lm3875 and tube pre loud buzzing - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 March 2006, 03:54 PM   #1
webby is offline webby  United Kingdom
diyAudio Member
 
Join Date: Jul 2004
Location: england
Unhappy lm3875 and tube pre loud buzzing

Hi all,
Can you guys help me out?
I have two chipamps and two ASL wave 8 monoblocks, running bi amped with a passive pre no problems. But when i try and use my Tube pre with the chipamps i get a very load buzzing through the speakers, the kind that makes you jump and hit the kill switch! This is the same if i just the tube pre and chipamps, no bi amping.
My aim was to run the tube pre + lm3875 for woofers + wave 8's for the tweeters.
Is this possible and what should i check?
All the tube kit is branded AV Reavox but its the same as asl i believe?

Many Thanks

Ian
  Reply With Quote
Old 4th March 2006, 03:31 PM   #2
webby is offline webby  United Kingdom
diyAudio Member
 
Join Date: Jul 2004
Location: england
Default Bump

Bump.
No one have any ideas?
Cheers
Ian
  Reply With Quote
Old 8th March 2006, 12:16 PM   #3
webby is offline webby  United Kingdom
diyAudio Member
 
Join Date: Jul 2004
Location: england
Hi all,
still no ieads?
This has got me really stumped, any help would be greatfully recieved.
Cheers
ian
  Reply With Quote
Old 8th March 2006, 12:33 PM   #4
Nuuk is offline Nuuk  United Kingdom
diyAudio Member
 
Nuuk's Avatar
 
Join Date: Feb 2003
Location: Somerset, SW England
Some more details may help!

Inverted or non-inverted chipamp?
Do you have the circuit that you used?
Do the chipampss work OK without the pre attached?
How long are the interconnects between pre and chipamps?
Is the buzzing the same on both channels?
Is the buzzing level changed by adjusting the volume control?
Is there a DC blocker on the output of the pre?
Is there a DC blocker on the input of the chipamps?
Have you tried different interconnects?
__________________
The truth need not be veiled, for it veils itself from the eyes of the ignorant.
  Reply With Quote
Old 8th March 2006, 01:04 PM   #5
webby is offline webby  United Kingdom
diyAudio Member
 
Join Date: Jul 2004
Location: england
Thanks for the reply Nuuk,
It a chipamp.com non inverted gainclone.
I Tried QED 1meter interconnects and .5m diy, same problem.
The tube amps run fine with either tube pre or passive. And the chip amps only buzz when the tube pre is used. Same loud buzz from both speakers and volume make no difference.
How can i check if there isa DC blocker, i dont know about either tube pre or chipamps?
Cheers
ian
  Reply With Quote
Old 8th March 2006, 03:06 PM   #6
Nuuk is offline Nuuk  United Kingdom
diyAudio Member
 
Nuuk's Avatar
 
Join Date: Feb 2003
Location: Somerset, SW England
You could try measuring the DC offset on the preamp if you have a multimeter.

Is it possible for us to see the internals of your chipamp? If so it should be easy to spot the DC blocker.
__________________
The truth need not be veiled, for it veils itself from the eyes of the ignorant.
  Reply With Quote
Old 8th March 2006, 04:27 PM   #7
webby is offline webby  United Kingdom
diyAudio Member
 
Join Date: Jul 2004
Location: england
Hi Again,
Here is a link to the chipamp kit i used;
http://www.chipamp.com/lm3875.shtml
Is this enough te tell if it has a dc blocker?
Save me taking it all apart!

How do i measure the dc offset on the valve pre, i have a DMM?
Cheers
Ian
  Reply With Quote
Old 8th March 2006, 04:55 PM   #8
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
When they say DC blocker, I think they are reffering to an input capacitor... usualy a largeish polyprop cap (.22 -4.7uf, depending on lower rolloff) I don't see one.

To measure offset, set DC to lowest range and just measure outputs..
  Reply With Quote
Old 8th March 2006, 05:34 PM   #9
webby is offline webby  United Kingdom
diyAudio Member
 
Join Date: Jul 2004
Location: england
Hi Again,
I measured DCV on the outputs;
Chipamp 85.4mv left output 85.6mv right output
Tube amps 0 for both
Tube pre I am not exactly where is should be measuring, I put the probe in the output RCA and the other probe on the side of the RCA for both left and right channels, but couldnít get a stable reading. Started off at 1.5V then dropped to a few MV then 0.
Very confusing?
I guess there is no dc blocking on the chipamps then, I built the PCBís as they came. Whet do I need to do?
Thanks
Ian
  Reply With Quote
Old 8th March 2006, 05:41 PM   #10
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
I suggest you drop them a mail in this regard for a suggested value for the input cap.
  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
Carver HR-752 making a loud buzzing nikkormat42 Solid State 0 12th September 2008 01:54 AM
Loud 60 cycle Hum from tube amp. Brenden Tubes / Valves 10 16th June 2008 11:41 PM
hi, want to make tube amp + small loud speakers electrofan Introductions 5 17th April 2008 06:15 AM
Loud Buzzing on Start? [Orginal T-amp] kenny12 Class D 3 12th July 2006 01:42 PM
lm3875 chipamp and tube pre loud buzzing webby Tubes / Valves 0 8th March 2006 12:32 PM


New To Site? Need Help?

All times are GMT. The time now is 04:26 AM.


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