Ordering guide:
No potentiometer: the finished board does not have a potentiometer;With potentiometer: ordinary potentiometer, as shown in the figure;Upgrade ALPS27: With ALPS27 potentiometer.
PREAMP 9 preamplifier is another fully discrete preamplifier designed by LJM. PREAMP 9 is a pure single-ended structure and a pure Class A design.The so-called single-ended means that the entire waveform of the signal is amplified by a transistor or tube at one end. Work in Category A.The mixer NEVE is a single-ended amplifier circuit that has always used discrete components, while most other manufacturers use simple operational amplifier circuits.Therefore, NEVE single-ended fully discrete circuits have always been the representative of analog circuits, which have a wider dynamic range than other manufacturers.Since single-ended is a single transistor amplifies the signal of the entire waveform, the single-ended circuit does not have any crossover distortion.This means that very weak signals, usually overlooked out-of-band signals, can also be heard.PREAMP 9 has a warmer, sweeter, and fuller sound quality than an operational amplifier.The single-ended amplifier circuit is the oldest original amplifier circuit, it has a good sound and taste. But the single-ended circuit has weak anti-interference ability to the power supply,Therefore, the power supply part of PREAMP9 is more complicated and adopts a three-stage filtering method.The first stage uses LM317T produced by MOTOROLA ONSEMI as the first stage of voltage stabilization filter,The second stage uses a large-capacity inductor and capacitor RC filter, plus a third-stage transistor RC filter. As the power supply of the P9 front stageProvides very pure, battery-like direct current.PREAMP 9 adopts the pure single-ended amplifier circuit imported from BC547 C with full NPN structure. The single-ended circuit has no complementary pair tube, only NPN does not have PNP tube. Only use the same kind of tube as the amplifying circuit and constant current source load. PREAMP9 adopts a full-frame design method, because this circuit is more complicated, in order to reduce the size of the previous stage. And post-chip components have a shorter routing distance.In this way, the P9 front stage can be installed in any ordinary power amplifier rear stage. It can be installed directly on the volume control panel of the rear stage of the power amplifier. P9 front stage, PCB size without potentiometer is about 50*73 MMAll LJM products have been debugged by the instrument, and even if different components are of the same model, the performance is different.The P9 front stage is completely sound-based, and there is no beautification of any appearance.The previous stage did not use so-called fever components or disassemble components.The main filter capacitor of the P9 front stage adopts the ULTRA LOW ESR filter capacitor imported from Japan. The new version of the 2018 version adds the filter capacitor in parallel, and the filter power performance is better.The voltage regulator tube adopts MOTOROLA (M) mark, ONSEMI and other new original voltage regulator tubes.All transistors are imported with original copper pins, BC547C selected after testing, and all magnifications are around 600.PREAMP9 preamp will also make the entire audio system better to hear. This is the reason for the so-called preamplifier sound and the latter's power.The main parameters of PREAMP9 are as follows:THD+N <0.05%SNR >100 DBFrequency response: 20HZ -20KHZ -0.05DBFFT test test platform AP SYS TWO, output voltage signal: 1.06V
Frequency response 20HZ-25KHZ (-0.05 DB)
Input voltage: between AC20V and AC28V (AC12-0-12 can also be used without the middle wire)Input transformer power> 5VAQuiescent current: 25 MAVoltage amplification factor = GAIN 10 timesP9 front stage can choose standard power distribution potentiometer, or without potentiometer.It is recommended to use PREAM9 preamplifier with L series post amplifier or MX series pure post amplifier.Especially when paired with L12-2, L20, L20SE, L15, etc., the performance is close to full marks.If the P9 front stage is matched with MX50SE or L7, it is recommended to adjust the gain of the amplifier for L20V7 amplifier.For L7, MX50SE, L20, the 330 ohm resistor on the amplifier is changed to 470 ohm, and there is one on each board.This reduces the magnification of the rear stage, and when combined with PREAMP 9, the sound will not be too loud when using high-sensitivity speakers. It is not recommended to use PREAMP9 with other non-LJM-produced post-circuits, as it may not achieve the best matching effect.In particular, circuits similar to JLH1969 are not suitable for P9 preamplifiers.The potentiometer is compatible with type 16 or ALPS 27, the model is A203 A 20K, or A503 A 50K.
