions are still missing. At the same time, high technical characteristics and audiophile advantages of the UMZCH BB are achieved by simple circuit solutions and a minimum of active elements. In fact, this is a relatively simple amplifier: one channel can be assembled in a couple of days without haste, and the setup only involves setting the required quiescent current of the output transistors. Especially for novice radio amateurs, a method of node-by-node, cascade testing and adjustment has been developed, using which you can be guaranteed to localize possible errors and prevent their possible consequences even before the UMZCH is fully assembled. All possible questions about this or similar amplifiers have detailed explanations, both on paper and on the Internet.

At the input of the amplifier there is a high-pass filter R1C1 with a cutoff frequency of 1.6 Hz, Fig. 1. But the efficiency of the mode stabilization device allows the amplifier to work with an input signal containing up to 400 mV of DC component voltage. Therefore, C1 is excluded, which realizes the eternal audiophile dream of a path without capacitors and significantly improves the sound of the amplifier.

The capacitance of capacitor C2 of the input low-pass filter R2C2 is selected so that the cutoff frequency of the input low-pass filter, taking into account the output resistance of the preamplifier 500 Ohm -1 kOhm, is in the range from 120 to 200 kHz. At the input of op amp DA1 there is a frequency correction circuit R3R5C3, which limits the band of processed harmonics and interference coming through the feedback circuit from the output side of the UMZCH to a band of 215 kHz at a level of -3 dB and increases the stability of the amplifier. This circuit allows you to reduce the difference signal above the cutoff frequency of the circuit and thereby eliminate unnecessary overload of the voltage amplifier with high-frequency interference signals, interference and harmonics, eliminating the possibility of dynamic intermodulation distortion (TIM; DIM).

Next, the signal is fed to the input of a low-noise operational amplifier with field-effect transistors at the DA1 input. Many “claims” to the UMZCH BB are made by opponents regarding the use of an op-amp at the input, which supposedly worsens the sound quality and “steals the virtual depth” of the sound. In this regard, it is necessary to pay attention to some quite obvious features of the operation of the op amp in the UMZCH VV.

Operational amplifiers of pre-amplifiers, post-DAC op-amps are forced to develop several volts of output voltage. Since the gain of the op amp is small and ranges from 500 to 2000 times at 20 kHz, this indicates their operation with a relatively high voltage difference signal - from several hundred microvolts at LF to several millivolts at 20 kHz and a high probability of intermodulation distortion being introduced by the input stage of the op amp. The output voltage of these op-amps is equal to the output voltage of the last voltage amplification stage, usually performed according to a circuit with an OE. An output voltage of several volts indicates that this stage operates with fairly large input and output voltages, and as a result, it introduces distortion into the amplified signal. The op-amp is loaded by the resistance of the parallel-connected OOS and load circuits, sometimes amounting to several kilo-ohms, which requires up to several milliamps of output current from the output repeater of the amplifier. Therefore, changes in the current of the output repeater of the IC, the output stages of which consume a current of no more than 2 mA, are quite significant, which also indicates that they introduce distortions into the amplified signal. We see that the input stage, voltage amplification stage and op-amp output stage can introduce distortion.

But the circuit design of the high-fidelity amplifier, due to the high gain and input resistance of the transistor part of the voltage amplifier, provides very gentle operating conditions for op-amp DA1. Judge for yourself. Even in a UMZCH that has developed a nominal output voltage of 50 V, the input differential stage of the op-amp operates with difference signals with voltages from 12 μV at frequencies of 500 Hz to 500 μV at a frequency of 20 kHz. The ratio of the high input overload capacity of the differential stage, made on field-effect transistors, and the scanty voltage of the difference signal ensures high linearity of signal amplification. The output voltage of the op-amp does not exceed 300 mV. which indicates the low input voltage of the voltage amplification stage with a common emitter from the operational amplifier - up to 60 μV - and the linear mode of its operation. The output stage of the op-amp supplies an alternating current of no more than 3 µA to the load of about 100 kOhm from the VT2 base side. Consequently, the output stage of the op-amp also operates in an extremely light mode, almost at idle. On a real musical signal, voltages and currents are most of the time an order of magnitude less than the given values.

From a comparison of the voltages of the difference and output signals, as well as the load current, it is clear that in general the operational amplifier in the UMZCH BB operates in a hundreds of times lighter, and therefore linear, mode than the op-amp mode of preamplifiers and post-DAC op-amps of CD players that serve as sources signal for UMZCH with any depth of environmental protection, as well as without it at all. Consequently, the same op-amp will introduce much less distortion in the UMZCH BB than in a single connection.

Occasionally there is an opinion that the distortions introduced by the cascade ambiguously depend on the voltage of the input signal. This is mistake. The dependence of the manifestation of cascade nonlinearity on the voltage of the input signal may obey one or another law, but it is always unambiguous: an increase in this voltage never leads to a decrease in the introduced distortions, but only to an increase.

It is known that the level of distortion products at a given frequency decreases in proportion to the depth of negative feedback for this frequency. The open-circuit gain, before the amplifier reaches the OOS, at low frequencies cannot be measured due to the smallness of the input signal. According to calculations, the open-circuit gain developed to cover the negative feedback allows one to achieve a negative feedback depth of 104 dB at frequencies up to 500 Hz. Measurements for frequencies starting from 10 kHz show that the OOS depth at a frequency of 10 kHz reaches 80 dB, at a frequency of 20 kHz - 72 dB, at a frequency of 50 kHz - 62 dB and 40 dB - at a frequency of 200 kHz. Figure 2 shows the amplitude-frequency characteristics of the UMZCH VV-2010 and, for comparison, similar in complexity.

