transformer VA - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 17th March 2005, 08:10 AM   #1
pjanda1 is offline pjanda1  United States
diyAudio Member
 
pjanda1's Avatar
 
Join Date: Jan 2005
Location: Boulder, CO
Default transformer VA

I'm beginning an LM3875 project. I've read over many of the archieve threads on tranformer selection. It looks to me like 160VA should be more than adaquate for a stereo amp, yet many choose a larger unit. Is there any empirical reason to go larger? I'm specifically looking at the 22v 160va Avel from PE. I also want it small because I want to squeeze it into the smallest possible chassis.

thanks!
  Reply With Quote
Old 17th March 2005, 12:38 PM   #2
Nuuk is offline Nuuk  United Kingdom
diyAudio Member
 
Nuuk's Avatar
 
Join Date: Feb 2003
Location: Somerset, SW England
160va is enough (IMHO) for a good stereo Gainclone.

Larger transformers may have an advantage for reasons that I will not state here.

BUT, and I welcome comments from others here, I have found larger transformers to be a little noisier (ie louder hum).
__________________
The truth need not be veiled, for it veils itself from the eyes of the ignorant.
  Reply With Quote
Old 17th March 2005, 01:01 PM   #3
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
You could manage with a smaller transformer. Think average power outtake. I think down to 80 VA isn't too wrong.
__________________
/Per-Anders (my first name) or P-A as my friends call me
Super Regulator SSR03 Group buy
  Reply With Quote
Old 17th March 2005, 01:13 PM   #4
diyAudio Moderator
 
pinkmouse's Avatar
 
Join Date: Apr 2002
Location: Chatham, England
I have a mono LM3875 running from a 30VA 18-0-18. It's used as a loudspeaker test amp, but goes more than loud enough for most uses.
__________________
Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
  Reply With Quote
Old 17th March 2005, 01:17 PM   #5
diyAudio Member
 
chris ma's Avatar
 
Join Date: Sep 2001
Location: Pickering, Canada
Default Re: transformer VA

Quote:
Originally posted by pjanda1
I'm beginning an LM3875 project. I've read over many of the archieve threads on tranformer selection. It looks to me like 160VA should be more than adaquate for a stereo amp, yet many choose a larger unit. Is there any empirical reason to go larger? I'm specifically looking at the 22v 160va Avel from PE. I also want it small because I want to squeeze it into the smallest possible chassis.

thanks!
For mee.-self anyway
I picked larger ones so that it can be recycled for other projects in the future. There is not much different in the $ amount for higher VA, but the trouble of looking/buying one and wait for it.. the delivery time....

The Butcher
  Reply With Quote
Old 17th March 2005, 02:13 PM   #6
diyAudio Member
 
mod_evil's Avatar
 
Join Date: Dec 2004
Location: Rio
Send a message via MSN to mod_evil
As i transformer VA to Ampers?

I have 127v in the frist and 15-0-15 em second.... of transformer.

Thanks.
  Reply With Quote
Old 17th March 2005, 03:35 PM   #7
sam9 is offline sam9  United States
diyAudio Member
 
sam9's Avatar
 
Join Date: Jun 2002
Location: Left Coast
You would think VA=Watts but it doesn't. On the other hand that's a way of thinking about it that may be crudely useful. I think it is more accurately considered a thermal rating -- the higher the VA the cooler it remains. Not surprisingly there is a relationship between weight and VA.

While you could determine the VA rating needed to drive the amplifier with a continuous (i.e., day after day non-stop) sine wave at max power as a way to ensure the VA rating is totally adequate-- as a practical matter, normal (or even vigorous) home use requires rather less than that.

Dopes the above sound vague? Good choice of transformer VA rating is a bit vague by nature.
  Reply With Quote
Old 17th March 2005, 06:21 PM   #8
diyAudio Member
 
Join Date: Nov 2004
Location: The Sticks, NS
Quote:
Originally posted by sam9

While you could determine the VA rating needed to drive the amplifier with a continuous (i.e., day after day non-stop) sine wave at max power as a way to ensure the VA rating is totally adequate-- as a practical matter, normal (or even vigorous) home use requires rather less than that.
A lower VA rated transformer will have a lower voltage at the demanding peaks of the audio signal which is when the voltage is needed most. While I agree that a transformer wouldn't need to push that current continuously but it still has to maintain desired voltage when the peak current is required.

When you think about it there is not much difference in price of transformers to go up a size or 2 just to be safe. Personally, I don't want to skimp here.
  Reply With Quote
Old 18th March 2005, 06:16 AM   #9
kmj is offline kmj  Sweden
diyAudio Member
 
kmj's Avatar
 
Join Date: Feb 2004
Location: Falkenberg
Quote:
I picked larger ones so that it can be recycled for other projects in the future
A wise choise, for as someone in the tube-forum said "You don't just build ONE amplifier"
  Reply With Quote
Old 18th March 2005, 10:06 AM   #10
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
I used an 80VA 18-0-18 to run a stereo amp with 8 ohm speakers. It sounded a bit 'thin' when driven hard.

Changing to a 160VA 20-0-20 gave a much better sound.

Even though the AC voltage was higher, the DC voltage was about the same with the 160VA unit because it had better regulation.
  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
Using mains transformer as output transformer Elias Tubes / Valves 176 11th March 2013 09:35 PM
Modulation transformer for a driver transformer? ironradio Tubes / Valves 6 28th December 2008 05:05 PM
filament transformer vs plate transformer contaxchen Tubes / Valves 10 14th January 2005 10:43 AM
toroid Transformer as power Transformer for tube tone Tubes / Valves 7 11th February 2003 08:57 AM
toroid Transformer as output Transformer for tube preamp? tone Tubes / Valves 15 2nd February 2003 04:36 AM


New To Site? Need Help?

All times are GMT. The time now is 09:26 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