Acoustic Plan MagAmp

Acoustic Plan MagAmp
Acoustic Plan MagAmp
The Idea

As a young engineer, Lars Lundahl was interested in high fidelity music reproduction and built a number of tube (valve) amplifiers. Later, while working on servo systems for the Swedish J35 Draken "Dragon" fighter airplane, he developped a thorough understanding of magnetic amplifiers. Now, after having manufactured high qualitiy transformers in his own company for almost 40 years, Mr. Lundahl has managed to realize an old dream - combining his knowledge of tube (valve) amplifiers and transformers to build a hifi magnetic amplifier. The result is astonishing, both from the point of view of sound quality and the interest the amplifier has aroused among audiophiles.

The Principle

The principle of a magnetic amplifier is very different from that of a standard audio amplifier where the amplifying elements are tubes (valves) or trnsistors. For each channel, four magamps make a class A push-pull output stage.
A magamp is an inductive component (like a transformer) consisting of two separate windings and a magnetic core. The core is made from one amorphous strip and has a very high initial permeability and a sharp saturation charcteristic.
Each single magamp works as a controlled rectifier. In the control phase, the saturation level of the core is preset by a control signal. In the working phase, the magamp stops the current until the core becomes saturated, after which current flows through the load. The width of the output pulse is thus proportional to the core preset.
A pair of magamps work together to give continuous operation. When one is in the control phase, the other is in the working phase.
A current recycling system recycles the direct current through a switch transformer. Though this system, excessive heat dissipation (a common problem for class A amplifiers) is avoided and power consumption is reduced.
Each channel requires two pairs of magamps for push-pull operation. Therefore, in a stereo amplifier there are eight magamps.

The Differences

The first thing that strikes you when listening to a magnetic amplifier is the pure and natural sound. The sounds of instruments are neither improved nor distorted, and each instrument is clearly identifiable, even in a large orchestra. This is a quality we noticed from the very beginning.
Secondly, in spite of the rather modest output power rating, there is a large amount of power for deep bass and high intensity crescendos.
This is probably due to a soft saturation curve. In addition, the amplifier is very robust and outputs can be opened or short-circuited without risk. However, in spite of the output transformers, the outputs should not be bridged. This is due to the operation principles of the amplifier.



4 x Line


input 1- 4

200 mV

s/n ratio:


95 dB(A)



2 x 15W

dimensions (w x h x d):

260 x 170 x 350



19 kg incl. external power supply


frontplate blue, casing silver
others on request


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