Sunday, August 23, 2015

Mu-metal Part 3

In Parts 1 and 2 of this 3-part series, I found a new friend: mu-metal. It worked wonders in my line conditioner so I thought I might give it a go in my low-level equipment. In Part 2 I applied the same chassis shielding technique to my OPPO BDP-105 with the same positive results. In this part, we'll look at how (if?) further shielding in the OPPO would benefit and then apply that treatment to my Onkyo P-3000R preamp.

Tearing down the OPPO is getting to be a routine; I've done it now 10 or 11 times for various reasons but I was excited about adding mu-metal to the switching power supply (SPS) section. Reading how nasty this supply is made me believe that there were more issues with SPS than just the high-frequency band smearing associated with their inherent design. And I had a surprise when pulling off the cover of the SPS: mu-metal on the inside. At least two sides of the supply were already shielded so now the side between the supply and the remaining electronics needed to be shielded.

So the first thing I did was to remove the rail and coat it with mu-metal. Instead of carpet tape, I used a spray contact cement on both the cut-to-fit mu-metal pieces and the bracket.

Next, I wrapped a band of mu-metal around both transformers and used a cable tie to hole it in place (yes, I wrapped the already shielded toroid too). WARNING: Make sure that the mu-metal is properly insulated so that it does not short out the wires on the transformer! Remember the edges of this metal is sharp and it will easily cut through any insulation these wires may have.

The next step is to make "hats" for the tops of the transformers and then use another cable tie to hold the hat in place.

While the cover was off, I also added a 0.01uF/200v shunt capacitor to the fuse. Doing this takes care of any thermal non-linearities in the resistance of the fusing element.

Put it back together and all should be well.

First, I want to say that the P-3000R is an under-rated preamp and with a few minor tweaks brings it up to truly high-end quality (change those Full-Wave Bridges to four discrete FRED diodes [2 FWB = 8 FRED diodes] and see for yourself!). So I was happy with the way the preamp sounded with these mods, but hey, what do I have to lose but a little time and maybe a band-aid for the nasty paper cuts on the edges of the mu-metal?

So I first performed the same chassis wrapping as with the OPPO.

And then I did the same transformer wrapping.

Button it up, plug it in, and turn it on. Be prepared to be amazed.

What I noticed was even more low-level grunge removed (I had no idea that it was there). The inner detailing is now a quantum level better than before and I am not exaggerating one bit. The instruments show more nuances than I suspected were captured by the recording process. It is in a word breathtaking.

Now you must realize that your system is a chain and the weakest link limits how much you will observe on yours as compared to mine. Know that all of my gear is seriously tweaked and the attention to detail is unsurpassed. But as you make these changes in your own system, each thing you do you will eventually hear even if the changes are not as obvious. You just have to identify what in the chain is the limiting issue and once it is resolved everything can come alive.

So grab your scissors and glue, buy some mu-metal off eBay, and shield!

Yours for higher fidelity,

Philip Rastocny

I do not use ads in this blog to help support my efforts. If you like what you are reading, please remember to reciprocate by purchasing one of my eBooks or through a PayPal donation, My newest title is called Where, oh Where did the Star of Bethlehem Go? It’s an astronomer’s look at what this celestial object may have been, who the "Wise Men" were, and where they came from. Written in an investigative journalism style (like that of the Discovery Channel), it targets one star that has never been considered before and builds a solid case for its candidacy.

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