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PostPosted: 09 May 2011, 15:04 
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Hi.

With digital gadgets all over the place in homes & works, e.g. LED/LCD/plastic TVs, cellphones, WiFi-PCs, cordless phones, frigs, washer, etc etc ..., our audios are now working in a hostile environment of RFI (radio frequency interference).

We can no longer build our audios like it was done decades back when digital was still an alien termnology despite tube is a historic heritage itself.

RFI emitted by digital gears comes airborne to our audios, as well as thru the powerlines which our audios shared. RFI

So our audios should be shielded off from airborne RFI as much as possible. A full metal chassis, properly earthed, will help a lot in shielding off airborne RFI.

Powerline conditioners (or in simple basic language, RFI powline filters) should be installed inline upstream of the power bars where our audios plug into to stop RFI getting into our audio gears via their power supplies.

I always thought powerline conditioners are money making gadgets offered by vendors to those affordable audiophiles. It could be done without :? But after I tested the EMI/RFI level in our powerlines with a wideband powerline & EMI noise analyser, I know what I had been thinking was partially wrong!

Why "partially" wrong? Yes, RFI voltages riding on the poweline voltage were detected & measured in my analyser in homes & commercial places in different area. The analyer even pulled out AM broadcasts from the powerlines via its built-in loudspeaker !!!!!! :o So powerline fitlers are needed bigtime! :up:

Yet I am not totally wrong as I do not need to finance those vendors for their expensive brandname powerline conditioners. Sorry, I'm a cheap jack. 8-)

Thanks goodness. I've saved a big bundle by choosing a DIY type "basic" factory-built filter of an English make - one each for both my discrete 120V & 240VAC powerlines which are hooked up direct from my home breaker panel to power my rig exclusively.

They do good job for my audio rig. These filters get RFI filter spectrum starting way below 0.1MHz to over many hundred MHz (not showing the upper limit of the curve) with peak insertioin RFI loss up to 52dB at 32MHz.

That said, we should neglect the miner details.For tube HV PS using sand diode rectifiers, make sure to install RFI snubber upstream of the diodes to kill the RF spikes generated by the diodes on momentariy switching offs. Otherwise those spikes will get into yr amp via the windings of the power iron.

c-J

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PostPosted: 09 May 2011, 18:55 
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have you done a comparative analysis with/without ? was there any tangible difference?


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PostPosted: 10 May 2011, 09:23 
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Hi.
Vask wrote:
was there any tangible difference?

Yes, the EMI noise level depends on locations.
The objective of this powerline EMI nosie level test (I carried out 2 years back) is to find out do a DVD/CD player & the like digital gears really inject noise into a powerline. If they do, then we need to do something to stop such noises going into our other analogue gears.

What I did was to measure EMI nosie levels on a powerline with a DVD./CD player plugged to it. I did the measurements with the DVD player switched on and off in 2 home & a commercial locations powered by different hydro companies. I could read noticeable noise level popping up whenever the DVD player was switched on. Noise was heard from built-in the monitor loudspeaker of the analyser.

What amazed me was the analyser detected AM broadcasts from the powerlines in the 2 home locations! It proves our powerlines are polluted like a sewer ! :bawling:

How can we expect good sound from our audios unless something positive must be done to purify the powerline at home.

c-J

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PostPosted: 10 May 2011, 10:49 
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cheap-Jack wrote:
How can we expect good sound from our audios unless something positive must be done to purify the powerline at home.

The answer involves a few simple steps that will help immensely. Steps need to be taken both at the power line (mains) and in the design of each unit built.

1. A dedicated surge arrester needs to be placed in the main power system. These can be either portable "plug-in" units (up stream of all your audio gear) or a whole house arrestor can be installed at the breaker panel. This will protect your equipment against voltage surges external to your premises.

2. Always use 3-wire IEC connections to your boxes (Hot-Neutral-Ground). In the 21st century there is no room for 2-wire mains power coming into equipment. The ground lead should be directly tied to the chassis; NO EXCEPTIONS. Decisions on how and where to tie signal grounds to chassis (safety) grounds need to be made based on the topology of the audio setup and how it is intended to be used.

3. All designs should include a dedicated EMI filter in line with the mains power input. Note: the fusing must be BEFORE the EMI filter. This means using a separate EMI filter module or using an IEC module with a built in fuse and EMI filter. If you use an IEC input module with an EMI filter and no fuse then your power cord must be rated to handle the full rated current of the circuit breaker on the mains.

4. An appropriately sized MOV needs to be placed across the Hot (Line) and Neutral mains power just downstream of the EMI filter. This will protect your equipment from local power surges. Appliance motors and transformers both have failure modes which can produce large mains voltage surges. The MOV will protect each individual unit from external surges and help arrest local surges which may be caused by transformer or power tube catastrophic failure.

