Shown above is the circuit for each channel.
Ultra-high performance, completely transparent RCA to true balanced XLR active converter.
The board incorporates ultra-high performance op-amps from Burr-Brown (Texas Instruments), including the OPA1612 and OPA1632. It also contains two extremely low noise linear regulators (LDOs), LT3042 and LT3090 to achieve the best possible performance.
The acrylic case may be purchased at this link.
Specifications:
Input impedance (RCA): 47kΩ
Output impedance (XLR): 100Ω
Gain: 8dB
Input Power Voltage: 9V +/-5%
Input Power Connector: Barrel Plug (2.1mm I.D. x 5.5mm O.D. x 9.5mm) – center positive
Max Output Voltage: 8 Vrms (20.28dBu)
Max Output Current: 70 mArms
Signal-to-Noise Ratio (SNR), 8Vrms Output: 132dB
Frequency Response: DC – 80kHz+
Why use an active converter?
There are three ways to get from RCA (unbalanced) to XLR (balanced)
(1) Use an RCA to XLR adapter
With an RCA to XLR adapter, you break the balanced input on your amplifier or pre-amp because 1/2 of the XLR input is shorted to the RCA’s shield. Depending on the design of the balanced input this can have multiple undesirable effects.
(2) Use a transformer-based RCA to XLR Converter
A transformer-based converter can work well as long as it is properly matched to both the RCA and XLR side impedances. However, even if it is properly matched the transformer creates AC coupling which causes bass phase shift.
(3) Use an active converter
With a DC-coupled active converter, all the issues associated with the first two approaches are eliminated.
RCA to XLR Adapter Test Results
Signal-to-Noise Ratio (SNR) 
Frequency Response – Gain & Phase 
THD+N Ratio vs Output Level @ 1kHz 
THD+N Ratio VS Frequency at 5V Out THD+N Ratio VS Frequency at 4V Out 
Intermodulation (IMD) Distortion vs Output Level 
Multitone 
10kHz Square Wave 5V Output 
Crosstalk, One Channel Driven
