When driving low impedance loads, what is the killer? - Prevention?

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a.wayne

a.wayne

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Joined 2008
Krell FPB 600


At 185 pounds, don't even try to lift this thing yourself. Much of the FPB 600s weight comes from its massive pair of toroidal transformers which are wired in parallel and act as the heart of this heaving beast.Rated at 600 watts into 8 ohms, the power output doubles as the load is halved. We are talking nearly 2400 fully regulated watts into 2 ohms. This amp also features the latest 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 amp supplies the necessary power. After a grace period of fifteen seconds and no additional high current signal demands, the amp returns to its appropriate power setting. This feature allows for Class A bias output without all the wasted electricity and heat.
 
CBS240

CBS240

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Joined 2005
CBRworm said:

So that goes back to my original question, if I were to put in more modern output transistors like MJ21193/94 would they be more tolerant of a highly reactive load and less likely to 'POOF' or will they still die the same death, or will the load be put on the driver transistors.

The outputs in the amp from the factory are 4 pairs of NEC 2SC600 and 2SD555 (or maybe I have that backwards).
Click to expand...

Take a look at the datasheets of each type and compare the SOA graph. (remember to de-rate) I believe the MJ21193/4 is a more modern ring emitter type BJT and is quite robust.
 
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AndrewT

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Joined 2004
a.wayne said:
Krell FPB 600
Click to expand...
I have yet to search for test results, if any, and I guarantee we will find that this amp does not deliver "only" 600W into 8r0.
I would expect that 600W to be the manufacturer's rated output when mains voltage is at the minimum specified by Krell.
I further suspect that Krell will rate this amp into loads far less than 4ohms, is it a 2ohm amplifier or maybe a 1ohm amplifier?
 
C

CBRworm

Member
Joined 2007
That's a very interesting article.

When I chart my speakers impedance I measure volts vs current at multiple frequency points. How would I measure phase angle?

So I guess the long and short of it is that I should keep using the Adcom amp instead of trying to beef up the SX-1250
 
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