Don't dream, act!
Experiments with various preamplifiers, volume and tone controls have shown that the best sound quality is achieved with a minimum number of amplification stages, with passive controls. In this case, adjustments at the input of the power amplifier are undesirable, since they lead to an increase in the level of nonlinear distortion of the complex. This effect was recently discovered by the famous audio equipment developer Douglas Self.
Thus, the following structure emerges for this part of the sound amplification path:
- passive bridge regulator of low and high frequencies,
- passive volume control,
- a pre-amplifier with a linear amplitude-frequency response (AFC) and minimal distortion in the operating frequency range.
The obvious drawback of adjustments at the preamplifier input is that the deterioration in the signal-to-noise ratio is largely offset by the high signal level of modern sound reproduction devices.
Proposed preamplifier Can be used in high-quality stereo audio amplifiers. The tone control allows you to adjust the amplitude-frequency response (AFC) simultaneously on two channels in two frequency regions: lower and upper. As a result, the characteristics of the room and acoustic systems, as well as the personal preferences of the listener, are taken into account.
And again a little history
The first contender for the role of a pre-amplifier with a tone control was D. Starodub’s circuit (Fig. 1). But the design never took root in a power amplifier: careful shielding and a power supply with an extremely low ripple level (about 50 μV) were required. However, the main reason was the lack of slider variable resistors.
Rice. 1. Diagram of a high-quality tone control block
Through trial and error, I came up with a simple pre-amplifier circuit (Fig. 2), with which, however, the sound reproduction system far surpassed the sound of commercially produced equipment, at least that which my friends and acquaintances had.
Rice. 2. Schematic diagram of one pre-amplifier channel for UMZCH S. Batya and V. Sereda
The basis is taken from the circuit of the pre-amplifier of the stereophonic electrophone by Yu. Krasov and V. Cherkunov, demonstrated at the 26th All-Union Exhibition of Radio Amateur Designers. This is the left side of the circuit, including the tone controls.
The appearance of a cascade on transistors of different conductivities in the pre-amplifier (VT3, VT4) is associated with a discussion of amplifiers with the teacher of the television technology laboratory at the Department of Radio Systems A. S. Mirzoyants, with whom I worked as a student. During the work, linear cascades were needed to amplify the television signal, and Alexander Sergeevich reported that, in his experience, the best characteristics are possessed by “topsy-turvy” structures, as he put it, that is, amplifiers on transistors of the opposite structure with direct coupling. In the process of experimenting with UMZCH, I found out that this applies not only to television equipment, but also to sound reinforcement equipment. Subsequently, I often used similar circuits in my designs, including field-effect transistor - bipolar transistor pairs.
An attempt to use transistors of different structures in the first stage (composite emitter follower VT1, VT2) did not bring success, because with all the excellent characteristics (low noise level, low distortion), the circuit had a significant drawback - lower overload capacity compared to the emitter follower.
Pre-amplifier specifications:
Input resistance, kOhm= 300
Sensitivity, mV= 250
Depth of tone adjustments, dB:
at a frequency of 40 Hz=± 15
at 15 kHz=± 15
Depth of stereo balance adjustments, dB=± 6
Since new ideas arose during the design of amplifiers, I gave the old designs to someone, or sold them at a fixed rate of watt of output power / ruble. On one of my trips to Leningrad, I took this amplifier with me to sell it to a friend of a friend. Volodka said that this guy has a lot of Western equipment, and took the device to him for an audition. In the evening he told me the results: the young man turned on the amplifier, listened to a couple of things and was so satisfied with the sound that he paid the money without a word.
To be honest, when I found out that the comparison would take place with imported equipment, I didn’t particularly hope that the amplifier would make an impression. In addition, it was not fully completed - the top and side covers were missing.
Let's consider the circuit diagram of one pre-amplifier channel (Fig. 2). High-impedance volume (R2.1) and balance (R1.1) controls are installed at the input. From the middle terminal of resistor R2.1, through the transition capacitor C2, the sound signal is supplied to the composite emitter follower VT1, VT2, which is necessary for the normal operation of the passive tone control, made in a bridge circuit. In order to eliminate the attenuation introduced by the tone block and amplify the signal to the required level, a two-stage amplifier is installed on transistors VT3, VT4.
The preamplifier's power supply is unstabilized, from the positive arm of the power amplifier. The supply voltage is supplied to cascades VT3, VT4 through filter R17, C10, C13, and to the input emitter follower - R8, C4. The VD1 diode plays an important role: without it, it was not possible to completely eliminate the background of alternating current with a frequency of 100 Hz at the output of the power amplifier.
Structurally, the preamplifier is made in a “line”, all parts are installed on a printed circuit board, closed on top with a U-shaped screen made of steel 0.8 mm thick.
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Thank you for your attention!
The calculation was performed using the following relationships: R1 = R3; R2 = 0.1R1; R4 = 0.01R1; R5 = 0.06R1; C1[nF] = 105/R3[Ohm]; C2 = 15C1; C3 = 22C1; C4 = 220C1.
With R1=R3=100 kOhm, the tone block will introduce attenuation of about 20 dB at a frequency of 1 kHz. You can take variable resistors R1 and R3 of a different value, even if, for definiteness, resistors with a resistance of 68 kOhm were available. It is easy to recalculate the values of fixed resistors and capacitors of the bridge tone control without referring to the program or table. 1: we reduce the resistance values of the resistors by 68/100=0.68 times and increase the capacitances of the capacitors by 1/0.68=1.47 times. We get R1=6.8 kOhm; R3=680 Ohm; R4=3.9 kOhm; C2=0.033 µF; C3=0.33 µF; C4=1500 pF; C5=0.022 µF.
For smooth tone control, variable resistors with an inverse logarithmic dependence (curve B) are required.
The program allows you to clearly view the operation of the designed tone control Tone Stack Calculator 1.3(Fig. 9).
Rice. 9. Modeling of tone controls for the circuit shown in Fig. 8
Program Tone Stack Calculator is designed to analyze seven typical circuits of passive tone controls and allows you to immediately show the frequency response when changing the position of the virtual controls.
