[Folsom]

After years of going back and forth on using different sizes just swapping around (my units have different sizes in them instead of several smaller units). I've come to realize the size of what you can use isn't always what you should use.

Digital equipment: I always use high filtration 25mh CMC's that are 3A. I haven't ever found a poor return on this to date. You only get blacker backgrounds and increase subtle response the more you go. This is even true if the device is rated near 3A.

Motors and Misc *Important: The highest possible, instead of none, unless they have a different circuit in the house. Noise reduction with a CMC goes both ways, so your turntable could be polluting the rest of your system. Best to put it on the highest filtration CMC you can, but feel free to skip

Amplifiers: My recommendation on these is defiantly not to go with highest reasonable. In fact I recommend going one size bigger, and in some cases maybe two; think double the A. For example I use a 3875 amplifier and while it can run just fine off of a 3A CMC it doesn't sound that good. It will sound fuller off of another CMC that is larger sized. This is like when you switch to a 12ga power cord over whatever smaller one you might of briefly used. Things just open up. The filtration isn't worth the sacrifice this far down the chain.

That being said anyone found better CMC's they like more than Coilcrafts? All the ones I see, if they have higher mh have way too much resistance. I'll use ones with really low ratings, high A, and low resistance before increasing resistance for filtration. They really work well with the capacitors, to the point where even very low filtration 17A units I find are still way better than not using anything.

[Speedskater]

What's a "CMC" ??

Common Mode Choke ?

[Folsom]

Yup. One of the integral components to the infamous Felix.

You'll find them in a lot of commercial power distribution things, some Furmens, etc... but without the combination of capacitors in conjunction they don't do that much, and certainly can't do much when you need one with enough amperers for all your gear instead of selecting smaller ones more suited for the application that provide more filtration (and again that is why I posted recommendations on sizing).

[cheap-Jack]

(1)  Digital equipment:- I always use high filtration 25mh CMC's that are 3A. I haven't ever found a poor return on this to date. You only get blacker backgrounds and increase subtle response the more you go. This is even true if the device is rated near 3A.

(2)  so your turntable could be polluting the rest of your system. Best to put it on the highest filtration CMC you can, but feel free to skip

Amplifiers: My recommendation on these is defiantly not to go with highest reasonable. In fact I recommend going one size bigger, and in some cases maybe two; .
..They really work with capacitors

(1) Why 25mH CMC 3A ampacity? Any theory to back yu up or simply yr ears find such large inductance sound better?

FYI, the inline RFI filters (made in England) I've installed in my 120V/250V dedicated powerlines for my audio rig for many years are all 10A load, but the CMC inductance is only 0.35mH each coil, working with the right filter caps to provide 52dB RFI insertion loss at 32MHz.

My music sound so vibrant, so fast & so transparent!

(2) How come an analoge device, like as TT can "be polluting the rest of yr system"??? 

(3) Too large the CMC inductance makes the choke huge & bulky & costly. I worry more the adequate current loading of the CMC rather than its too large inductance which must be compensated with the value of its filter caps to provide the right RFI filter function.

c-J

[jtwrace]

FYI, the inline RFI filters (made in England) I've installed in my 120V/250V dedicated powerlines for my audio rig for many years are all 10A load, but the CMC inductance is only 0.35mH each coil, working with the right filter caps to provide 52dB RFI insertion loss at 32MHz.

Can you share what you use?

[Speedskater]

For those that are interested in this subject,  one could do well by going to a local technical collage and borrowing, or using Google books for segments of or spending $100 and buying a copy of Henry W. Ott's big new book.
Electromagnetic Compatibility Engineering  (850 pages)
http://www.hottconsultants.com/

First Read:
13.3 Power Line Filters
including 13.3.1 Common Mode Filtering

then read:
Chap. 2 Cabling
Chap. 3 Grounding
Chap. 6 Shielding
Chap. 7 Contact Protection

also read:
14.3.3 Lightning Surge
14.3.7 Power Line Transient Suppression
14.4 Power Line Disturbances

[Folsom]

(1) Why 25mH CMC 3A ampacity? Any theory to back yu up or simply yr ears find such large inductance sound better?