5. Power switches on the mains side of transformers need to be bypassed with an appropriately rated capacitor (X2 type).

6. The power section of amps should be shielded from the audio portions of the circuit. I generally accomplish this by using fixed aluminum plates inside the chassis to form a separate compartment for the power supply components.

7. And finally, the B+ power supply filter needs to be designed to provide adequate filtering not only at the primary ripple frequency, but at higher frequencies as well. This virtually always requires at least one sizable in-line inductor in the filter.

If you follow these simple rules you should have almost no problems with creeping EMI getting into your audio signal path.

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PostPosted: 10 May 2011, 11:58 
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Oooer , methinks I'd better ground my tinfoil hat

BDA


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PostPosted: 10 May 2011, 12:01 
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Better still live inside a faraday cage

BDA


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PostPosted: 10 May 2011, 12:23 
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Hi.
So you'r talking quite few things all together.
(1) powerline surge due to external electrical loads (O.T.)
Suncalc wrote:
1. A dedicated surge arrester needs to be placed in the main power system
Suncalc wrote:
An appropriately sized MOV needs to be placed across the Hot (Line) and Neutral mains power just downstream of the EMI filter

(2) switch-on surge of the amp. (O.T.)
Suncalc wrote:
5. Power switches on the mains side of transformers need to be bypassed with an appropriately rated capacitor (X2 type).

(3) EMI filters:- finally on topic, thanks.
Suncalc wrote:
All designs should include a dedicated EMI filter in line with the mains power input.

Suncalc wrote:
no fuse then your power cord must be rated to handle the full rated current of the circuit breaker on the mains.

Question: why the power cord "MUST" be "full rated current of the circuit breaker"???????
Do you know how large is the main circuit breaker panel? Mininum 100A for home. Are you telling us to get a 100A fuse for our amps? Are we runnning a outdoor rock concert or what?

The function of a fuse is to limit the current consumption of its downstream load. For an home tube audio rig, say maximum 500W, then the AC current load will be 500W/110V=4.5A/ So the fuse should be 5A say, but not over in order to protect the system downstream.

BTW, do you know what size of power cord to handle 100A AC? The conductor inside the power cord will be min. AWG#1. I doubt very much we can buy such huge size power cord off the shelf unless we DIY one!
Suncalc wrote:
4. An appropriately sized MOV needs to be placed across the Hot (Line) and Neutral mains power just downstream of the EMI filter.

Any UL/CSA rated power strips or bars are ALL come with built-in MOV which sell cheap in tons. So if we plug our gears onto such power strip, then we can save the hassle & cash to install one, right?

Please don't mind my being so straight forward up to the point as I want our readers get the correct information.

c-J

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PostPosted: 10 May 2011, 12:33 
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Hi
bda wrote:
Better still live inside a faraday cage

Yes, you would "live" (or work, to be precise) in a faraday like fully earthed shielded metal cage if you worked in a radio manufacturer. If you ever visit such a factory, you will know why & how.

c-J

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PostPosted: 11 May 2011, 12:12 
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I'm sorry c-J, you seem to have misunderstood my post. I place all these items under the same heading because they all have to do with main system power system integrity. Perhaps I can be more clear.

The inclusion of surge protection can have a direct impact on long term amplifier sound quality. Everyone knows that large voltage surges can wreak havoc; destroying equipment, burning out components, destroying tubes, etc. But far more insidious are the numerous small surges that never appear to do any damage but which can occur, in some systems, dozens of times a day. These repeated small surges have a cumulative effect of breaking down the insulation (and hence coil integrity) in mains transformers. This can lead to leakage, micro-arcing, and capacitive/inductive effects which actually generate high frequency noise in the transformer. The only way to combat this is appropriate surge protection. The fact that a transformer may have successfully passed a hi-pot test at the time of manufacture does not mean the repeated lower voltage surges cannot cause breakdown over time. A good rule of thumb is that the MOV in the amp should be no larger than about 150% of the rated primary voltage of the mains transformer. This helps to keep the main transformer "quiet" over it's entire design life.

Bypassing power switches with inductive loads is also noise related. The micro-arcing of unbypassed switches can cause carbon buildup on the switch contacts over time. This carbon buildup introduces a small resistance in the line. This new "carbon resistor" is a noise source. And with repeated switching over time, the noise will become big enough to affect the audio chain. This is a measurable phenomenon. It is why old switches in many unit are "noisy" (i.e slightly jiggling the power switch not only causes noise, but can change the overall noise level in the amp).

Now lets address this comment about fuses (please forgive me for getting off topic for a minute):
cheap-Jack wrote:
Suncalc wrote:
no fuse then your power cord must be rated to handle the full rated current of the circuit breaker on the mains.
Question: why the power cord "MUST" be "full rated current of the circuit breaker"???????

These is much confusion concerning the actual purpose of fuses and I want to be perfectly clear: The purpose of a fuse or circuit breaker is to protect wiring not loads. This is a point which many people do not seem to understand. After almost 25 years of designing equipment for both FAA and US Military certification, I still run into engineers who don't understand this basic concept. The breaker or fuse protects the wiring not the load.

