Ferrum OOR Headphone Amplifier with AC/DC Power Supply at Vinyl Sound Buffalo, New York

The Ferrum OOR is a fully balanced, fully discrete analogue headphone amplifier from Ferrum Audio (Warsaw, Poland), available with its AC/DC power supply at Vinyl Sound in Buffalo, New York. The OOR is the winner of the EISA Best Headphone Amplifier 2022-2023 Award and the Headfonia Best Amplifier 2024 Readers' Choice Award, recognised for a proprietary discrete power amplifier topology that achieves 130 dB dynamic range (A-weighted), 8 W output power into 60 Ω balanced, and a headphone output impedance below 0.3 Ω. The OOR operates with no integrated circuits in its amplification stage, carries the signal in a fully balanced configuration from both XLR and RCA inputs, and is engineered from the outset to be upgraded with the Ferrum HYPSOS Hybrid Power System via the proprietary Ferrum Power Link connector for sensing-corrected power delivery beyond what any standard DC adapter can provide.

Fully Discrete, Fully Balanced Amplifier Technology

The OOR's amplifier section uses Ferrum's proprietary discrete power amplifier technology, developed entirely in-house in Warsaw without reference to existing integrated circuit designs. The output transistors are driven in a configuration that prevents them from fully switching off, maintaining a state of readiness that eliminates crossover distortion and enables instantaneous response to transient demands. This approach contributes to the measured THD of 0.00011% (-119 dB) on the balanced output at 1 mW into 50 Ω and THD of 0.00008% (-122 dB) on the single-ended output at the same load. RCA inputs are converted to a balanced signal internally, so both XLR and RCA sources operate in fully differential mode throughout the amplifier. Three gain steps are switchable from the front panel: -4/+6/+16 dB balanced and -10/0/+10 dB single-ended, allowing the OOR to serve both sensitive IEMs and high-impedance planar magnetic headphones from the same unit.

Ferrum Power Link and HYPSOS Upgrade Path

The OOR includes a proprietary four-pin Ferrum Power Link connector on its rear panel alongside the standard 5.5/2.5 mm DC input. When connected to the HYPSOS via the FPL cable, the HYPSOS uses its 4T Sensing Design to read voltage at the OOR's internal power rails and correct delivery in real time, compensating for cable resistance and transient current demands that a standard DC supply cannot measure. The result is a measurably lower noise floor and higher dynamic range from the OOR than is achievable with the included AC/DC adapter. Sweet Spot Tuning in the HYPSOS allows fine voltage adjustment between 22 and 30 V on the fly, enabling optimisation of the OOR's operating point. The OOR ships with a carefully selected AC/DC power adapter for standalone use and is fully functional without the HYPSOS.

Key Features

• EISA Best Headphone Amplifier 2022-2023: The OOR won the Expert Imaging and Sound Association's top headphone amplifier award, recognising its discrete topology, output power, and ultra-low distortion in a compact desktop chassis.
• Fully Discrete Proprietary Amplifier Stage: No integrated circuits are used in the OOR's signal amplification path. The discrete topology is developed entirely in-house by Ferrum's engineering team in Warsaw for maximum analogue quality.
• 8 W into 60 Ω Balanced: Output power of 8 W into 60 Ω on the balanced output provides substantial headroom for low-impedance planar magnetic headphones, while 1,600 mW into 300 Ω handles high-impedance dynamic drivers with authority.
• 130 dB Dynamic Range: A-weighted dynamic range of 130 dB places the OOR among the highest-measured desktop headphone amplifiers available, contributing to its ability to resolve fine detail and low-level signal texture.
• Headphone Output Impedance Below 0.3 Ω: Near-zero output impedance ensures flat frequency response across all headphone impedance curves, including multi-driver dynamic headphones with complex impedance profiles.
• Three Selectable Gain Steps: Front-panel gain switching in three steps per input mode accommodates everything from high-sensitivity IEMs requiring minimum gain to demanding orthodynamic headphones needing maximum power.
• HYPSOS FPL Compatible: The proprietary four-pin FPL rear connector allows upgrade to the HYPSOS power supply for sensing-corrected delivery, measurably improving noise floor and dynamic performance beyond the included adapter.
• Balanced and Single-Ended Outputs: A 4-pin balanced XLR headphone output and a 6.35 mm single-ended jack are both available simultaneously, accommodating balanced and unbalanced headphone cables without re-termination.

Technical Specifications

Awards and Critical Recognition

• EISA Best Headphone Amplifier 2022-2023: Ferrum OOR (Expert Imaging and Sound Association)
• Headfonia Best Amplifier 2024: Ferrum OOR, Readers' Choice Award (Headfonia)

Frequently Asked Questions

What is the Ferrum OOR?