FYI, the inline RFI filters (made in England) I've installed in my 120V/250V dedicated powerlines for my audio rig for many years are all 10A load, but the CMC inductance is only 0.35mH each coil, working with the right filter caps to provide 52dB RFI insertion loss at 32MHz.

My music sound so vibrant, so fast & so transparent!

(2) How come an analoge device, like as TT can "be polluting the rest of yr system"??? 

(3) Too large the CMC inductance makes the choke huge & bulky & costly. I worry more the adequate current loading of the CMC rather than its too large inductance which must be compensated with the value of its filter caps to provide the right RFI filter function.

c-J

I think we are saying similar things actually.

1. I can't find any better combination of low resistance and high inductance than Coilcraft's 25mh 3A unit. My ears tell me that it doesn't seem to limit current response enough to actually cause any sort of problem I don't like. In theory knowing that the use of power inside of units like DAC's isn't very dynamic at such low levels compared to an amplifier. In fact many units don't even adjust volume because they use a shunting circuit with a pot/stepped-attenuator. But this is the most vulnerable spot for noise, when the noise and music are in a closer range of voltage, and before amplification of both. Noise reduction here means lack of noise further down the line. Noise is bad in an amplifier, but not as bad as pre-opamp or whatever inside a CD player prior to signal out. *more inductance, more noise attenuation *also their power supplies are likely to induce the most noise back into the rest of the system, covered in #2

2. The noise you are filtering out on the line comes from everything that feeds back to the system (TV's, radios, vacuums, refrigerators, etc). Switching power supplies often have a negative effect on a system without filtration (people prefer linear without filtration, and yet with they often like switching supplies). This is why the original Felix was so popular with Squeezebox switching power supplies. The power supplies work well for the needs of the Squeezebox, but too much noise was going somewhere, the Felix stopped that. People have gone as far as different circuit breakers for different parts of their stereo. While one thing may not induce the noise into the music, it might into the line. The CMC's induct noise on top of noise (actually it is undesirable common mode AC, where as the AC power is not common mode; you can't phase cancel it without a delay) in order to cancel it, so you can eliminate noise from something in your system from going back into your power distribution and polluting the rest of your system that does play a role in inducing noise into music. CMC's are a device that aids in noise cancellation instead of shunting. Capacitors that unload the noise from going to a turntable power supply do not unload it from the rest of the system (and it is a different type of noise). The worst offenders of common mode noise happen to be small transformers found in power supplies because they don't have the insulation to prevent capacitance that creates it. In fact this makes the value of CMC's go up two fold in a system, because the generated common mode noise may not go into the device with the power supply generating it, but it could be going into the rest of the equipment. In fact that makes me wonder if the average stereo is nothing more than an exchange program for common mode noise  .  This probably has a lot to do with the failure of systems that use isolation transformers that never get as good of a review as an Audience Adept conditioner. (especially bad if more than one unit in the system produces the same common mode noise, and another is good at amplifying it). It might even be a partial reason that systems sound better when we believe one unit is responsible for better sound when it has a CMC but rather it is relieving the system of problems from the unit we are "filtering" (like Squeezebox, the benefit may be partially due to reduction of noise to the SB, and partial to everything else in the stereo that use to be exhibiting the common mode noise from the SB).

3. Uh... I reduce the allowable resistance to what I consider acceptable amounts, and however much inductance I can get is added benefit. For this reason you won't ever see me using an 100mh 5lb 15a CMC because it also will have resistance like 100ohms or better. I run as low as possible resistance, the absolute highest being .3ohm in the 25mh 3A CMC. There are other CMC's with higher mh values at 2A (adequate for more digital devices) but the resistance is way high (double or more).

