power supply problem - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 10th January 2013, 08:40 AM   #11
diyAudio Member
Join Date: Mar 2012

Sorry for my initial answer.

Toroidals FEED the power supply. So i went a step back to get basis right.
2 options: be happy with what you have or change the PSU unit completely.

change........buy DIY complete kit (or have it soldered and tested...few USS extra) or buy BEST components for the price you want to spend. And solder yourself. Test the capacitators before you solder them! So you know what you have bought.....GOOD or BAD components.

Tip: make a drawing and calculate your stuff. And check again. Then your plan will work.

71 Volt on Ac= 100 volt DC after rectification (quite high already).
Or is it 71 volts DC?? ...which is 50 volts AC (before rectification).
  Reply With Quote
Old 10th January 2013, 10:29 AM   #12
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
Mooly's Avatar
Join Date: Sep 2007
Originally Posted by madtecchy View Post
Im sure this is in the wrong section .... "Chipamps"??

It was, but now it isn't... thanks
  Reply With Quote
Old 10th January 2013, 12:29 PM   #13
diyAudio Member
Join Date: Mar 2012
Oke. Good luck with fixing.

Remember; everybody has burned something!
Me also; this is the way to perfection...You carry on!
I try to learn from my mistakes.

In the end; my audio sounds better and detailed!
  Reply With Quote
Old 11th January 2013, 03:10 AM   #14
diyAudio Member
Join Date: Feb 2011
Hi. Thanks for the replies,.

I am measuring 72.5 volts across the transformer with my Mills multimeter set on ac, 49 volts dc across the smoothing capacitors, then 96 volts dc across the two wires which go to the positive and negative terminals of the amp boards. The amp boards are disconnected for protection just in case the power supply may have been faulty. Does this appear to be okay.

I am going to follow up on your suggestion and replace the power supply, new transformer, bridge rectifier and smoothing capacitors, put the old parts on ebay as there are quite a few Quad groupies on there.

I didn't get a reply to the idea of using several small capacitors in parallel rather than one large one. Is this a stupid question?

For the transformer should i get a toroidal 35-0-35, and what should the current capacity be, There is a 2.5 amp mains fuse before the Quad transformer.

Many thanks. John.
  Reply With Quote
Old 11th January 2013, 06:39 AM   #15
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
Mooly's Avatar
Join Date: Sep 2007
There's nothing wrong with the Quad transformer.

A 35 volt toroid might give over the voltage you want simply because it will be specified as 35 volts at max current draw. You'll have to multiply the 35 volts by the "regulation figure" of the transformer which should be quoted and will be in the 5 or 6% region for a 250va transformer.

Lots of small caps. Some prefer that approach. A practical problem is that the wiring adds fractions of an ohm here and there and could mean that the caps nearest the bridge wiring wise do more of the work. The ripple current won't be spread equally.

Toroidal transformers draw huge switch on surges and for ratings above 300va a soft start circuit is recommended to prevent random fuse blowing. A 250 va transformer would probably get away with a T3.15A fuse (time lag delay).
  Reply With Quote
Old 11th January 2013, 08:49 AM   #16
diyAudio Member
Join Date: Mar 2012
if you measure your transformer; it gives you 1 result=corrrect AC voltage.
THis is really important. Is this one 2 pieces transformator combined together to feed 2 PSU and than 2 power amp boards. Otherwise you don get this high output on AC.

rule 1 = 100 watt RMS per amp board= 200 watt toroidal , my advice; take 2x 300 watts toroidal or 1 x 500 watt.

to get 49 volts DC= ac voltage x 2square root (ac voltage x 1,4142) with 35 volts it will give 49,49 volt DC. take 34 volt or 32 volts AC (antekinc.com) example: type AS-3434 AS versions have purple ground wire. sound better.

Try to find lowest and highest working DC voltage for Quad power amps. if it is 40-49 volts DC...try to get 44 to 45 volts DC. Then you are SAFE. And it will work.

If DC = below 50 volts ....so max 35 volts AC you can use 2x of this kit


i use them als to feed my L20 power amps (350 watt RMS 4 ohm)

Good luck.

First you measure and calculate.....and again.
  Reply With Quote
Old 14th January 2013, 02:10 AM   #17
diyAudio Member
Join Date: Feb 2011
Hi. Many thanks for all the replies.

I will post the results once the parts arrive.

Many thanks. John.
  Reply With Quote


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
Power Supply problem mjock3 Power Supplies 21 10th February 2012 05:08 PM
Power supply problem Niila Tubes / Valves 6 12th April 2008 01:39 AM
Power Supply problem Landoctor Chip Amps 3 8th September 2007 07:50 PM
Power supply problem krzanik Tubes / Valves 19 1st May 2007 03:56 PM
Power supply problem argonrepublic Parts 0 23rd January 2006 05:35 AM

New To Site? Need Help?

All times are GMT. The time now is 12:38 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2