2 plus 2, Biamplifiying the MK-121C

Read more on the Acoustat 2 plus 2 in our home audio section

Robert Sabelis2008-01-29 21:59

Dear Andy, This weekend I get my refurbished/repaired Class A Levinson ML-2\'s back. New large cans etc... When I drove my 2 + 2 with them the 15 Volts max output of these amp is rather quickly attained. I also have a ML-3 Class AB2 amp then can blow out the audio inputfuses on the MK121C medaillon quite easily without clipping. I prefer the sound of the ML-2 over the ML-3 except for the higher soundpressure levels of course. I read in this thread your comment on biamplifiying the interface but I\'m not quite sure about the connections and the merist of it. 1. I bought my set 2 + 2\'s new so I have the Owners manual with the schematics. Can you explain me a little bit deeper how to make the proper connections for this biamplifiying scheme? 2. Approx. at which frequency does the interface \"cross\" from low to mid/high. In other words how much of the load burden will be taken by the natural supplier of the low end, the ML-3 amp for giving the ML-2\'s some more dynamic headroom. I\'ll intend to keep these three amps so there\'s no efficiency question involved. I can drive the three amps with my ML-7a pre because It has two sets of output connectors. Any suggestions? Thanks in advance, Robert


Andy Szabo2008-01-30 22:53

Other owners of the MK-121 series speakers have successfully bi-amped the interface, so you may find some helpful comments among the other Q&A sections. Doing it is relatively simple. Note that the low frequency (LF) transformer is directly connected to the audio input through a 1-ohm resistor and the fuse. I suggest you use the original input jacks for the LF input, maintaining the fuse and resistor in-circuit. The high frequency (HF) transformer is connected to the fuse through a resistor-capacitor network. I suggest you disconnect that circuit at the fuse, and connect it to a second set of input jacks, preferrably through another fuse for maximum safety. The advantages of bi-amping are questionable. Most who have done it seem to be happy, but that may be a case a \"wishful hearing\" after doing all that work. There is no exact crossover point between the LF and HF sections: rather, there is considerable overlap between the two sections. If your aim is to increase dynamic output, you will probably gain some, but not nearly as much as the sum of the two amplifiers\' wattages. In other words, you would gain more by using a higher-wattage amplifier in single-amp mode. But, I can understand your desire to retain the use of the ML amplifiers. If nothing else, they sure will make a neat display of equipment, and keep your room warm year \'round!

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