I avoid resistance because my finding is that there is no correction for transient response of more than enough available current. Batteries sound slow to me, transformers are about as bad, and capacitors are better but... This is why I wire everything with large gauge wire, and the same reason a lot of people recommend nothing smaller than 12ga anywhere for power cords. The shorter the run the smaller is ok, like in amplifiers etc I don't wire them with 12ga since I usually like to make 3875 amplifiers. I think if your system doesn't have flaws that come through in allowing it to "breath" open current as opposed to stored current, it sounds vastly better in a lot of musical type qualities as opposed to imaging etc. I actually prefer this over trying to create a more constant voltage; you won't ever find me trying to run balanced power supplies if I think the instantaneous current draw will be hampered at all. You know in uber expensive stuff they go as far as to run primarily 12ga traces on PCB board while at the same time never exceeding 45% turns in the traces. Nelson Pass designs amplifiers based on the principle of believing they need to be fast to sound good. I believe it for the equalities that make my ears happy.

Personally I think people that play with powercords a lot are basically trying to cancel noise, and find a balance of constraint to their system because otherwise it doesn't sound refined when the full body is littered with excessive noise. It is like being at a concert and there is so much extra noise on the guitar amplifier that the compression used on the extremes of it have to be turned up a lot in order to stop a body of sound that is audibly identifiable.

Anyway that basis of my principles of options for CMC's is that with devices that are dynamic in power usage it is better way over-shoot current allowance instead of trying to hit near home for more filtration, and that they benefit the entire system by reducing noise reduction of non-inducing devices.

Blabber typer I am...

[Folsom]

* Technically any system could be improved by using larger, better insulated, transformers. You don't have to increase the voltage. Your power bill will go up a little bit though  . Using 250va toroidal's for Squeezeboxes or something... ha. That combined with CMC's would readily reduce common mode noise to about nothing I'd assume.

[Speedskater]

I just came across an interesting page on mains filters.
The link is to the home page so go to "mains filters and hi-fi" page.  Remember that this is a British page so some of the words are odd (like yobbo) and the 2 British power systems are very different from the US system.

http://www.acoustica.org.uk/

[Folsom]

He thinks 10uf is big... ha!

I have no idea why you would want to use mains capacitors all around the house,  . When using neutral to ground it makes more sense because you are unloading it to an unused resource of current. When you do the mains then there isn't any reason that noise can't be picked up at your stereo. That is why using capacitance directly at the power distribution makes the most sense.

The concept of using a resister is interesting; not I'm not sure it would serve much purpose when the capacitor is at the power distribution point. Perhaps there is no benefit because the load is greater than the equipment at any given point, so the filter part doesn't do much.

I wonder just how different their power is from ours, because you can't make the same claims about no benefit in this country.

[Speedskater]

Well they drive on the wrong side of the road, what can you expect?

It seems that the UK now has two different types of power systems with respect to ground. And they have ring circuits, we only have what they call spurs.

In the US single phase power system we have three wires entering the home (Hot, Hot & Neutral/Ground).
In the UK, Neutral and Ground are different wires. (I think).

[Speedskater]

Most US experts try to keep line noise off the Safety Ground because the Safety Ground is connected to the chassis and so are all the unbalanced interconnects.

[Speedskater]

That resistor is similar to your relay controlled discharge circuit.

[Folsom]

He's using it to lower the fast peaking.

[Speedskater]

This resistor?

Not shown, but a wise precaution, is a high-value resistor in parallel with the Cx cap, c.100-250Kohms, to ensure the cap is discharged when the equipment is unplugged to prevent a shock off the plug pins.

[Speedskater]

Or this resistor:

For those interested, try 1uF in series with a 47-50ohm, 3W resistor across L and N. Use only suitable mains-rated parts in a double-insulated enclosure.

[Folsom]

Or this resistor:

For those interested, try 1uF in series with a 47-50ohm, 3W resistor across L and N. Use only suitable mains-rated parts in a double-insulated enclosure.

This one, he is making the argument that it sounds better with this design. The shock factor is secondary.

I'm unsure about the affects of impedance by doing this; as towards the overall filter. I don't know how frequencies will respond to series resistor with capacitor given that they have a tendency to change when ESR of a capacitor changes. Well perhaps I just got to put my mind to it.