After the level of asymmetric pure power amplifier circuit design

Transistor amplifier, the general without the use of output transformers, low cost, it made more suitable for music lovers. Among them, the Pure Class A amplifiers there is no crossover distortion, warm tone, Nai Ting, deeply loved by enthusiasts; A power amplifier characteristics, but also includes the static power consumption, heat capacity, high requirements of the component production process, in particular, high requirements on the power transformer, or even listen to sense smaller than the high bias class AB amplifier. To try to solve these problems, such as drawings, circuit design, the actual use of good effect, the circuit is characterized by:

(1) non-symmetrical form, can prevent the even harmonics weaken;

(2) In addition to expanding power flow control, the former class of all circuits are single-ended Working Group on the state, there is no crossover distortion;

(3) the circuit simple, less components, easy to produce PCB, power consumption and low cost;

(4) from the actual audition, carefully selected for each component type, parameters, to ensure reliability, speak a good level.

The circuit consists of three parts:

After the level of asymmetric pure power amplifier circuit design

Differential input section

This part of the design features are: constant current source to replace the emitter resistors, Ti Gaogong mode Yi Zhi Bi, issued to Guang Ya Yuan Jian 2 Guanwei set, 既 simplify the circuit, Tong Shi Ye better voltage stability performance. As the C2240 work in single-ended tube state, in order to ensure sufficient dynamic, without the risk of decapitation distortion, this level of quiescent current

(1.8V-0.7V) / 330Ω = 1.67mA (actual test 1.8mA)

This deviation mainly caused by the junction voltage bias estimates. Should be noted that transistors magnification β, and decreases with Ib, will cause nonlinear distortion, due to differential input amplifier stage is located before the main voltage, such adverse effects will be more significant, for there to use Toshiba C2240 (on the tube C2240/A970), the control for audio-specific low-power control, bandwidth 100MHz, its obvious advantages: low noise, β Ib with the change rate is very small, which can increase the level of linearity.

Part of the main voltage amplification

The main function of the level audio signal voltage is amplified to require amplification with sufficient bandwidth, use the A970, bandwidth of 100MHz, this level of quiescent current: (1.8V-0.7V) / 100Ω = 11mA (actual test close to 12mA)

BG3 emitter dynamic resistance greater impact on the circuit, taken as 100Ω, to retain a certain amount of local current feedback.

BG3 BG4 mirror for the current source, not involved in voltage amplification, the part of the circuit is still working in the Group A status, C1, C2 of the settings can prevent high-frequency amplifier self-excitation occurs.

Promote and expand the flow of some high-power

Promote the use of power on the tube tube D669/B649 (140MHz), high-power tube selected C5200/A1943 (30MHz), using C2330 as the bias at this level, you can see C2330 between the collector and emitter, and no parallel capacitors provide signal communication channels, as C2330 collector and emitter voltage between Uce (that help implement the static bias voltage), adjustable through 1kΩ resistor adjustment, and can better maintain the fixed value, e point of the voltage will be lower than c points in the form of Uce change with the c point, so do not worry amplified positive and negative half cycle of waveform asymmetry, using digital storage oscilloscope, waveform symmetry could be observed well.

About Toshiba's C5200/A1943 on the tube, the article describes sound more, do not dwell on them. In this talk about the quiescent operating point of the tube, quiescent current is set at 50mA, the actual debugging revealed that the current is 50mA ~ 300mA between changes, to enhance the sound quality without much effect, of course, below 30mA, the amplifier Sheng Yin become thin, analytical decline. Machine's voltage gain is: = 26.5 (28.465dB)

Circuit voltage negative feedback, some literature is better than the current sense voltage feedback to listen to the negative feedback circuit, in fact, the negative feedback voltage amplifier is also very characteristic. This line does not use the mid-point potential of DC servo technology, stable, still retains the negative feedback grounded capacitors, which will affect the lines Cf sound, the capacitor used ELNA audio-specific reverse 100μF capacitor in series was.

1, the power part

200W transformer capacity above recommended the use of fast recovery rectifier diode FR307 for actual use, only using a pair of 10000μF filter capacitor, speaker on already clean, increasing the filter capacitor is conducive to play a dynamic power amplifier.

2, debugging

The machine debug is as follows, check the correct line, it will 1kΩ variable resistor adjusted to maximum power on, measure the output midpoint voltage, the voltage is not more than 1V, after the passage of:

(1) regulating differential input stage of the sliding arm of resistance, so that the midpoint potential close to 0V;

(2) adjusting the power supply to control the static bias 50mA.

Repeat steps (1), (2) the machine into normal operation, power to burn machine for half an hour or so, once again, to adjust, you can power an audition.

As a non-symmetrical structure of the line, there is unavoidably boot time impact, while more effective protection for speaker, it is recommended to install speaker protection circuit.

If you want to improve the circuit's power and damping coefficient, can be combined and a pair of high-power tube C5200/A1943, found in the debugging process will be replaced with FET K413/J118 C5200/A1943, the sound is very mellow, but the K413 / J118 for industrial pipe, open high voltage, because lines do not change, try.

On the machine's performance parameters, the absence of applicable test equipment, to not mislead the reader, in this can not give. While on a route, the most important thing is to see whether the ear line to speak out, so this gives me only a few music lovers with the subjective evaluation. After using the class to sub-key Wu DP-5010CD for the source, the monster 400MK Ⅱ signal lines, Swans shock 6A speaker to audition equipment, test the balance of the signal, 20Hz ~ 20kHz sweep signal, pilot a few Tsai Chin album, you can say it out loud with plenty of emotion, sound, solid, well shut up type of income: in the play "Silkworm" track, urgent drums, drum hammer next to the drum sound, clear and legible, highly penetration. After the level of the signal to noise ratio high, even if the ears close to the speakers are hard to perceived noise, dynamic big, wide sound field of the human voice and string performance commendable, analytical high.