Rice. 11. Schematic diagram of the tone block and pre-amplifier for the “student” UMZCH
An experimental test of several instances of operational amplifiers showed that even without a capacitor in the grounded branch of the negative feedback divider, the constant output voltage is a few millivolts. However, for reasons of versatility of use, coupling capacitors (C1, C6) are included at the input of the tone control unit and the output of the pre-amplifier.
Depending on the required sensitivity of the amplifier, the resistance value of resistor R10 is selected from the table. 2. You should strive not for the exact value of the resistor resistances, but for their pairwise equality in the amplifier channels.
table 2 
▼ 🕗 02/25/12 ⚖️ 11.53 Kb ⇣ 149 Hello, reader! My name is Igor, I'm 45, I'm a Siberian and an avid amateur electronics engineer. I came up with, created and have been maintaining this wonderful site since 2006.
For more than 10 years, our magazine has existed only at my expense.
Good! The freebie is over. If you want files and useful articles, help me!
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Thank you for your attention!
Igor Kotov, editor-in-chief of Datagor magazine
The main disadvantage of a passive tone control is the low gain. Another disadvantage is that to obtain a linear dependence of the volume level on the angle of rotation, it is necessary to use variable resistors with a logarithmic control characteristic (curve “B”).
The advantage of passive tone controls is less distortion than active ones (for example, the Baxandal tone control, Fig. 12).
Rice. 12. Active tone control by P. Baxandal
As can be seen from the diagram shown in Fig. 12, the active tone control contains passive elements (resistors R1 - R7, capacitors C1 - C4) included in the one hundred percent parallel negative voltage feedback of the operational amplifier DA1. The transmission coefficient of this regulator in the middle position of the tone control sliders R2 and R6 is equal to unity, and variable resistors with a linear regulation characteristic (curve “A”) are used for adjustment. In other words, an active tone control is free from the disadvantages of a passive tone control.
However, in terms of sound quality, this regulator is clearly worse than a passive one, which even inexperienced listeners notice.
Rice. 13. Placement of parts on the printed circuit board
Elements related to the right channel of the preamplifier are indicated with a prime. The same marking is made in the printed circuit board file (with *.lay extension) - the inscription appears when the cursor is moved to the corresponding element.
First, small-sized parts are installed on the printed circuit board: wire jumpers, resistors, capacitors, ferrite “beads” and a socket for the microcircuit. Lastly, terminal blocks and variable resistors are installed.
After checking the installation, turn on the power and check the “zero” at the outputs of the operational amplifier. The offset is 2 – 4 mV.
If desired, you can drive the device from a sinusoidal generator and take the characteristics (Fig. 14).
Rice. 14. Installation for characterizing the preamplifier
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Thank you for your attention!
Igor Kotov, editor-in-chief of Datagor magazine
Sources mentioned
1. Digest // Radiohobby, 2003, No. 3, pp. 10, 11.2. Starodub D. Block of tone controls for a high-quality bass amplifier // Radio, 1974, No. 5, p. 45, 46.
3. Shkritek P. Reference guide to audio circuitry. – M.: Mir, 1991, p. 150 – 153.
4. Shikhatov A. Passive tone controls // Radio, 1999, No. 1, p. 14, 15.
5. Rivkin L. Calculation of tone controls // Radio, 1969, No. 1, p. 40, 41.
6. Solntsev Yu. High-quality pre-amplifier // Radio, 1985, No. 4, pp. 32 – 35.
7. //www.moskatov.narod.ru/ (Program by E. Moskatov “Timbreblock 4.0.0.0”).
Vladimir Mosyagin (MVV)
Russia, Veliky Novgorod
I became interested in amateur radio from the fifth grade of high school.
Diploma specialty - radio engineer, Ph.D.
Author of the books “For a young radio amateur to read with a soldering iron”, “Secrets of amateur radio craftsmanship”, co-author of the series of books “To be read with a soldering iron” in the publishing house “SOLON-Press”, I have publications in the magazines “Radio”, “Instruments and Experimental Techniques”, etc. .
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To participate in the voting, register and log in to the site with your username and password.The high-fidelity UMZCH described in the UMZCH was developed for subjective examination of the sound of digital laser CD players (LDCs).
During the examination, powerful high-quality acoustic systems (AS) were connected to the output of the UMZCH, and its input was connected to the output of the PCD in order to ensure minimal phase and nonlinear distortions, as well as reduce the noise level through the simplest resistive voltage divider, which was used as a wire-wound variable resistor SP5 -21-A-2 with a resistance of 15 kOhm.
With this divider you can set the volume to 90-94 von, which is necessary for conducting a subjective examination, since at this volume a normal balance of the spectrum is ensured and there is no need for additional frequency correction. Subsequently, adjustment was carried out only when the type of speaker was changed or the rated output voltage of the tested PCD differed from the standard one (2 V eff).
When using the described UMZCH as the base amplifier of a high-quality sound reproducing complex, it must be supplemented with a finely compensated volume control and a tone control with a sensitivity of 150...200 mV. A description of such a control unit, developed by the author, is given in the article published below.
Main technical characteristics
- Input impedance, kOhm - 150
- Rated input voltage, mV - 150
- Rated output voltage, m V - 800
- Relative noise level: weighted value - 94dBA, unweighted value - 88dB
- Volume control depth, dB - 36
- Tone control depth, dB + 10...—10
- Harmonic coefficient, %, at the nominal level of the OUTPUT signal.<0,001 %
- Overload capacity, dB 4-18.
Schematic diagram and operating principle
The block diagram is shown in Fig. 1. Its first stage is assembled on op-amp DA1.1 (DA2.1) and serves as a stereo balance regulator. Using resistor R21, the gain of each channel can be changed within ±4 dB.
The second stage of the block is assembled on op-amp DA1.2 (DA2.2) and is a modification of the active loud-compensated volume control, described in detail in.
