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RE: Question about Krell amp models

Be aware that some of those old Krell amps can sound wonderful but models like the KSA-250 run in true Class A bias.... all the time. In other words, this amp draws about 1300 watts from your AC outlet continuous whether it is playing music or not. 1300 watts might require it's own dedicated AC line and breaker and at 1300 watts, it is essentially an electric space heater

They're built like tanks but hot running amps of that age will likely need service, especially the capacitors.

I like the KSA-xxS models. The "S" suffix denotes Krell's "Sustained Plateau Biasing" scheme which keeps the amp in true Class A operation so long as the music is playing but throttles it back when the music stops.

I had the baby Krell KSA-50S and for a 'small' 50wpc amp, that box drew about 800-watts continuous as the music played loud and the heatsinks became very hot. When the music stopped, it would continue to draw 800-watts for many seconds until it throttled itself back down to a more reasonable levels.

I believe some of the newer Krell amps use a similar biasing scheme. It's a way to get true Class A operation but only while the music is present so as not to unnecessarily heat up the listening room if the amp is ON but sitting idle.

My KSA-50s to the left back around 2005



Edits: 01/22/15 01/22/15
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