Burl Audio B4

The Burl Audio B4 is a 4-channel microphone/line preamplifier and A/D converter module engineered for the B80 and B16 Mothership modular chassis. Built to transform the Mothership into an audiophile studio stage box or a tracking front end, the B4 pairs custom BX6 input transformers with Class-A discrete BOPA14 op-amps directly driving Burl’s mastering-grade ADC conversion path. By eliminating cables, patch bays, and redundant buffer stages between the preamp and converter, the B4 captures mic and line sources with rich transients, harmonic depth, and spatial realism.

Turning the stepped gain control down on the B4 engages dedicated line-level taps on the BX6 transformer. This provides a clean $10\text{ k}\Omega$ line input for mixing stems and synth tracks back through the Class-A transformer path.

The front panel features 4 individual rotary encoders for precision gain adjustments in $7\text{ dB}$ steps, along with hardware phantom power per channel. Digitally controlled preamplification allows full remote gain recall across Dante or SoundGrid networks when placed in machine rooms or on stage. Loading a single 4U B80 Mothership with ten B4 cards yields up to 40 channels of Class-A transformer-coupled mic preamps in a single frame.

Key Features

• 4-Channel Mic/Line ADC: Combined microphone/line preamplifier and A/D conversion card in a single slot.

• Proprietary BX6 Input Transformers: Custom-wound transformers designed specifically for true mic ($2.5\text{ k}\Omega$) and line ($10\text{ k}\Omega$) input impedance matching.

• Class-A Discrete Signal Path: Direct-coupled, capacitor-free circuit powered by Burl NextGen BOPA14 discrete op-amps.

• 40 Channels Per B80 Frame: Scale up to 40 complete mic pre / ADC input channels in a single 4U chassis.

• XLR Rear Panel Connectivity: 4 female XLR inputs mounted directly on the card faceplate for patch-free tracking.

• Configurable DSP Modes: Hardware jumper options for Short Delay vs. Long Delay ADC filters and sample-accurate Avid delay compensation.

Technical Specifications

• Form Factor: Single-Slot Daughter Card (B80 and B16 Mothership Compatible)

• Channel Count: 4 Channels (Mic/Line ADC)

• Preamp Type: Class-A Discrete Transistor with NextGen BOPA14 Op-Amps

• Input Transformers: Proprietary Burl Audio BX6

• Gain Range: Up to $59\text{ dB}$ (Stepped Gain Control)

• Input Impedance:

  • Microphone Input: $2.5\text{ k}\Omega$

  • Line Input: $10\text{ k}\Omega$

• Frequency Response:

  • Line Level ($0\text{ dB}$ Gain): $10\text{ Hz}-30\text{ kHz}$ ($-0.03\text{ dB}$ @ $10\text{ Hz}$, $-1.5\text{ dB}$ @ $30\text{ kHz}$)

  • Full Gain ($59\text{ dB}$ Gain): $10\text{ Hz}-30\text{ kHz}$ ($-0.03\text{ dB}$ @ $10\text{ Hz}$, $-2.5\text{ dB}$ @ $30\text{ kHz}$)

• Analog Input Connectors: 4x XLR Female

• Conversion Resolution: 24-Bit / $44.1\text{ kHz}$ to $192\text{ kHz}$