High gain up to OOS coverage is the main feature of the circuit design of BB amplifiers. Since the goal of all circuit tricks is to achieve high linearity and high gain to maintain deep OOS in the widest possible frequency band, this means that such structures are the only circuit methods for improving amplifier parameters. Further reduction in distortion can only be achieved by design measures aimed at reducing the interference of harmonics of the output stage on the input circuits, especially on the inverting input circuit, from which the gain is maximum.

Another feature of the UMZCH BB circuitry is the current control of the output stage of the voltage amplifier. The input op-amp controls the voltage-current conversion stage, made with OK and OB, and the resulting current is subtracted from the quiescent current of the stage, made according to the circuit with OB.

The use of a linearizing resistor R17 with a resistance of 1 kOhm in the differential stage VT1, VT2 on transistors of different structures with serial power increases the linearity of the conversion of the output voltage of the op-amp DA1 to the collector current VT2 by creating a local feedback loop with a depth of 40 dB. This can be seen from comparing the sum of the emitters’ own resistances VT1, VT2 - approximately 5 Ohms each - with resistance R17, or the sum of thermal voltages VT1, VT2 - about 50 mV - with the voltage drop across resistance R17 amounting to 5.2 - 5.6 V .

For amplifiers built using the circuit design under consideration, a sharp, 40 dB per decade of frequency, decrease in gain above a frequency of 13...16 kHz is observed. The error signal, which is a product of distortion, at frequencies above 20 kHz is two to three orders of magnitude less than the useful audio signal. This makes it possible to convert the linearity of the differential stage VT1, VT2, which is excessive at these frequencies, into increasing the gain of the transistor part of the UN. Due to minor changes in the current of the differential cascade VT1, VT2, when amplifying weak signals, its linearity does not deteriorate significantly with a decrease in the depth of local feedback, but the operation of op-amp DA1, on the operating mode of which at these frequencies the linearity of the entire amplifier depends, will make the gain margin easier, since all voltages The distortions that determine the operational amplifier's distortion, starting from the difference signal to the output signal, decrease in proportion to the gain in gain at a given frequency.

The phase advance correction circuits R18C13 and R19C16 were optimized in the simulator in order to reduce the differential op-amp voltage to frequencies of several megahertz. It was possible to increase the gain of the UMZCH VV-2010 compared to the UMZCH VV-2008 at frequencies of the order of several hundred kilohertz. The gain in gain was 4 dB at 200 kHz, 6 at 300 kHz, 8.6 at 500 kHz, 10.5 dB at 800 kHz, 11 dB at 1 MHz and from 10 to 12 dB at frequencies higher 2 MHz. This can be seen from the simulation results, Fig. 3, where the lower curve refers to the frequency response of the advance correction circuit of the UMZCH VV-2008, and the upper curve refers to the UMZCH VV-2010.

VD7 protects the emitter junction VT1 from reverse voltage arising due to the flow of recharging currents C13, C16 in the mode of limiting the output signal of the UMZCH by voltage and the resulting maximum voltages with a high rate of change at the output of the op-amp DA1.

The output stage of the voltage amplifier is made of transistor VT3, connected according to a common base circuit, which eliminates the penetration of the signal from the output circuits of the cascade into the input circuits and increases its stability. The OB cascade, loaded onto the current generator on transistor VT5 and the input resistance of the output stage, develops a high stable gain - up to 13,000...15,000 times. Choosing the resistance of resistor R24 to be half the resistance of resistor R26 guarantees equality of the quiescent currents VT1, VT2 and VT3, VT5. R24, R26 provide local feedback that reduces the Early effect - the change in p21e depending on the collector voltage and increases the initial linearity of the amplifier by 40 dB and 46 dB, respectively. Powering the UN with a separate voltage, modulo 15 V higher than the voltage of the output stages, makes it possible to eliminate the effect of quasi-saturation of transistors VT3, VT5, which manifests itself in a decrease in p21e when the collector-base voltage decreases below 7 V.

The three-stage output follower is assembled using bipolar transistors and does not require any special comments. Don't try to fight entropy by skimping on the quiescent current of the output transistors. It should not be less than 250 mA; in the author's version - 320 mA.

Before the activation relay AC K1 is activated, the amplifier is covered by OOS1, realized by switching on the divider R6R4. The accuracy of maintaining the resistance R6 and the consistency of these resistances in different channels is not essential, but to maintain the stability of the amplifier it is important that the resistance R6 is not much lower than the sum of the resistances R8 and R70. When relay K1 is triggered, OOS1 is turned off and the OOS2 circuit, formed by R8R70C44 and R4, and covering contact group K1.1, comes into operation, where R70C44 excludes the output low-pass filter R71L1 R72C47 from the OOS circuit at frequencies above 33 kHz. The frequency-dependent OOS R7C10 forms a roll-off in the frequency response of the UMZCH to the output low-pass filter at a frequency of 800 kHz at a level of -3 dB and provides a margin in the OOS depth above this frequency. The decrease in frequency response at the AC terminals above the frequency of 280 kHz at a level of -3 dB is ensured by the combined action of R7C10 and the output low-pass filter R71L1 -R72C47.