The principle of frequency compensation of this regulator in the low-frequency region is based on changing the time constants of the OOS circuits, covering the op-amps C3R5R7.1 and R7.1R9C6 (C15R26R7.2 and R7.2R30C18), when regulating the volume, as well as changing the frequency response of the frequency-dependent divider R5R6C4 (R26R27C16 ) when moving the volume control slider R7.1 (R7.2).
Frequency compensation in the higher frequency region is provided by circuit C5R8 (C17R28), connected in parallel with part of resistor R7.1 (R7.2). In the extreme left (according to the diagram) position of the engine R7.1 (R7.2), the condition C3R5 = C6(R9+R7.1) (C15R26 = C18(R30+R7.2)) is satisfied.
Schematic diagram of a high-quality volume, balance and treble/bass tone control.
Circuit C4R6 (C16R27) is shunted according to the principle of virtual short circuiting of op-amp inputs, and circuit C5R8 (C17R28) is shunted by the corresponding section of resistor R7.1 (R7.2), so the cascade has a unit and frequency-independent (in the audio range) transmission coefficient.
The frequency responses formed by the cascade in the extreme and middle positions of the volume control R7 are shown in Fig. 2 and differ little over the entire control range from the ideal loudness compensation curves constructed on the basis of the Fletcher-Munson equal loudness curves.
The peculiarity of the described volume control is the close to exponential dependence of the transmission coefficient at medium frequencies with a linear functional dependence of the resistance on the angle of rotation of the axis of resistor R7.
This ensures maximum smoothness of control, since turning the axis by the same angle corresponds to equal volume increments. Electronic switches using VT1.1 transistors. and VT1.2 (VT1.3 and VT1.4) allow you to disable loudness compensation.
The op amp DA3.1 (DA3.2) has an active tone control for lower R13.1 (R13.2) and higher R14.1 (R14.2) frequencies. In Fig. Figure 3 shows the frequency response generated by this cascade in different positions of the regulators. As can be seen from the figure, the maximum correction depth is 10 dB, which is quite sufficient for a high-fidelity sound reproduction complex.
At the same time, limiting the depth of correction made it possible to reduce the mismatch in the frequency response and phase response of the right and left channels to levels of no more than 0.2 dB and 3 degrees, respectively, in the frequency range 20...20,000 Hz in any position of the regulators (the same applies to to the volume control), which is important for maintaining a constant position of apparent sound sources with natural stereo sound.
The use of active volume and tone controls made it possible to provide the required dynamic range of the device as a whole using fairly simple means.
To measure harmonic distortion, the first harmonic suppression technique described in . In Fig. Figure 4 shows spectrograms of the signal at the output of the volume and tone control unit when a signal from the generator is applied to its input, the spectrum of which is shown in Fig. 5 (the first harmonic with a frequency of 1 kHz in both spectrograms is suppressed by 60 dB).
The relative level of the largest second harmonic is -108 dB, which corresponds to a nonlinear distortion coefficient for the second harmonic of 0.0004%, and taking into account higher harmonics, the total harmonic distortion coefficient does not exceed 0.001%.
Due to the drop in the loop gain of the op-amp at higher audio frequencies, the level of intermodulation distortion of the device is slightly higher. In Fig. Figure 6 shows spectrograms of the output signal when the sum of two sinusoidal voltages with a frequency of 19 and 20 kHz is applied to the input of the device.
In the spectrogram, the levels of useful components (19 and 20 kHz) are suppressed by 45 dB, the relative level of the intermodulation component of the difference frequency (1 kHz) is equal to -92 dB, which corresponds to an intermodulation distortion coefficient of 0.0025%.
Construction and details
The control unit is powered by voltage stabilizers made on transistors VT2, VTZ and zener diodes VD2, VD3 and connected directly to the buses of the unstabilized power supply UMZCH.
The device uses fixed resistors MJ1T-0.125, dual variable precision wire resistors SP5-21A-2 (R7, R13, R14) and SP5-21B (R21). With slightly worse results, you can use SPZ-30g (R7, R13, R14) and SPZ-30a (R21). In this case, the imbalance between volume and frequency response will not exceed 2 dB. K50-16 are used as oxide capacitors, the others are KM-4, KM-5, KM-6, K73-11.
The values of all permanent resistors and capacitors SZ-C6, C9, C15-C18, C21 should not differ from those indicated on the circuit diagram by more than 5%, capacitors C8, C10, C20, C23 - by more than 10%, the rest - by 20 ...80%.
Replacing the K157UD2 op-amp with others is undesirable due to their good noise properties and high linearity, as well as the ability to operate with a relatively low-impedance load.
Both channels of the device are assembled on a printed circuit board made of fiberglass. The pattern of printed tracks is shown in Fig. 7, a, and the location of the parts is in Fig. 7, 6.
With reduced requirements for the volume imbalance of the frequency response and phase response, the limits of volume and timbre control can be expanded.
So, in order to increase the depth of volume control to 60 dB, you should change the values of four resistors (R6 = R27 = 470 Ohm, R9-R30 = 1 kOhm) and two capacitors (C4 = C16 = 1 μF), and to increase the tone control limits to ±16 dB, you need to reduce the resistance of eight resistors (R15 = R16 = R33 = R34 = 300 Ohm, R12-R17 = R32 = R36 = 2.7 kOhm).
Printed circuit board for high quality volume, balance and tone control.
Setting up
A properly assembled volume and tone control unit does not require adjustment. Printed circuit boards for the tone block are supplied by the Mayak cooperative (see Radio 1990, No. 7, p. 80).
N. SUKHOV. Kyiv, Ukraine.
Literature:
- Sukhov N. UMZCH of high fidelity. - Radio, 1989, No. 6, p. 55—57.
- Sukhov N., Bat S., Kolosov V., Chupakov A. High-quality sound reproduction technology. - Kyiv: Tekhnika, 1985, p. 27, fig. 2.8. 6.
- Newcomb A., Young R. Practical loudness: an active circuit design approach.— Journal of the Audio Engineering Society, 1976, Vol. 24, N I, pp. 32—35, fig. 1.
