quad 303 Crackling - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

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 29th February 2008, 12:43 PM   #1
diyAudio Member
Join Date: Feb 2008
Default quad 303 Crackling

Hi Folks

Has anyone any experience of a quad 303 power amp developing a fault where it crackles like mad!
I use one for monitoring in my little studio and have done so for 20 years or so! I have changed the electrolytics in it, some 13 years ago!
It is a very useful amp as it provides a true audio representation of my mixes, which will then sound equally as balenced on others' systems. Exactly what I need.

The fault sounds is as if the mains fuse is loose or plugged in to dodgy adaptor, that sort of thing. I have obviously checked out such things. It is common to both channels. I don't use the 33 preamp.


  Reply With Quote
Old 29th February 2008, 10:09 PM   #2
burbeck is offline burbeck  United Kingdom
diyAudio Member
Join Date: Aug 2004
Location: Ratae Coritanorum
hi Tony,
i had a 303 that constantly crackled, and got worse over an hour or so. i traced the fault to a small sig BJT, squirted them one by one with freezer spray (just a squib) until the faulty device was found, worse or better crackling etc. works on electrolytics too. ssssh trade secret
  Reply With Quote
Old 1st March 2008, 11:05 AM   #3
diyAudio Member
Join Date: Feb 2008
Hi Burbeck

Thanks for that. Yeah spent about 15 years in the repair trade and have tried freezer, nothing seems to be worse or better for a squirt so to speak!

It's definately power supply as i can see it on the scope. When I disconnect red and Blue wires 67V and ground from the PSU, Rail looks good. I will load it later on today to make sure, if all is well I will have a gander at the little PSU board.

Thanks again for your reply. I intend to publish my findings to help anyone else who may experience this later on
  Reply With Quote
Old 3rd March 2008, 04:51 AM   #4
diyAudio Member
Join Date: Jun 2004
Location: HKSAR

If any of you guys happen to look for a replacement board for it, you can email me.

Slightly modified to use PNP-NPN for output and to-126 for drivers.
Attached Images
File Type: jpg 0000001-12.jpg (54.9 KB, 272 views)
  Reply With Quote
Old 3rd March 2008, 06:36 AM   #5
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
Mooly's Avatar
Join Date: Sep 2007
Repaired an old Quad 303 about 15 years ago. Can't remember exact fault (symptoms) now but I do remember cause. It was a small electrolytic, one of those "orange" ones in a plastic encapsulation.
Regards Karl
  Reply With Quote
Old 3rd March 2008, 07:33 AM   #6
diyAudio Moderator
pinkmouse's Avatar
Join Date: Apr 2002
Location: Rotherham, England
Originally posted by bigpanda
Slightly modified to use PNP-NPN for output and to-126 for drivers.
Interesting, do you have schematics?
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 3rd March 2008, 08:58 AM   #7
diyAudio Member
Join Date: Jun 2004
Location: HKSAR
I had it done according to here :

Paragraph : "Upgrading the output stage"
  Reply With Quote
Old 21st March 2008, 09:10 PM   #8
diyAudio Member
Join Date: Feb 2008
Default Quad 303 Crackle

Hi Folks. I hope this proves useful to someone...............
I was pretty certain that this fault was power supply related, as it affected both channels. After a dose of freezer and a good visual inspection. I had to fire the scope up (had to find it first!)

The DC rails showed the crackle quite clearly, noise and dips on the trace as opposed to a nice flat line. I have a schematic so was able to disconnect the feed derrived from the caps and the bridge, from the PSU board, enabling me then to check transformer, main electrolytics and Bridge in one foul swoop so to speak. Remember to ground your scope from the negative side of the caps, blue wire in my case. This waveform looked good to me. I figured that as the amp crackled like crazy even at idle with no speaker load, then it was a good bet the fault would lie further on. ie PSU board or Tranny.

I checked on ebay and there's a guy on there called Ivan (his ebay name is "Gazember")who upgrades Quads regularly. More importantly for me he sells off the "pulls" (Old PSU boards and Trannies) Sure enough 24.00 and a week or so later I have board and Trannies in my hand. I went for the PSU transistor first. Figuring this was what took the most abuse. The old one measured ok (never a good sign) and of course there was no difference, however replacing the little PSU board did the trick and she's now happily back where she belongs. singing like she always did.
  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
Crackling when using a RAKK DAC Jitterbug Digital Source 0 4th April 2006 07:04 PM
crackling sound CDM 4 Thomas Hage Parts 4 8th November 2005 07:06 AM
amp crackling/farting? twizza Solid State 3 16th March 2005 06:45 AM
Help with crackling noise Free0 Digital Source 0 15th June 2004 01:37 AM
Crackling/Static on my GC. azira Chip Amps 2 25th May 2004 09:48 PM

New To Site? Need Help?

All times are GMT. The time now is 07:58 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