M7C Preamplifier User Manual
Contents
1. M7C Preamplifier User Manual Analog Metric M7C PREAMPLIFIER USER MANUAL INTRODUCTION Circuit design is with reference to the classical Marantz 7C It produces sweet and detail sound Capacitors in audio grade are used for high voltage filtering and AC signal coupling Low voltage dropout regulator LT1085 is employed in regulating power supply for tubes filament which gives a maximum output driving current of the IC is 3A which is far enough for filament power supply To enhance the performance of the power supply unit the lengths of power routing path and signal paths are minimized so as to minimize the total path impedances The placement of the components of the built in rectifying and regulating circuits are packaged closely together and are far from the amplifier core Also the R14 and R30 are provided for an alternate the biasing at second amplifying stage FEATURES e Three vacuum tubes 12AX7 e Two single ended inputs and two single end outputs for stereo e Voltage gain 20dB e Dynamic range output voltage max 20Vrms www analogmetric com Page 2 M7C PREAMPLIFIER USER MANUAL Analog Metric Metric S N ration gt 90dB Built in voltage regulation circuit Power requirements one 200V AC 100mA and one 12 6V AC 1A PCB dimension 110mm W x 200mm L PCB thickness 2 5mm double layer 20z copper PRECAUTIONS Do not use finger or any body parts to touch the components or board It 1s hazardous s2. ince the high voltage capacitors may not be fully discharges after switched off the power supply Turn off the power supply if the transformer is getting hot or some smoke is observed or strange buzz sound is heard Fuse should be used either in power transformer or main socket to avoid accidentally large current drawing Always contact technicians or experts to seek help PROCEDURES 1 Solder all the components according to the schematic part list and photo 2 Unplug the vacuum tubes Connect the power supply and measure the voltage at J1 and J2 without applying input signal The voltage of J1 connecter marked with 200 0 should be 200VAC for high voltage supply and J2 connector marked with 12 6 0 should be 12 6VAC for filament power supply 3 If the AC voltages at the J1 and J2 are corrected Then measure the voltages at C13 which is near 240V DC and the voltage between PIN 4 and PIN 5 of tube sockets are 12 6V 4 If everything is ok you can plug the tubes in the sockets and turn on the power supply 5 Good luck and enjoy it If you have any problem in assembly please contact us by email to tech analogmetric com www analogmetric com Page 3
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