- Sukhov N., Bvt S., Kolosov V., Chupakov A. High-quality sound reproduction technology. - Kyiv: Tekhnika, 1985, p. 35, fig. 2.17.
- Sukhov N. UMZCH of high fidelity. - Radio, 1989, No. 7, p. 59, fig. 7.
Volume and tone control of a modern stereo complex
The sensitivity of the human ear noticeably depends on frequency, which is clearly visible from the equal loudness curves in Fig. 1.
Fig.1
To ensure high quality reproduction over the entire volume range, it is necessary to compensate for the corresponding differences in hearing sensitivity. Currently, this problem is solved using volume controls that have close to optimal loudness compensation.
Many radio amateurs involved in the design of high-quality equipment know how difficult it is sometimes to find a variable resistor with taps for a thin-compensated volume control.
Meanwhile, there are several ways to use conventional resistors for loudness compensation.
The proposed controller (Fig. 2) is based on the controller described in.
Fig.2
In order to obtain the maximum signal-to-noise ratio at low volumes, the tone block on a low-noise chip is turned on first, and only then the volume control.
Bench frequency f=1 /2-R28C10
The increase in frequency response at frequencies below 100 Hz corresponds to 12 dB/oct., due to the additional action of the circuit R23, C8. Circuit R20C7 helps limit the rise in frequency response at frequencies below 20 Hz. The rise in frequency response at frequencies above f=l/-R-C 8 kHz is limited by resistor R25 at 10 dB.
If you need to sharply reduce the volume ("intimate" effect), switch S2 is provided. At the same time, the effect of tone compensation remains practically unchanged. It is advisable to use the same switch to change the sensitivity of the power level indicator.
Almost all schemes do not compensate for frequencies in the region of 3...4 kHz, which require a rollover of 4 to 8 dB over the entire range of volume changes in a narrow frequency band, as well as frequencies of 12...16 kHz near the limit of audibility, which require a steep rise .
Considering the high level of the other parts of the stereo complex (players, tape recorders, tuners, etc.), i.e. having a flat frequency response throughout the entire audio range, to adjust the tone, as a rule, a two-band tone control is sufficient.
The development is based on the circuit of the Arcturus-001 amplifier. In addition to adjusting the tone, the regulator amplifies the signal three times. This solution made it possible to abandon the normalizing amplifier.
In order to eliminate the above-mentioned shortcomings of the thin-compensated volume control, a third tone control was introduced at a frequency of 3.5 kHz, with which you can obtain the effect of “presence” by setting the desired increase in the frequency response, as well as more complete compensation by attenuating the signal by 4 - 5 dB. For the same purpose, an inductance was introduced into the HF regulator, which contributes to a steeper increase in the frequency response at a resonance frequency of about 15 kHz.
Considering the difficulties with ferrite rings (their shortage and the complexity of winding), the inductance of the mid-frequency regulator is made using a transistor equivalent - a gyrator. The operation of such a gyrator is described in detail in.
The regulators are powered from a bipolar stabilized source with a voltage of +15V through RC filters 100 Ohm, 100 µF (not shown in the diagram).
The equalizer can be used as an inertia-free noise suppressor in the tape recorder path, producing recording with a midrange increase of about 5 - 6 dB and, accordingly, playback with the same blockage. At the same time, the noise reduction will be approximately the same 5 - 6 dB.
The midrange resonance frequency is calculated using the formula
Fo=1/2-(R6R10C3C4)1/2,
where resistors are in kOhm, capacitors are in µF, frequency is in kHz.
Substituting the denominations in the formula we get:
The quality factor of the resonant circuit is two. With C4 equal to 2700 pF, the resonance frequency is 3.5 kHz.
All five variable resistors are used type SPZ-33-23P group A, which are soldered directly into the boards. The volume control is made on a separate board. All electrolytic capacitors are Tala K50-35, the rest are K73-17 or KM-56. Fixed resistors type C2-23 or MLT with a power of 0.125 W. The inductor is wound on a 2000NM K18x5x5mm ring and contains 100 turns of PEL-1 0.27 wire. Instead of an equivalent inductance (elements R6, RIO, R11, C4, VT1) between points A and B, you can turn on an inductance of 60 MGn, 250 turns of PEL-1 0.18 wire on the same ring. In this case, capacitor C3 with a capacity of 0.01 μF must be replaced with 0.033 μF.
In the absence of rings, inductance L1 can be completely eliminated, while the rise in the HF components of the signal will be in a wider frequency band.
Literature:
- M. Sapozhkov. "Electroacoustics", M, 1978.
- A.S. No. 1185573 publ-126-86 p.9
- S. Fedichkin. "Loud-compensated volume control" "Radio" No. 9/84 p.43,44
- N. Sukhov and others. “High-quality sound reproduction technology.” Kyiv. Technique. 1985 p.27.
- A. Vorontsov, V. Voronov. "Arcturus-001-stereo." Radio No. 1 /77, pp. 34 - 37
- L. Stasenko. "Multiband with analogues of LC filters" "Radio" No. 10/79 pp. 26 - 27
- N. Sukhov. "Inertia-free noise suppressor." "Radio" No. 2/83, p. 50.
High quality volume, balance and tone control on the LM1036N.
To give the sound the necessary coloring, various tone blocks are installed in the sound-reproducing equipment, capable of separately and smoothly changing the adjustment of high and low frequencies. These regulators are divided into passive (which do not amplify the input signal level) and active (in which the input signal is amplified).
We will now look at one option for a high-quality active tone block with the ability to adjust the volume and sound balance in high-end bass amplifiers.
The circuit is implemented on an integrated circuit LM1036N. It is produced by National Semiconductors, the price is not high. Dual variable resistors mounted on a printed circuit board are used as regulators. This allows you to securely hold the structure in the amplifier housing without the use of additional fasteners. The module has a mode for enabling/disabling loudness compensation. The schematic diagram of the device is shown in the figure below.
