preamp circuit

  
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Using a K-12 tube amp with a NAD C542 CD player, there is no need for a buffer or line level preamplifier. The K-12 is a very polite and sweet amp with all the warmth of it`s `hot bottle` heritage. However, when I compare the K-12 with my monoblock chip amps (LM3875), I was never convinced that the chips amps really delivered the passion of the m
preamp circuit - schematic

usic which the K-12 does so easily. There was always something missing when it came to a convincing delivery. I felt a little of that beautiful valve warmth was required, so I tried a very affordable Valve Preamp kit from Silicon Chip Online. The preamp kit is based around a common 12AX7 dual triode. The line level (Hi-Fi) version of the kit has the gain set at 4 (6 dB). What makes this kit very inexpensive is that power comes a switch mode power supply, fed from a 17 volt DC wall wart! Photograph 01 shows a stock build of the kit. The schematic of the preamplifier section is shown in Figure 01. (Please note that this circuit is © Silicon Chip Online and permission to host the schematic on this site has been provided by Silicon Chip Online. The schematic of the switch mode power supply section is shown below in Figure 02. (Please note that this circuit is © Silicon Chip Online and permission to host the schematic on this site has been provided by Silicon Chip Online. Prior to building the preamplifier kits, I purchased some nice Sprague capacitors in order to upgrade the signal path capacitors. Photograph 02 shows the completed power supply and preamp module with the upgraded capacitors. Once I had put together the boards, I proceeded to add snubbers to the preamp and power supply sections. Photograph 03 shows the snubbers added to the underside of the PCBs.



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