This is a simple preamplifier for turntables equipped with moving magnet or high-output moving coil cartridges. It was designed primarily as a board that could be embedded into other projects, such as custom integrated amplifiers, preamplifiers or self-contained turntables. It is equally suited as a high-quality yet low-cost external preamplifier.
An RIAA preamplifier boosts the signal significantly as a magnetic cartridge produces a much lower output than a typical line-level source such as a CD player. It is also necessary to reverse the RIAA filter applied during the vinyl cutting process to attain correct frequency response.
The RIAA equalisation filter is a low pass filter with transition points at 2122Hz, 500Hz and 50Hz. RIAA implementation is not difficult, but does require close-tolerance parts. The circuit here if used with quality components implements a filter very close to the ideal RIAA response. R1, R2, R3, R4, R5, C3, C4, C5 and C6 are used to bias the non inverting inputs of the NE5532 dual op-amp. C1, C2, C13 and C14 are for ac-coupling at the input and output respectively. All other components should be of the best possible tolerance as they are critical to the performance of the stereo filter. Lead spacing for the electrolytic capacitors is 2 mm.
A quality power supply is important, though a decent switch-mode power supply is fine. You could also build a simple regulated linear power supply or use a battery. The power supply can be anything from 8 to 20V DC and the preamp will draw no more than 35MA.
The DC power barrel jack is the Würth 6941xx301002. The RCA connectors are Switchcraft PJRAN2X1U01X. These are just suggestions, there are compatible variants for both.
The download includes KiCad files and is made available for DIY use only. No permission is granted for commercial usage unless obtained in writing. Thank you to Måns for assisting with the PCB design.
Parts list
- R1: 100K
- R2: 120K
- R3: 100K
- R4: 120K
- R5: 18K
- R6: 18K
- R7: 820R
- R8: 820R
- R9: 220K
- R10: 22K
- R11: 220K
- R12: 22K
- R13: 1K
- R14: 1K
- C1: 4.7uF/16v
- C2: 4.7uF/16v
- C3: 22uF/25v
- C4: 22uF/25v
- C5: 100pF
- C6: 100pF
- C7: 10uF/25v
- C8: 10uF/25v
- C9: 3n3
- C10: 15nF
- C11: 3n3
- C12: 15nF
- C13: 100nF
- C14: 4.7uF/25v
- C15: 4.7uF/25v
- C16: 10uF/25V
- U1: NE5532. 8-Pin socket recommended.
If you’d like to build your own you can find most if not all of the parts you’ll need at Bitsbox Electronics. I have no affiliation with them, but they’re great for one-off projects or prototypes as you don’t have to order huge quantities to avoid large handling or delivery fees. I use JLC PCB for PCB production, but any PCB manufacturer should accept these files.
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