Royer Labs SF-24V is a stereo vacuum tube ribbon microphone — the pinnacle of Royer's SF series and the world's first commercially produced stereo ribbon microphone with tube electronics. Two matched 1.8-micron aluminum ribbon elements are mounted one above the other in a true coincident Blumlein configuration (crossed figure-eights, 45 degrees off axis), each driven through an independent tube circuit derived from the same electronics as Royer's TEC Award-winning mono R-122V. The tubes are JAN military-specification 5840W pentodes wired in triode configuration as cathode followers, burned in at the Royer factory before shipment. Output signals are transformer-coupled and galvanically isolated via Jensen transformers housed in the dedicated external power supply, which also contains the plate supply (135 VDC) and filament supply (6 VDC) sections.
Tube electronics — headroom, detail, and air
The triode cathode follower configuration eliminates typical tube coloration while retaining the advantages of thermionic technology: greater headroom and faster transient response compared to the FET-based SF-24. The higher output level comes entirely from the internal toroidal step-up transformers (free gain) — the tube circuit itself operates below unity gain and contributes no noise of its own; self-noise remains below 18 dB. Jensen transformers in the power supply provide galvanic isolation and output balancing, virtually eliminating induced noise on long cable runs. Active tube electronics maintain a constant, optimal impedance load on both ribbon elements regardless of the downstream preamp's input characteristics — the SF-24V works with any professional preamplifier without impedance matching concerns or overload risk. Output impedance is 450 ohms — higher than the FET SF-24's 200 ohms, a result of the transformer-coupled output stage.
Stereo configurations and mono operation
The Blumlein configuration — two figure-eights at 90 degrees — provides true single-point stereo capture with no inter-channel time-of-arrival delay to correct. Alternatively, the SF-24V operates in M/S configuration with standard matrix processing in the console or DAW. Phase compatibility between the two channels is complete — stereo-to-mono summing produces no artifacts, which makes the microphone viable as a wide mono source when capturing performers with unstable positioning relative to a single-axis microphone. Each channel can be used independently as a standalone mono figure-eight microphone. The SF-24V ships with a dedicated external power supply, a 7-pin XLR cable, shockmount, and a handcrafted Padauk wood presentation case. Lifetime warranty to the original owner.
KEY FEATURES
- World's first commercially produced stereo vacuum tube ribbon microphone
- Two matched 1.8-micron aluminum ribbons in Blumlein configuration (figure-eights, 45° off axis)
- Two independent tube circuits: JAN mil-spec 5840W pentode wired in triode configuration
- Tubes burned in at Royer factory before shipment
- Tube electronics derived from TEC Award-winning R-122V
- Greater headroom and faster transient response than FET SF-24
- Sensitivity -38 dB — condenser microphone output level
- Self-noise below 18 dB — free gain from toroidal transformers, no noise from tube stage
- Jensen transformers in power supply: galvanic isolation and balanced output
- Constant optimal ribbon load impedance regardless of preamp
- Supports Blumlein and M/S configurations from a single mic position
- Full phase compatibility — stereo-to-mono summing without artifacts
- Each channel independently usable as a mono figure-eight microphone
- Ribbon elements protected from phantom power, electrical transients, and miswired cables
- Dedicated external power supply (135 VDC plate / 6 VDC filament)
- Handcrafted Padauk wood presentation case; lifetime warranty
TECHNICAL SPECIFICATIONS
- Acoustic operating principle: electrodynamic pressure gradient with vacuum tube electronics
- Vacuum tube: JAN mil-spec 5840W pentode, triode-wired cathode follower
- Polar pattern: crossed figure-eights (Blumlein)
- Generating element: 1.8-micron aluminum ribbon
- Frequency response: 30–15,000 Hz +/- 3 dB
- Sensitivity: -38 dB (re. 1V/Pa +/-1 dB)
- Self-noise: below 18 dB
- Output impedance: 450 ohms @ 1 kHz
- Recommended load impedance: 1,500 ohms or greater
- Maximum SPL: above 130 dB
- Microphone output connector: XLR 7-pin (stereo)
- Power supply output connectors: 2x XLR 3-pin
- Power requirements: plate 135 VDC @ 2 mA; filament 6 VDC @ 150 mA (dedicated PSU)
- Supply current: 4 mA per channel
- Microphone dimensions: 270 mm x 39 mm (base) x 25 mm (top)
- Weight: 583 g (20.5 oz)
- Finish: Dull Satin Nickel; optional Optical Black
- Includes: SF-24V microphone, dedicated power supply, 7-pin XLR cable, shockmount, Padauk wood case
