Isolation Transformers Power Requirements - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 14th October 2010, 09:18 PM   #1
diyAudio Member
 
Joshua_G's Avatar
 
Join Date: Nov 2008
Location: Small village, Israel
Default Isolation Transformers Power Requirements

I'm going to order from a local factory 3 Isolation Transformers with floating secondary windings:
One for all the digital sources, one for all the analogue sources (TT, phono stage and pre-amp) and one for the power amp.

I know that the isolation transformers power ratings should be way above the actual power consumption of the gear they are feeding, I only don't know by how much. Should the isolation transformers' power rating be 2x the power consumption of the gear, 3x, 4x, or what?

My stereo setup is expansive High-End one.
  Reply With Quote
Old 14th October 2010, 09:58 PM   #2
diyAudio Member
 
Join Date: Mar 2010
No, a good quality isolation transformer will have built in safety factor so you don't need to get them rated higher than your actual load. Of course, smaller transformers will get hotter so if that's a concern, get bigger ones. You will spend more money, and the wasted power may be more or less depending on the specific design parameters.

So I wouldn't go beyond double, and in fact would like to run near 100% of rating, especially for the power amplifier which will draw different power depending on the signal and probably will need even less safety factor.
  Reply With Quote
Old 14th October 2010, 10:24 PM   #3
diyAudio Member
 
Speedskater's Avatar
 
Join Date: Sep 2002
Location: Lakewood, Ohio
Quote:
Originally Posted by bob91343 View Post
So I wouldn't go beyond double, and in fact would like to run near 100% of rating, especially for the power amplifier which will draw different power depending on the signal and probably will need even less safety factor.
While it's very true that the power amp's continuous current is low compared to it's max. power. But a power amp will draw a large amount of current for a small fraction of each power line cycle. Some say that these pulses may be 5, 10 or even 20 times it's rated current. So I would oversize the power amp's isolation transformer to provide a low source impedance for these current pulses.
__________________
Kevin
  Reply With Quote
Old 14th October 2010, 10:39 PM   #4
diyAudio Member
 
Joshua_G's Avatar
 
Join Date: Nov 2008
Location: Small village, Israel
Quote:
Originally Posted by Speedskater View Post
While it's very true that the power amp's continuous current is low compared to it's max. power. But a power amp will draw a large amount of current for a small fraction of each power line cycle. Some say that these pulses may be 5, 10 or even 20 times it's rated current. So I would oversize the power amp's isolation transformer to provide a low source impedance for these current pulses.
This is more in accord with many reports I heard from fellow audiophiles that often isolation transformers, or mains step-up/step-down transformers decrease the dynamics of amps. This is more so on power amps than on pre-amps, which mostly work on class A, so there aren't large swings in their power consumption.

So, does anyone has any data, preferably based on experience, about the recommended power overhead of isolation transformers?
  Reply With Quote
Old 18th October 2010, 01:52 AM   #5
diyAudio Member
 
Join Date: Apr 2010
Location: seattle, wa
The question is not can you run it at full ratings, but the temperature rise.

Modern toroidal transformers have almost zero core loss (5 watts for a 1Kva unit), but temperature rise is still typically 60C at "rated" output. However, as it is 80-90% copper losses, running at 70-80% rated load means its actually affordable to get that 30-40C rise.

Poor power factor from a rectifier load may require significantly larger transformers, and this de-rating is easily estimated from calculating the rms current feeding the rectifier. there's no extra losses, its all I^2R.
(This is where a choke input filter can really help out.)

Is there any reason you can't use one transformer with three secondaries?
It would save weight, and if you are building more than a few it would cost less.

Most of the low to mid range audio equipment I fix has an E-I transformer powering it, and its crap. The cores are run partly saturating, and this is why they have a 30C temp rise @ no load.
in many cases, the 105C thermal fuse is the only failed part.

Any difference in sound caused by running an amp/preamp off an isolation transformer is caused by the fact that its no longer grounded.

