Building an isolation transformer

Carlman · « **on:** 15 Jan 2004, 06:04 pm »

OK, so with all the buzz about the the BPT 3.5 and previously about the OneAC's and Powervar's... I figured maybe I can build one that would work for less than the 3.5 but, be better than the OneAC's...

I found this article: http://www.hometheaterhifi.com/volume_10_3/feature-article-isolation-transformer-8-2003.html

However, it doesn't have any circuit boards and that's the crux of my question in this post... What does that circuitry do?

Looking at the OneAC that I own and at the photos of the BPT, they have some circuitry that does something. I'd be happy to build a board that serves the same purpose but, I'd need a schematic. In fact, I'd really like to do this.

Has anyone done this before or have any advice? Other than to buy the BPT. I don't have an extra 2500 lying around so, my budget will be about 500 max.

JoshK · « **Reply #1 on:** 15 Jan 2004, 06:18 pm »

If I am not mistaken the PCBs are just for Caps that act as a filter. The ones in the OneACs (having just got done modding one) are populated with Caps and one single resistor.

I bought a aluminum full sized chassis and I am taking two larger OneACs transformers and placing them in it wired up to some hubbell outlets and my version of a VH power cord.

Carlman · « **Reply #2 on:** 15 Jan 2004, 07:25 pm »

Anyone know where I can see schematics of a PCB that provide this filtration? Thanks.

WerTicus · « **Reply #3 on:** 27 Jan 2004, 03:05 pm »

i dont have a diagram but you simply put caps that are obviously rated with enough voltage (double is enough) from the + to ground and from the - to ground

the more capacitors the better quality the filtration....

i would put (for a power amp) 10,000uf x 2 and then some 100uf x2 and some 1ufs x2 should be sweet

WerTicus · « **Reply #4 on:** 27 Jan 2004, 03:07 pm »

oh yeah and a resistor goes from + to ground and from - to ground to bleed the caps when its off so they dont stay charged all day which is bad for them.

_scotty_ · « **Reply #5 on:** 27 Jan 2004, 05:38 pm »

WerTicus, AC will pass through a capacitor to ground. If you put a big enough capacitor to ground all of the AC will go there. This is called a dead short. The capacitor sizes you mentioned in your post might qualify.
The capacitors will also tend to heat up and explode. A lot of amperage is flowing through them to ground. A cap larger than 1ufd is probably not necessary. The noise you are trying to reduce is at very high frequencies.
If the cap is too large all of the power goes to ground with nothing left over to power your gear. A motor run capacitor might live in this apllication, they are also good sized, 20ufd is not uncommon. The transformer mentioned in the artcle is made with an internal electrostatic
shield which help reduce HF noise. I would try the xformer plain first.
It alone might be sufficient.

JoshK · « **Reply #6 on:** 27 Jan 2004, 10:00 pm »

Carlman,

Can the transformers still be purchased? Or do we need to arranage another group buy? I want one too, so I would be interested in getting in on a group buy.

_scotty_ · « **Reply #7 on:** 27 Jan 2004, 11:04 pm »

JoshK, The transformer was still available at the Plitron website the k last time I went there for $250
single piece price. A box from Par-Metal would run about $60 http://www.par-metal.com/ . I think the total price could be kept under $350 with a little luck and a DIY powercord.

JoshK · « **Reply #8 on:** 27 Jan 2004, 11:15 pm »

I already have a par-metal case, and in fact I have the back cut out and installed 5 Hubble outlets already. I have made up a VH recipe DIY power cord of 9awg. I have a few OneACs that I was going to use inside the case but I am thinking of ordering one of these now. I still may see if I can cram one OneAC in there for dedicated digital. We'll see.

WerTicus · « **Reply #9 on:** 28 Jan 2004, 03:17 am »

i must be thinking of dc then.

Carlman · « **Reply #10 on:** 28 Jan 2004, 03:35 am »

I've recently used up a lot of my hifi funds so, this project will be on hold for me. I will still build it, though.. and maybe with some hindsight from JoshK.. I'm not an electrician... just a regular guy that wants some good power for my equipment.

Here's a link to the specs on that transformer:
http://www.plitron.com/PDF/857502.pdf

The part number at Plitron is 8575-X0-02. I ordered my transformers for my AKSA from them.. it took about a month and a half to get them.

So a group buy may be a good thing for time and cost considerations. However, just say you're a 'secrets reader' and get them for 312 CAD. Unless you think you can get 10+ on the GB.

