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In Reply to: No need to add a shield... posted by Duster on December 19, 2006 at 09:52:02:
Thanks Duster, I appreciate you input. Just wondering why/how a shield might cause adverse sonic effects. I've read many posts that allude to this based on listening tests but am having trouble wrapping my mind around it.I'm relatively new to this and have started out by making a power strip (for the home theater) and a switch box to turn on/off my Sunfire stereo amp. For the switch box I used a short section of some standard 12/3 Coleman cable and employed the braided sheild method I described. Can't say I was floored. It sounds better than the keychain RF remote switch I was using but not as good as plugging it directly in the UPC-200. Now I'm wondering about rewiring the switch box with a short run DH Labs cable with no shield.
Any further insights are appreciated.
Rich
Follow Ups:
I'm not an EE, so it's a bit tough for me to put on a "tech hat" in order to explain this: A shield may help protect a power cord from external noise, and it may help keep potential noise emitting from a power cord from affecting adjacent gear, but it can do this "at a sonic price". The current-carrying conductor's electrical and magnetic fields are affected by a metal shield, and this often colors the sonic signature of a power cord. A capacitive coupling of the shield to the current-carrying conductors may also affect a power cord's sonic signature due to the dielectric involvement of the cable's jacket (in the case of the Power Plus, I think it's double-layer jacket is PVC...).Often, the most transparent sounding cables are unshielded types, including line-level interconnects (a high twist ratio or other geometries such as star quad can deal with noise quite well without need of a shield). The main reason for the preference of a shielded power cord when placed on digital gear is to help keep digital noise generated by the digital device from "polluting" adjacent gear, while a turntable's motor's power cord can benefit from it being shielded due to a phono-level signal's sensitivity to incoming EMI. In both cases, it's adjacent gear that's being protected, not the device that the shielded power cord is plugged into (think of a TT's motor being "a seperate animal" from it's cartridge and phono-level wiring). I hope this basic layman's explanation helps... perhaps an EE or another inmate can add further insight :-)
Copper shields on cables stop electric fields but not magnetic fields. The twist geometry is all that will reduce magnetic fields from current in the power cord from coupling to adjacent cables and equipment: the more twists, the more closely the magnetic fields reverse in space around the power cord and the less likely they are to have a nonzero coupling to adjacent objects.If the AC current is rich in harmonics (ie, polluted with RF noise), even tight twists will not stop radiation of noise, so the electrostatic shield helps. Most often, digital gear puts RF noise onto the AC cord, but power amps with sloppy rectifier diodes in the main supply can also be sources.
Attenuating radiation is a good thing, but the shield increases the capacitance (and the dielectric involvement of the insulation material) from hot and neutral to AC ground. Coupling noise onto the AC ground is a bad thing. Thus, it is not obvious whether a shield on any particular power cord will help more than it hurts the overall system performance.
Most power cord shields are terminated by direct connection to the AC ground at the source (plug) end. This creates an additional problem. The shield is free to resonate and further pollute the AC ground closest to where other components are connected.
...thanks to you both for your useful responses. I have decided to try changing out my shielded design for the standard DH Labs cable in my switchbox for my amp. I'll make the decision then on how to proceed with the cable from the wall outlet to the UPC-200.Thanks Again.
Rich
....nonshielded, unmodified connected from the power conditioner to the switchbox with the Sunfire amp plugged directly into the box. A little too early to tell (it was after midnight) but immediate impressions were favorable. I was a little surprised that any differences would be noted, but I was very tired. I'll be able to do some more listening tonight.Sounds like I might be making a DIY DH Lab Cord to go between the wall outlet and the conditioner with no shield or modifications. I'm using a shielded Volex 17604 there now, another interesting comparison to make. This is kind of fun....although my wife thinks I'm nuts.
Rich
I have a DIY DH Labs power plus ac cord from the wall outlet to my power strip...it sounds great to me.the wall outlet is an Oyaide SWO-XXX, so the male plug is a P-079 from the same mfgr. The female is a Furu FI-11Ag plug.
I missed out on listening last night but plan to do some more tonight. I've got the cable, some techflex, and a little shrinkwrap just waiting for the ends as a Christmas gift - I think she got me the Marincos from Parts Express. Then I can make a DH cable to between the outlet and the UPC-200 conditioner. If for some reason I don't like the DH I'll try the VH recipe.Thanks for the encouragement.
Rich
I didn't do extensive A/B tests and it may be psychological bias but I think I much prefer the DH cable unshielded. I can't put my finger on it but the standard shielded 12 gauge I created seemed to be a little "sterile" - not bright but not involving. It seems to me the DH Labs cable (no shield) added a touch of warmth and seemed more natural. Not sure if that makes any sense. Not a night and day, knock your socks off difference and as I mentioned I didn't do much swapping. But very noticable to me.I think all of these small differences really add up. Changes to my power supply/distribution in the last month have included:
1. Replaced the standard wall outlet with a Hospital Grade Isolated Ground Cooper outlet (from Lowes) - I know, not the end all in outlets but it was a cheap tweak.
2. Added a PS Audio UPC-200 to provide non-current limiting conditioning for my Sunfire 300 Amp and Musical Fidelity A3.2CR Preamp.
3. Replaced the stock Musical Fidelity pre cord with a Volex 17604.
4. Replaced my cheesy keychain RF remote on/off switch between the Sunfire and UPC-200 with a DIY manual switchbox using DH Lab Cable.
5. Replaced the stock UPC-200 cable with a shorter DIY DH Lab Power cable.
Done for now, at least until I can't resist the urge to swap out the stock Sunfire power cable with a DH Labs replacement. And not to forget running a dedicated 20 amp line (my listening room has it's own 15 amp line so I'm in pretty good shape). It NEVER ends...
But a little dull-sounding compared to a tweaked audio cord. If your DIY cord does not sound better, you need to do some more research.
...I see an after Christmas shootout coming up! Truly I expect the DH Lab cable to be better, we'll see (or hear).Rich
I agree with Duster that no addt'l shield is needed. I have 3 separate runs of DH Labs bulk AC Power Plus cable...they run analog and digital equipment.I think its a great cable for the $, and i live in a RFI/EMI rich environment. so far i've not noticed any issues that an active shield would address.
Duster, any idea if the design of the cable removes/cancels interference? ie, like the CV Flavor 4 design??
As I recall, Darren Hovsepian mentioned that the Power Plus features a high twist ratio which helps cancel noise. VH Audio's Flavor 4 is a star quad design (4-conductors, cross connected) which further cancels and supresses noise (and lowers inductance which is a good thing...).
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