Musical Fidelity - A1 Integrated Class A Amplifier

The 1985 cult classic reissued: 25 watts per channel in pure Class A, with a discrete current-mode MM/MC phono stage and a top plate that is the heatsink.

The A1 arrived in 1985 and became one of hi-fi’s genuine cult objects. Twenty-five watts per channel in pure Class A, at a price that put Class A operation within reach for the first time, and a reputation for driving difficult loudspeakers that its power rating had no business supporting. The slim chassis with its full-width finned top plate was as recognisable as the sound, and it ran hot enough to become part of the legend.

The 2023 version is a reissue rather than a homage. Musical Fidelity has kept the circuit topology, the appearance and the published specifications of the 1985 original, while modernising the hardware around them: the shared-winding mains transformer has been replaced by dual-mono split-rail windings with fully independent left and right supplies, per-channel supply capacity is doubled, a motorised ALPS RK series potentiometer arrives with a supplied remote, polypropylene capacitors run through the signal path, and a “direct” switch bypasses the preamplifier gain block for roughly 10dB less gain. Read Musical Fidelity’s “kept all specifications” claim as meaning the same published figures and the same circuit topology, not unchanged hardware — the direct switch alone adds a specification that did not exist in 1985.

One structural point is worth stating clearly, because Musical Fidelity’s own copy invites confusion. The power amplifier uses discrete symmetrical topology and the phono input is a discrete current-mode stage, but the line-level preamplifier gain block uses a TL071 JFET op-amp — the same part as the 1985 original, which is why it is there. The A1 is not a wholly discrete amplifier, and we would rather say so than let the word carry more weight than it should.

The phono stage covers both moving magnet and moving coil, selected by a rear-panel switch, with 40dB of gain on MM into 50k ohms and 100pF, and 60dB on MC with what Musical Fidelity calls automatic input impedance matching at 1k ohm nominal. There is no headphone socket, no mono switch and no subsonic filter; the A1 is a purist integrated with one phono input, five line inputs, a tape output, a variable preamp output and a single set of speaker terminals.

Heat is not a side effect of the design, it is the design. The entire top of the A1 is a heatsink and nothing may be placed on it at any time. Musical Fidelity requires at least 50mm of clear space behind the amplifier and at least 250mm above it, and states that a heatsink surface temperature of 55 to 65°C is average in a room at 20°C — the company’s own comparison is the heat thrown off by a 75-watt light bulb. Parts of the amplifier can become hot enough to cause burns, so take particular care around children. And note Musical Fidelity’s instruction in capitals: you must connect the A1 to a pair of loudspeakers before you switch it on.

Features

• 25 watts per channel into 8 ohms in pure Class A — a faithful reissue of the 1985 original’s circuit topology, appearance and published specifications
• Dual-mono split-rail mains transformer with fully independent left and right supplies, replacing the original’s shared winding
• Doubled per-channel power supply capacity and filtered mains supplies
• Discrete symmetrical power amplifier topology; discrete current-mode MM/MC phono input stage
• Line preamplifier uses the same low-noise TL071 JFET op-amp as the 1985 design
• Polypropylene capacitors throughout the signal path
• Motorised ALPS RK series volume potentiometer with remote control supplied
• NORMAL / DIRECT switch — DIRECT bypasses the preamplifier gain stage for roughly 10dB less gain
• Rear-panel MM/MC selector with automatic impedance matching and increased gain on moving coil
• The entire top plate is the heatsink — nothing may be placed on it at any time

