Overview

The FM255 MkIIR is an upper-tier line stage from FM Acoustics’ Resolution Series. It offers true-balanced I/O, switchable true-impedance attenuators, and a Swiss-made remote with fast/slow volume steps. Production has ended; the FM 256-RC carries the line forward, and FM states the 255 series served as a mainstay for nearly three decades[1][2].

Scientific Validity

\[\Large \text{0.5}\]

There are no credible third-party measurements (THD+N, S/N, crosstalk, etc.) publicly available. The manufacturer claims high interference rejection (~100 dB at inputs), robust cable drive, and true-balanced outputs, but these do not substitute for independent audibility-relevant data[1][3]. Per policy, with unknown measured transparency we set the baseline at 0.5 pending independently verified results.

Technology Level

\[\Large \text{0.7}\]

Engineering highlights include fully discrete “enhanced Class A” circuits, true-impedance input attenuators, true-balanced I/O with automatic optimization to various loads, and a dual-speed remote volume control. Swiss hermetically sealed relays rated for high switching cycles are used across the series materials[1][3]. However, absent modern third-party bench data, we refrain from awarding a higher score typical of state-of-the-art measured designs.

Cost-Performance

\[\Large \text{0.1}\]

Comparator (equal-or-better): Benchmark LA4—balanced/unbalanced I/O, remote, and proven transparency with extremely low distortion and very high S/N (105.5 dB in-band; 108.7 dB A-weighted)[4]. Price: 2,599 USD (remote included)[5].
Subject unit market price (current used): FM255 MkII series at 15,900 EUR (audio-markt, 2024-05-19). ECB rate 1 EUR = 1.1606 USD (2025-08-12) → 18,453.54 USD[7][8].
Formula: 2,599 USD ÷ 18,453.54 USD = 0.1409… → round to 0.1.
Equivalence note: LA4 offers the same user-facing functions (line-level preamp with balanced/unbalanced I/O and remote) and objectively superior/transparent measured performance (S/N, THD+N, channel separation)[4][5].

Reliability & Support

\[\Large \text{0.4}\]

The FM255 MkIIR is discontinued and support centers on the FM 256-RC[2]. FM Acoustics maintains service and emphasizes modular construction, but service access is via a limited distributor network and long-term parts availability is less certain than for current mass-market models[1][6].

Rationality of Design Philosophy

\[\Large \text{0.5}\]

Discrete Class-A topology, careful grounding/shielding, and interference rejection are rational means. Yet, without verifiable transparency-level bench results, claims remain difficult to validate against modern, measurement-driven designs[1][3][4]. We therefore assign a moderate score.

Advice

If you value FM Acoustics’ build style and ergonomics (true-balanced paths, fast/slow volume), the FM255 MkIIR remains desirable. However, given present market pricing (~18,454 USD) against a transparent, fully measured alternative like the LA4 at 2,599 USD, value is weak[4][5][7][8]. If you prefer FM’s approach and want room-mode control, consider the current FM 256-RC with analogue ARC; otherwise, prioritize measurement-centric preamps for best price-to-performance[2][4].

References

[1] FM Acoustics, “Resolution Series 255-MKII-R (Heritage)”, https://www.fmacoustics.com/company/heritage/fm-255-mkii-r/ , last updated 2025-07-28 (accessed 2025-08-13)
[2] FM Acoustics, “Resolution Series 256-RC (successor)”, https://www.fmacoustics.com/products/line-stages/fm-256-rc/ , last updated 2025-07-28 (accessed 2025-08-13)
[3] FM Acoustics (datasheet), “The Resolution Series® 255 MK-II and MKII-R”, https://audioniuli.com/wp-content/uploads/dat_2552.pdf , n.d. (accessed 2025-08-13)
[4] Stereophile, “Benchmark LA4 line preamplifier Measurements”, https://www.stereophile.com/content/benchmark-la4-line-preamplifier-measurements , 2019-12-24 (accessed 2025-08-13)
[5] Stereophile, “Benchmark LA4 line preamplifier Specifications (Price 2,599 USD, remote included)”, https://www.stereophile.com/content/benchmark-la4-line-preamplifier-specifications , 2019-12-24 (accessed 2025-08-13)
[6] FM Acoustics, “Questions & Answers / Support”, https://www.fmacoustics.com/miscellaneous-1/questions-answers/ , n.d. (accessed 2025-08-13)
[7] audio-markt, “FM Acoustics FM 255 mk2 (used 15,900 EUR)”, https://www.audio-markt.de/en/market/fm-acoustics-fm-255-7199396437 , 2024-05-19 (accessed 2025-08-13)
[8] European Central Bank, “US dollar (USD) – ECB euro reference exchange rate (1 EUR = 1.1606 USD)”, https://www.ecb.europa.eu/stats/policy_and_exchange_rates/euro_reference_exchange_rates/html/eurofxref-graph-usd.en.html , 2025-08-12 (accessed 2025-08-13)

(2025.8.13)