Very Low Noise Pick-up Preamplifier
Posted on Mar 12, 2013 11670
The preamplifier was designed to signal sources such as low-impedance moving coil cartridges (MC) on turntables high fidelity (and yet still there). The impedance of the amplifier is 100 W. To keep the noise levels low, three double-type transistors MAT03 SSM2220 or linked together to form a differential amplifier. Connecting this amp in front of an operand (OR27) is reduced to very low levels in noise input of the latter. The connections of the bases of the amplifier's inputs act as `super operator` very low noise input. One advantage of pnp transistors compared with the corresponding npn is much lower noise low frequencies. On the other hand, creates a relatively high current polarization at the entrance, about 5.5 Ma, as effect of the regulation of 2 mA for each transistor in combination with the relatively low gain transistor pnp.
The trimmer R 1 and resistance A7/A8 offset tolerances of the A4 and A5 at the exit of the differential amplifier. The tranxistor T4 LED D1 and the power source for forming the differential amplifier. The D1 is flat red LED's mounted on the T4 for better thermal coupling. Because thorythoW entry of the order of 0.4 nV / (Hz) (theoretical resistor value for 1I, Z) is an important feedback to grow as little as possible the total picture noise. Therefore the impedance of the feedback circuit should be much less than 1O W. In contrast, one needs OR27 specified minimum load impedance that can not be less than 600 ohms, so the price feedback resistance is less than 600 W. To ensure low prices for the A9 should be someone compromise the value of the maximum gain (about 24 dB, or 15.7 times in our case). Fitting extra resistance, R11, ahead of feedback operational amplifier that does not clutter while adding A9 only 0.3 nV / (Hz) 1 / 2 noise input, which in fact based on the measured data is 0.52 nV / (Hz) 1 / 2. If you want higher profits, can be image noise 0.4 nV / (Hz) 1 / 2 with a lower price for the R9.