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Products

Power amplifiers
M1.2 Reference
     
description  specs
M2.2
    
description  specs
ML2.2
    
1 description 1 specs
ML3 Signature
    
1 description  1 specs
Preamplifiers
LL2.1(regular/deluxe)
     description  specs
LL1.1 Signature
    
1 description 1 specs
L2 Reference
    
description  specs
LP1 Signature
    
1 description 1 specs
LP2.1 (regular/deluxe)
                phono preamp
    1 description   1 specs


What's special about the load selector switch on
LAMM power amplifiers M1.2 Reference/M2.2/M1.1/M2.1/?

First, about the idea behind a load switch. Vacuum tube amplifiers (those that utilize the output transformer) have secondaries with taps to accommodate different speaker loads, and this feature ensures the optimal functioning of the amplifier with various speakers. Solid-state amplifiers are a different story (meaning solid-state amps with no output or matching transformers). It is commonly thought that solid-state amp can be loaded with loads of various impedances; therefore, the lowest value of load impedance that can be connected to an amp is taken into account during the circuitry design stage of that particular amp. This means ONLY that the amp will work with this impedance without malfunctioning. In general, when very low or relatively low (about 2-3 Ohms or less) load impedances are connected to an amp, the quality of sound becomes questionable. There are reasons for that, and the main ones are concerned with the correct choice of a Q-point to ensure at least some resemblance of constancy of the harmonic structure of (1) signal versus frequency, (2) signal versus output power, and (3) signal versus load.

As a rule, modern design philosophies are quite removed from the correct fulfillment of these three variables. From our point of view, one of the ideal solutions for these problems when solid-state amps are concerned are: PURE class A operation of an amp (without any tricks), and PURE class A operation not only at the MAXIMUM load, but also at the LOWER load impedances. Standard situation, even if an amp operates in pure class A at 8 Ohms, is that it doubles the power at 4 Ohms resulting in 1/4 of the doubled power in class A and the rest in class AB. We, at LAMM, chose to do the following to handle this issue. We tentatively divided an entire impedance range into two: from 16 to 8/7 Ohms and from 7/6 to 1 Ohm and below. As a result, we implemented a special load switch in our hybrid amplifiers. When the switch position is changed, it changes the supply voltage and idle current of the output stage, which allows the amplifier to operate in PURE class A mode at the maximum and lower load impedances. The M1.1 is a 100W monoblock operating in pure class A at 8 AND 4 Ohms (the M1.2 Reference is a 110W monoblock operating in pure class A at 8 AND 4 Ohms).

This separation into two impedance ranges is not cut in stone. If speaker has an impedance of 6 Ohms, the M1.1/M1.2 Reference can have the load switch at either 8 or 4 Ohms position. In this situation, listening and experimenting are necessary to figure out which combination sounds better. Also, the room acoustics have to be taken into account. Our equipment is designed with a wide "safety" margin, so that if the amplifier is set for an 8-Ohm operation, it can be loaded it with 8, 4, 2, and even 1 Ohm. In this case, only the output power will increase. However, we don't recommend to do this as harmonic structure of the sound will be changed enough to become audibly noticeable. However, this kind of experiments is very educational in revealing the differences in sound between the M1.1/M1.2 Reference with properly selected load switch and the M1.1/M1.2 Reference with improperly selected load switch (which in such situations operates and sounds similar to conventional amps). Similar tests had been made by Ken Kessler and described in his review (HI-FI NEWS & RECORD REVIEW, January'96, pp. 38-39). He came to a singular conclusion about which speakers sound the best with which load switch position on the M1.1. Our amplifiers were designed by the purist for the purists, with attention to every little detail.