Device characteristics:
Frequency range, Hz................................................... ............20.....20000
Signal-to-noise ratio, dB.................................................... ...................80
Channel separation, dB................................................... ............... ....75
K harmonics at Uin 0.3V at a frequency of 1 kHz, %...................................0.06
Rin, kOhm................................................... ..........................................thirty
Rout, kOhm................................................... .......................................20
Volume control range, dB...................................................75
Tone control range at frequencies 40Hz and 16 kHz, dB......... +-15
The regulator board is made of one-sided foil fiberglass. The view from the conductors side is shown in the following figure.
There is nothing special to describe here; after assembly, you do not need to make any adjustments; a correctly assembled circuit starts working immediately. This control option is perfect for working with the low-frequency amplifier on the TDA7294.
This section contains materials on audio frequency power amplifiers (APPA), preamplifiers, tone controls (active and passive), input switches, microphone amplifiers, protection systems for sound reproduction equipment, including speakers, and other blocks of the sound reproduction path, digital or analog.
An updated file archive on the topic "Amplifiers and AF filters" is located .
An article devoted to the design and calculation of crossovers on lamps, including 1st and 2nd order filters. It is proposed to calculate crossovers and other elements of lamp circuits in the TUBE CAD program, available for download.
Monophonic, active speaker with bi-ampling “For the Dacha”.
Brief introduction.
The goal of the project was to create an acoustic unit that reproduces music from third-party sources (mobile phones, players, etc.). Taking into account the fact that there is no listening position “in the field” that provides a stereo effect, it was decided to make a monophonic device.
The following were accepted as aggravating circumstances:
- Two-way, active system with a bridge amplifier in the low-frequency channel (to increase efficiency)
- Phase-inverted design (also to increase efficiency)
- The use of consumer goods, high-quality speakers
- Electronic correction of the frequency response of a high-quality woofer in a given acoustic design (FI)
- Unipolar power supply,
- Widespread UMZCH ICs (TDA2005 for LF and K174UN14 for MF-HF)
- Active tone control,
- Loud volume control
- Overload indicator of any UMZCH
- Active limiter for overload of any UMZCH.
- Forced cooling of power supply and UMZCH radiators, with proportional control
- Elimination of a current loop when powering a sound source from an AC power supply.
- On-board telescopic antenna, for connecting a source with a built-in radio receiver, a short cable.
During the execution of the project, some developed and prototyped circuit solutions were excluded from the final design, in order to avoid further complication.
Cropping was applied to:
- active 2-channel crossover on 4 op-amps (see Fig.1), containing a 4th order low-pass filter, a phase inverter (all-pass filter) and a signal combiner to isolate the mid-high frequency components of the signal (replaced by passive RC filters).
(click to enlarge)
- shaper OOSN+POST for bridge UMZCH LF channel on 4x op-amp (see Fig.2)- replaced by a degenerate Linkwitz corrector - not a full T-bridge - 2 resistors and 2 capacitors. ()
(click to enlarge)
AC box – bass reflex, calculated using the program and configured using the program
Case material – chipboard 16mm. The inside is padding polyester, in two layers, secured with a furniture stapler; the outside is linoleum, glued to liquid nails, smeared with a thin layer. Protective metal, galvanized mesh with a transparency coefficient of 62.5%.
The bass reflex port is located at the bottom, on the rear wall. The back wall at the border of the port is beveled, widening towards the exit of the port; a wooden corner covered with a ribbed (like corduroy) carpet () is glued into the joint of the back wall of the FI tunnel and the bottom wall of the AC. Strips of the same carpet, 5 mm wide, are glued along the wide walls of the FI, in a checkerboard pattern, with a step of 3 cm. All these measures are aimed at suppressing overtones in the FI tunnel.
The interface between LF and MF-HF is approx. 500Hz.
The woofer is some kind of rootless midbass, with a power of 30 W.
MF-HF – car broadband with Panasonic EAB-43
The bass reflex is tuned to the resonance frequency of the woofer.
The overall frequency response of the speaker turned out to be quite linear. It is limited from above by the input low-pass filter of the second order with a cutoff frequency, at the level of –3 dB – 14.3 KHz, and from below, along the front, by the bass reflex setting – 100 Hz. The sound pressure drop from the bass reflex port begins at a frequency of 40 Hz, which is a very good indicator for a woofer, which is obviously a “midbass” speaker, IMHO.
At the entrance (see Fig. 1) adder - limiter on an op-amp with an OEP-2 optocoupler in the OOS, at the input of the op-amp - RC high-pass filter with a cutoff at a frequency of 48 Hz.
Then a Chebyshev low-pass filter with a cut-off level of –3 dB at a frequency of 14.3 KHz to suppress supra-tonal components from the DAC output of cheap gadgets.
Switchable, loud-compensated volume control “according to Sukhov” (see Radio No. 4 1980 p. 38, Radio No. 10 1990 p. 59,
Active tone control on one op amp ( ) , tuned with an eye to the frequency response of the selected speakers installed in the speakers. The tone control only increases the frequency response of the speakers at low frequencies and high frequencies. The magnitude of the rise does not exceed 10 dB.
Separation filters:
in the MF-HF channel of the second order, passive, 800Hz and 723Hz.
in the second-order LF channel – active, 482Hz.
Suppression of resonant overshoot of the woofer - passive, not full, T-bridge with attenuation of -6 dB at the resonance frequency of the selected speaker (80 Hz)
A total of three housings of double op-amps KR140UD20 were used.
The telescopic antenna allows you to connect a sound source containing a radio receiver with a short wire. To operate this external antenna, the common contact of the audio signal input socket is isolated from the common speaker wire via an RF choke with an inductance of 100 μH.
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Amplifiers for portable equipment.
Amplifiers for car audio systems.
Amplifiers for stationary Hi-Fi equipment and televisions.
Typical switching circuits for the UM IS and the characteristics of the UM IS are given.
Audio DAC and ADC
Audio codecs
Signal processors for various purposes.
