The position of Marantz7 in the pre-tube is paramount, and the enthusiasts who play the tube have not heard of the big names of Marantz7, I believe it is very rare. In the late 1950s, the main line of Marantz7 is shown in Figure 4. In the circuit, V1 and V2 are used for voltage amplification, and V3 is connected to the cathode follower as a signal buffer. Its function is equivalent to connecting the emitter with the NPN tube. The most distinctive feature is the overall loop feedback design, which is a major factor in the Marantz 7 fame. However, in order to prevent high frequency self-excitation, a 22PF capacitor is connected between V1 and V2 to form a high frequency local feedback to reduce the high frequency amplification factor, and the output terminal is connected to a three-pole negative-negative negative feedback network. The frequency and high impedance are very three-pole negative-negative negative feedback network. The high-frequency and high-impedance of this network is very small (about 20 km below). This design poses a considerable burden on V3.
The high-frequency open-loop gain is not enough, and the negative feedback is not ideal for improving the high-frequency distortion, but the strange thing is that the audio industry has a good impression of the Marantz7 sound. In this production, V1, V2, V3 first used the export tube 12AX7 produced in Beijing, but the negative feedback network was changed to the second level as shown in the dotted line of Figure 4, and the self-excited C*22PF capacitor was eliminated, which is effective. Improve distortion. 12AX7 belongs to the high U tube, the magnification is very large, but its internal resistance is also large. When V3 adopts 12AX7, it seems that it is not the best choice. I used the American 5751 and 12AU7 generations to change, and the high frequency improved. The dynamic is larger and the stability of the sound field is better. When 12AU7 is used as the cathode output, the bile phase 12AX7 and 5751 are less. 12AU7 can be replaced by 6N10 or ECC82. Toshiba's 5963 sound has certain qualities. Their pins are the same. The filament can be powered by 6.3V or 12.6V. AC 6.3V is used in this machine.
Marantz7's analytical power and high and low frequency extension are not very good, especially when compared with the best contemporary tube preamps such as Matisse Refernce, Audio Research Referance 1, Convergent SL-1, etc., these deficiencies will be hidden, but Marantz7 The most attractive place is the unspeakable mid-range sound color. I think its tone is still biased towards the sun type. It can bring out the brilliance and power of the music. When the brass music is replayed, the "brightness" of the instrument is full. When playing strings, the sound of the piano is also soft and textured, and the vocals are more emotional.
The author's modified Marantz7 line sound evaluation is quite high (V1 for V1 and V1, and 5AU7 for Amperexr for V3). The tone is soft and smooth, and the texture is strong. The performance of high and low frequency playback can still be called first-class, with certain extension. Degree and intensity, but the intermediate frequency is better. Compared with the two-stage 6SN7 negative feedback amplification line, the Marantz7 line is superior. If both V1 and V2 use Telefunken's ECC803S and V3 also uses Telefunken ECC802C, I believe that Marantz7 can make it unnecessary for other predecessors.
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