02/10/2026
Hey guys, Let me share my latest audio project. This is a really nice DI box featuring two 12DW7 tubes, each containing two triodes, powered by a DC/DC step-up converter delivering 300VDC. The box is powered by a 9 V DC / 2 A supply. The wiring is based on the legendary Ampeg SVT vacuum tube preamplifier. The output buffer is a cathode follower. Each 12AU7 triode (1/2 12DW7) is biased by a constant current source (CCS) to deliver the best performance and limit total harmonic distortion. An excellent Lundahl audio transformer (from Sweden) is used to create the balanced signal. An adjustable attenuator (pad) has been installed to provide maximum input headroom. The output level can be adjusted over a range of more than 25 dB. The bandwidth is 15 Hz – 35 kHz at THD< 0.1%, with 5 dBu from 15 Hz to 50 Hz and >15 dBu from 50 Hz to 35 kHz. This prototype will be tested by a professional recording studio in Normandy next week.
