Diamond differential BTL power amplifier circuit

Figure l-45 is a 100w diamond differential BTL power amplifier assembled with discrete components. VT3 ~ VT64 tubes form
a diamond-shaped differential inverting stage. Their emitter resistance is larger to form a strong current series negative feedback, so that
the distortion of this stage is extremely small, the frequency response is extremely wide, and the phase shift is very small.
    The signals after diamond differential inversion are input into two sets of voltage excitation stages respectively, that is, the collector outputs
of VT3 and VTs are respectively input into the bases of the excitation stages v, r7 and VT8; the collector outputs of VT4 and VT6 are respectively input into the excitation stages VTg and VTio. The base
.
    The voltage excitation stages VT7~VTco not only have small resistance resistors in the emitter series to obtain current negative feedback, but also
connect resistors across the collector and base of each tube to form voltage parallel negative feedback. There are three purposes for this processing: first, to stabilize the midpoint potential of the output terminal
so that the power consumption of each power amplifier tube is equally distributed; second, to appropriately reduce the voltage drop t on the emitter resistor
, which is conducive to improving the power supply voltage utilization; third, By reducing the output internal resistance of the voltage excitation stage, tlp reduces the internal resistance of the signal source of the subsequent stage, so that
the nonlinearity of the input characteristics and output characteristics of the subsequent transistor can compensate each other to a certain extent, improving the linearity of the subsequent stage
, and at the same time also The output internal resistance of the amplifier is reduced, which is beneficial to improving the damping characteristics of the amplifier.
    The voltage parallel negative feedback signal of the voltage excitation stage can also be obtained from the output terminal of the final stage. However, due to the large number of jumper stages in this connection method
, the additional phase shifts at each stage in the feedback loop will cause the feedback signal to be out of sync with the input, resulting in
deterioration of the feedback effect and the stability of the amplifier. Experimental observation can prove that: using a distortion meter to observe the waveform distortion degree t, it is found that the two have similar
effects , but in the high frequency band of 10k to 20kHz, the phase shift of the latter connection method increases significantly, and Distortion also
increases.
    Due to the above-mentioned measures, the open-loop index of the entire amplifier has been greatly improved: open-loop distortion <0. 3%. The open-
loop frequency response is better than 20H～20kHz±0,2dB, and the additional phase shift is less than 50 0