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Bricolo 4th June 2004 11:00 PM

Isolation transformers
 
Hi all,


I'd like to know a few things about isolation transformers.


My gainclone's trafo is vibrating, it's not loud but noticeable when the music is at low volume. It's a mechanical vibration and it seems that it's due to DC on the power line.

I've been told that an isolation transformer will help.
But what is an isolation transformer? Does it have something special compared to a classical one, or is it simply a 1:1 trafo?

What size is needed? My gainclone is 2*60W, and uses a 225VA trafo. I'd like to place the gainclone on the isolation transformer, and if possible, the cd player too (a few VAs). Will 500VA be ok or should I look for a bigger one?
I can have a 500VA one for 40, new. Is it a good price?



Alex

RetroAudio 4th June 2004 11:33 PM

I guess I have a question as well about vibrating xfmrs. I recently bought 20 small ones and 6 of them vibrated when hooked up under noload. Since some did and some did not, I assumed that the hummers were faulty, although I didn't see how such a number could be bad. The hum was very noticeable. Faulty or not, don't think they can be used for audio anyway. The hummers did measure an off voltage, lower as I recall.

Bricolo 5th June 2004 09:08 AM

Were they all similar?

Bas Horneman 5th June 2004 10:14 AM

Hallo Alex,

I know KYW (aka Thorsten) had a DC blocking setup for gainclones...

There was some controversy about if and how it would actually work...

Maybe that is a cheaper way to go..

Regards,
Bas

Bricolo 5th June 2004 11:27 AM

I didn't see it on his website, where can I find the schematic?


BTW, I've also good things about the repercusion on sound, with isolation transformers. That's why I'm also interested.

Bas Horneman 5th June 2004 11:48 AM

here is a link to it...it is actually quite complex with all the transformers...sorry about that......


the isolation transformer actually looks like a better option.. ;-)

http://www.diyaudio.com/forums/showt...840#post191840

analog_sa 5th June 2004 11:58 AM

Quote:

here is a link to it...it is actually quite complex with all the transformers...sorry about that......
The transformers have no relation to the dc blocking. You only need the two bridges and two caps. The shown ps combines dc blocking with half flux in the cores.

Quote:

the isolation transformer actually looks like a better option.. ;-)
There seem to be 3 types of people - those who like the sound with iso tranies, those who don't and the ones that can never tell the difference :)
I find dc blocking to solve the problem of dc without dramatically changing the sound of the powered system - if anything i seem to prefer dc blocking soundwise. And i still haven't listened to an iso transformer i like.

Bricolo 5th June 2004 12:31 PM

Quote:

Originally posted by analog_sa


The transformers have no relation to the dc blocking. You only need the two bridges and two caps. The shown ps combines dc blocking with half flux in the cores.



There seem to be 3 types of people - those who like the sound with iso tranies, those who don't and the ones that can never tell the difference :)
I find dc blocking to solve the problem of dc without dramatically changing the sound of the powered system - if anything i seem to prefer dc blocking soundwise. And i still haven't listened to an iso transformer i like.

did you have DC problems, or have you built this "just to be sure"?

analog_sa 5th June 2004 01:29 PM

Quote:

did you have DC problems, or have you built this "just to be sure"?
Who doesn't? I didn't have problems to the extent that the transformers would buzz, just added tha caps to an existing non-buzzing supply and noticed a slight sonic change; not entirely positive (a bit softer bass) but pleasant enough in the midrange.

My isolation tranformers (700VA) otoh kill the dynamics big time (even on preamps). I can well imagine some listeners might prefer the dead dynamics as digital mellows down a lot and you get some of the famous 'black background' :)

markp 5th June 2004 02:04 PM

An isolation transformer is just a 1:1 ratio. It takes the 'hash' and noise out of the transformed power that comes down your power line from the electric company. It also blocks DC but if you have DC on your AC wall power you have more to worry about than your stereo! The hum comes from some of the windings which were not done tight enough to stop the vibration, its not bad but not what you what either in a hifi setup. Mount the units with good hardware tightly and it should help.


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