Buzzing in A40 - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 13th August 2003, 05:32 PM   #1
diyAudio Member
Join Date: Dec 2001
Location: Earth
Default Buzzing in A40

the a40 is a monoblock design but sharing the same chasis
on the left channel buzzing is high but on the right channel buzzing is very high. Both their ps are soft regulated by a caps multiplier. BUt a sawtooth waveform on the caps is present
buzzing is really loud. For the jfet current source, only the resistor option is used .any ideas to help solve the problem
  Reply With Quote
Old 13th August 2003, 06:51 PM   #2
diyAudio Member
Join Date: May 2001
Blog Entries: 7
Have you tried caps across the current source resistors?

However, if the buzzing is "really" loud this may not be the problem.
  Reply With Quote
Old 13th August 2003, 07:22 PM   #3
The one and only
Nelson Pass's Avatar
Join Date: Mar 2001
It was quite common for people to get an N channel Jfet
(used in the current source which biases the two diodes
which in turn bias the main current sources) which has a different
pinout than the one used in the project. If this is the case,
there will be excessive current through the Jfet and lots of
ripple voltage will appear at the output of the amp. Check
the current through the resistor Gate to Source on this Jfet
and see if the current exceeds a few mA. If it does, replace the
Jfet and confirm the proper current < 5 mA or so.
  Reply With Quote
Old 13th August 2003, 09:35 PM   #4
diyAudio Member
ElectroNick's Avatar
Join Date: Dec 2002
Location: The Netherlands
Don't know if you have the same problem, but i had a hum too, untill i used 2 bridge-rectifiers per PS.

Good luck

  Reply With Quote
Old 14th August 2003, 12:24 AM   #5
diyAudio Member
Join Date: Dec 2001
Location: Earth
tried caps across current source, used 2 bridge rectifier per ps must now try jfet current source, snubber network across the diodes, and try cap compensations. Does that help? i understand that is for low pass filter, changing to something bigger would roll off high frequency when feedback, can that reduce the buzzing
  Reply With Quote
Old 14th August 2003, 12:48 AM   #6
diyAudio Member
Join Date: May 2001
Blog Entries: 7
So, I do understand you correctly that you are currently using a resistor in place of the JFET?

If so, definitely try the JFET first.

What's the amplitude of the sawtooth?
  Reply With Quote
Old 14th August 2003, 12:56 AM   #7
diyAudio Member
Join Date: Dec 2001
Location: Earth
sorry i meant the sawtooth on the rectifying cap. is around 0.2volts. Ripple after the caps multiplier is 25mv but sine wave.
  Reply With Quote
Old 14th August 2003, 01:35 AM   #8
diyAudio Member
Join Date: Jan 2002
Location: Tyrone Ga. U.S.A.
If you are running 2 transformers you might start with disconnecting power to one of them. I say this because
I had a simmilar problem when I used 2 transformers
in the same chassis the other times I used a singlr transformer
with no problems. If this stops the hum you may have some
weird ground loops. If you still have the hum why not try the
amp without the cap multipler ?

Good luck,
  Reply With Quote
Old 14th August 2003, 04:00 AM   #9
diyAudio Member
Join Date: Dec 2001
Location: Earth
without the cap multiplier buzz was there aready. Same level after inserting cap multiplier. would try disconnecting 1 trans. I have tried different grounding scheme, Inserting base resistor on the pin of output trans,lift and isolate ground via 10ohm and 0.1uf. When connecting cd player and preamp, buzz and hum increases. Could be bad wiring layout.
  Reply With Quote
Old 25th August 2003, 12:42 PM   #10
diyAudio Member
Join Date: Aug 2003
Location: Tampere
Send a message via MSN to jhaapala
Default Ground loop noise

I have (also) build a40 using two separate toroidal

Didn't work to use on ground
point for the both power supplys.
Very irritating buzzle noise appeared.

So i builded them as two separate blocks
in the same chassis. Works very fine.
  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
Buzzing Pre-amp stevebell Solid State 10 12th June 2008 04:26 PM
Buzzing noise on RF 250.2 tavo04 Car Audio 15 12th February 2008 01:28 PM
SMPS buzzing????? theAnonymous1 Power Supplies 5 14th August 2005 01:33 AM
Buzzing sound Måsen Digital Source 0 13th March 2005 09:39 AM

New To Site? Need Help?

All times are GMT. The time now is 11:31 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