Krell KSA 100S Power Amplifier Class A

Power Output

• 100 W per channel into 8 Ω (stereo)

• Power doubles with each halving of impedance:

  • ~200 W into 4 Ω

  • ~400 W into 2 Ω

  • ~800 W into 1 Ω — good for demanding speaker loads

Frequency Response

• ~20 Hz – 20 kHz, extremely flat and wide (1 Hz – 150 kHz in extended ranges)

Distortion & Noise

• Total Harmonic Distortion (THD): ~0.1 % at 1 kHz; ~0.5 % at 20 kHz at full power

Gain & Damping

• Gain: ~26 dB

• Damping factor: > 60 (good speaker control)

Inputs & Load

• Balanced (XLR) and single-ended (RCA) inputs

• Input sensitivity: ~1.4 V RMS

• Input impedance: ~47 kΩ

Physical

• Weight: ~80 lb (~36 kg)

• Dimensions: ~19.25″ × 8.5″ × 19.25″ (wide footprint)

• Heavy heat-sink design and solid construction

Class Bias

• “Sustained Plateau Bias” system: multi-level biasing that allows extended Class-A-like behaviour with reduced heat and power consumption versus pure Class A

Design & Engineering

Krell’s S-series amplifiers (including the KSA-100S) were engineered to combine Class-A-like smoothness with higher electrical efficiency. The sustained plateau bias scheme adjusts transistor bias in discrete steps, elevating it when the music level demands and dropping it for lower levels. This design aims to balance the warmth and detail of Class A with the practicality of cooler operation.

Construction quality is rugged and overbuilt: robust chassis, custom-machined aluminum faceplates, gold-plated binding posts, and large toroidal transformers are typical Krell traits.

 Sound Quality & Listening Impressions

Strengths

• Refined midrange and openness: vocals and acoustic instruments deliver with a natural flow.

• Forceful and authoritative bass: solid low-frequency grip with plenty of headroom.

• Power delivery: ample current reserves for driving demanding speakers.

• Sonic balance: avoids harshness, even at higher output levels.

• Many users note it delivers an immersive, deep soundstage with strong dynamics.

Nuances & Observations

• Some reviewer comparisons noted that the KSA-100S has a slightly lighter dynamic drive or bass “weight”compared to larger Krell models or similarly high-end amplifiers, but this varies with system matching.

• Its character can be described as controlled and powerful, with a slightly forgiving top-end rather than aggressive or forward.