Krell anticipator circuits of the 1990s
"Krell FPB-600 Stereo Power Amplifier
This big power amp features the evolution of the plateau biasing circuit introduced in the KSA series of amps. This circuit anticipates the power demands of the output by monitoring the incoming signal as the demand for power increases, the more power the amplifier supplies. After a grace period of fifteen seconds and no additional high current signal demands, the Krell FPB-600 amplifier returns to its appropriate power setting. This feature allows for Class A bias output without all the wasted electricity and heat."
Do you believe the anticipator can up the bias quickly enough? A guy hits a huge bass drum, the anticipator circuit senses this and ups the bias in time for the hit to be amplified in Class A?
We are talking a micro second. Once he hit it the start of the moment was over. This was a con. Created by Krell because they were under pressure from the emerging green lobby to cut power consumption. Qualified Krell service engineers have not been able to explain to me how it can work.
Me? I still have my KRS200s. Pure Class A. So there's my answer.
If anyone is interested. I re-read the thread I posted earlier about They also have an iBias system similar to the KRELL XD. The designer of those amps explained how the iBias predicts the needed power. His amps go into Class AB for a second if they go beyond the existing limit of Class A. Then the Class A ramps up.
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That baloney works pretty good on the new XD lineup. I currently have the KRELL 175XD stereo and it is supposed to be 175 watts in Class A. Though that max power in Class A is only available when demanded. Thus, the unit is not heavy and nor very hot since it is not wasting Class power when the music is not demanding it. I went and demoed the CODA #16 amp since I was considering upgrading from the CODA #8. I felt the KRELL 175XD was better than the #8. When I heard the CODA #16, which has the first 100 watts in Class A, I could hear a very similar sonic characteristic between the 175XD and the #16. I thought the #8 sounded not as smooth and relaxed (a little grainier), while the other 2 sound smooth and relaxed. Maybe the #16 was a little clearer, like a Benchmark AHB2. There is another amp from Japan (I think) that does something like the iBias. This is my question to the designer or distributer. The thread is a good read.
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KRELL is going to release a uber XD amp around Christmas time, KSA 400i. It will be an iBias amp with some new enhancements. It is supposed to be better than the base XD amps. Which makes it a must listen for me. The 2 base XD amps I have owned have been very good to excellent (K-300i and 175XD). The power rating for the new KSA 400i: 400 -> 800 -> 1600 -> 3200 Watts 8 -> 4 -> 2 -> 1 Ohm SoundStageNetwork.com | SoundStage.com - Talks The iBias designer is on this video talking about the new amp. He actually explains how iBias works in this video. |
@clearthinker Did you watch the video I posted? I think that answers the initial question you posed on this thread. |
@jaytor The type of iBias described by the WestministerLab designer seems to me different than what KRELL seems to be saying with the new iBias XD amps. I am under the impression that the new KRELL stays in Class A all the time. I was going to email Walter Schofield at KRELL and talk about the iBias but then I saw that he is no longer with KRELL. All I know is that I put back my KRELL 175XD into my office system this morning and it sounds great. So smooth and yet powerful.
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