The resonant properties of loudspeakers lead to the emission by the diffuser of damped sound vibrations, overtones after pulse action and the generation of its own voltage when the turns of the loudspeaker coil cross the magnetic field lines in the gap of the magnetic system. The damping coefficient shows how large the amplitude of the diffuser's oscillations is and how quickly they attenuate when the AC load is applied as a generator to the full impedance of the UMZCH. This coefficient is equal to the ratio of the AC resistance to the sum of the output resistance of the UMZCH, the transition resistance of the contact group of the AC switching relay, the resistance of the output low-pass filter inductor usually wound with a wire of insufficient diameter, the transition resistance of the AC cable terminals and the resistance of the AC cables themselves.

In addition, the impedance of loudspeaker systems is nonlinear. The flow of distorted currents through the conductors of AC cables creates a voltage drop with a large proportion of harmonic distortion, which is also subtracted from the undistorted output voltage of the amplifier. Therefore, the signal at the AC terminals is distorted much more than at the output of the UMZCH. These are so-called interface distortions.

To reduce these distortions, compensation of all components of the amplifier's output impedance is applied. The UMZCH's own output resistance, together with the transition resistance of the relay contacts and the resistance of the inductor wire of the output low-pass filter, is reduced by the action of a deep general negative feedback taken from the right terminal of L1. In addition, by connecting the right terminal of R70 to the “hot” AC terminal, you can easily compensate for the transition resistance of the AC cable clamp and the resistance of one of the AC wires, without fear of generating UMZCH due to phase shifts in the wires covered by the OOS.

The AC wire resistance compensation unit is made in the form of an inverting amplifier with Ky = -2 on op-amps DA2, R10, C4, R11 and R9. The input voltage for this amplifier is the voltage drop across the “cold” (“ground”) speaker wire. Since its resistance is equal to the resistance of the “hot” wire of the AC cable, to compensate for the resistance of both wires it is enough to double the voltage on the “cold” wire, invert it and, through resistor R9 with a resistance equal to the sum of the resistances R8 and R70 of the OOS circuit, apply it to the inverting input of the op-amp DA1 . Then the output voltage of the UMZCH will increase by the sum of the voltage drops on the speaker wires, which is equivalent to eliminating the influence of their resistance on the damping coefficient and the level of interface distortion at the speaker terminals. Compensation for the drop in the AC wire resistance of the nonlinear component of the back-EMF of loudspeakers is especially necessary at the lower frequencies of the audio range. The signal voltage at the tweeter is limited by the resistor and capacitor connected in series with it. Their complex resistance is much greater than the resistance of the speaker cable wires, so compensating for this resistance at HF makes no sense. Based on this, the integrating circuit R11C4 limits the operating frequency band of the compensator to 22 kHz.

Of particular note: the resistance of the “hot” wire of the AC cable can be compensated by covering its general OOS by connecting the right terminal of R70 with a special wire to the “hot” AC terminal. In this case, only the resistance of the “cold” AC wire will need to be compensated and the gain of the wire resistance compensator must be reduced to the value Ku = -1 by choosing the resistance of resistor R10 equal to the resistance of resistor R11.

The current protection unit prevents damage to the output transistors during short circuits in the load. The current sensor is resistors R53 - R56 and R57 - R60, which is quite enough. The flow of amplifier output current through these resistors creates a voltage drop that is applied to the divider R41R42. A voltage with a value greater than the threshold opens transistor VT10, and its collector current opens VT8 of the trigger cell VT8VT9. This cell enters a stable state with the transistors open and bypasses the HL1VD8 circuit, reducing the current through the zener diode to zero and locking VT3. Discharging C21 with a small current from the VT3 base may take several milliseconds. After the trigger cell is triggered, the voltage on the lower plate of C23, charged by the voltage on the LED HL1 to 1.6 V, increases from the level of -7.2 V from the positive power supply bus to the level of -1.2 B1, the voltage on the upper plate of this capacitor also increases by 5 V. C21 is quickly discharged through resistor R30 to C23, transistor VT3 is turned off. In the meantime, VT6 opens and through R33, R36 opens VT7. VT7 bypasses the zener diode VD9, discharges capacitor C22 through R31 and turns off transistor VT5. Without receiving bias voltage, the output stage transistors are also turned off.

Restoring the initial state of the trigger and turning on the UMZCH is done by pressing the SA1 “Protection Reset” button. C27 is charged by the collector current of VT9 and bypasses the base circuit of VT8, locking the trigger cell. If by this moment the emergency situation has been eliminated and VT10 is locked, the cell goes into a state with stable closed transistors. VT6, VT7 are closed, the reference voltage is supplied to the bases VT3, VT5 and the amplifier enters operating mode. If the short circuit in the UMZCH load continues, the protection is triggered again, even if capacitor C27 is connected to SA1. The protection works so effectively that during work on setting up the correction, the amplifier was de-energized several times for small soldering by touching the non-inverting input. The resulting self-excitation led to an increase in the current of the output transistors, and the protection turned off the amplifier. Although this crude method cannot be suggested as a general rule, but due to the current protection, it did not cause any harm to the output transistors.

Operation of the AC cable resistance compensator

The efficiency of the UMZCH BB-2008 compensator was tested using the old audiophile method, by ear, by switching the compensator input between the compensating wire and the common wire of the amplifier. The improvement in sound was clearly noticeable, and the future owner was eager to get an amplifier, so measurements of the influence of the compensator were not carried out. The advantages of the “cable cleaning” circuit were so obvious that the “compensator + integrator” configuration was adopted as a standard unit for installation in all developed amplifiers.

