TK Audio


500-series Class A preamp

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SP501 line art

SP501 is a single slot 500-series class-A unit with a unique hybrid design including both vintage and modern circuits derived from TK’s flagship DP1 stereo preamp. The midrange crunch of the germanium sound of the mid 60’s, the low mid punch and thick sound associated with British Class A from the early 70’s as well as the more modern tone from the 80’s and 90’s are finally all available in a single unit.

SP501’s input stage is built around a high quality Swedish Lundahl transformer followed by a germanium stage that adds more harmonics. Two different output stages can be selected – either an electronically balanced stage, or a discrete transformer-balanced class-A stage sporting a heavy Carnhill output transformer. Vintage Class A mode produces a fat and punchy sound with mid-range character and a warm top end, while the electronically balanced output stage is less colored and perfect for clean amplification. A sweepable HPF from 30Hz to 400Hz allows precision crafting of the low end.


  • Lundahl input transformer
  • Carnhill output transformer
  • Selectable germanium circuit for extra harmonics
  • Sweepable high-pass filter, 30-400Hz, 12dB/oct
  • Hi-Z instrument input
  • Selectable output stages, electronically balanced or discrete class-A