Classic Reproduction Maran HDAM Sweet-Vocal Amplifier: Audiophile-Grade Amplifier Board with Original Field-Effect Input Transistors

Marantz HDAM Audio Linear Amplifier Circuit (Japan) delivers exceptional sound quality: powerful low end, rich midrange, and delicate highs, resulting in a comfortable listening experience with a tube-like flavor—far surpassing typical op-amp preamps. Unfortunately, the core transistor K170 was discontinued in later production, and substitutes like the K246 or K30 could not fully restore its beautiful sonic character.

In 2024, we sourced original Toshiba replacement transistors from overseas that perfectly match the characteristics of the K170. Each SMD package contains two matched 2SK transistors, eliminating the need for manual pairing and offering even lower distortion. The output stage employs two pairs of Toshiba 2SC5200 and 2SA1943 driver transistors, capable of delivering up to 15A peak current—far outperforming digital amplifiers and the LM3886. The circuit includes comprehensive protection: over-temperature, output over-voltage, and delay startup.

Premium components are used throughout: genuine transistors, German WIMA capacitors, 1% precision resistors with copper leads, Japanese Omron relays, and a dual-layer PCB with immersion gold plating.

PCB Dimensions: 184 x 122 mm
Power Supply Voltage: AC 18V x 2 to AC 28V x 2
Output Power: 70W @ 8Ω / 100W @ 4Ω
Frequency Band: 10–40 kHz
Maximum Capacitor Mounting Height: 35 mm
Product Weight: Approx. 868 g

Adjustment: Very simple. After ensuring correct soldering, power on and adjust the variable resistor so that the voltage across the TEST points is 20–40 mV. This corresponds to a quiescent current of 100–300 mA. Turning left reduces the current; turning right increases it.