Krell KSA-100 (1980)

A high-power stereo amplifier designed by Dan D'Agnostino, built for dynamic performance and low-impedance drive capability.

Overview

The Krell KSA-100 is a stereo power amplifier released in 1980 by American manufacturer Krell. Dan D'Agnostino designed it, and it was described as a "super booster" - a high-current amplifier that can drive difficult speaker loads with authority. It delivers 100 watts per channel into 8 ohms, 200 watts into 4 ohms, and 400 watts into 2 ohms. It can output up to 800 watts per channel at 1 ohm. The circuit is pure complementary, running pure Class A, with an oversized power supply.

Specifications

Rated output	100W + 100W (8 Ω, 20 Hz to 20 kHz, both channels driven)
Rated output	200W + 200W (4 Ω)
Rated output	400W + 400W (2 Ω)
Input Sensitivity / Impedance	1V/22k Ω
Total harmonic distortion factor	0.05% or Less (20 Hz to 20 kHz, 1W to Rated Output)
Frequency characteristic	0.5 Hz ~ 100 kHz -3dB; 20 Hz ~ 20 kHz -0.5 dB (1W ~ Rated Output)
Signal-to-noise ratio (IHF-A)	110dB
Rated load impedance	2 Ω or more
Damping factor	120(1kHz)
Slew rate	80 v / μ sec
Power	100 VAC, 50Hz/60Hz
Power consumption	610W (maximum idling)
External dimensions	Width 483x Height 226x Depth 612 mm
Weight	Approximately 35 kg

Design

The KSA-100 uses a pure complementary circuit with pure Class A operation. Negative feedback is limited to 15 dB to favor dynamic performance. The power block has a heat sink and an extremely quiet cooling fan, which hold the power block temperature between 75 and 80 degrees Celsius. The power supply uses a 160,000 μF capacitor and two 1.1 kW-class toroidal transformers. That adds up to the equivalent of a 400W-class amplifier operating in Class B.

Context

D'Agnostino designed the KSA-100 and Krell introduced it in 1980 as a high-current, high-power amplifier for driving low-impedance speakers with control and stability. The power supply and thermal management are built for performance under demand.