It's surprising how much unnecessary debate has flared up on the Internet regarding the usefulness/uselessness of cable resistance compensation. As usual, those who especially insisted on listening to a nonlinear signal were those to whom the extremely simple cable cleaning scheme seemed complex and incomprehensible, the costs for it exorbitant, and the installation labor-intensive ©. There were even suggestions that since so much money is spent on the amplifier itself, it would be a sin to skimp on the sacred, but one should take the best, glamorous path that all civilized humanity follows and...purchase normal, human © super-expensive cables made of precious metals. To my great surprise, fuel was added to the fire by statements from highly respected specialists about the uselessness of the compensation unit at home, including those specialists who successfully use this unit in their amplifiers. It is very unfortunate that many fellow radio amateurs were distrustful of reports of improved sound quality in the low and midrange with the inclusion of a compensator, and did their best to avoid this simple way of improving the performance of the UMZCH, thereby robbing themselves.

Little research has been done to document the truth. From the GZ-118 generator, a number of frequencies were supplied to the UMZCH BB-2010 in the region of the resonant frequency of the AC, the voltage was controlled by an oscilloscope S1-117, and Kr at the AC terminals was measured by the INI S6-8, Fig. 4. Checking the effectiveness of wire resistanceResistor R1 is installed to avoid interference to the compensator input when switching it between the control and common wires. In the experiment, common and publicly available AC cables with a length of 3 m and a core cross-section of 6 square meters were used. mm, as well as the GIGA FS Il speaker system with a frequency range of 25-22000 Hz, a nominal impedance of 8 Ohms and a nominal power of 90 W from Acoustic Kingdom.

Unfortunately, the circuit design of harmonic signal amplifiers from C6-8 involves the use of high-capacity oxide capacitors in OOS circuits. This causes the low-frequency noise of these capacitors to affect the device's low-frequency resolution, causing its low-frequency resolution to deteriorate. When measuring a Kr signal with a frequency of 25 Hz from GZ-118 directly from C6-8, the instrument readings dance around the value of 0.02%. It is not possible to bypass this limitation using the notch filter of the GZ-118 generator in the case of measuring the efficiency of the compensator, because a number of discrete values of the tuning frequencies of the 2T filter are limited at low frequencies to 20, 60, 120, 200 Hz and do not allow measuring Kr at the frequencies of interest to us. Therefore, reluctantly, the level of 0.02% was accepted as zero, the reference.

At a frequency of 20 Hz with a voltage at the AC terminals of 3 Vamp, which corresponds to an output power of 0.56 W into an 8 Ohm load, Kr was 0.02% with the compensator turned on and 0.06% with it turned off. At a voltage of 10 V ampl, which corresponds to an output power of 6.25 W, the Kr value is 0.02% and 0.08%, respectively, at a voltage of 20 V ampl and a power of 25 W - 0.016% and 0.11%, and at a voltage of 30 In amplitude and power 56 W - 0.02% and 0.13%.

Knowing the relaxed attitude of manufacturers of imported equipment to the meaning of inscriptions regarding power, and also remembering the wonderful, after the adoption of Western standards, the transformation of an acoustic system with a low-frequency loudspeaker power of 30 W into , long-term power of more than 56 W was not supplied to AC.

At a frequency of 25 Hz at a power of 25 W, Kr was 0.02% and 0.12% with the compensation unit on/off, and at a power of 56 W - 0.02% and 0.15%.

At the same time, the necessity and effectiveness of covering the output low-pass filter with a general OOS was tested. At a frequency of 25 Hz with a power of 56 W and connected in series to one of the AC cable wires of the output RL-RC low-pass filter, similar to that installed in an ultra-linear UMZCH, Kr with the compensator turned off reaches 0.18%. At a frequency of 30 Hz at a power of 56 W Kr 0.02% and 0.06% with the compensation unit on/off. At a frequency of 35 Hz at a power of 56 W Kr 0.02% and 0.04% with the compensation unit on/off. At frequencies of 40 and 90 Hz at a power of 56 W, Kr is 0.02% and 0.04% with the compensation unit on/off, and at a frequency of 60 Hz -0.02% and 0.06%.

The conclusions are obvious. The presence of nonlinear signal distortions at the AC terminals is observed. A deterioration in the linearity of the signal at the AC terminals is clearly detected when it is connected through the uncompensated, not covered by the OOS resistance of the low-pass filter containing 70 cm of relatively thin wire. The dependence of the distortion level on the power supplied to the AC suggests that it depends on the ratio of the signal power and the rated power of the AC woofers. Distortion is most pronounced at frequencies near the resonant one. The back EMF generated by the speakers in response to the influence of an audio signal is shunted by the sum of the output resistance of the UMZCH and the resistance of the AC cable wires, so the level of distortion at the AC terminals directly depends on the resistance of these wires and the output resistance of the amplifier.

The cone of a poorly damped low-frequency loudspeaker itself emits overtones, and, in addition, this loudspeaker generates a wide tail of non-linear and intermodulation distortion products that the mid-frequency loudspeaker reproduces. This explains the deterioration of sound at mid frequencies.

Despite the assumption of a zero Kr level of 0.02% adopted due to the imperfection of the INI, the influence of the cable resistance compensator on the AC signal distortion is clearly and unambiguously noted. It can be stated that there is complete agreement between the conclusions drawn after listening to the operation of the compensation unit on a musical signal and the results of instrumental measurements.

