Swampy's Mains Filter

[Mike]

As the title says, instructions for building a mains filter.

This is a very inelegant method of posting but due to restrictions on file size I've had to chop it up and save it as individual JPEG's on imageshack.
I can email the original PDF if reqd, just PM me with your email address.

I'm not sure if these are going to be clearly legible.

[Mike]

Ah!...

You can also access the pdf HERE

The file is called 'feed-through-filter2'


Cheers...

[alb]

If anyone is desperate to see one of these, or hopelessly worried about any adverse effect it may have, i can bring mine to Chesterfest.

[Yomanze]

Hi alb, what about the positive effects? :P

[alb]

There were no negative effects as far as i remember.
Some say these filters can rob the life from valve equipment, i didn't notice.
The good news is that it works in preventing noisy mains spikes etc.
I tend to use it with digital stuff all the same. My mains isn't noticeably bad anyway, just the occasional click from lamps being switched on.
I think the parts were quite cheap maybe £10.
Worth building one at that price.

[Primalsea]

To give you guys some idea of what I was on about I run a simulation of the Swampy Filter and have posted the result. On the top graph the upper trace is a light load of around 25w the lower trace is a heavy load of over 500w. The bottom graph shows the phase response.

Now bare in mind that any analogue stage effectively modulates its power supply into the signal that you hear I would expect the filter to effect the sound.

As you can see there's a couple of areas with a large gain in the audio band but RF is reduced effectively. The gain could be a problem in some systems.

All this was based on resistive loads, most equipment is reactive which I would expect make the response graphs even worse.

However with most things it's a case of suck it and see.