Introduction ..................................................... ........................................................ ...................................3
Contents......................................................... ........................................................ .........................................5
1. Reference designs .................................................... ........................................................ ........................7
2. Focus products ................................................... ........................................................ ............................13
2.1 Tuners. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
TEF6862HL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
TEF690x. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
TEF6730. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
2.2 Analog Signal Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
TEF6890H,TEF6892H + TEF6894H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
2.3 Digital Signal Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
SAA7706H. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
SAA7709H. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
SAF7730HV. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
2.4 Audio amplifiers and voltage regulators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
2.4.1 Integrated Power Amplifier and Stabilizer (IPAS) TDA8588AJ/BJ/J,TDA8589AJ/BJ. . . . . . . . . . .32
2.4.2 Stand-alone audio power amplifiers - Quad amplifiers TDA8569Q and TDA8571J. . . . . . . . . . . .34
TDA8592J/Q,TDA8593J/Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Dual amplifiers TDA8560/1/3/6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
Dual amplifier TDA1566TH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
Single amplifiers TDA1560Q and TDA1562Q class H power amplifiers. . . . . . . . . . . . . . . . . . . . . . . .40
TDA1564/TDA1565 run-cool stereo power amplifier. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
2.4.3. Multi-output voltage regulators TDA3681J/TH,TDA3682ST,TDA3683J. . . . . . . . . . . . . . . . . . .42
TDA3601/8 and TDA3615/8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
2.5 HD Radio™ processor solutions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45
SAF3550. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46
2.6 Storage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47
SAA7326 (CD10 II) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48
TZA1026 (CD10 II) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50
SAA7826. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
SAA7806. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53
SAA7836. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54
SAA7818. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56
TZA1038HW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58
3.Additional products. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
4.Packages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68
A large selection of materials (as of January 2013 - 74 pages) on preamplifiers and filters, mainly for subwoofers and multi-band active sound reproduction systems. Among other things, phase-linear crossovers for bi-ampling and “tri-ampling” are considered - for discerning connoisseurs of multi-channel AAS. Attention is paid to the so-called “all pass filter”, which transmits, without attenuation, frequencies throughout the entire input range (adjusted for the speed of the amplifier and passive components), but shifts the phase of the signal. Such filters are used to equalize the group delay time in phase-linear crossovers. A detailed copy of the Active Filters by Linkwitz topic was made from the Linkwitz website. The author examines the theory and practice of constructing multi-band active speaker filters, with an analysis of each component link, showing graphs of the frequency response/phase response and calculation formulas. Also, for those who like to independently develop active crossovers and other filters, brief educational materials on low-pass and high-pass filters are provided at transistors and op-amps.
A selection of materials (as of January 2013 – 40 pages) on active and passive tone controls. If, in the current times of digital sound, you want to make a tone control for your amplifier, or go through (reconfigure) an existing one, it is important to remember that for the sake of low dynamic distortion and other sound degradation, you should not make a control with a tone control range of more than 6 dB. Levels of +15 or +20 dB are a thing of the past with magnetic tape. In addition, attenuation of the LF or HF level is also unlikely to be required. Please pay attention to the diagrams of active tone controls on transistors. If you are sensitive to the presence of capacitors in the sound path, active transistor tone controls can be a good alternative to active op-amp controls, especially considering that class A in their output stages is a rare rarity.
There can be a long debate about the benefits/harms of RT. Everything here is individual, and everyone decides for themselves. It is important to consider the following:
For HF side:
Up to how many KHz can you hear audio signals?
Up to how many KHz can your speaker reproduce high frequencies without attenuating the level?
Up to how many KHz can your HF sound source reproduce without attenuation?
For the low frequency side:
Do you have a Subwoofer in your system?
What is the quality factor and resonance frequency of the woofer head in your speaker?
What is the acoustic design of a low-frequency speaker, how does it affect the reproduction of low-frequency components?
If you have an external spectrum analyzer for a musical signal (I have one, according to the scheme of S. Biryukov and V. Frolov -), look at what kind of music you listen to - what is there with the low-frequency and high-frequency components. Maybe, indeed, a tone control is not needed, especially if you have a speaker with one broadband speaker, for example 2GD-40, which reproduces HF above 12.5 KHz mediocrely, and at LF its parameters promise a fair amount of booming in the region of 100 Hz - such a speaker straining with an increased signal level that it cannot reproduce will only worsen the sound.
If you use a measuring microphone and the appropriate software, you can try to take the frequency response at the listening point, from the left and right ears, at head level, and then try to adjust the levels with a multi-band tone control (equalizer). Proponents of “pure sound” and “short path” will most likely reject this approach, like many others who listen to music without fixing their head in a listening chair - after all, a displacement of several tens of centimeters will already change the local frequency response and phase response. :-)
Just don’t forget to put a voltage follower in front of the RT, and load the RT onto the high-impedance input of the next amplifier stage. Examples of pre-amplifier circuits, with tone controls, where you can implant a circuit designed independently, can be found in the article “AF Pre-amplifiers” in the collection. Pages 72 - 91
A selection of materials on the topic. Biampling is the name given to two-way reproduction of an audio signal (music). The division into stripes may be more or less complete. Less complete - when there is only one amplifier, and there are a pair of speakers and filters for them (passive). More complete separation is when the input signal enters a filter bank that separates the signal at a certain point (at the cutoff frequency), selected with an eye to the characteristics of the speakers used. Next, the signal goes to two amplifiers, the power of which is determined by the crossover frequency and the sensitivity of the speaker. Next, the speakers themselves. Each player reproduces a band specially prepared for him, with optimal power. The speaker responsible for the low-frequency portion of the range is not overloaded with high-frequency components, and vice versa. In addition, you can include in the low-frequency channel to eliminate the “mumbling” of some high-quality speakers, or, which is a little more complicated but more effective, a unit for forming a negative output impedance. Details about biampling are in the link in the title.
These are the so-called “white pages” - instructions for designing UMZCH on an IC.