The improvement clearly audible when the cable cleaner is turned on can be explained by the fact that with the disappearance of distortion at the AC terminals, the midrange speaker stops producing all that dirt. Apparently, therefore, by reducing or eliminating the reproduction of distortions by the mid-frequency loudspeaker, the two-cable speaker circuit, the so-called. “Bi-wiring,” when the LF and MF-HF sections are connected with different cables, has an advantage in sound compared to a single-cable circuit. However, since in a two-cable circuit the distorted signal at the terminals of the AC low-frequency section does not disappear anywhere, this circuit is inferior to the version with a compensator in terms of the damping coefficient of free vibrations of the low-frequency loudspeaker cone.

You can’t fool physics, and for decent sound it’s not enough to get brilliant performance at the amplifier output with an active load, but you also need to not lose linearity after delivering the signal to the speaker terminals. As part of a good amplifier, a compensator made according to one scheme or another is absolutely necessary.

Integrator

The efficiency and error reduction capabilities of the integrator on DA3 were also tested. In the UMZCH BB with op-amp TL071, the output DC voltage is in the range of 6...9 mV and it was not possible to reduce this voltage by including an additional resistor in the non-inverting input circuit.

The effect of low-frequency noise, characteristic of an op-amp with a DC input, due to the coverage of deep feedback through the frequency-dependent circuit R16R13C5C6, manifests itself in the form of instability of the output voltage of several millivolts, or -60 dB relative to the output voltage at rated output power, at frequencies below 1 Hz , non-reproducible speakers.

The Internet mentioned the low resistance of the protective diodes VD1...VD4, which supposedly introduces an error into the operation of the integrator due to the formation of a divider (R16+R13)/R VD2|VD4.. To check the reverse resistance of the protective diodes, a circuit was assembled in Fig. 6. Here op-amp DA1, connected according to the inverting amplifier circuit, is covered by OOS through R2, its output voltage is proportional to the current in the circuit of the tested diode VD2 and the protective resistor R2 with a coefficient of 1 mV/nA, and the resistance of the circuit R2VD2 - with a coefficient of 1 mV/15 GOhm . To exclude the influence of additive errors of the op-amp - bias voltage and input current on the results of measuring the diode leakage current, it is necessary to calculate only the difference between the intrinsic voltage at the output of the op-amp, measured without the diode being tested, and the voltage at the output of the op-amp after its installation. In practice, a difference in the op-amp output voltages of several millivolts gives a diode reverse resistance value of the order of ten to fifteen gigaohms at a reverse voltage of 15 V. Obviously, the leakage current will not increase as the voltage on the diode decreases to a level of several millivolts, characteristic of the difference voltage of the op-amp integrator and compensator .

But the photoelectric effect characteristic of diodes placed in a glass case actually leads to a significant change in the output voltage of the UMZCH. When illuminated with a 60 W incandescent lamp from a distance of 20 cm, the constant voltage at the output of the UMZCH increased to 20...3O mV. Although it is unlikely that a similar level of illumination could be observed inside the amplifier case, a drop of paint applied to these diodes eliminated the dependence of the UMZCH modes on illumination. According to the simulation results, the decrease in the frequency response of the UMZCH is not observed even at a frequency of 1 millihertz. But the time constant R16R13C5C6 should not be reduced. The phases of the alternating voltages at the outputs of the integrator and compensator are opposite, and with a decrease in the capacitance of the capacitors or the resistance of the integrator resistors, an increase in its output voltage can worsen the compensation of the resistance of the speaker cables.

Comparison of the sound of amplifiers. The sound of the assembled amplifier was compared with the sound of several industrially produced foreign amplifiers. The source was a CD player from Cambridge Audio; a pre-amplifier was used to drive and adjust the sound level of the final UMZCHs; the Sugden A21a and NAD C352 used standard adjustment controls.

The first to be tested was the legendary, shocking and damn expensive English UMZCH “Sugden A21a”, operating in class A with an output power of 25 W. What is noteworthy is that in the accompanying documentation for the VX, the British considered it better not to indicate the level of nonlinear distortions. They say it’s not a matter of distortion, but of spirituality. “Sugden A21a>” lost to the UMZCH BB-2010 with comparable power both in level and in clarity, confidence, and noble sound at low frequencies. This is not surprising, given the features of its circuit design: just a two-stage quasi-symmetric output follower on transistors of the same structure, assembled according to the circuit design of the 70s of the last century with a relatively high output resistance and an electrolytic capacitor connected at the output, which further increases the total output resistance - this is the latter the solution itself worsens the sound of any amplifiers at low and mid frequencies. At medium and high frequencies, the UMZCH BB showed higher detail, transparency and excellent scene elaboration, when singers and instruments could be clearly localized by sound. By the way, speaking of the correlation of objective measurement data and subjective impressions of sound: in one of the journal articles of Sugden’s competitors, its Kr was determined at the level of 0.03% at a frequency of 10 kHz.

The next one was also the English amplifier NAD C352. The general impression was the same: the pronounced “bucket” sound of the Englishman at low frequencies left him no chance, while the work of the UMZCH BB was recognized as impeccable. Unlike NADA, the sound of which was associated with dense bushes, wool, and cotton wool, the sound of BB-2010 at medium and high frequencies made it possible to clearly distinguish the voices of performers in a general choir and instruments in an orchestra. The work of the NAD C352 clearly expressed the effect of better audibility of a more vocal performer, a louder instrument. As the owner of the amplifier himself put it, in the sound of the UMZCH BB the vocalists did not “scream and nod” at each other, and the violin did not fight with the guitar or trumpet in sound power, but all the instruments were peacefully and harmoniously “friends” in the overall sound image of the melody. At high frequencies, the UMZCH BB-2010, according to imaginative audiophiles, sounds “as if it were painting the sound with a thin, thin brush.” These effects can be attributed to differences in intermodulation distortion between the amplifiers.

