Transformers: How big is TO big?? - Page 4 - 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 25th April 2008, 03:34 PM   #31
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Quote:
Originally posted by AndrewT
most recommendations for a 100W amplifier fall in the range 100VA to 200VA.
You will find that a middle ground value of 1.5times the maximum output power works well.
Well, I just tried that out. AndrewT is right.
I used TDA7924 shoving pairs of 8 ohm drivers (bit less than 4 ohms sum), a 50vct, 2 amper transformer, 100va, and 9023uF per rail.
Oh, and a very huge heatsink.
It made 100 very pretty watts and a lot of heat.

The 100va was fine.
With a party EQ'ing and some rather incredible concert like sounds. . . the power supply would hold up to the clipping point without a problem.

With a more like textbook-case power supply, th
  Reply With Quote
Old 25th April 2008, 03:59 PM   #32
diyAudio Member
 
jacco vermeulen's Avatar
 
Join Date: Oct 2004
Location: At the sea front, Rotterdam or Curaçao
Send a message via Yahoo to jacco vermeulen
Quote:
Originally posted by danielwritesbac
I used TDA7924
Maybe due time to read the datasheet of the TDA7294.
__________________
The buck stops Here
  Reply With Quote
Old 25th April 2008, 05:00 PM   #33
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Quote:
Originally posted by jacco vermeulen
Maybe due time to read the datasheet of the TDA7294.
Oh yes, I'm aware that you're not supposed to push them that hard. That [100w] isn't a recommendation. It was a stress test.
They're only $2, so I hope you don't mind if I decide to "play" with one of them. It played nicely and it survived the test.
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.
  Reply With Quote
Old 25th April 2008, 05:05 PM   #34
diyAudio Member
 
jacco vermeulen's Avatar
 
Join Date: Oct 2004
Location: At the sea front, Rotterdam or Curaçao
Send a message via Yahoo to jacco vermeulen
I meant the "100 very pretty watts" part in your post, pretty mean or pretty awfull is my guess.
__________________
The buck stops Here
  Reply With Quote
Old 25th April 2008, 05:57 PM   #35
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Quote:
Originally posted by jacco vermeulen
I meant the "100 very pretty watts" part in your post, pretty mean or pretty awfull is my guess.
The cause of the 100w was mostly due to a stronger than normal load. Ah, this wasn't the manufacturer's "free and worth exactly that" design in their pdf, though. It was just a test of a new design. Either way, I think its supposed to be run at 50w.

Oh, what did it sound like? Well, that's not really the point during a stress test, but, okay. . . There wasn't any audible distortions. There just wasn't much difference, except louder and the heatsink got warm. It was nice--some form of hifi, but not quite top rank, and that seems like a typical comment about an ST amp. I much prefer the sound of a good BTL Tripath or a little LM1875, although the ST did nicely.

Well, we're on the power supply forum so. . . This TDA7294 had 220uF ceramic compound caps on the amp board instead of 2200uF electrolytic. There's a difference in heat at the heatsink. Does that mean there's a difference in efficiency?
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.
  Reply With Quote
Old 4th September 2010, 09:56 AM   #36
diyAudio Member
 
kipman725's Avatar
 
Join Date: Jun 2007
Location: London/N.lincs
Send a message via MSN to kipman725
I am sceptical for the need for a transformer VA greater than the maximum output power. Music is often assumed to be 10dB peak to avrage ratio. Therfore the avrage power is only a third of the maximum. What you are attempting to avoid is core saturation which will take a few cycles of operating above the maximum power rating of the transformer and I just don't think this will happen so easily. As for copper losses they should be not important for all sane sized capacitor banks, as the voltage of the capacitor bank sags it's conduction time increases. Personaly I go for about 0.8x max output rating in transfomer VA rating I shall do some maths to verify this assumption later however.
  Reply With Quote
Old 4th September 2010, 12:29 PM   #37
diyAudio Member
 
Sch3mat1c's Avatar
 
Join Date: Jan 2003
Location: Milwaukee, WI
Send a message via ICQ to Sch3mat1c Send a message via AIM to Sch3mat1c
Core saturation is NOT caused by loading.

In fact, loading reduces Bmax slightly.

Cap input rectifiers have a power factor in the 0.5-0.7 range, or even less when using oversized transformers and capacitors, as many erroneously believe in. Not only does this mean you need a relatively large transformer, it also means you need a bigger power line circuit, very important for large amplifiers (>500W).

Tim
__________________
Seven Transistor Labs
Projects and Resources
  Reply With Quote
Old 4th September 2010, 12:35 PM   #38
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by kipman725 View Post
I shall do some maths to verify this assumption later however.
let's see the modeling and we can then comment more usefully.

If you are assembling a 68W into 8ohm chipamp and intend using a 54.4VA transformer, I would be very surprised to find that amp performance could not be improved, very cheaply, by increasing the transformer VA rating.
__________________
regards Andrew T.
  Reply With Quote
Old 4th September 2010, 01:50 PM   #39
sangram is offline sangram  India
diyAudio Member
 
Join Date: Sep 2002
Location: India
Quote:
I would be very surprised to find that amp performance could not be improved, very cheaply, by increasing the transformer VA rating.
I totally agree. I've seen a pretty big jump in performance going from a 160VA transformer to a 450VA transformer on a 150-watt chip amplifier. Maybe 450VA is overkill and 300VA would have been enough, but I'm not very trusting of transformer ratings in this part of the world....
  Reply With Quote
Old 4th September 2010, 02:30 PM   #40
diyAudio Member
 
Join Date: Mar 2002
Location: Canada
Quote:
Originally Posted by kipman725 View Post
I am sceptical for the need for a transformer VA greater than the maximum output power. Music is often assumed to be 10dB peak to avrage ratio. Therfore the avrage power is only a third of the maximum. What you are attempting to avoid is core saturation which will take a few cycles of operating above the maximum power rating of the transformer and I just don't think this will happen so easily. As for copper losses they should be not important for all sane sized capacitor banks, as the voltage of the capacitor bank sags it's conduction time increases. Personaly I go for about 0.8x max output rating in transfomer VA rating I shall do some maths to verify this assumption later however.
I am crazy with my 2x LONO 1000va each at 90vct ac ? no sir... I try it with 630va(already 4 time your and industry standard) under same chassis(exactly same voltage 4x 0-45ac),all from plitron No contest here, with 1000va it is magical and effortless, amplifier disapear ! not box at 130 pounds

But will follow AndrewT suggestion for better grounding !
Attached Images
File Type: jpg power amp HD 001.jpg 2.jpg (152.0 KB, 97 views)
__________________
Praudio

Last edited by Praudio; 4th September 2010 at 02:54 PM.
  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
Help identifying a pair of output transformers and power transformers mjk130 Parts 3 30th January 2009 10:44 AM
FS: Transformers alexcd Swap Meet 0 19th November 2008 08:34 PM
WTB : Transformers korben69 Swap Meet 1 27th June 2008 06:05 PM
my first amp (transformers???) fitchmicah Chip Amps 5 7th January 2007 07:26 PM
Back to Back transformers as Isolation transformers mikee55 Chip Amps 2 17th March 2006 11:38 AM


New To Site? Need Help?

All times are GMT. The time now is 12:26 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