Specifications

• Type: Pure Class A stereo integrated amplifier with MM/MC phono stage; 2023 reissue of the 1985 original
• Power Output: 25 watts per channel into 8 ohms, pure Class A
• Output Voltage: 42.5 volts peak to peak
• Output Current: 25 amps peak to peak — Musical Fidelity’s claim, published without test conditions. See note below
• Damping Factor: 150
• Gain at Maximum Volume: 32dB in DIRECT mode; 42dB in NORMAL mode
• Direct Switch: NORMAL engages the preamplifier gain stage; DIRECT bypasses it, giving roughly 10dB less gain
• Output Devices: 2 per channel. Musical Fidelity describes them as “Planar Audio transistors”, by which it means planar-process audio output transistors; no part numbers are published
• THD + Noise: <0.05% typical; <0.01% A-weighted. Published in the owner’s manual only, with no stated power level or bandwidth
• Signal-to-Noise Ratio: 82dB
• Channel Separation: 85dB
• Frequency Response: +0, −1dB, 10Hz – 40kHz
• Line Input Sensitivity: 300mV RMS nominal, 8V RMS maximum. Note this is a nominal source level rather than the input required for rated output, which works out at roughly 112mV
• Line Input Impedance: 25k Ω
• Tape Output Impedance: 220 Ω
• Preamp Output Impedance: 100 Ω
• Phono Stage: Discrete current-mode MM/MC input stage with a low-noise current-to-voltage converter feeding further amplification and RIAA equalisation
• Phono RIAA Accuracy: ±1dB
• Phono, Moving Magnet: 5mV nominal sensitivity; 100pF / 50k Ω loading; 40dB gain; 75dB signal-to-noise
• Phono, Moving Coil: 450µV nominal sensitivity; 1k Ω loading with automatic impedance matching; 60dB gain; 70dB signal-to-noise
• Phono Mode Selection: Rear-panel MM/MC switch, not a front-panel control
• Inputs: 1 x MM/MC phono on RCA with ground post; 5 x line level RCA
• Outputs: 1 x fixed line level RCA tape out; 1 x variable line level RCA preamp out; speaker outputs on 4mm banana plug / binding posts
• Speaker Outputs: One stereo set (one left pair, one right pair, four posts). There is no A/B speaker switching
• Headphone Output: None. The manual suggests connecting an outboard headphone amplifier to the tape outputs
• Front Panel: On/off, infrared receiver, volume (motorised ALPS RK series), NORMAL/DIRECT switch, source selector
• Mono Switch: Not fitted
• Subsonic Filter: Not fitted
• Remote Control: Supplied; volume control
• Heat and Clearance: The whole top of the A1 is a heatsink and nothing should be placed on it at any time. Allow at least 50mm of clear space behind and at least 250mm above. A heatsink surface temperature of about 55 to 65°C is average in a room at about 20°C. Some parts of the product may become very hot and cause burns, so take special care around children and vulnerable persons
• Critical Setup Note: Musical Fidelity states, in capitals: you must connect the A1 to a pair of loudspeakers before you switch it on
• Mains Voltages: 115/230VAC 50/60Hz, factory pre-set internally; 100VAC 50/60Hz optional
• Power Consumption: 130 watts maximum. Musical Fidelity lists 0W in standby, qualified as the power switch being off — the A1 has no low-power standby state, and as a pure Class A design its idle draw is close to maximum
• Dimensions (W x H x D): 440 x 68.3 x 283.3 mm
• Weight: 10.5 kg unboxed; 12 kg in the shipping carton
• In the Box: 10-amp IEC mains lead, A1 remote control, CR2032 batteries
• Warranty: Two years, administered by the local national distributor — Harmonia Distribution has handled Musical Fidelity in the United States since 15 November 2025. Cover is for the original owner only, is non-transferable, and requires the original sales invoice as proof of purchase date. Older Musical Fidelity literature quoting a five-year term with separate categories for disc players and servers is obsolete
• Country of Manufacture: Not published. Musical Fidelity was founded in London in 1982 and has been owned since 2018 by Audio Tuning Vertriebs GmbH of Austria, the parent of Pro-Ject. The company states that its products are designed and voiced in the UK and continental Europe, which is a design statement rather than a manufacturing one, and it publishes no country of manufacture for this model
• Not Published: Idle power consumption; weighting and reference level for the 82dB, 75dB and 70dB signal-to-noise figures; phono overload margins; power output into 4 or 2 ohms; whether the 283.3mm depth includes rear terminals; warm-up time; recommended minimum loudspeaker impedance; finish options; output transistor part numbers
• Note: Two points where Musical Fidelity’s figures and its descriptions do not sit comfortably together. The phono input is described as a current-mode stage, a topology whose defining characteristic is a very low input impedance, yet the published moving coil loading is 1k Ω nominal — itself unusually high for MC, where 100 Ω is typical. We report both as published rather than reconcile them. Separately, 25 amps peak to peak from two output devices per channel on 42.5V peak-to-peak rails is an aggressive headline figure for an amplifier that needs about 2.5 amps peak to make 25 watts into 8 ohms, and Musical Fidelity states no test conditions for it. The 50k Ω MM loading is confirmed across all three Musical Fidelity documents and matches the figure published for the M5si, so it is a house value rather than a typo, though the industry standard is 47k Ω