Electrically there is almost no difference between the wall outlet and the isolation tx. if you were to stick a resistor to drop 3 volts and an inductor to drop 3 vac from the line at full load, this would simulate 90% of all iso tx's out there. (aside from the floating ground)

the next step in that debate would be to run your amp off a stack of batteries.. would zero ripple change anything?
  Reply With Quote
Old 18th October 2010, 06:49 AM   #6
AJT is offline AJT  Philippines
diyAudio Moderator
 
AJT's Avatar
 
Join Date: May 2003
Location: Palatiw, Pasig City
Quote:
Modern toroidal transformers have almost zero core loss (5 watts for a 1Kva unit), but temperature rise is still typically 60C at "rated" output. However, as it is 80-90% copper losses, running at 70-80% rated load means its actually affordable to get that 30-40C rise.
heat is inevitable in any transformer because of its weight and chemical composition, choice of flux densities also have a lot to do with this...

Quote:
Electrically there is almost no difference between the wall outlet and the isolation tx.
maybe, if your isolation transformer has the same kva rating as the pole transformer where your power was derived from....otherwise, comparing a 25kva transformer to a 2.5kva isolation transformer say, which do you think will have lower impedance?

why not request your utility company to provide you with a balanced service? the type where L1 an L2 are neither line and neutral derived and isolated from the pole to your residence....
__________________
the best advertisement for a good audio design is the number of diy'ers wanting to build it after all the years....never the say so of so called gurus....

Last edited by AJT; 18th October 2010 at 06:54 AM.
  Reply With Quote
Old 18th October 2010, 11:47 AM   #7
diyAudio Member
 
Join Date: Apr 2010
Location: seattle, wa
the core loss i mentioned is a legit value from an american company.

well, of course the grid is going to have lower impedance.. but we're talking about .5 ohms vs .1 ohms... (the 1 gauge AL wires feeding your house are not negligible in this case)
but that's not going to make a difference anyway.

if you can hear the difference between a 1 ohm and a .1 ohm resistor in the ac line... (and a 1% and 5% choke for good measure) then the power supply needs to be scrapped.

Also, you might be surprised at just how bad the grid is in parts of the country.. lots of third harmonics in there. in some cases you can actually see the distortion with just an oscope, no sa required
  Reply With Quote
Old 18th October 2010, 12:15 PM   #8
AJT is offline AJT  Philippines
diyAudio Moderator
 
AJT's Avatar
 
Join Date: May 2003
Location: Palatiw, Pasig City
Quote:
Also, you might be surprised at just how bad the grid is in parts of the country.. lots of third harmonics in there. in some cases you can actually see the distortion with just an oscope, no sa required
something an isolation transformer will not cure.....
__________________
the best advertisement for a good audio design is the number of diy'ers wanting to build it after all the years....never the say so of so called gurus....
  Reply With Quote
Old 18th October 2010, 11:08 PM   #9
diyAudio Member
 
Speedskater's Avatar
 
Join Date: Sep 2002
Location: Lakewood, Ohio
Quote:
Originally Posted by johansen View Post
Any difference in sound caused by running an amp/preamp off an isolation transformer is caused by the fact that its no longer grounded.
An isolation transformer does not eliminate the safety ground (EGC). The isolation transformer uses it's own separate EGC back to the service entrance.
__________________
Kevin
  Reply With Quote
Old 18th October 2010, 11:26 PM   #10
diyAudio Member
 
Joshua_G's Avatar
 
Join Date: Nov 2008
Location: Small village, Israel
Quote:
Originally Posted by Speedskater View Post
An isolation transformer does not eliminate the safety ground (EGC). The isolation transformer uses it's own separate EGC back to the service entrance.
Indeed, however the 2 wires supplying the AC are floating to the safety ground.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
FREE! Two 7 KV (!) isolation transformers (Signal Transformer) for balanced power. markmaloof Swap Meet 0 22nd January 2010 08:15 PM
Free Isolation Transformers Ric Schultz Swap Meet 3 29th November 2006 09:34 PM
Isolation transformers Bricolo Parts 36 28th June 2004 07:46 PM
need help with audio isolation transformers azira Parts 9 18th June 2004 09:44 PM
Isolation transformers - buzzing schpeltor Parts 8 9th September 2002 10:06 PM


New To Site? Need Help?

All times are GMT. The time now is 08:03 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2