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A. GENERAL INFORMATION
The latest generation of high-resolution source components and speakers places
new demands on the power amplifier. The Krell KSA 150 and KSA-250 meet
these challenges with fresh design sophistication and long-term value. Both
products can drive any speaker with an effortless quality that makes their power
seem endless. Extreme clarity is maintained at all power levels. They both utilize
Krell refined high-bias Class A and direct-coupled circuitry from input to output.
Their power supplies and output stages are massive. High voltage rails with
extensive regulation are provided for the input circuitry. All materials and
electronic components are of the finest quality and operate within their optimum
performance ranges. Virtually all hand wiring has been eliminated, resulting in a
dramatic improvement in sonic clarity.
The KSA-150 and KSA-250 both utilize Class A circuitry throughout the audio
and power supply regulation stages. Class A gain stages deliver excellent sonic
performance under diverse conditions because all active components are
turned on at all times. This allows each component to operate in its most linear
and precise regions. The amplifiers are able to respond to the full range of input
signals with equal accuracy.
The KSA-150 and the KSA-250 are conservatively rated at 150 and 250 watts
per channel into 8 ohms, respectively. The 150 will actually generate 220 watts
into 8 ohms, and the 250 will generate 320 watts into 8 ohms. The 8-ohm power
ratings do not account for the amplifiers superb sonic performance nor describe
their maximum power. The Krell definition of power and the ability to drive low
impedances is that the output must double into successively low impedances.
The immense power supplies in both products allow them to double their power
into one ohm.
There are many advances in thermal construction and control circuitry in the
KSA -150 and KSA -250. All heat bearing structural components and external
heat sinks have been designed in-house to improve thermal tracking and cooling.
This construction provides very low thermal resistance between the output
transistors and the heat sinks, resulting in superior thermal tracking. It also
results in a considerable reduction in overall size. Greater amplifier life
expectancy is an added design benefit.
Automatic self-adjusting bias and DC offset control circuitry have been developed
for the KSA-150 and the KSA-250. These circuits compel the amplifiers to
conform to their intended operational parameters under all AC mains conditions.
A variation of approximately 10% in the AC can generally be accommodated,
guaranteeing consistent performance in all environments.
The KSA-150 and KSA-250 are protected by a series of opto-coupled, non-
intrusive circuits that constantly evaluate the amplifiers operation. Appropriate