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In Reply to: RE: Add some carbon fiber to the face plate. posted by Al Sekela on May 30, 2007 at 09:57:32
Hi Al,
Thanks for the critique. Removing the straps was inspired by your comments.
I have never understood the carbon fiber idea. Is it to remove the disruption caused by the RF bouncing back and hitting the power cables and other RFs?
So I would place the fiber on the top of the plate. What about lining the inside of the box. Is there other places that the CF works well? What about creating a covering for Power Cables?
The transformer is setting on top of a gator board clone to reduce vibrations. I will apply magnets on the ends of the transformer covers and also some dynamat.
Do you have any feelings about the 193L choke or adding a cap?
I also have two isolation transformers in use. One is plugged into the balanced power outlet and one is wired into the main feed for the balanced power. I will try magnets on them also.
Thanks!
Follow Ups:
a
It is essentially the same technique used to make stealth aircraft.
Electromagnetic waves are reflected by good conductors, such as the aluminum plate in your project or aircraft skin. If the waves encounter a resistive surface, such as the carbon fiber or the secret materials used on stealth aircraft (hint: see Stillpoints ERS cloth), they are converted to heat and little of their energy is reflected. If the resistance is too high, they pass through until they hit the underlying metal, and then they are reflected. There is some optimum value of surface resistivity that will totally absorb the waves. I don't know what it is, but typical carbon fiber material seems to be reasonably close. Lucky for us that carbon fiber is also used to make golf club shafts and the like, and the materials are available at non-audio prices.
Power cords support electromagnetic resonances, both in normal- and common-mode. This resonance makes RF noise worse for audio equipment. The carbon fiber on the surface of your aluminum plate would act to absorb the common-mode resonance waves on power cords plugged into it. If you covered your power cords with carbon fiber sleeve, also available from Soler, it would act to absorb both normal- and common-modes. Note that Oyaide makes AC plugs with carbon fiber outer shell material, and AC power cable that incorporates carbon fiber. Thus, this is not something I invented, but I've used the ideas in my DIY projects.
There might be some advantage to lining your box with the material, but I don't have experience with this. Please be careful with it. The fibers come loose easily until you fix them with epoxy and will cause trouble if they come into contact with live exposed objects.
The Hammond 193L or M chokes are on my short list of tweak projects. I expect they will work better than the loaded transformers I'm using now. As Alan said, do not use a cap in conjuction with the choke.
Add the 193L or 193M to the balanced output across the first outlet in the daisy chain....you will love the results.
Don't add a parallel cap.
Alan
Is a choke needed on the protected end of the balancing transformers?
Surely passing through the transformers has a major attentuation of the same RFI that a choke would also effect? or is the choke to protect that outlet from the RFI from equipment and cable further down the protected chain?
I am a noob and would love to know.
Filtering the AC for audio is complicated because most components have power supplies that generate their own RF noise, and allow RF noise from the line to get inside. Putting the choke filters as close to the individual outlets as possible will reduce the effects of generated noise on other components in the system, and reduce the ability of the local wiring to pick up the noise from other components.
So the same applies to the placement of a RC bridge?
I have the output of a balancing transformer going out to a duplex outlet socket.
The transformers output is wired into the back of outlet 1, which has my CD player plugged into the front. The second 'downstream' socket has two paralleled Auricaps betwenn hot an neutral with a 100ohm ceramic resistor on each negative leg, in the front I have a powerboard plugged in which feeds my lesser equipment (DVDplayer, table lamp, Playstation).
My reasoning is that the balancing transformer attenuates RFI in from the mains straight to the CD player (in socket 1), then the RC bridge separates the cd player from the other noisy stuff plugged into the powerboard.
Is my reasoning correct?
Since a source of noise is from the second outlet, Is this the best place to have the RC bridge or alternativeley a choke (replacing the caps and resisistors)?
I expect it would be less effective than a choke as a sink for locally-generated noise.
So the placement position is correct, but a choke would be better than the paralleled RC's?
Last night I pulled the RCs out of the output stage of the balancing transformer and the sound became noticeably rougher in the highs. So its doing something in that position, so putting a choke in the same spot would probably be better again?
The resistor in your R-C networks may be damping some resonance in the balanced transformer. A choke might be better or worse for this application.
The choke on the output for RFI filtering. The transformer doesn't really offer that much noise suppression. Normal balanced transformer are only able to provide between -9db and -12db pending frequency. It would be different if you were using a bifilar transformer like the Plitron NBT models...those can surpress up to -65db...but normal trannies offer very little improvement....the biggest change is the split phase reaction in the component power cord. BTW, I use a 25A NBT in balanced mode...and I have 5 - 193L's on the secondary and 1 - 193M. I also use Shakti Stones to couple with the transformer, Shakti On Lines for the wiring, and large Bybee's on the primary and secondary...and all offer an improvement in noise rejection and line frequency resonate. There is much more to PFC than just typical line filtering. Right now you are off to a good start.
It's a shame you used glue to secure the outlets...it would not have been my first choice...glues all ring at different frequencies. Instead I would have recommended a .015" thickness of EAR C-1002 to be secured to the metal cover to isolate the ringing frequency between the cover and outlet straps. Then I would have used brass hardware to secure the outlet.
Next, lets take a look at the wiring. I don't care what kind of wire you use...that's not important...but what is important is the outlets resonate character. You should place 5 wires per outlet...this is called star wiring...2 hot, 2 neutral, and 1 ground. On the rear of the outlet you will see 4 wire terminals per side (hot and neutral). Place one wire into the bottom terminal and 1 wire into the top terminal per side...this is for input wiring only....now take 1 wire and place it into the 2nd and 3rd terminal per side...this is the outgoing wiring. Why you may ask??? Because the copper wire alters the resonate frequency of the wire clamp inside the outlet. This neat little trick will reduce 50% of your harmonic ringing at the outlet. I like to use dual runs of Cardas 11.5ga for this application and the Cardas 9.5ga for the earth ground.
I hope the tips help bring you closer to audio nirvana.
Alan
A wealth of information form Alan and Al! Thanks!
I was thinking that by gluing the outlets to the aluminum vibrations would be reduced, but I only do this as a hobby.
I created a schematic of my interruption of your description of the Star wiring. Let me know if I go any of this right.
Looks good to me. Don't be afraid to add a choke per outlet....it does a fantastic job with outlet isolation and filtering.
Alan
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