This article introduces a set of self-made high-performance low-cost AV combination suitable for middle school students' electronic hobbies, which will improve the listening experience of the living room with a family area of ​​more than ten square to dozens of squares.
Figure 1 is a schematic diagram of the AV combination. The signal switch, four-way surround sound processing circuit is the main signal and the surround and center signal output of UPC1892 of Japan NEC Company, and the high and low tones, volume, parallel left and right channels, surround Effect control and selection of three sound field effect modes; the front is handled by 3D sound field effect processing, the processed signal is linearly amplified by NE5532 to drive the power amplifier, and the final stage is powered by 2 blocks of TDA1514A and TDA1521. (Amplifier can also be used LM1875, LM4766, LM3886, TDA7294, etc.)
NE5532 application enthusiasts are already proficient, and need not be described here.
UPC1892 is a four-channel surround sound processing circuit with excellent performance introduced by Japanese NEC company in 1995. The circuit uses a matrix-type phase-shifting surround sound processing system, which can separate two-channel signals and mono signals into two main channels. The signal and a surround channel signal, a center channel signal (the author actually found that one of the two sub channels of UPC1892 is the center signal). The circuit is equipped with a concert hall, movie theater and analog stereo and stereo pass-through sound field effect mode. The circuit is equipped with surround sound effect control, main power amplifier balance, high and low bass and volume control. Each part of the control uses DC level control to reduce the noise of the circuit to a very low limit. UPC1892 is equipped with amplifier, low-pass filtering, mode control, phase shift, effect processing, compensation absorption, tone, volume, balance and other circuits. It is a large-scale integrated circuit. The application circuit is shown in Figure 3. The typical operating voltage is + 12V, and the control part is + 5V. The sound mode control is controlled by the high and low level programming of pins 7 and 8 of UPC1892. The functions of each potentiometer are as follows: RP1 is the surround back channel effect control, RP2 is the front left and right channel balance control, RP3 is the front left and right channel volume control, RP4 is the front center channel volume control, RP5 and RP6 are respectively Low and high tone control of the front left and right channels. The function of toggling K1K2 is: K1 high level, K2 low level are concert hall mode, K1 low level, K2 high level are cinema mode, K1K2 high level is analog stereo mode, K1K2 low level is Stereo pass-through state.
Because the spatial sense information of the front channel of UPC1892 is not strong, 3D sound field effect processing is used to perform three-dimensional optimization and enhancement processing of the spatial sense information of the front channel. This clever combination enables the listener to realize that the listening position is no longer affected. The limitation, and the sense of space of the music is very strong, and at the same time it solves the shortcomings of the lack of rear sound field for the 3D sound field effect processing. The sound field created is very wide, the scene feels excellent, and even the presence of the speaker system is not felt. The production drawing of 3D sound field effect processing is shown in Figure 4. For the detailed principle, please refer to the article on page 5 of the fifth issue of this magazine in May 1998. For audiophiles with power amplifiers, UPC1892 and 3D sound field effect processing can be added to make the amplifier an AV fever combination.
If the AV system needs more shock, it can also increase the subwoofer output: use the NE5534 and other single op amps as low-pass filters and add subwoofer power amplifier circuits and subwoofer speakers. (M51134P is best for super bass processing)
This AV combination front channel uses Philips' TDA1514A power amplifier circuit specially designed for digital audio. Generally, households with dozens of square meters have the best audio equipment with a "golden power" of about 30W. TDA1514A output power POut = 50W (THD-0.08%): VP = ± 27.5V; conversion rate: 15V / μs, signal-to-noise ratio 85dB, ripple suppression: 75dB, TDA1514A circuit is equipped with waiting, noise suppression state, with overheat protection , Short circuit protection, power tube safe working area protection and electrostatic discharge protection. Low offset voltage, high ripple suppression, and extremely low thermal resistance. The application circuit is shown in Figure 5. The characteristics of this circuit: the use of constant current negative feedback and a DC servo system. A linear element resistance RA (0.5Ω2W) is used to feed back the current flowing through the speaker voice coil to the power amplifier input, so that the amplifier drives the load in a fixed current mode, and the speaker oscillates under the control of the current. The characteristic is that when the playback frequency reaches the low frequency and near the resonance peak, the constant current circuit enhances the strength of the bass and the resolution of the treble, so that the playback sound of the entire system sounds full, thick and clear, and has the charm of a tube amplifier .
The DC servo circuit is mainly used to accurately correct the DC potential drift of the output terminal of the TDA1514A circuit after canceling the negative feedback DC blocking capacitor.
The center and surround channels use the high-fidelity amplifier produced by Philips to integrate the TDA1521 as a 15W × 2 power amplifier circuit. It is simple to manufacture and only requires a few peripheral components (see Figure 6). Both speakers of the surround channel are connected in parallel It can be output in the surround channel of TDA1521.
The biggest advantage of using integrated amplifiers is that the stereo balance is good, and the consistency of large quantities is fully guaranteed, which is far superior to discrete component amplifiers in terms of reliability and cost performance. As for the selection of Yuanzuo, it must be high-quality: the resistors use five-color ring metal film resistors, the capacitors should use advanced capacitors and CBB polypropylene non-inductive capacitors, and the integrated circuits should use genuine ones.
Power supply part: In order to effectively improve the transient characteristics and high frequency characteristics of the whole machine, the front and rear power supplies must be powered separately. Practice has proved that the power supply characteristics of the pre-stage circuit have an important impact on the playback characteristics of the whole machine, so the pre-stage NE5532 should use an active servo circuit. Amplifier-level rectifier filter power board and speaker protection board, etc., can be self-made, I believe the majority of audiophiles are already proficient, needless to say.
In terms of assembly, there are currently power amplifier cases on the market, which can also be obtained by mail order. Depending on the chassis, there are different solutions. You can listen to it after the assembly is completed and the inspection is correct. During the audition, MS381 is placed in the spatial sound processing state, UPC1892 is placed in the concert hall, movie theater, or analog mode (depending on the need), and the mono signal (such as video, bilingual selection of feature films) is used in the analog stereo mode.
After assembling, the author piloted the movie "Broken Arrow Action". This film belongs to the kind of thrilling plot and grand scene. It is a good disc using the new Dolby AC-3 all-digital method. The author switched the working mode of UPC1892 to the cinema mode. The feeling during the viewing process was not a personal experience nor an indescribable feeling. When the helicopter propeller propelled across the ground when the helicopter crashed and exploded in the disc, the sound swept straight to the front. It was shocking ... the roar of the plane from far to near, the roar flying over the head, the sound effect was very realistic ... The minutes of the fight between Willis Hill and Spade Jian on the train compartment a few minutes after Di Jian opened the nuclear bomb After the train collided, it caused an explosion of oil surge ... The sound image positioning is accurate, which makes the scene feel full during the viewing process. The thrilling scene and explosion sound are very impactful and shocking!
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