Center-tap Choke - 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 2nd December 2010, 12:28 PM   #1
diyAudio Member
 
Join Date: Dec 2008
Default Center-tap Choke

Hi everyone.

Just made some tests with different inductors in place between the power transformer center-tap and the filter caps, with no choke or inductor in place (straight wire) the voltage over the caps are about +- 36v.

When i add an inductor the positive side gos to 39v and the negative goes to 34.4v, how is this possible? the power supply i tested this with were on a gainclone typ amp.

Thanks, Sonny.
  Reply With Quote
Old 2nd December 2010, 12:37 PM   #2
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
are you sure its center tapped, and not just a double choke
maybe the choke is only intended for series use

or maybe simply connected wrong, out of phase
  Reply With Quote
Old 2nd December 2010, 12:55 PM   #3
diyAudio Member
 
Join Date: Dec 2008
I made a schematic for some clarity =) if i remove the choke (just a straight wire) the voltage over the capacitors become even, +36v / -36v.

With the choke in place the voltage becomes +39v / -34.4v.

Can try to change phases on mains/choke etc. but i doubt that is going to make any difference.

Thanks, Sonny.
Attached Images
File Type: jpg pwr.jpg (30.1 KB, 106 views)
  Reply With Quote
Old 2nd December 2010, 01:29 PM   #4
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
never seen a choke in series with ground
  Reply With Quote
Old 2nd December 2010, 01:35 PM   #5
diyAudio Member
 
Frank Berry's Avatar
 
Join Date: Sep 2003
Location: Midland, Michigan
You're forcing the choke to pass alternating current. Chokes don't like AC. You really need two chokes ... one on the + output of the bridge and one on the - output of the bridge.
__________________
Frank
  Reply With Quote
Old 2nd December 2010, 01:55 PM   #6
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
Quote:
Originally Posted by Frank Berry View Post
Y ... one on the + output of the bridge and one on the - output of the bridge.
shouldnt chokes be between 1.and 2. supply cap ?
  Reply With Quote
Old 2nd December 2010, 02:06 PM   #7
RJM1 is offline RJM1  United States
diyAudio Member
 
Join Date: Jan 2010
Location: Titusville, Fl.
Itís probably due to the difference in the amount or capacitance on each rail. Large aluminum electrolytic usually have a tolerance of +100% -10%. This could easily give you a 20% difference in the amount of capacitance per rail. (See attached)
Attached Images
File Type: jpg Rail-Difference.JPG (40.9 KB, 100 views)
  Reply With Quote
Old 2nd December 2010, 02:30 PM   #8
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Are you drawing exactly the same current from each rail? i.e. nothing in the circuit connects to the 0V rail, or if it does it draws only negligible current.

You have, in effect, two choke input supplies but with the added complication that the choke is common so it sees the difference current. Choke input supplies are very sensitive to current drawn until the current exceeds a threshold value, at which point the DC output is 90% of the secondary RMS voltage. Your supply will be very sensitive to the difference current.

What are you trying to achieve?
  Reply With Quote
Old 2nd December 2010, 02:43 PM   #9
diyAudio Member
 
Join Date: Dec 2008
Just made some tests and measurements. There isn't much unbalance in capacitance between the positive and negative rail, about 7uF. Sure thing if you load a choke input supply lightly it will more or less become a capacitor input filter. I'm not sure if the LM3875 draws equal from + and - rail, but it should because it's not power grounded.

However it's strange that i get an increase in voltage on the positive rail from 36v to 39v

I'm trying to achieve better sound i want to isolate the signal ground from the noisy power transformer (and mains crap) and to decrease the CT ripple current.
  Reply With Quote
Old 2nd December 2010, 02:57 PM   #10
diyAudio Member
 
Frank Berry's Avatar
 
Join Date: Sep 2003
Location: Midland, Michigan
Reverse the connections on the choke. That may have an effect on the circuit if the imbalance is caused by the way the choke was wound. If this is the case, you'll see the same imbalance ... but in the other direction.
__________________
Frank
  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
Center tap wiring tom wesley Chip Amps 3 11th July 2010 07:34 PM
No center tap Help FastEddy Power Supplies 57 19th April 2010 07:01 PM
Supply, Full wave, choke on center tap? kegger Tubes / Valves 3 10th February 2008 05:02 AM
Center-tap to ground? cbutterworth Power Supplies 0 17th January 2007 03:41 PM
Gainclone and center tap marcus7601 Chip Amps 2 29th November 2006 02:12 PM


New To Site? Need Help?

All times are GMT. The time now is 02:07 PM.


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