Note: This board is a single-channel design, dual-channel stereo, two pieces are required
This power amplifier board is made according to the sample circuit of the "Audio Design Manual" of Douglas, UK. The circuit is very simple, scientific and rigorous. The value of each component can withstand scrutiny.
Input stage: adopt perfect closed-loop constant current source structure + current mirror technology. Balance the differential pole operating point. The music details are rich, and the static output midpoint is very stable (differential pair and current mirror transistor require matching)
Voltage level: The addition of an emitter follower makes the voltage level distortion as low as negligible and effectively reduces the phase shift between the input and output signals. This action makes a great contribution to the low-frequency intensity. The power amplifier driver chip produced by the famous NEC company also has this structure. (upc1225/upc1342)
Output stage: This power amplifier board adopts the powerfully-protected junior tube 2SA1216/2SC2922. This tube has a strong driving force. A pair of major power amplifiers easily beats 3 pairs of parallel conventional power amplifier pairs. The sound quality is very delicate, full and full of power. (If the multi-pipe parallel scheme cannot be accurately paired, the sound is obviously rough and incomparable)
The key components of this power amplifier board are all purchased from Europe (RS), and the differential pair and current mirror are strictly matched.
The power amplifier board is wired correctly, so you can&x27;t hear any noise at all, and the background is very clean.
Douglas stated in the book that the so-called "defect-free" is not absolute perfection, but refers to the correction of 8 known distortions in traditional power amplifier circuits, not absolute defect-free According to the amplifier made by the sample circuit, the total harmonic distortion measured at 1KHZ 8 ohm load is 0.0005%, and the total harmonic distortion measured at 10KHZ 8 ohm load is 0.003%. Conversion rate 35V/us
Static current adjustment: (must install the heat sink for testing)
It has been adjusted before shipment. Don&x27;t adjust it without the instrument.
The DC file of the multimeter measured the MV value/0.22=quiescent current. For example, the test point value is DC 6.6 MV, quiescent current=6.6 MV/0.22=30ma, and crossover distortion is avoided if greater than 10ma.
To avoid ground loops, a one-point grounding scheme is adopted
Friendly reminder: Don’t reverse the wiring of your two speakers. Even if they are connected incorrectly, they will sound normally. However, the phase of the two speakers is positive and the other is reversed, and the sound pressure cancels each other out, which will affect the sense of hearing.
Debugging must read:
"1" This power amplifier board is powered by positive and negative DC (±24V--±50V). Never connect the output of the transformer to this board directly. The output of the transformer must be rectified and filtered before it can be connected to the board. Be careful not to reverse the positive and negative connections.
"2" The heat sink must be installed before the board is energized and debugged, and each official must add a mica insulating sheet (we will deliver) the temperature compensation tube screw must be covered with insulating rubber particles, and then use a multimeter to check whether the heat sink and the amplifier tube are sure to be insulated
"3" Advantages of the mono power amplifier board, the chassis selection is flexible, but the ground loop must be considered. It is the responsibility of the old fever to know that the first fever needs to learn. The only connection point between the whole machine and the chassis is the merging point of the two RCA input socket ground wires. The ground wire of the 220V socket must be connected to the equipotential terminal of the building, and it can be connected to the chassis. If the ground of the 220V socket is suspended in the air, remember that it cannot be connected to the chassis
Electrical parameters:
Power supply voltage: DC ±24V to ±55V (transformer double 18V~double 35V)
Signal amplifier tube: new pure imported ON (ON Semiconductor) MPSA56 MPSA06
Voltage amplifier tube/push tube: ON (ON Semiconductor) MJE340/MJE350
The last big tube: pure imported Sanken 2SC2922/2SA1216 (17A 200W)
Input coupling: West Germany ERO 1813 10UF/100V
Resistance: Military 718 ?6?7?6?7?6?7?6?7?6?7?6?7?6?7
Power decoupling: Nippon Chemical Industry
Conversion rate: 35V/us
Distortion: 1KHZ is less than 0.0006% 10KHZ is less than 0.006%
Frequency response: 20HZ~20KHZ (+0DB, -0.5DB) Note: not -3DB
Output power: ±55V 8 ohms: 125 watts 4 ohms: 200 watts (the power supply is ideal enough)