Lets take your example of the main power panel in a typical residence. As you said, the main panel may have a main breaker of 100A to 250A dependent on the size of the service panel. But if you add up all the branch circuits you will generally find that the sum total of branch circuits far exceeds the value of the main breaker (this is accepted practice under US electrical code). So with no faults, the branch circuits could easily over power the main breaker and cause it to trip. So what does the main breaker protect? The answer is that it's purpose is to prevent the wiring between the main panel and the distribution box from being overloaded (i.e. it is protecting the wiring). Now the branch circuits all have smaller values than the main breaker. In the US they are typically 15A or 20A, with larger values reserved for single point of use items (usually large appliances, electric water heaters, furnaces, etc.). For 15A circuits the branch circuit wiring must be at least 14AWG and for 20A circuits 12AWG. This is because smaller wiring would present excessive heating at the breaker values and present a fire risk. But what about the cords we plug into these circuits? These may be 16AWG, 18AWG, or even 20AWG. A fault in the load could easily cause excessive current draw in the lower rated power cord and still not trip the branch circuit breaker. Then our power cord would see excessive heating and itself become a fire risk. How do we protect against this? The answer is that we use a fuse or breaker in the load device that will trip before the current carrying capacity of the power cord is exceeded. Now obviously the cord needs to be rated to supply the current that the load will draw, but the limiting factor on the fuse is the capacity of the power cord, not the size of the load.

When I said "circuit breaker" in my post, the item to which I was referring was the branch breaker, not the main panel breaker. Now with the purpose of fuses clearly understood, we can reassess the comment about the EMI filters. The filter itself is a potential source of fault current on the cord (given a shorting failure mode). So if the fuse is before the filter but after the power cord, the fault will trip the fuse and prevent the power cord from overheating. But if the fuse is not there, then a fault in the EMI filter can cause excessive current to be drawn which may destroy the cord and present a fire hazard. The only way to protect against this eventuality is ensure that the power cord is rated for the full current of the branch circuit breaker (generally 15A or 20A). In this way, if the fault current is less than the breaker value then there will be no excessive heating in the cord and no fire hazard will exist and if the fault current is larger that the breaker value, then the breaker will trip to protect the circuit and, again, no fire hazard will exist.

As an example, look at the this IEC entry module designed by Qualtek (http://www.alliedelec.com/search/productdetail.aspx?SKU=6894318). If you look at the data sheet you will see that the fuse in the 880 series is indeed before the EMI filter, just as I explained above. But if you look farther down, you'll see that in the 882 series, the opposite is true. So what gives? The answer is that the 880 series is designed for equipment which will be using generalized power outlets (think desktop computers, lab equipment, etc.). But the 882 series is meant for equipment which is installed in a "configured power environment". The best example of this is a 19" equipment rack. Here all the equipment plugs into the power system supplied by the rack. And in this installation, all the power cords must be rated for the value of the breaker in the rack's power system.

Now, as to your final question about power strips. Yes, in general these contain an MOV but there are two limiting factors. First, their MOVs are generally rated at a very high voltage. These don't protect against the repeated small surges that can cumulatively damage power transformers over their lifetimes. If they were rated lower, then this would affect their reliability and seriously hurt sales. Some of the more expensive ones are better but still not great. The second factor is that in general these power strips contain some type of EMI filter. (One might say good, this is what we want.) However, the MOVs in these strips are generally upstream of the EMI filter which can significantly attenuate the peak levels of the surges. So they really only protect against surges generated up stream of the strip. Anything plugged into the strip which causes a surge (like a big power amp turning on) will affect all the other items installed in the strip. (Some may think that I'm "picking nits" but I just trying to explain my reasoning here.) So whereas I think that in general these power strips are a good thing to use, I do not rely on them when making design decisions.

Sorry for the long... long post, but I wanted to make sure that everyone understands my reasoning for including all the items from my post above.

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PostPosted: 11 May 2011, 14:29 
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Hi.
Thanks for clarifying what you meant to say.- e.g. branch circuit breakers.
Suncalc wrote:
The purpose of a fuse or circuit breaker is to protect wiring not loads. This is a point which many people do not seem to understand.

Sorry, I disagree. NO load, no current flowing thru the wires & the circuit breakers (main/branch). So the circuit breaker will never trip & the wires, being a current carrier, will be safe for ever as long as there is no load or normal load.

In fact, the most criitcal part of stopping any overload damage is the inline fuse immediately upstream of the load.
Take the example of our amps, the AC fuse of right ampacity inside our amp, say 2A or whatever, should limit the max current needed by the load - the amp. Any fault beyond the load will be stopped by blowing the inline fuse way before any damage can possibly be done to the wires insulation & tripping the circuit breakers.

So the circuit breaker (main/branch) is to stop the load being overloaded for whatever reasons & cut off any damage beyond that point.

Of course there is always chances of accident !


c-J

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