2*150W no large loop feedback high fidelity power amplifier circuit principle

Circuit principle: As is well known, the large loop feedback from the output stage of the amplifier to the front stage can improve the frequency response and harmonic distortion of the amplifier, but the effects on the transient characteristics of the amplifier and some dynamic indicators are more harmful. In particular, the feedback voltage on the speaker is fed back to the front stage, which will cause signal distortion. A high-fidelity power amplifier circuit introduced in this paper cancels the large loop feedback and uses a DC-based fully symmetric differential preamplifier. The emitter-level constant current source circuit has good stability and good linearity. The output terminal DC potential servo circuit composed of LF356 can automatically maintain the potential of the output terminal. The whole circuit is shown in Figure 4-16. The amplifier uses dual transformers and two Power is supplied from a fully independent power supply circuit to minimize the effects of left and right channel interactions. In addition, the amplifier also adopts the pre-stage power supply voltage of ±64V, the latter stage voltage is ±50V, and the two-stage power supply method is separately. The dynamic range of the pre-amplifier of the amplifier becomes large and is not affected by the post-stage power supply, further improving the fidelity. degree. The front stage adopts the parallel voltage regulator circuit to supply power, has the characteristics of stable voltage and fast response to power supply changes, and can improve the dynamic index of the whole machine. The circuit also has a complete protection circuit for protection against power-on shock, output point potential change, and output tube overload.
In the circuit, the parallel regulator tube is 2SC2775A, 2SA985A, the power supply excitation tube is BC489, BC490 (or 2SB647, 2SD667), the differential pair tube is BC546, BC556 (or 2SC2389, 2SA1038), and the other tubes can be selected with appropriate polarity and withstand voltage. Small power tube. There are two options for the power amplifier of this circuit: one with the Japanese Ken tube; the other with the American tube, with the three-tube tube amplifier (model B-2150S), the tone is cool and strong, and the power is good with the American tube ( Model B-2150M) The sound is warm, soft and delicate, each with its own characteristics. The measured performance of this amplifier is as follows (for reference only)
(1) The output power can reach 150W×2 (continuous wave);
(2) Harmonic distortion <0.02% (30W);
(3) Intermodulation distortion <0.03%;
(4) Signal to noise ratio >100dB;
(5) Frequency response 3Hz~100kHz (±1dB);
(6) Damping coefficient > 200 (100 Hz, 1 W);
(7) Conversion rate >100V/μs;
From the above indicators, this amplifier circuit is indeed a "fever-grade" high-fidelity discharge circuit, especially suitable for enthusiasts to enjoy various music programs.

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