Kinergetics KMP-2 Magnetic Tape Deck Processor

The Kinergetics company is probably best known for its preamplifiers and CD players. In their time they were very well reviewed, especially the CD unit. One of the most interesting approaches to their good audio performance was the clever use of feedback to reduce hystereses induced distortion. Any device that contains a ferrous core, such as transformers, many inductors, moving magnet cartridges and magnetic tape heads produce hystereses distortion. This distortion is caused by the magnetic material retaining some of the original magnetic field even though the constantly changing audio signal has reversed direction and should be reshaping the field. In a way this is similar to what a capacitor does as it builds and discharges its capacitive field.
The Kinergetics approach is to pass the audio signal through a similar magnetic device (in the case of the KMP-2 a magnetic tape head) that is carefully tied into a distortion reducing feedback loop. The idea is to eliminate the effects of hysteresis distortion by using the same distortion generator but opposing it. Kind of like audio jiu jitsu, lever your opponent's size against them.
Here is a photo of the inside of the KMP-2, you can see the magnetic head in the center.



  • SeleniumFalcon
    SeleniumFalcon Posts: 3,074
    edited May 28
    The companion piece from Kinergetics was the KMP-1 (sorry don't have a photo, but it looked exactly like the KMP-2 on the outside). Which contained a magnetic phono cartridge in place of the tape head. The advertising tagline was that the KMP-1 would allow your moving magnet or moving iron phono cartridge to sound more like a moving coil version. This was at the time when moving coil cartridges were beginning to be the audio enthusiast's choice.
    To give credit to this concept, the patents for this kind of distortion reducing design were registered to Mr. Kenneth W. Cowans and Mr. M. Owen Bennett. There is the possibility that John Curl, when he worked at the Ampex company, also used the same feedback scheme in a tape recorder circuit some years before Cowans and Bennett's patent.
  • SeleniumFalcon
    SeleniumFalcon Posts: 3,074
    More recently a Danish audio company, Purifi, has applied the same type of hysteresis distortion reduction in their class D amplifiers. Evidently the ferromagnetic material of the amplifier's output filter coil is a major reason these designs tend to have a somewhat grainy quality to the sound.