Musical Fidelity A1 Class A Integrated Amplifier

The A1 through time - Improvements to the original. Updated transformer to more efficient “dual mono split rail” windings. High quality and updated ALPS RK series potentiometer as volume control. IR remote control added for volume. Gain block before volume control totally by passable using “direct” switch (-10dB). All transistors including output devices are carefully selected modern equivalents. All capacitors in signal path are polypropylene (PP) type. Resistors are modern low noise metal film types. Care and attention made to not change any component specification from original but to update them to modern .equivalent with long lifespan Layout faithfully follows original within circuit sections on circuit board Circuit sections better laid out, in particular the separate supplies and power amplifiers Phono stage and preamplifier improved for less noise and hum The A1 in Brief 25W Pure Class A power @ 8 Ohm Discrete symmetrical topology Planar Audio transistors with 25A maximum output Dynamic class A, slides (NOT switches) smoothly into Class B, allowing more current as needed Therefore drives difficult speakers with no problems Updated transformer to “dual mono split rail” windings Fully independent left and right power supplies Each power amplifier now has double supply capacity Transformer noise and heat dissipation reduced Filtered main supplies Gain block before volume control totally bypassable using “direct” switch High quality and updated ALPS RK series potentiometer Low noise TL071 JFET preamplifier circuitry Discrete current-mode MM/MC phono input stage Low noise current to voltage converter for further amplification and RIAA equalization Automatic input impedance matching (1K nominal) for MC along with increased gain Original (1985) A1 appearance and circuits with modern improvements Remote control added for volume Modern updated low noise components A1 - Specifications Amplifier Power: 25 Watts per channel into 8 Ohms Voltage: 42.5 Volts peak to peak

• The A1 is built around a completely discrete and symmetrical Class A topology. It‘s able to output 25W of pure Class A power @ 8 ohms load with 25A of maximum output. While the numbers here might seem rather low, the ability for the output stage to drive difficult speakers is a small miracle in itself. The amp design being dynamic class A, and if Class A standing current is exceeded, it will automatically allow more. It therefore “slides” (NOT “switches”) smoothly into class B style operation.
• The new A1 has received an updated transformer from shared (1985 original) to more efficient “dual mono split rail” windings. The amp stages are supplied by fully independent left and right power supplies for better power handling and stereo imaging and each power amplifier now has double supply capacity resulting in reduced ripple and noise. The transformer‘s noise and heat dissipation are reduced due to better efficiency and updated components.
• The low noise preamplifier circuitry is the same as the original 1985 design and, as we have highlighted above, greatly benefits from the improved, fully smoothed and regulated power supplies. Among the discernible alterations, one that immediately catches the eye is the addition of a new „direct“ switch at the preamp stage. With this switch you can totally bypass the gain block before the volume control, resulting in roughly 10dB less gain.
• The A1 employs a discrete current-mode input stage for lowest noise amplification of MC and MM cartridges. A low noise current to voltage conversion stage is used for further amplification and RIAA equalization. Automatic input impedance matching for the selected MC input, along with increased gain increases the versatility of the A1‘s phono stage.
• The A1 has one secret. This secret is simple: it makes music. It sounds sweet and fluid and creates a beautiful atmosphere around natural instruments. Especially in small to mid-sized rooms, carefully set up with a pair of great two-way speakers. It is not a powerhouse, but music lovers will cherish its abilities. It‘s also not a product that you‘ll want to hide. A perfect example of form follows function. The oversized heatsinks define the A1‘s look, but they are essential for its operation.