The design guideline of the sound of Phoenix AV-999 is to have the main functions of the home theater amplifier under the premise of satisfying high fidelity, including Dolby digital 5.1 channel input, 5 × 120W (8Ω, RMS) power output and subwoofer line output , Dolby professional logic surround sound, karaoke, etc.
First, the power amplifier circuit
The schematic diagram of the AV-999 principle box is shown in Figure 1. Five 120W power amplifier circuits (as shown in Figure 2) are independent of each other. Both pre-amplifier and post-amplifier adopt up-down symmetric push-pull amplifier circuit. This is a mature circuit that Phoenix Voice has long adopted and can be seen in many pure music amplification systems.
One of the distinguishing features of this machine is the use of the newly developed SAP15N / SAP15P composite counter tube developed by Sanken Japan. The tube (see Figure 3) uses the latest invention of TRAITR (high speed thermal reaction type semiconductor), which is equipped with a temperature test correction circuit that can stabilize the power triode operation. The tube encapsulates the drive tube and the final power tube. The emitter resistance of the final tube and the temperature compensation diode for the bias current are packaged in 2GR and have 5 pins. In the past, the method of stabilizing the high-power tube was to connect the compensation tube next to the power tube. In this way, the compensation tube requires a certain time in terms of temperature balance and speed. Therefore, the music signal must be evenly amplified after the temperature is sufficient, or even Overcompensation is caused, that is, the higher the temperature, the smaller the bias current, which will produce zero-crossing distortion for Class A and Class B amplification. This machine avoids this kind of disadvantage after adopting SAP15N / SAP15P composite alignment. After adopting this pair of tubes, the consistency of line performance indicators is better, the performance is more stable, the sound quality is good, and the positioning is accurate. The distortion is also very small at low volume, and it increases the penetration of the sound. The main parameters of the tube are I = 15A, Pc = 150W. One pair per channel, equivalent to four triodes per channel, can provide a powerful power output.
Another feature of the AV-999 amplifier circuit is the application of pre-stage voltage negative feedback. We know that the setting of negative feedback has a great influence on the performance of the power amplifier. Generally, the negative feedback of the power amplifier circuit is taken from the output (see Figure 4a). The distortion generated by the current amplification stage depends on the large-loop negative feedback to improve. This feedback method often makes the power amplifier objectively improve the distortion index, and the subjective listening It is not satisfactory. The distortion generated by the last stage is input to the previous stage through negative feedback, and then compensated and adjusted after the previous stage is amplified. This compensation and adjustment must be lagging, which will inevitably reduce the transient response speed of the system and easily induce transient intermodulation Distortion and distortion and phase shift of high-frequency signals, which appear as a rigid "transistor sound" in the sense of hearing. In addition, the back electromotive force generated by the speaker and the radio frequency interference noise induced by the speaker line are also fed into the pre-stage through the feedback network to induce transient intermodulation distortion, which pollutes the input signal and affects the sound quality.
In order to avoid the above shortcomings, the sound of Phoenix AV-999, like the flagship music prince and music princess, uses pre-stage voltage feedback and uses capacitors to isolate the pre-stage and the final stage, as shown in Figure 4b. Because this capacitor is located on the signal channel, in order to ensure pure sound quality, metalized polypropylene capacitors are used. In this way, the final stage becomes a 0dB post-amplifier without negative feedback. Therefore, the preamplification of this unit is taken as a high gain amplifier.
The third characteristic of AV-999 is that the circuit design adopts the principle of simplicity and supremacy. Because semiconductors and other devices are non-linear, the more they are used in a linear circuit, the more additional distortion, and the more complicated the processing. But simplifying the circuit brings other problems. For example, the selection of the matching tube is extremely strict, and other components also need to be very sophisticated. The influence of coupling capacitors on sound quality cannot be ignored, and different capacitors will have different timbre. In this regard, the manufacturer was finalized after many trials and auditions.
2. Dolby Professional Logic and Karaoke System
AV-999's Dolby professional logic decoding system uses M69032P or JRC2177 integrated circuits certified by Dolby Laboratories. The integrated circuit contains all the necessary functions of Dolby surround sound system (such as input automatic balance control circuit, adaptive matrix decoding circuit, working mode and center channel mode control circuit, 7kHz low-pass filter, modified Than noise reduction circuit and test noise generator circuit, etc.). After decoding, it is a 5-channel amplified 5 × 120W (8Ω, RMS) power output and subwoofer signal output (the connected subwoofer speakers need to bring their own power amplifiers, so-called active subwoofer speakers or external power amplifiers).
