Thermionic Culture Robin All-Valve DI Box

The Thermionic Culture Robin is an all-valve passive DI box built around a high-specification E.A. Sowter transformer for impedance matching between instruments and mic preamp inputs. With no solid-state transistors or ICs anywhere in the circuit, the Robin requires no 48V phantom power—and phantom power must be switched off when using it. The Sowter transformer operates at a 10:1 ratio: the Robin presents a load to the instrument that is 100 times the input impedance of the connected mic preamp, effectively isolating the instrument from low-impedance loading. A Bypass switch removes the transformer from the circuit entirely for a direct connection, and the Amp Jack connects directly to the DI Jack so a separate amplifier can be used simultaneously. An Earth Lift switch disconnects Pin 1 of the XLR output from the circuit to eliminate hum loops when external amplifiers or grounded mains-powered instruments are in use.

Key Features

• All-valve passive design — no solid state — no transistors or ICs; phantom power must be OFF when in use
• E.A. Sowter high-spec transformer — 10:1 ratio; input impedance presented to the instrument is 100× the mic preamp input impedance (e.g., a 1kΩ mic preamp input results in a 100kΩ load to the instrument); flat frequency response over the audio range; no measurable distortion added by the transformer
• Bypass switch — removes the transformer from the circuit and connects the instrument directly to the mic preamp input; works well with higher-impedance mic preamp inputs such as the Snow Petrel
• Amp Jack — connected directly to the DI Jack; allows a separate amplifier to be used simultaneously without re-patching
• Earth Lift switch — disconnects the ground connection (Pin 1 of the XLR output) from the circuit to prevent hum loops when an external amplifier is in use or when the instrument is powered from a grounded mains supply
• Switch guards — protect the switches from accidental activation; rugged construction throughout

Specifications

• Circuit Type: All-valve passive; no solid state
• Transformer: E.A. Sowter (high spec)
• Transformer Ratio: 10:1
• Input Impedance: 100× connected mic preamp input impedance
• Frequency Response: Flat over audio range
• THD Added: No measurable distortion
• Phantom Power: Must be OFF
• Bypass Switch: Yes (transformer out of circuit)
• Amp Jack: Direct connection to DI Jack
• Earth Lift: Yes (disconnects Pin 1 XLR output)
• Switch Guards: Yes
• Output Connector: XLR
• Construction: Handcrafted in England