Tripath AMP1-B noise disappears after 5 minutes problem - diyAudio
Go Back   Home > Forums > Amplifiers > Class D

Class D Switching Power Amplifiers and Power D/A conversion

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 11th September 2005, 08:08 PM   #1
Bgt is offline Bgt  Netherlands
diyAudio Member
 
Join Date: Jan 2005
Location: NL, Voorschoten
Default Tripath AMP1-B noise disappears after 5 minutes problem

Well, wrote this somewhere else. After 5 minutes my hissing noise diappears and becomes an ultra low level high tone(4kc).
The electronic transf. uses a 40kc cycle rectified by schottky diodes.
When I measure on the plug on the amp1b pcb on the + and- supply line i see a 3mc disturbance in the noise at about 200mv.
If I put 2 off 470uf FC Panasonic caps on the supply lines at the plug my amp becomes very silent. Not completely but on high efficiency boxes there is a kind of whistle left. Would never have found this without a scope. When you put the probe on the psu pcb the lines are very clean but the wire from psu pcb to amp1b pcb is an inductance so 3mc is easy to be there. It also shows the caps delivered with the amp are bad ones. Will change them for FC's and test again.




Click the image to open in full size.
__________________
Kind regards,
Bert
  Reply With Quote
Old 16th September 2005, 07:17 AM   #2
Bgt is offline Bgt  Netherlands
diyAudio Member
 
Join Date: Jan 2005
Location: NL, Voorschoten
changing the caps for low esr 680uf/35V ones improves the noise but I am left with the 4kc tone, which is very soft on volume but hearable on efficient speakers. Has to do with earthing.
__________________
Kind regards,
Bert
  Reply With Quote
Old 16th September 2005, 01:38 PM   #3
diyAudio Member
 
theAnonymous1's Avatar
 
Join Date: Feb 2004
Location: Anonymityville
Hi Bgt, this was stolen from the 41.hz forums.......

Quote:
words of Jan Fredriksson:
"I am very happy with the ones I have built except
there was a weak, hardly audiable, but slightly annoying
tone from all of them. I found that the 100uF cap used to
filter the internal 10V generator is not good enough
or big enough. Replacing it with a better or slightly
bigger cap solved the problem."
That would be the 100uf 35v C34 hes speaking of. I wonder if 1000uf would be overkill. I have some Panasonic FC 1000uf 16v caps I would like to try. I know the original is a 35v cap, but I don't see the problem of using a 16v cap instead.

The "tone" from my AMP1-B's isn't half as loud as the hiss. I'm going to try lowering the modulator gain and see if it helps the hiss issue any. I already know its set way to high for my rail voltage, but I'm not sure if thats a real issue for anything but clipping.
  Reply With Quote
Old 16th September 2005, 01:55 PM   #4
Bgt is offline Bgt  Netherlands
diyAudio Member
 
Join Date: Jan 2005
Location: NL, Voorschoten
Quote:
Replacing it with a better or slightly
I did, no change. Changed it for a low esr 100uf/35V cap. Will try a higher value. I found out it nearly disappears if you change the earthing of the unit. But than it has more humm.
__________________
Kind regards,
Bert
  Reply With Quote
Old 16th September 2005, 04:53 PM   #5
diyAudio Member
 
theAnonymous1's Avatar
 
Join Date: Feb 2004
Location: Anonymityville
When I connect my supply ground to earth ground I don't get any change in sound good or bad. I'm using SMPS though so there's no trafo hum that can find its way to my speakers.
  Reply With Quote
Old 16th September 2005, 06:57 PM   #6
Bgt is offline Bgt  Netherlands
diyAudio Member
 
Join Date: Jan 2005
Location: NL, Voorschoten
Quote:
Originally posted by theAnonymous1
Hi Bgt, this was stolen from the 41.hz forums.......



That would be the 100uf 35v C34 hes speaking of. I wonder if 1000uf would be overkill. I have some Panasonic FC 1000uf 16v caps I would like to try. I know the original is a 35v cap, but I don't see the problem of using a 16v cap instead.

The "tone" from my AMP1-B's isn't half as loud as the hiss. I'm going to try lowering the modulator gain and see if it helps the hiss issue any. I already know its set way to high for my rail voltage, but I'm not sure if thats a real issue for anything but clipping.

Ok, cured it. Put a 1000uf/25V FC capicitor there and the whistle is gone. Cured the hiss with a 10uF MKT cap. on the PSU + and 0V where the power lines enter the PCB. It is now very quiet. Earthing remained the same...no humm.

Now for a test I exchanged the Amp1B for a stereo UCD180AD system and switched it on. I think I have to sit in the speaker to hear a tiny bit of hiss. Remarkable.


Tried this all out with a very efficient dual paper cone speaker from the 80's.

I am happy how it is now. Now snubberizing it a bit.

Thanx for the tip
__________________
Kind regards,
Bert
  Reply With Quote
Old 16th September 2005, 07:04 PM   #7
Bgt is offline Bgt  Netherlands
diyAudio Member
 
Join Date: Jan 2005
Location: NL, Voorschoten
Quote:
I'm using SMPS
Mine is also a kind of switched supply. I have to use schottky's because of the 40kc where the 50Hz sinus is made off. Tried it with normal bridge rectifiers, well forget it. The nice thing of this PSU is the low crest factor, the mains input is rectified and than smoothened(how do you write this?) with some 0,5uF MKT caps. It has hardly any input current.
__________________
Kind regards,
Bert
  Reply With Quote
Old 17th September 2005, 06:04 AM   #8
diyAudio Member
 
theAnonymous1's Avatar
 
Join Date: Feb 2004
Location: Anonymityville
Quote:
Cured the hiss with a 10uF MKT cap. on the PSU + and 0V where the power lines enter the PCB.
Wow, I looked for some 10uf MKT caps on the net and their not cheap. I need three of them @ $7 each. Think any other type of cap would work?
  Reply With Quote
Old 17th September 2005, 07:34 AM   #9
diyAudio Member
 
theAnonymous1's Avatar
 
Join Date: Feb 2004
Location: Anonymityville
Well, I got rid of the "tone" with a 1000uf cap as did you Bgt, but I can't get rid of the hiss. Lowering the modulator gain had no effect. I tried bypassing the the power coming into the board with every kind and size of cap I have available to me and it made no difference.
  Reply With Quote
Old 17th September 2005, 09:50 AM   #10
Bgt is offline Bgt  Netherlands
diyAudio Member
 
Join Date: Jan 2005
Location: NL, Voorschoten
Hi, normal electrolytes cannot take the hiss away, remember it is 3MC. I ordered the MKT blocs at Farnell. Take any highgrade polyester cap.
__________________
Kind regards,
Bert
  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
FS: 41hz.com AMP1 Tripath TA2022 Tekko Swap Meet 7 18th December 2008 11:28 AM
Tripath amp1 vs 300B vs AlephX,Gainclone.Showdown of the diy favourites. protos Chip Amps 7 30th October 2005 04:05 PM


New To Site? Need Help?

All times are GMT. The time now is 03:12 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