HDAM Discrete‑FET Hi‑Fi Preamplifier Board

   recreation of the preamplifier stage from Marantz’s top‑tier power amplifiers. Circuit topology: HDAM + SA1. High‑speed discrete preamplifier, also known as the Super Dynamic Amplifier Module.

Features Toshiba original surface‑mount dual matched FETs at the input (sonic performance surpasses K389). Output stage built with genuine discrete transistors.

Sound characteristics:

Spacious soundstage, black background, smooth non‑harsh high‑frequencies, rich midrange, tight and bouncy bass. Tonality leans toward tube‑amplifier and vinyl‑style classic analogue character. Outperforms op‑amp‑based designs by a wide margin.

Voltage gain: 4.7 times 
Power supply:  regulated +/- DC12‑15 V
PCB Size: 10 × 7 cm
4‑layer PCB construction

   The HDAM circuit was developed in the early 1990s. At that time, most power amplifiers relied on integrated operational amplifiers (OP‑AMPs). Integrated op‑amps offer proven performance, high reliability, minimal external components and low cost. Nevertheless, they have inherent drawbacks: First, limited slew rate. Low slew rate degrades transient speed, imaging and textural detail in audio reproduction. Second, conventional op‑amps introduce noise during amplification, which contaminates the original signal. To achieve superior audio performance, Marantz engineered the HDAM discrete amplifier circuit to overcome these limitations of integrated op‑amps.