Vacuum Oil Impregnation — the Inner Damper

During vacuum oil impregnation—a process familiar from vacuum-packed coffee—the air is displaced from the capacitor winding, and a special oil, whose dielectric and hydromechanical properties optimize the desired acoustic characteristics of the winding structure, is drawn into even the finest cavities under a vacuum. This stabilizes the wrap. The oil completely wets film and paper surfaces and forms a stabilizing layer inside the wrap. This acts like an internal damper: The internal strength of the wrap package increases once again, vibration amplitudes are minimized and extensive movements of the wrap are strongly suppressed.

It is important that the excitation is generated not only from outside as a result of structure-borne noise, housing vibrations or vibrations, but also from the operation itself. Signal-dependent forces act in a capacitor: Changing field forces and current distributions can mechanically excite the coil. When the coil reacts to this with movement, macro-microphonic feedback is created — the capacitor “speaks” and modulates the music signal. This is exactly where vacuum oil impregnation comes in: It calms the wrap structure deep into the inner geometry, binds interfaces and reduces macro-microphonic effects where they occur — in the wrap itself. The capacitor is much quieter, more stable and more controlled during operation, even at high levels and rapid pulses.

The composition of the oils used and the design of the process are decisive here. Viscosity, wetting behavior, long-term stability and interaction with film and paper determine how well the coil is stabilized at depth — without compromising electrical properties. Process control is just as important: vacuum level, time course, temperature control, and pre and post-treatment. This interplay is the result of deep specialist knowledge and decades of research and experience. Although the basics come from standard industrial processes, they were further acoustically optimized from there. For example, processes are available today that ensure an optimal balance of electrical and mechanical properties — and thus enable not only reliability, but also audible silence and precision when playing music.

Acoustic effects

• Fine details such as reverberation decays, fading processes and quiet room information are clearly noticeable because the wrap is calmed down inside.
• The sound remains calm and structured even with high dynamics; loud passages do not drown out the quieter details.
• Transients — blowing noises, string strokes, cymbal impulses — come precisely and completely without being sharp or strained.
• Overall, the impression is of relaxed, controlled playback, which is nevertheless full of richness of detail.