Build this RCA-designed, RIAA-equalized high-fidelity stereo preamp for magnetic phono cartridges.

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Warnings and safety precautions!
All vacuum tube circuits operate at dangerous voltage levels, including this project. The dual triodes used in this project and other vacuum tube amplifiers operate at over 300 volts. Accidental contact with an energized circuit of this nature can be fatal.
Working on, testing, and adjusting live tube circuits requires extreme safety. In general, be cautious and have a safety plan in place!
Remember, safety first, always!
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This preamp project is based on a design from the "RCA Receiving Tube Manual" RC-30 edition, page 702, circuit 29-16. The stereo phono preamp consists of a two-stage matched pair of 12AX7 twin triodes, in a common-cathode voltage amplifier configuration. The passive RIAA equalization network is connected between the two amplifier stages.
This network boosts the low frequencies and reduces the high frequencies of audio signals coming from the output of the moving magnet phono cartridge. This is important for achieving the correct equalization curve during vinyl playback and ensuring a more balanced music listening experience. The QA400 audio analyzer's frequency response test result will also show the effect of the equalization curve.
The "New Orthophonic," as mentioned in the book, was developed by RCA in 1954, contributed to the standardization of vinyl record playback, leading to what is recognized at present as the RIAA curve. This standardization was crucial for ensuring accurate playback of vinyl records, allowing analog music to be experienced with the same fidelity that the recording industry intended.