The AV-999 karaoke system is the same as that of the company's Phoenix Voice OK-110 karaoke audio-visual pre-stage. The AV-999 karaoke system uses discrete components fully symmetrical push-pull amplifier circuits (see Figure 5) to take advantage of its large dynamics and low distortion.
The karaoke reverberation part adopts M50195 chip of Mitsubishi Corporation of Japan, with a full range of function adjustment buttons (such as the microphone volume and accompaniment music volume are adjusted independently), so that the singing voice and the accompanying sound can be balanced and integrated.
Another feature of the local karaoke system is the specially designed surround back channel karaoke effect. It can be added or removed according to personal hobbies, and the signals of the two surround channels are different, each rated output power is 120W (8Ω). When the surround karaoke sound effect is added, it can create a real sense of space, envelopment, and presence, just like singing in the lobby. Therefore, AV-999 is not only suitable for home use, but also suitable for public entertainment places such as dance halls and auditoriums from the perspective of huge power and karaoke's unique design.
3. Main technical indicators
(1) The output power of the main channel of pure music: 120W + 120W (8Ω, RMS); frequency response of the main channel: 20Hz ~ 20kHz (-0.5dB); harmonic distortion: 95dB (A); output impedance: 4 ~ 8Ω Treble adjustment: ± 10dB (10kHz); bass adjustment: ± 10dB (100Hz).
(2) Directional logic surround sound channel separation: 35dB (1kHz, -10dB); each channel output harmonic distortion: <0.2% (1kHz); line output signal-to-noise ratio: 90dB (A); power amplifier output signal Noise ratio: 85dB (A); frequency response: center channel (C) 20-20 (-1dB), surround channel (S) 100-1 (-3dB); built-in amplifier output power: center (C) 120W (8Ω, RMS), surround sound (S) 120W + 120W (8Ω, RMS)
; Subwoofer line output gain: 0dB.
(3) Partial frequency response of digital karaoke: 10Hz ～ 20kHz (-0.5dB); total harmonic distortion: <0.15% (1kHz); delay time: 65ms, 130ms, 260ms; adjustable reverberation time: 0-5s continuous Adjustable; power supply voltage: 220V ± 10%, 50Hz; total weight of the whole machine: 16.8kg, dimensions: 430 × 360 × 125mm (L × W × H)
Fourth, equipment matching points
AV-999 itself does not have AC-3 decoding function, the author realizes that this can bring greater mobility to the user, especially the economy. When your requirements are not very high, you can choose a DVD player with built-in AC-3 decoder (for ordinary DVD players, with or without AC-3 decoding function, the cost is only a few tens of yuan, but if you use AC-3 If the decoding function is built into the AV amplifier, the cost will increase by at least 500 yuan). The decoded 5.1 channel signal goes directly into AV-999, of which 5 channels drive the front left, front right, front center, rear left and rear The right five full-channel speakers with the same specifications, and the 0.1 channel only provides subwoofer small signals below 120Hz. The subwoofer is driven by the power amplifier (which can be placed in the subwoofer or a separate power amplifier).
When you have high requirements for home theater and think that the decoder built into the DVD player is not enough, you can buy a separate AC-3 decoder and connect it in series between the DVD player and AV-999 to form a more advanced digital Home theater, but it will cost an extra two thousand yuan. Taking a step back, you can also purchase an AV amplifier with an AC-3 decoder. For this amplifier, the manufacturer needs to pay an AC-3 certification fee of more than 10,000 US dollars. Of course, this will be added to the cost of the AV amplifier. In fact, according to the national consumption level and general housing conditions, the first plan can already be said to be quite good.
The selection of subwoofers is mainly based on the size and hobbies of your own audiovisual room. When the audio-visual room is small (such as less than 20 square meters) and your main speakers are good enough (such as a three-way floor box with a 10-inch woofer), then you will not feel insufficient bass without subwoofer. If your audio-visual room reaches a hall of 30-40 square meters or even hundreds of square meters for professional use, it is necessary to consider purchasing a subwoofer.
When using AV-999 to play music, select the pass-through key, which can make the high-fidelity music program skip the Dolby surround and karaoke circuit to the amplifier circuit behind (see Figure 1). The high-fidelity two-channel pure music amplifier only has a good 20 cm long wire in the line.
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