[ducretet]

Hello everyone,
I have a lot of noise (interference) problems on my workbench. It happens with any radius.
I have seen the following article in the "library" section:

https://philcoradio.com/library/index.ph...workbench/

But, I don't get it. Could someone explain it clearly?
Thank you very much.

[RodB]

Hello Ferran,
I'll try to clear it up for you. In America the AC power supply is referenced to earth ground. Most house wiring is 120 volts AC 60 cycles. Houses are full of hundreds of feet of wire. The ground wire for all the power in a house comes to a single point and that is electrically connected to earth ground. All that wire acts as an antenna both for transmitting and receiving lots of electrical noise and interference from motors, fluorescent lights, wall worts, etc. And that's how it gets into our radios.

The objective with the capacitors is to attempt to filter out the noise to earth ground before it gets to the power input to the radio. It uses (2) .1mfd capacitors, one connected to each side of the AC power. The other lead of each cap is connected together then attached to earth ground with as short a wire as possible. Typically earth ground is the cold water pipe in a house. The plug would then be plugged into my power strip. I would use Y2 safety caps at 0.1mfd.

If I were to make this I would put it in a small box with a power cord and plug and a separate ground wire. If the box is metal then it to would be connected to the ground wire.

   

This will only handle noise on the power lines. You will still have to deal with the noise and interference transmitted through the air. Maybe others have a simpler explanation but I hope this helps.

[David]

Wall warts  can be a real problem things like power supplies for lap tops, phone chargers some LED lights and touch lamps. Try using a portable radio walk around your place and try and find the trouble makers. Have a touch lamp even turned off still sends out a signal in the air have to unplug the thing! High voltage power line near your place say 1 or 2 KM away can send out lots of noise over the air. During the summer storm season with a power outage thing are nice an quiet on the air waves and listening to a radio is so nice.

[morzh]

If you want to make a good filter, take Schaffner "high-filtering" input filter,

https://www.digikey.com/en/products/deta...gKwdPD_BwE

(One like this; go to their datasheets and pick one with the highest filtering capabilities), and make an AC power box for your radios.


I use Schaffner in my devices as an input filter (they make pluggable one, though I would recommend the other types, they have stronger filtering) with good success.

[ducretet]

I so much that has been helpful. Thank you very much to all.

In the next few days I will study the most appropriate resolution for my case.

[radiorich]

Hello morzh,
Yes, I built two units one I put one those filters in a box and mounted a buck transformer, and I even added a fuse and power switch and power cord.
Another one I used an isolation transformer and fuse holder and power switch.


Rob, I have never thought about that simple capacitive circuit design.

Sincerely Richard

[Chas]

Having two neighbors that worked at Cornell/Corcom and well as my work in industrial electronics I have accumulated a large box of line filters.

I have also changed over 12) 4' florescent ballasts from early magnetic to late magnetic with built in filtering, meaning, I have a dozen of "fluorescent" RF filters, left over.
I generally use smaller 3 amp filters inside the chassis of console radios to good advantage.

However, larger units are way overkill (20 amp).

Many of the filters use a dual pi-section common mode design. Most have a particular range of RF attenuation, such specifications, if they can be found, are useful to be sure that the application is successful.

A improperly designed (homemade) or poorly installed filter is practically useless as the RF noise will simply "go around" the filter. Of primary issue is the Earthing of the filter, too long a path or a noisy path is useless.

Filters have bypass caps, the AC pass of the caps can accumulate if filters are on multiple equipment on the same branch circuit, the ground fault detector can give way. The filter must use a ground path as the leakage current will be enough to be felt. Most of the caps in these filters use at least a 0.1 mf.

Filters do fail but very rarely, the caps will short from a high voltage, high current surge. I have seen a case rupture in an integral IEC (cord socketed) Corcom pi section filter. I was surprised to learn later this was a 30 amp 240 circuit that was layman installed without GFI... Yes, the device had an auto voltage selecting power supply...

Chas

[morzh]

Chas

Well-designed filter, beside using the Y- and X- rated caps, will also use a good MOV. And a common mode choke.

And, well, a fuse does not hurt to add either.

[radiorich]

Hello Chas,
I have never thought of adding one inside of a console before!

Sincerely Richard

[Chas]

I did an extensive rebuild of a Zenith 6S524 some time ago. The owner had complained about noise in his home so I added the filter to the inside of the back apron of the chassis. I kept the leads short from the power entrance to the filter. FWIR it was a 3 amp Cornell single pi section with a common mode choke in a completely sealed can. It worked very well at reducing the line noise.

chas

[GarySP]

Quick question ... Why the separate ground wire to earth ground. My service is grounded both to the water pipe (copper) coming into the basement, and to a 8 foot ground rod driven into the earth. Why couldn't it be tied to the existing ground with a three-pronged plug, then plugged into a grounded power supply? Help an old man understand! Take care and BE HEALTHY! Gary

[morzh]

Separate GND wire means that no current flows through it and so no voltage develops over it either. This makes for clean GND that itself does not introduce noise in the system.

[radiorich]

Hello Chas,
Nice sounds like a great idea.


Morzh , Far as my radio repair bench that is in my spare room there is no ground at my outlet just at my ground rod that I installed for my Antenna, and it is tied to my repair bench I have a metal cased power strip.
My house was built in 1929 most of the wire was updated in the 50s with 2 wire romax then so years ago a new service and panel was put in and some new circuits added those are the only ones which are 3 wires .

Sincerely Richard

[poulsbobill]

Power supply grounds (your ac wire) can be very noisy. (they are grounding everything in the house) You are better off with a separate rf ground you put in the ground near the set and run a copper wire to it. And a switch to turn on/off as some of my old zeniths sound better w/o the ground.

Bill

[David]

Many years ago was helping a friend with a sound system that was just installed at his church. When turned on always a buzz I always carried one of those adapters that allowed a 3 prong plug to be used in a outlet with only 2 prongs. No buzz! Over the years several breaker panels had been added to different parts of the many building all feeding into the main service. The new panels all had the grounds and neutrals tied together making for a nice feed back loop. We simply isolated the neutral from the grounds in all the added panels no more buzz. The same problem can happen with a backup generator feeding to a main panel with a transfer switch if the bond between the ground and neutral is not removed in the gen sets, most sets have the ground and neutral together for safety.