Why two bridges are better than one? - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

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 13th October 2002, 07:58 AM   #1
diyAudio Member
 
Andypairo's Avatar
 
Join Date: Sep 2002
Location: near Milano , Italy
Default Why two bridges are better than one?

Somewhere else in this forum I read the suggestion to use two rectifier bridges instead of one, but i was wondering if there are other motivations apart from a (slightly) reduced output voltage and fewer thermal dissipation needed for each bridge..

I am building a Aleph 30 with a 500 VA 22V CT transformer (I know, 600> VA were better... but i had this one lying around), so I also need advice for lowering the rails voltage.

I was thinking about a coil between bridge and filtering caps, I guess about 1mH should be enough.. suggestions?

Thanks

andypairo
  Reply With Quote
Old 13th October 2002, 10:00 AM   #2
skaara is offline skaara  Slovenia
diyAudio Member
 
Join Date: Jun 2002
Location: Europe, Slovenia
You should do it like this: rectifier-caps-choke-caps
  Reply With Quote
Old 13th October 2002, 10:23 AM   #3
diyAudio Member
 
Join Date: Mar 2002
Location: CROATIA
Hello Andypairo,

If you would use two diode bridges than it is better
idea to use transformer with two separate secondary
windings instead with the transformer that have
Center Tap.

Best regards,
Kristijan Kljucaric
http://web.vip.hr/pcb-design.vip
Attached Images
File Type: gif ale3-pwr.gif (10.6 KB, 1997 views)
  Reply With Quote
Old 13th October 2002, 01:56 PM   #4
diyAudio Moderator Emeritus
 
roddyama's Avatar
 
Join Date: Jan 2002
Location: Michigan
Hi Andypairo,

Iím assuming you meant to say you have 44V CT. That would give you 22V to each bridge. A choke input PSU is going to give you too low a voltage for an Aleph 30. It calls for 25V rails and youíll only have about 18V rails and less with higher loads.

I would go with Skaara on this one and run a PI filter PSU (CLC). If you use your 1mH (assuming low DC resistance), and add input and output caps like in Kristijanís schematic, your rails will run from 23V to 26V (light load to high load) according to Duncans PSU Designer.

Hope this helps,
Rodd Yamas***a
  Reply With Quote
Old 13th October 2002, 03:17 PM   #5
diyAudio Member
 
Join Date: Jan 2001
Location: Scandinavia
Even though kristijan-k has come up with an excellent solution, the original question remains unanswered:

Why is 2 bridges better than one apart from the obvious (current capability, thermals etc.)

First of all, as kristijan-k has written, there is no gain unless you have two distinct secondary transformer windings. If you do, you can treat the two rails as separate entities and then connect their zero's

This allows you to take control of where large currents circulate, and not let that point be ground which is often by definition also "signal ground" and sensitive to noise induced from such currents.

If you have a center tap transformer there is no benefit from such an approach.

Herein lies the answer.

Petter
  Reply With Quote
Old 13th October 2002, 08:20 PM   #6
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
If you use one bridge with two secondaries and some
net DC current flows through the ground, there will be
a tendency toward saturation (and mechanical noise)
in the transformer if the two windings are not precisely
identical. Most of the time this is not a problem, but
when it is, two bridges prevents it.
  Reply With Quote
Old 14th October 2002, 05:53 AM   #7
diyAudio Member
 
Andypairo's Avatar
 
Join Date: Sep 2002
Location: near Milano , Italy
Thanks for the answers, I have 2 split secondaries and also a vibration problem (but only without inserting chokes,now I'm using a single bridge), you probably solved this problem...

The trafo is a toroid, so the secondary windings should be very closely similar but I'll give this method a try.

Another question: the service manual indicates 30000 uF per rail (and channel), kristijan-k's schematic more than twice (with the add of a choke).
Is the latter common to both channels?

I'll download also Duncan's PSU designer (Thanks roddyama) and will make some simulations by myself...

Andypairo
  Reply With Quote
Old 14th October 2002, 07:25 AM   #8
diyAudio Member
 
Andypairo's Avatar
 
Join Date: Sep 2002
Location: near Milano , Italy
Quote:
Originally posted by Petter
Even though kristijan-k has come up with an excellent solution, the original question remains unanswered:

Why is 2 bridges better than one apart from the obvious (current capability, thermals etc.)

....

Herein lies the answer.

Petter
You got it! That's what I wanted to know...

By the way, my caps are a connected in a array-style since I only found 6800 uF ones.
Like this (I wish I had a digital camera..):

------------ -Rail
CCCCC - Caps
------------ Gnd
CCCCC Caps
------------ +Rail

Where shoul be placed Input (Bridge) and output (amp)connections?

1- In at the left, out at the right
2- Both in the same place (center?)
3- Somewhere else?

Hi

Andypairo
  Reply With Quote
Old 14th October 2002, 08:34 AM   #9
skaara is offline skaara  Slovenia
diyAudio Member
 
Join Date: Jun 2002
Location: Europe, Slovenia
It doesnt matter if you gi from left to right of reversed!
You just have to connect them (electrically and physically) like i told you and like shown on kristjans schematic
  Reply With Quote
Old 14th October 2002, 09:24 AM   #10
diyAudio Member
 
Andypairo's Avatar
 
Join Date: Sep 2002
Location: near Milano , Italy
Ok but what about star grounding or similar layout techniques?
Caps are connected by soldering on their pins a 2mmq wire, so I souldn't have series resistance problems, anyway I wanted to minimize it.

BTW placing smaller caps (say 100 uf or so on) close to the board(s) can help or it's overkill?

Hi

Andypairo
  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
2 or 4 bridges? Raka Chip Amps 26 29th July 2012 01:53 PM
Parallel bridges? Skorpio Power Supplies 6 27th June 2009 04:56 AM
two bridges on one secondary jpfastre Solid State 10 3rd January 2007 08:13 PM
tda2030, bridges vlljpior Chip Amps 2 29th September 2006 06:54 AM
Bridges for life ! mpmarino Parts 4 11th December 2004 10:11 PM


New To Site? Need Help?

All times are GMT. The time now is 02:49 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