The sound of the Rotel RB 981 UMZCH was similar to the sound of the NAD C352, with the exception of better performance at low frequencies, yet the BB-2010 UMZCH remained unrivaled in the clarity of AC control at low frequencies, as well as the transparency and delicacy of sound at mid and high frequencies.

The most interesting thing in terms of understanding the way of thinking of audiophiles was the general opinion that, despite their superiority over these three UMZCHs, they bring “warmth” to the sound, which makes it more pleasant, and the BB UMZCH works smoothly, “it is neutral to the sound.”

The Japanese Dual CV1460 lost its sound immediately after switching on in the most obvious way for everyone, and we didn’t waste time listening to it in detail. Its Kr was in the range of 0.04...0.07% at low power.

The main impressions from comparing the amplifiers were completely identical in their main features: the UMZCH BB was unconditionally and unequivocally ahead of them in sound. Therefore, further testing was deemed unnecessary. In the end, friendship won, everyone got what they wanted: for a warm, soulful sound - Sugden, NAD and Rotel, and to hear what was recorded on disk by the director - UMZCH BB-2010.

Personally, I like the high-fidelity UMZCH for its light, clean, impeccable, noble sound; it effortlessly reproduces passages of any complexity. As a friend of mine, an experienced audiophile, put it, he handles the sounds of drum kits at low frequencies without variations, like a press, at medium frequencies he sounds as if there is none, and at high frequencies he seems to be painting the sound with a thin brush. For me, the non-straining sound of the UMZCH BB is associated with the ease of operation of the cascades.

UMZCH VVS-2011 Ultimate version

Amplifier specifications:

High power: 150W/8ohm
High linearity: 0.0002 – 0.0003% (at 20 kHz 100 W / 4 ohms)

Full set of service units:

Maintain zero constant voltage
AC wire resistance compensator
Current protection
Output DC voltage protection
Smooth start

Electrical diagram

The layout of printed circuit boards was carried out by a participant in many popular projects LepekhinV (Vladimir Lepekhin). It turned out very well).

VVS-2011 amplifier board

Start-protective device

AC amplifier protection board VVS-2011

The VHF VVS-2011 amplifier board was designed for tunnel ventilation (parallel to the radiator). Installation of transistors UN (voltage amplifier) and VK (output stage) is somewhat difficult, because installation/disassembly has to be done with a screwdriver through holes in the PP with a diameter of about 6 mm. When access is open, the projection of the transistors does not fall under the PP, which is much more convenient. I had to modify the board a little.

Amplifier board

VVS-2011 amplifier wiring diagram

One thing I didn’t take into account in the new PCBs is the ease of setting up protection on the amplifier board

C25 = 0.1 nF, R42* = 820 Ohm and R41 = 1 kOhm. All SMD elements are located on the solder side, which is very inconvenient when setting up, because You will need to unscrew and tighten the bolts securing the PCB to the stands and the transistors to the radiators several times.

Offer: R42* 820 Ohm consists of two SMD resistors located in parallel, from here the proposal: we solder one SMD resistor immediately, we solder the other output resistor overhang to VT10, one output to the base, the other to the emitter, we select the appropriate one. We picked it up and changed the output to SMD, for clarity.

UMZCH VVS-2011 Ultimate version

UMZCH VVS-2011 version Ultimate author of the scheme Viktor Zhukovsky Krasnoarmeysk

Amplifier specifications:
1. Large power: 150W/8ohm,
2. High linearity - 0.000.2...0.000.3% at 20 kHz 100 W / 4 Ohm,
Full set of service units:
1. Maintain zero constant voltage,
2. Compensator for resistance of AC wires,
3. Current protection,
4. DC output voltage protection,
5. Smooth start.

UMZCH VVS2011 scheme

The layout of printed circuit boards was carried out by a participant in many popular projects LepekhinV (Vladimir Lepekhin). It turned out very well).

UMZCH-VVS2011 board

ULF amplifier board VVS-2011 was designed for tunnel ventilation (parallel to the radiator). Installation of transistors UN (voltage amplifier) and VK (output stage) is somewhat difficult, because installation/disassembly has to be done with a screwdriver through holes in the PP with a diameter of about 6 mm. When access is open, the projection of the transistors does not fall under the PP, which is much more convenient. I had to modify the board a little.

I didn’t take one point into account in the new software— this is the convenience of setting up protection on the amplifier board:

C25 0.1n, R42* 820 Ohm and R41 1k all elements are SMD and are located on the solder side, which is not very convenient when setting up, because You will need to unscrew and tighten the bolts securing the PCB to the stands and the transistors to the radiators several times. Offer: R42* 820 consists of two SMD resistors located in parallel, from here the proposal: we solder one SMD resistor immediately, we solder the other output resistor overhang to VT10, one output to the base, the other to the emitter, we select it to the appropriate one. Selected, change output to smd, for clarity:

Victor Zhukovsky, Krasnoarmeysk, Donetsk region.

UMZCH BB-2010 is a new development from the well-known line of UMZCH BB (high fidelity) amplifiers [1; 2; 5]. A number of technical solutions used were influenced by the work of SI Ageev. .

The amplifier provides Kr of the order of 0.001% at a frequency of 20 kHz at Pout = 150 W into an 8 Ohm load, small signal frequency band at a level of -3 dB - 0 Hz ... 800 kHz, slew rate of the output voltage -100 V / µs, signal-to-noise ratio and signal/background -120 dB.