I too have some elements of this case lying around and would like to do it... so, I will definitely be interested in your results if you try it.

-C

penance · « **Reply #11 on:** 28 Jan 2004, 08:39 am »

you can use cap's to ground or from live to earth
normally values les than 1UF
But they must be X or Y rated for AC supply use

DTH · « **Reply #12 on:** 1 Feb 2004, 02:06 pm »

This is an interesting thread. Does anyone know of any online info from people who have built a diy project with a part like this transformer? Josh, it would be cool if you post some pics when you are done with your project.

How similar is this isolation transformer:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2591877137&category=11772

to the Plitron part discussed here? Besides being power rated a little lower is there any other obvious difference?

JoshK · « **Reply #13 on:** 2 Feb 2004, 03:25 am »

Now that I have broadband access again at home I shall be post pics of my project soon in the gallery.

Carlman · « **Reply #14 on:** 12 Feb 2004, 02:47 pm »

I got to thinking about this some more and was wondering if I could incorporate a small stepdown of voltage... My house runs 125V and most gear specifies it's operation around 118. I know there's a little variance but, I'd rather run the gear as close to what it wants as possible.

I know when I was building my amp, it was recommended that I use a 33-0-33 voltage configuration vs. the normal 35-0-35 to accomodate the higher voltage to provide 'optimum' results. So, I'm wondering if the same holds true for this DIY isolation transformer.

My guess is even if the sonics do not improve, the components will last longer. It just seem right to match the voltage... to me... anyone?

-Carl

Bill@LakeGeorge · « **Reply #15 on:** 12 Feb 2004, 04:47 pm »

Quote from: Carlman

I got to thinking about this some more and was wondering if I could incorporate a small stepdown of voltage... My house runs 125V and most gear specifies it's operation around 118. I know there's a little variance but, I'd rather run the gear as close to what it wants as possible.

I know when I was building my amp, it was recommended that I use a 33-0-33 voltage configuration vs. the normal 35-0-35 to accomodate the higher voltage to provide 'optimum' results. So, I'm wondering if the same holds true ...

I accomplish this by using a variac before the power conditioner and you can dial in voltage, it does make a difference.

JoshK · « **Reply #16 on:** 12 Feb 2004, 05:12 pm »

I am not that familiar with VARIACs. Do they have a watt rating like step down transformers which can sometimes limit dynamics?

Carlman · « **Reply #17 on:** 12 Feb 2004, 08:16 pm »

Do you mean something like this?:
http://used-line.com/cgi-bin/used/~4452451_/Variac_W10MT3.htm

Is there a modern day equivalent?...edit......
I found a bunch on Ebay from Staco and some other brands... I think this would be great if you were demo'ing equipment and needed to change the voltage from place to place.... But, I would rather build something that isn't variable and it is corrected for the voltage I have now... cleans the power, and that has 6 outlets all in one unit.

bhiggins · « **Reply #18 on:** 12 Feb 2004, 08:38 pm »

Quote from: Carlman

Is there a modern day equivalent?

Variable transformers (or variable autotransformers) are obtainable from most places that sell electronic test equipment.

One company that makes them is Superior Electric.

http://www.superiorelectric.com/

Another is Staco:

http://www.stacoenergy.com/

The company I work for uses one from the latter to test under voltage conditions on various pieces of equipment that we manufacture. It has AC in, AC out, and a fuse, in addition to the big dial. As for being modern, the looks are pretty dated. You could definitely use it to compensate for an over-voltage condition. It is not adaptive and would have to be manually adjusted using a multimeter to get the correct output. There are different power ratings available.

~Ben

Bill@LakeGeorge · « **Reply #19 on:** 12 Feb 2004, 08:46 pm »

Quote from: Carlman

Do you mean something like this?:
http://used-line.com/cgi-bin/used/~4452451_/Variac_W10MT3.htm

Is there a modern day equivalent?...edit......
I found a bunch on Ebay from Staco and some other brands... I think this would be great if you were demo'ing equipment and needed to change the voltage from place to place.... But, I would rather build something that isn't variable and it is corrected for the voltage I have now... cleans the power, and that has 6 outlets all in one unit.

Carl something like that I picked up a couple on ebay, new, for about $120 each. I noticed an immediate difference I was getting about 128 volts and dialed it back to 117 audio and video immediately improved.