The Ferrum OOR is a fully balanced, fully discrete analogue headphone amplifier manufactured by Ferrum Audio in Warsaw, Poland. It delivers 8 W into 60 Ω on its balanced output, achieves 130 dB dynamic range (A-weighted), and uses a proprietary discrete power amplifier circuit with no integrated circuits in the signal path. It won the EISA Best Headphone Amplifier 2022-2023 Award and is available at Vinyl Sound in Buffalo, New York, with its included AC/DC power adapter and an upgrade path to the HYPSOS Hybrid Power System via Ferrum Power Link.

How does the Ferrum OOR compare to the Benchmark HPA4?

The Ferrum OOR and Benchmark HPA4 are both fully balanced, ultra-low-distortion desktop headphone amplifiers. The Benchmark HPA4 uses a passive transformer-based volume control stage and is based on Benchmark's AHB2 amplifier topology optimised for extremely low noise floor and -132 dB THD+N. The OOR uses a fully discrete proprietary power amplifier with no ICs and a three-step switchable gain stage, and uniquely benefits from the HYPSOS FPL power upgrade path. The OOR's output power of 8 W into 60 Ω balanced is substantially higher than the HPA4's output into equivalent loads. The HPA4 does not have a dedicated headphone output impedance below 0.1 Ω specification published for comparison, while the OOR specifies below 0.3 Ω. The OOR provides three gain steps and both single-ended and balanced inputs; the HPA4 provides balanced inputs and a fixed gain stage with passive level control.

How does the OOR compare to the Burson Soloist 3X GT?

The Ferrum OOR and Burson Soloist 3X GT are both discrete, fully balanced desktop headphone amplifiers in the high-end category. The Burson uses Burson's proprietary discrete op-amp modules (V7 Vivid or V7 Classic) in a class A biased topology, offering a warm and organic character. The OOR uses Ferrum's own discrete power amplifier circuit, measured at 130 dB dynamic range against the Soloist 3X GT's published figures. The OOR is significantly more compact at 50 mm height versus the Soloist 3X GT's larger chassis and offers the HYPSOS FPL power upgrade, a path not available for the Burson. The OOR also connects directly to the WANDLA as a matched system with shared power supply, a level of integrated design Burson does not offer.

What headphones pair best with the Ferrum OOR?

The OOR is designed to drive all headphone types across its three gain settings. On low gain, sensitive IEMs and efficient dynamic headphones operate quietly with full analogue volume range. On mid gain, headphones such as the Sennheiser HD 800 S (300 Ω) and Focal Utopia benefit from the 1,600 mW into 300 Ω balanced output with ample headroom. On high gain, demanding planar magnetic headphones including the Hifiman Susvara, Audeze LCD-4, and Abyss AB-1266 receive the OOR's full 8 W into 60 Ω, which provides the power and damping factor these headphones require for controlled bass and dynamic authority. The headphone output impedance below 0.3 Ω maintains flat frequency response across all headphone types.

Does the OOR include a preamplifier output for loudspeakers?

Yes. The OOR includes balanced XLR and unbalanced RCA line outputs on its rear panel, operating as a preamplifier stage with the same fully balanced, discrete signal path as the headphone output. Output impedance is 44 Ω balanced and 22 Ω single-ended, appropriate for driving any standard power amplifier input. The OOR can therefore serve as a headphone amplifier and analogue preamplifier simultaneously, making it suitable for hybrid headphone and loudspeaker desktop systems without a separate dedicated preamp.

What is included with the Ferrum OOR and what are the upgrade options?

The OOR ships with a carefully selected AC/DC power adapter (100-240 V AC input) that powers it fully for standalone use. The proprietary Ferrum Power Link cable for HYPSOS connection is not included and is available separately. The HYPSOS Single Output or HYPSOS Dual Output power supplies are the primary upgrade path, both available at Vinyl Sound Buffalo. The HYPSOS Dual Output allows simultaneous FPL-connected power delivery to both the OOR and a second Ferrum component such as the WANDLA from a single power supply unit.

Where can I buy the Ferrum OOR in Buffalo or Western New York?

The Ferrum OOR with AC/DC power supply is available at Vinyl Sound, an authorised Ferrum Audio dealer in Buffalo, New York, serving customers throughout Western New York and the USA. Vinyl Sound carries the full Ferrum Audio lineup including the HYPSOS power supply and WANDLA DAC for complete stack demonstrations.