At the input of the amplifier there is a high-pass filter R1C1 with a cutoff frequency of 1.6 Hz, Fig. 1. But the efficiency of the mode stabilization device allows the amplifier to work with an input signal containing up to 400 mV of DC component voltage. Therefore, C1 is excluded, which realizes the eternal audiophile dream of a path without capacitors © and significantly improves the sound of the amplifier.

Operational amplifiers of pre-amplifiers, post-DAC op-amps are forced to develop several volts of output voltage. Since the gain of the op amp is small and ranges from 500 to 2,000 times at 20 kHz, this indicates that they operate with a relatively high voltage difference signal - from several hundred microvolts at LF to several millivolts at 20 kHz and a high probability of intermodulation distortion being introduced by the input stage of the op amp. The output voltage of these op-amps is equal to the output voltage of the last voltage amplification stage, usually performed according to a circuit with an OE. An output voltage of several volts indicates that this stage operates with fairly large input and output voltages, and as a result, it introduces distortion into the amplified signal. The op-amp is loaded by the resistance of the parallel-connected OOS and load circuits, sometimes amounting to several kilo-ohms, which requires up to several milliamps of output current from the output repeater of the amplifier. Therefore, changes in the current of the output repeater of the IC, the output stages of which consume a current of no more than 2 mA, are quite significant, which also indicates that they introduce distortions into the amplified signal. We see that the input stage, voltage amplification stage and op-amp output stage can introduce distortion.

The use of a linearizing resistor R17 with a resistance of 1 kOhm in the differential stage VT1, VT2 on transistors of different structures with serial power increases the linearity of the conversion of the output voltage of the op-amp DA1 to the collector current VT2 by creating a local feedback loop with a depth of 40 dB. This can be seen from comparing the sum of the emitters’ own resistances VT1, VT2 - approximately 5 Ohms each - with resistance R17, or the sum of the thermal voltages VT1, VT2 - about 50 mV - with the voltage drop across resistance R17 amounting to 5.2 - 5.6 V .

The output stage of the voltage amplifier is made of transistor VT3, connected according to a common base circuit, which eliminates the penetration of the signal from the output circuits of the cascade into the input circuits and increases its stability. The OB stage, loaded onto the current generator on transistor VT5 and the input resistance of the output stage, develops a high stable gain - up to 13,000...15,000 times. Choosing the resistance of resistor R24 to be half the resistance of resistor R26 guarantees equality of the quiescent currents VT1, VT2 and VT3, VT5. R24, R26 provide local feedback that reduces the Early effect - the change in p21e depending on the collector voltage and increases the initial linearity of the amplifier by 40 dB and 46 dB, respectively. Powering the UN with a separate voltage, modulo 15 V higher than the voltage of the output stages, makes it possible to eliminate the effect of quasi-saturation of transistors VT3, VT5, which manifests itself in a decrease in p21e when the collector-base voltage decreases below 7 V.

The three-stage output follower is assembled using bipolar transistors and does not require any special comments. Don't try to fight entropy © by skimping on the quiescent current of the output transistors. It should not be less than 250 mA; in the author's version - 320 mA.

The current protection unit prevents damage to the output transistors during short circuits in the load. The current sensor is resistors R53 - R56 and R57 - R60, which is quite enough. The flow of amplifier output current through these resistors creates a voltage drop that is applied to the divider R41R42. A voltage with a value greater than the threshold opens transistor VT10, and its collector current opens VT8 of the trigger cell VT8VT9. This cell enters a stable state with the transistors open and bypasses the HL1VD8 circuit, reducing the current through the zener diode to zero and locking VT3. Discharging C21 with a small current from the VT3 base may take several milliseconds. After the trigger cell is triggered, the voltage on the lower plate of C23, charged by the voltage on the HL1 LED to 1.6 V, increases from the level of -7.2 V from the positive power supply bus to the level of -1.2 V 1, the voltage on the upper plate of this capacitor also increases at 5 V. C21 is quickly discharged through resistor R30 to C23, transistor VT3 is turned off. In the meantime, VT6 opens and through R33, R36 opens VT7. VT7 bypasses the zener diode VD9, discharges capacitor C22 through R31 and turns off transistor VT5. Without receiving bias voltage, the output stage transistors are also turned off.

Restoring the initial state of the trigger and turning on the UMZCH is done by pressing the SA1 “Protection Reset” button. C27 is charged by the collector current of VT9 and bypasses the base circuit of VT8, locking the trigger cell. If by this moment the emergency situation has been eliminated and VT10 is locked, the cell goes into a state with stable closed transistors. VT6, VT7 are closed, the reference voltage is supplied to the bases VT3, VT5 and the amplifier enters operating mode. If the short circuit in the UMZCH load continues, the protection is triggered again, even if capacitor C27 is connected to SA1. The protection works so effectively that during work on setting up the correction, the amplifier was de-energized several times for small soldering connections ... by touching the non-inverting input. The resulting self-excitation led to an increase in the current of the output transistors, and the protection turned off the amplifier. Although this crude method cannot be suggested as a general rule, but due to the current protection, it did not cause any harm to the output transistors.

Operation of the AC cable resistance compensator.

