Krell KSA-250 Amplifier - TRUE American Muscle - Original Box
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Krell KSA-250 Amplifier - TRUE American Muscle - Original Box
479 South Broad Street
Glen Rock NJ 07452
This musclecar amplifier is in super nice condition all around, with no noticeable scratches or dents.
We love the massive yet artful looking heatsink cooling fins, as well as the super heavy-duty rear panel connections.
Requires a dedicated 20 amp electrical receptacle and for good reason!
"The KSA-250 is rated as delivering 250 watts per channel into 8 ohms...The KSA-250 will deliver 500 watts per channel into 4 ohms, 1,000 watts per channel into 2 ohms and 2,000 watts per channel into 1 ohm. The KSA-250 is capable of driving impedances below 1 ohm."
Fully tested and working as it should, looking for its new home.
More from Krell:
The latest generation of high-resolution source components and speakers places new demands on the power amplifier. The KSA-250 meets 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-250 utilizes 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-250 is conservatively rated at 250 watts per channel into 8 ohms. The 250 will actually generate 320 watts into 8 ohms. The 8-ohm power ratings do not account for the amplifier 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 -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 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-250 is protected by a series of opto-coupled, non- intrusive circuits that constantly evaluate the amplifiers operation. Appropriate protective action exists for a wide range of problematic conditions. Collectively, the protection circuitry is designed to avoid damage caused by other defective components, faulty wiring, mishandling of the system or amplifier failure.
Krell is committed to balanced operation in all products. Balanced systems have long been standard in professional audio applications and the same advantages apply to home audio equipment. There is a 6dB increase in gain without an increase in noise and there is a decrease in overall system noise caused by stray AC and RF fields. Sonic performance is drastically improved, particularly in dynamic and soundstage presentation.
The KSA-250 is rated as delivering 250 watts per channel into 8 ohms. The amplifier’s maximum power into 8 ohms is 320 watts per channel.
That every Krell product uses Class A circuitry in all gain and supply stages is a foundation of our design philosophy. A second design commitment that relates to amplifiers is that every unit be capable of doubling its output into successively lower impedances. The KSA-250 will deliver 500 watts per channel into 4 ohms, 1,000 watts per channel into 2 ohms and 2,000 watts per channel into 1 ohm. The KSA-250 is capable of driving impedances below 1 ohm.
Given the above, the AC power supplied to the amplifier is crucial to getting maximum performance. The KSA-250 requires a dedicated 20-amp line. It too, should only be operated with the power cord supplied with the unit.
Our Testing Process for Amplifiers (Solid State) at SkyFi:
We start with a visual inspection of all internal components to make sure there are no signs of stress or aging. Capacitors are checked for telltale sings of bulging or leaking, resistors are checked for signs of overheating or cracking, and transistors are checked for signs of stress or damage.
We then power up the unit carefully and run a simple 1k sine wave while monitoring the output on an oscilloscope for signs of distortion or noise. Finally, we run the amplifier to its full rated power into the appropriate resistive load provided by our Sencore amplifier tester. If there is an issue, it will usually be noticeable at this point. If everything reads clean, we will often test for THD (Total Harmonic Distortion) measured by our Keithley distortion meter, and compare it against the original manufacturers specifications. The amplifier then remains powered on to "burn in" on our test bench for a few hours to make sure there are no heat related issues. If there are balanced inputs available they will be also be tested.
Final testing involves pushing actual music thorough the amplifier. We've learned over time that some issues are only noticeable to a trained ear while listening to familiar source material. Our test bench has reference vintage KEF speakers that we're very familiar with which quickly reveal any discrepancies. Some amplifiers will then move into our listening room where they are tested with our in-house reference speakers of choice.
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