1.0 Introduction ................................................ ........................................................ ........................................... 2
2.0 Objective............................................. ........................................................ ........................................... 2
3.0 Conclusion ................................................ ........................................................ ........................................... 2
4.0 Thermal Background ................................................... ........................................................ ........................... 2
4.1 TYPICAL CHARACTERISTIC DATA .................................................... ........................................................ ... 3
4.2 SINGLE-ENDED AMPLIFIER Pdmax EQUATION: .................................................... ................................... 3
4.3 BRIDGED-OUTPUT AMPLIFIER Pdmax EQUATION .................................................... ........................... 3
4.4 PARALLEL AMPLIFIER Pdmax EQUATION .................................................... .......................................... 4
4.5 BRIDGED/PARALLEL AMPLIFIER Pdmax EQUATION ............................................... ........................... 4
4.6 THERMAL CONCLUSION ............................................... ........................................................ .................. 4
4.7 THERMAL TESTING CONDITIONS .................................................... ........................................................ .... 5
5.0 BR100-100W Bridge Circuit ............................................ ........................................................ .................. 5
5.1 AUDIO TESTING ............................................... ........................................................ ............................... 5
5.1.1 Linearity Tests .................................................... ........................................................ ................................ 5
5.2 SCHEMATICS ................................................... ........................................................ ................................... 6
5.2.1 Bridged Amplifier Schematic .................................................... ........................................................ ............ 6
5.2.2 Electrical Design Notes ................................................. ........................................................ .................... 6
6.0 PA100-100W Parallel Circuit ............................................ ........................................................ ................. 7
6.1 AUDIO TESTING ............................................... ........................................................ ........................... 7
6.1.1 Linearity Test .................................................... ........................................................ ................................... 7
6.2 SCHEMATICS ................................................... ........................................................ ................................... 8
6.2.1 Parallel Amplifier Schematic ............................................... ........................................................ ............. 8
6.2.2 Electrical Design Notes .................................................... ........................................................ .................... 8
7.0 BPA200–200W Bridged/Parallel Circuit ............................................... ........................................................ ..... 9
7.1 AUDIO TESTING ............................................... ........................................................ ............................... 9
7.1.1 Linearity Tests .................................................. ........................................................ ................................ 9
7.1.2 Output Power Tests ............................................ ........................................................ .......................... 9
7.1.3 Noise Floor Tests ................................................. ........................................................ ........................... 10
7.1.4 Electrical Design Notes ................................................. ........................................................ .................. eleven
7.2 SCHEMATICS ................................................... ........................................................ ................................. 12
7.2.1 Detailed Bridged/Parallel Amplifier Schematic ............................................... .................................... 12
7.2.2 Servo Circuits .................................................... ........................................................ ................................ 13
7.2.3 Power Supply Circuit ................................................... ........................................................ ...................... 14
7.2.4 Basic Bridged/Parallel Amplifier Schematic .................................................... ........................................ 15
8.0 Parts List and Vendors .................................................... ........................................................ .......................... 16
8.1 BUILD OF MATERIALS FOR BR100 AMPLIFIER ............................................... ................................. 16
8.2 BUILD OF MATERIALS FOR PA100 AMPLIFIER ............................................... .................................. 16
8.3 BUILD OF MATERIALS FOR BPA200 AMPLIFIER ............................................... ............................... 18
9.0 Heat Sink Drawings .................................................. ........................................................ .............................. 19
9.1 BR100 AND PA100 HEAT SINK DRAWING ............................................... .......................................... 19
9.2 BPA200 HEAT SINK DRAWING ................................................. ........................................................ ......... 20
One of the ways to limit the distortion of the audio signal that occurs when the UMZCH is overloaded (power limitation) is to smoothly limit the level of the INPUT signal as the output signal level approaches the limitation zone. This is done, as a rule, using a resistive-optocoupler voltage divider controlled by a circuit that controls the level of the output signal. This type of limiter is called a limiter. Below the link is a small selection of diagrams and technological solutions on the topic.
Class D amplifiers are characterized by the highest (more than 90%) efficiency compared to other classes. In such an amplifier, from the input and additional sawtooth signals, an output pulse-width (PWM) signal of high frequency is formed, with an amplitude reaching the voltage on the power buses. Conversely, this PWM signal is converted into analog form by integration on the inductor and then to the speaker. The lower the frequency of the signal, the higher the accuracy of reproducing its analog value from the PWM sequence. Therefore, a subwoofer is the best place for such a PA. There are attempts to make a full (broadband) amplifier in class D, but many experts in the field of sound are very critical of the quality of the signal at the output of such PAs.
A selection of articles dedicated to obtaining, if possible, the highest quality sound from archaic, despised by audiophiles, type ICs , , , , . A very competent design approach has been applied, allowing impressive results to be achieved with small means.
Please note that in one of the PA circuits, a limiter is used, already mentioned here.
We continue the topic of competent use of simple, easily accessible ICs. Here are examples of what can be done using such a well-deserved IP as the TDA2030.
A simple and, in its own way, beautiful UMZCH, assembled on three available ICs. Input selector – , volume and tone control – , power amplifier – bridged. In the amplifier, using internal means of the ICs used, a limiter is implemented that reduces signal distortion in areas of power limitation. This is done very simply - from the output of the TDA1555Q distortion detector, the signal is fed into the electronic volume control circuit of the TDA 1524 IC. When distortion occurs, the signal from pin 15 of the TDA1555Q PA IC is transmitted to the BC TDA1524 electronic volume control, which leads to a decrease in the level of the IC input signal The PA, thereby the growth of distortion (signal limitation), slows down significantly. The article also describes approaches to assessing the quality of the assembled PA and its components.
On my own behalf, I will add that in modern times, it is better to replace one TDA1555Q PA IC with two (if we want to use bridge connection, which has a number of advantages mentioned in the article) PA IC. The main difference is that the old IC operates in class B, with virtually no quiescent current of the output transistors, which introduces a certain amount of “step” distortion, while the proposed replacement operates in class AB, which gives at least a twofold gain in the coefficient harmonics At the same time, both microcircuits use complementary pairs of transistors in the output stages, which is a serious advantage. Also, both microcircuits have a distortion detector output, which makes it possible to implement the limiter function in the UMZCH on an updated element base.
