DIY Power Conditioning

Add an X capacitor and then a ferrite bead to a surge protector for RFI suppression.

Mains capacitor

My idea to begin with was to fit a mains filter capacitor to a power plug and plug it into the cord end of my stereo's surge protector. This, I thought, would be the equivalent to much more expensive conditioning that is sold as high-end accessories. The capacitor used is called an X capacitor, and is designed to be safely used to filter EMI/RFI from mains inputs. So I bought the following plastic plug and X2 capacitors from Amazon.

	Leviton 101-WP 15 Amp, 125 Volt, NEMA 1-15P, 2P, 2W, Plug, Straight Blade, Residential Grade, Polarized, Non-Grounding, White
	uxcell Safety Capacitors Polypropylene Film 0.47uF 275VAC X2 MKP 5 Pcs

When I received the parts, I ground the wire side of the plug down until I had opened a path for the capacitor leads and shortened it enough for them to reach and be tightened into the wire terminals.

Figure 1: Leviton plug modified to receive the installation of the capacitor and the X2 capacitor to be installed.

Figure 2: Assembled capacitor plug ready for use.

Figure 3: X2 capacitor shown plugged into cord side of surge protector.

Listening evaluation

When I first installed the capacitor and played my stereo, it had a subtle hardness and glare to the sound. So I put on music to play and went about other activities. When it seemed to have settled, I thought that the speaker cable upgrade I made earlier had already made the biggest improvement. Yet there was an improvement and it seemed to be in the transparency of low level sounds.

Ferrite bead

After listening a long time, I decided that I would put a ferrite bead on the power cord near where it entered the power strip. So I bought a ferrite bead variety pack from Amazon and installed one.

Ceedmon 20 Pieces Clip-on Ferrite Ring Core RFI EMI Noise Suppressor Cable Clip for 3mm/5mm/7mm/9mm/13mm Diameter Cable, Black

Figure 4: Ferrite bead installed on cord next to plug in X capacitor.

Listening evaluation

As with the capacitor, when I first installed the ferrite and played my stereo, it had a subtle hardness and glare to the sound. So I put on music to play and went about other activities. When it seemed to have settled, I thought little had changed. The capacitor it seems had done the job. With more listening, the entire installation seemed worthwhile. The sound was not embellished in any way it just seemed more correct.

Finally

This seems a logical improvement to make to a high-fi even if not considered subjectively.

Document History
April 19, 2024 Created.