Mystery Magicians LBDI All-Tube Class A Direct Box and Instrument Preamp

The LBDI is a fully tube-based Class A direct box and instrument preamp delivering classic tube tone for tracking, reamping, and tone shaping. Running Phillips ECG 12AU7 NOS tubes at a robust 320 volts (not starved plate), this portable “lunch box” chassis with chromed handle ensures authentic Class A performance with natural harmonic richness, fast transient response, and ample headroom. The all-tube circuit handles guitar, bass, synths, keyboards, and other high-impedance sources, providing up to 53dB of maximum gain sufficient for high-impedance microphones like harmonica mics without external boosters. Switchable High/Low gain taps either the full first dual triode stage or second half for sensitivity control, while independent Input and Output Gain controls enable everything from clean headroom to rich, controlled saturation. A true bypassable three-band tube EQ offers ±15dB bass, ±6dB midrange, and ±10dB treble adjustment, while the intelligent Bright switch boosts high frequencies and rolls off lows at lower gain settings, progressively tapering as gain increases to prevent harshness. The dedicated reamp input accepts line-level signals for running prerecorded tracks through the tube circuitry, adding harmonic density and tonal depth impossible with plugins alone. Premium construction includes hand-wound in-house output transformers, audio-grade WIMA/Panasonic/TRW capacitors, metal film resistors, Japanese TOCOS sealed potentiometers, Omron audio-grade relays for all switching, and dual-tone hammertone powder-coated steel chassis with custom CNC-machined anodized aluminum knobs.

Key Features:

• True Class A Tube Circuit: Phillips ECG 12AU7 NOS tubes running at 320V (not starved plate) deliver authentic Class A performance with natural harmonic richness and fast transient response.
• Switchable Gain Architecture: High/Low gain switch taps full first dual triode stage (53dB maximum) or second half (32dB maximum) for sensitivity control, while Input and Output Gain controls enable clean headroom to rich saturation.
• Bypassable Three-Band Tube EQ: ±15dB bass, ±6dB midrange, ±10dB treble adjustment with intelligent Bright switch that boosts highs and rolls lows at lower gain settings, progressively tapering to prevent harshness at higher levels.
• Dedicated Reamp Input: Line-level input accepts prerecorded tracks for tube processing, adding harmonic density, controlled dynamics, and tonal depth to flat or poorly captured stems beyond plugin capabilities.
• High-Impedance Microphone Capability: 53dB maximum gain provides sufficient clean amplification for high-impedance microphones with 1/4-inch outputs (harmonica mics) without external boosters or transformers.
• Hand-Wound Output Transformers: Custom transformers built in-house ensure premium signal integrity and tonal character from input to balanced 150Ω output.
• Premium Component Selection: Audio-grade WIMA/Panasonic/TRW capacitors, metal film resistors, Japanese TOCOS sealed potentiometers, Omron relays for all signal switching, and custom CNC-machined aluminum knobs.
• Portable Lunch Box Design: Robust chromed handle and dual-tone hammertone powder-coated steel chassis enable easy transport for gigging musicians who need professional tube tone on top of amps.

Specifications

• Type: All-tube Class A direct box and instrument preamp
• Tube Complement: Phillips ECG 12AU7 NOS
• Operating Voltage: 320V (true Class A, not starved plate)
• Hi-Z Input Impedance: 1MΩ
• Reamp Input Impedance: 100kΩ balanced (Pin 2 hot, Pin 3 cold)
• Maximum Gain (High): 53dBu (Input and Output at maximum)
• Maximum Gain (Low): 32dBu (Input and Output at maximum)
• Reamp Input Gain: 10dBu maximum (Output at maximum)
• Output Impedance: 150Ω balanced (Pin 2 hot, Pin 3 cold)
• Recommended Load Impedance: 10kΩ or higher (150Ω minimum)
• Frequency Response: 5Hz – 50kHz (±0.5dBu)
• Maximum Output Level: +22dBu @ 1% THD+N (Input and Output at optimum position)
• THD+N @ +4dBu: 0.02% (second harmonic dominant)
• Signal-to-Noise Ratio (Reamp): -101.71dB below 12.19dBV reference @ 1% THD+N
• Signal-to-Noise Ratio (Hi-Z): -83.5dB below 11.15dBV reference @ 1% THD+N
• EQ: Three-band tube (±15dB bass, ±6dB mid, ±10dB treble), bypassable
• Bright Switch: Intelligent position-dependent preset (tapers with increased gain)
• Output Pad: -20dB balanced
• Additional Controls: Phase reverse, ground lift, front Thru (for tuners/amps/parallel processing)