Further development of the topic of multi-channel UMZCH with a limiter, based on the above-mentioned article by N. Sukhov about “Full UMZCH on three chips,” led to the discovery of an interesting family of UMZCH ICs with a diagnostic function - an extended version of the clipping detector. , – all these microcircuits have 4 UMZCH channels with complementary pairs of transistors in the output stage operating in class AB. Two amplifiers are inverting, two are non-inverting. The pinout is basically the same, the diagnostic output is a cascade with an open collector at pin No. 10. Using the ICs of this group, you can assemble bridge UMZCH or UMZCH 2+1, where the low-frequency channel is assembled using a bridge circuit, and the mid-HF sections have piece amplifiers.
A very wise article that explains in detail what sounds and in what combinations the human ear hears, or, conversely, does not hear. And this analysis is carried out in relation to the sounds reproduced by the pair UM+AS. After reading it, it becomes clear why the sound of tube PAs is so attractive, given their mediocre, to put it mildly, characteristics, and how PAs based on modern semiconductors pump up the audio output signal with components that are not present in the input signal. We can say that this article anticipated the direction of creating “High Fidelity UMZCH” - amplifiers designed for organoleptic detection of distortions in audio signal sources. For this loyalty, the entire UMZCH BB class, regardless of the names of the developers, became hated by audiophiles who suddenly discovered the inferiority of their vinyl or CD players.
The author used more modern, high-voltage transistors with increased performance and adjusted the circuit to optimize (increase stability) the operation of the slowest output stage. The article also contains Sukhov’s answers to questions from readers who decided to repeat this famous UM. Particular attention is paid to computer modeling of the described and other UMZCHs - as a means of analytical control of the characteristics of the device being developed or intended for repetition.
Perhaps, when choosing microcircuits for amplifiers, their connection circuits and assessing the quality of amplifiers (any), in general, the long-forgotten method of vector distortion indication, actively promoted in the 70s - 80s by I. Akulinichev, and now no longer used by anyone for the sake of computer programs that diagnose the amplifier through the sound card.
Akulinichev attenuated the output signal of the amplifier to the level of the input signal, and added them in antiphase on the vertical and horizontal deflection plates of the oscilloscope. All interference and distortion became visible “by eye”, without clouding by digital-to-analog converters. The “ideal” amplifier produced an elliptical loop, which, by adjusting the phase shift in the measuring attachment, could be folded into a segment. All the “steps”, ringing, nonlinearities, limitations, emerged on this loop in the form of intricate waves, squiggles and antinodes. At the same time, the magnitude of these squiggles vertically is proportional to the amount of distortion as a percentage. This is an excerpt from my post on one of the specialized amateur radio forums. Below are details and measurement techniques, a description of some practical experiments, as well as lists of references (twice) on the issues of vector analysis of UMZCH distortions.
Additionally, copies of Akulinichev’s articles have been added, according to his vector indicators of distortion, measurement results of Kni UMZCH on TDA2005 in INVERTING inclusion,
as well as the results of testing a large group of domestically produced op amps from Soviet times with a unipolar power supply of 5 - 15 V, at Ku = 10 this can be considered a kind of stress test of the op amp for applicability in sound reproducing equipment. A folder with photographs of oscillograms of op-amp testing results is located. Details on the experiments performed, a description of the test setup - the Akulinichev vector distortion indicator, and its modifications - are in the above-mentioned.
Addition.
Continuing the topic of practical application of a vector distortion indicator, I would like to present the results of two more experiments. We studied a PA IC containing two inverting and two non-inverting class AB power amplifiers, with separate inputs and outputs. This IC can be used to build a two-channel bridge UMZCH, UMZCH type 2.1, with a bridge LF channel, or simply as a four-channel power amplifier. An important feature of this IC, and a number of other UM ICs of the TDA73xx series, is the presence of the so-called “diagnostic output” or “clip detector” or “distortion detector”. An NPN transistor is connected to this pin, an open collector, which opens if the voltage at the output of any of the channels reaches the high or low limit, or the IC crystal heats up above the permissible value. The same device (4 independent channels plus diagnostic output) is available in the TDA155x series UM ICs, including the one on which Nikolay Sukhov made his “Full UMZCH on three microcircuits” . But there is a nuance - the older TDA1555Q chip operates in class B, has an order of magnitude higher level of distortion and, surprisingly, costs more (in St. Petersburg) than the TDA7377 under consideration.
This is what happened as a result of testing the TDA7377 UMZCH IC using Akulinichev’s vector distortion indicator:
TDA7377 Inverting channel
Please note that the measurements were carried out at a frequency of 30 kHz.
A little later, I tested the same TDA7377 IC in a “computer” way, using the mentioned program. Here are the results of a spectral analysis of the distortion introduced by the TDA7377 when operating at a frequency of 100 Hz. (When measuring at 1000 Hz, the measured distortion level is even lower; a significant part of the operating range is excluded from consideration.)
TDA7377 Non-inverting channel
TDA7377 Inverting channel
It can be noted that the spectral analysis of the distortion composition for this instance of TDA7377 also shows some (one hundredth :-)) advantage of the non-inverting channel, which may confirm the admissibility of assessing the quality of the UMZCH using Akulinichev’s distortion signal selection method.
ARTA Sofrware and spectral analysis of distortions of simple UMZCH ICs.
Having mentioned the spectral analysis of the distortion composition carried out for the TDA7377 IC, I also want to talk about other measurement results obtained “by chance” for the TDA20xx series ICs, which at that time turned out to be functional UMZCH prototypes suitable for experiments. Almost no comments. “Find ten differences,” as they say.
K174UN14, Inverting switching, 1KHz
This is a very brief summary of a fifty-nine-page topic on Vegalava, dedicated to schemes and concepts for protecting PAs and ACs from damage in emergency situations. Links are provided to the pages from which the most interesting, in my opinion, diagrams were taken. Questions about the protection scheme that interests you can also be asked here, through the feedback button.
