The DB Vacuum Tube Microphone Preamplifier is a classic transformer balanced tube microphone preamp with instrument DI. Features 63 dB of selectable gain, +48V Phantom Power, -20 dB PAD, phase reverse, and two custom switchable low shelf filters. The circuit includes special components such as Jensen transformers, paper-in-oil coupling capacitors, stepped gain attenuators, and NOS General Electric tubes from the 1960s. Allow 4-6 weeks for build and delivery.
DB - Vacuum Tube Microphone Preamplifier
An entire year of research and design led to the product you see here.
It would have been selfish to build just one for myself, so I am offering a limited run of this two-channel tube preamp. It is available to anyone who wants a classic transformer balanced tube preamp, with high quality components and useful features, at an affordable price.
The preamp’s key components are not easily found in modern production models. I tested numerous combinations of transformers, tubes, and coupling capacitors before deciding on the final tonal characteristics that sounded best to me.
Matched pairs of 1960s new-old-stock General Electric tubes meet or exceed published specifications of transconductance. The GE 5-Star 6072a is legendary for its larger-than-life 3D quality, while the choice of either a NOS RCA or GE 12AU7 contributes its hi-fi soundstage, tight bass, and neutral highs.
Jensen has led in transformer research for decades. Their JT115k input transformer is designed for the highest practical 1:10 step-up ratio within their company’s design tolerances. Paired with Jensen's JT-10K61-1M output, these are perfect transformers for a tube preamp.
Glass-sealed Russian paper-in-oil and Teflon bypass capacitors are used for coupling following tube gain stages. Polypropylene film and electrolytic caps are used elsewhere in the audio and PSU circuits.
High quality stepped-gain rotary switches are used instead of potentiometers for repeatable gain selection and to help maintain signal integrity.
- 63 dB Gain
- XLR Inputs/Outputs
- 1/4" Instrument Input
- -20 dB PAD
- +48V Phantom Power
- Ø Polarity Switch
- Low Shelving Filters
- Rear Panel Grounding Lug
- 120 VAC IEC Fused Power
- Jensen Transformers
- NOS General Electric 6072a
- NOS General Electric 12AU7
- Paper-in-Oil Coupling Capacitors
- Teflon Bypass Capacitors
- Stepped Attenuators
- DC Heater Supply
- Toroidal Power Transformer
- Turret Board Construction
- 20Hz-20kHz (+/- 0.2 dB)
- Noise EIN: -125dB (max)
- Input Impedance 2.4k ohms
- Output Balanced 600 ohms
- Low Shelf POS 1: Flat
- Low Shelf POS 2: -3dB at 75Hz
- Low Shelf POS 3: -3dB at 275Hz
- Dim (3U): 19" W x 5.25" H x 11" D
- Weight: 19.0 lb