Thursday, April 16, 2009

4 pole capacitors

The idea came from a request from a customer to mount Jensen 4 pole capacitors on our 405 dual mono power-supply board. This was not possible on Dada's standard board. But I was triggered by the idea. Is this a way to make extra money by selling snake oil? No!

BHC and Jensen manufacture this kind of capacitors. What is the theory behind the four pole capacitor? An electrolyt capacitor can be modelled as a resistance, an inductance and a pure capacitor in series. In a 4 pole capacitor these resistors and inductance are used as a HF filter. This is done by placing the input and output wires at separated places along the metal foil. In real life you can’t separate the individual components, but the filter effect is there. On the Jensen website the history of the 4 pole capacitor is explained, as in most cases, the 4 pole is an old idea.

In normal setups the capacitor in a power supply delivers a parallel supply current to the load. That’s why most people consider the Psu capacitor “out of scope” considering the signal path. In my view every component which has an influence on the signal path is a part of the signal path! In the case of the four pole capacitor, the foil is in series with the load. So the filtering capabilities also increase the internal impedance of the power supply. There is no difference in behaviour when you put an extra filter in the Psu, the plus is that you use the natural L and R part of the capacitor. The load current flows through the capacitor, so it will get warm at maximum power output of the amplifier! In a normal Psu setup the internal L and R are responsible for the increasing impedance of a capacitor at high frequencies, now they are used to filter the HF components!

The downside:

Only two manufacturers: BHC distrubited by DNM and Jensen.
Different pin layout, Jensen even has two different layouts!
A bit more expensive, compared to normal capacitors.
Complex setup especially with dual mono power supplies.

The plus side:

High quality capacitor's
The HF filter works!

We developed a new PCB for these capacitors; the layout is in accordance with the BHC T pin configuration.

Joost Plugge