A60+ Current-Feedback Amplifier Board Kit | 8-Pair Parallel Design, Dual-Channel Hi-Fi | Inspired by Accuphase A60

The A60+ board is an improved version based on the previously successful A60 design. Key enhancements include an increased number of output transistors (supporting up to 16 pairs / 32 pieces per channel), providing greater driving capability and the option to be adjusted to operate in Class A mode. Furthermore, the rectification section has been upgraded with a 120A low-resistance, high-speed rectifier, resulting in superior dynamic response.

The Accuphase A60 was a flagship amplifier of its generation, offering excellent density in both high and low frequencies, superb control, and outstanding detail and layering. Its circuit features a fully symmetrical architecture with current-feedback. A key characteristic of this design is the use of complementary push-pull circuitry from the input stage all the way to the output stage, enabling an exceptionally high slew rate of hundreds of volts per microsecond. This results in excellent drive capability for capacitive loads and overall sound quality that surpasses the earlier A2 model.

Material Selection Guide

Different transistor pairings yield distinct tonal characteristics. Please note that this is a pure power amplifier (main amplifier). Some customers have attempted to compare its bass performance with that of 2.1-channel speaker systems. For dedicated bass, purchasing a subwoofer would be a more suitable choice.

• Paired with Toshiba 2SC5200/A1943: Delivers a tube-like (valve) sound character, offering refined detail and a full, rich tonal quality with a slightly warmer, mellower tilt.

• Paired with ON Semiconductor Series High-Power Transistors: Produces a lively, articulate sound with excellent layering and harmonic overtones, and strong rhythmic drive.

• Paired with Japanese Sanken High-Power Transistors: Provides deep bass extension, powerful dynamics, and tight, solid, and forceful low frequencies.

In addition, a specially custom-made 500W toroidal transformer with independent power supply for each channel is available.

Based on personal comparison, thanks to the excellent circuit architecture, the use of Hi-Fi grade transistors (2SC2240, 2SA970, 2SA2705, 2SA114 complementary pairs), ON Semiconductor’s 15032/15033 for the output stage, and circuit parameters refined through countless adjustments, this amplifier delivers superior sound quality. It outperforms amplifiers like the KSA50 and various Goldmund-inspired clones in every aspect: bass performance, the sweetness of vocals, and the transparency of the highs.

The board features a built-in rectifier circuit, so you only need to connect a transformer; no external rectifier board is necessary. Wiring and installation are very straightforward. The fully symmetrical architecture, combined with precisely matched transistors, ensures the midpoint voltage is extremely stable without the need for adjustment.

To set the quiescent current per output transistor to 50-100mA, adjust the board’s single TEST point until the voltage drop across its two terminals measures 20-30 mV.

Important Note: Remember to use mica insulation sheets when mounting the output transistors, and ensure the mica sheets are fully coated with thermal paste.

Genuine Philips (PHILIPS) MRS25 1% Metal Film Resistors. High-stability metal film resistors featuring low current noise level, low temperature coefficient, and low tolerance.