It's surprising how much unnecessary debate has flared up on the Internet regarding the usefulness/uselessness of cable resistance compensation. As usual, those who especially insisted on listening to a nonlinear signal were those to whom the extremely simple cable cleaning scheme seemed complex and incomprehensible, the costs for it exorbitant, and installation labor-intensive ©. There were even suggestions that since so much money is spent on the amplifier itself, it would be a sin to skimp on the sacred, but one should take the best, glamorous path that all civilized humanity follows and...purchase normal, human © super-expensive cables made of precious metals. To my great surprise, fuel was added to the fire by statements from highly respected specialists about the uselessness of the compensation unit at home, including those specialists who successfully use this unit in their amplifiers. It is very unfortunate that many fellow radio amateurs were distrustful of reports of improved sound quality in the low and midrange with the inclusion of a compensator, and did their best to avoid this simple way of improving the performance of the UMZCH, thereby robbing themselves.

Little research has been done to document the truth. From the GZ-118 generator, a number of frequencies were supplied to the UMZCH BB-2010 in the region of the resonant frequency of the AC, the voltage was controlled by an oscilloscope S1-117, and Kr at the AC terminals was measured by the INI S6-8, Fig. 4. Resistor R1 is installed to avoid interference to the compensator input when switching it between the control and common wires. In the experiment, common and publicly available AC cables with a length of 3 m and a core cross-section of 6 square meters were used. mm, as well as the GIGA FS Il speaker system with a frequency range of 25 -22,000 Hz, a nominal impedance of 8 Ohms and a nominal power of 90 W from Acoustic Kingdom.

Unfortunately, the circuit design of harmonic signal amplifiers from C6-8 involves the use of high-capacity oxide capacitors in OOS circuits. This causes the low-frequency noise of these capacitors to affect the device's low-frequency resolution, causing its low-frequency resolution to deteriorate. When measuring a Kr signal with a frequency of 25 Hz from GZ-118 directly from C6-8, the instrument readings dance around the value of 0.02%. It is not possible to bypass this limitation using the notch filter of the GZ-118 generator in the case of measuring the efficiency of the compensator, because a number of discrete values of the tuning frequencies of the 2T filter are limited at low frequencies to 20.60, 120, 200 Hz and do not allow measuring Kr at the frequencies of interest to us. Therefore, reluctantly, the level of 0.02% was accepted as zero, the reference.

Knowing the relaxed attitude of manufacturers of imported equipment to the meanings of inscriptions regarding power, and also remembering the wonderful, after the adoption of Western standards, transformation of the 35AC-1 speaker system with a subwoofer power of 30 W into the S-90, long-term power of more than 56 W was not supplied to the AC.

At a frequency of 25 Hz at a power of 25 W, Kr was 0.02% and 0.12% with the compensation unit on/off, and at a power of 56 W - 0.02% and 0.15%.

Despite the assumption of a zero Kr level of 0.02% adopted due to the imperfection of the INI, the influence of the cable resistance compensator on the signal distortion at the AC terminals is clearly and unambiguously noted. It can be stated that there is complete agreement between the conclusions drawn after listening to the operation of the compensation unit on a musical signal and the results of instrumental measurements.

Integrator.

The Internet mentioned the low resistance of the protective diodes VD1...VD4, which supposedly introduces an error in the operation of the integrator due to the formation of a divider (R16+R13)/R VD2|VD4 . . To check the reverse resistance of the protective diodes, a circuit was assembled in Fig. 6. Here, op-amp DA1, connected according to the inverting amplifier circuit, is covered by OOS through R2, its output voltage is proportional to the current in the circuit of the tested diode VD2 and the protective resistor R2 with a coefficient of 1 mV/nA, and the resistance of the circuit R2VD2 - with a coefficient of 1 mV/15 GOhm. To exclude the influence of additive errors of the op-amp - bias voltage and input current on the results of measuring the leakage current of the diode, it is necessary to calculate only the difference between the intrinsic voltage at the output of the op-amp, measured without the diode being tested, and the voltage at the output of the op-amp after its installation. In practice, a difference in the op-amp output voltages of several millivolts gives a diode reverse resistance value of the order of ten to fifteen gigaohms at a reverse voltage of 15 V. Obviously, the leakage current will not increase as the voltage on the diode decreases to a level of several millivolts, characteristic of the difference voltage of the op-amp integrator and compensator .

Comparison of the sound of amplifiers. The sound of the assembled amplifier was compared with the sound of several industrially produced foreign amplifiers. The source was a Cambridge Audio CD player; the Radiotekhnika UP-001 pre-amplifier was used to drive and adjust the sound level of the final UMZCHs; the Sugden A21a and NAD C352 used standard adjustment controls.

Literature

1. Sukhov I. UMZCH of high fidelity. "Radio", 1989, No. 6, pp. 55-57; No. 7, pp. 57-61.

2. Ridiko L. UMZCH BB on a modern element base with a microcontroller control system. “Radio Hobby”, 2001, No. 5, pp. 52-57; No. 6, pp. 50-54; 2002, no. 2, pp. 53-56.

3. Ageev S. Superlinear UMZCH with deep environmental protection “Radio”, 1999, No. 10... 12; "Radio", 2000, No. 1; 2; 4…6; 9…11.

4. Zuev. L. UMZCH with parallel OOS. "Radio", 2005, No. 2, p. 14.

5. Zhukovsky V. Why do you need the speed of the UMZCH (or “UMZCH VV-2008”)? “Radio Hobby”, 2008, No. 1, pp. 55-59; No. 2, pp. 49-55.

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UMZCH VVS-2011 version Ultimate author of the scheme Viktor Zhukovsky Krasnoarmeysk

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