Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

NAD 3020i Hum
NAD 3020i Hum
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 28th May 2019, 07:53 PM   #11
renevoorburg is offline renevoorburg  Europe
diyAudio Member
 
Join Date: Mar 2019
Quote:
Originally Posted by Mooly View Post
Its very hard to make a judgement call on the ripple. Firstly you need to measuring from the correct ground point which really means measuring across C526 directly. Be sure the scope, if mains powered, does not introduce a ground loop. You should see a clean trace if you touch probe tip to probe ground whilst having probe ground connected to C526. Remember, positive end of C526 is ground.
I used the same ground for measuring the +28V output, the -28V and the +43V output. Only the -28V showed this ripple, for the others it was negligible.

Quote:
Originally Posted by Mooly View Post
Edit... and I assume 'full recap' means all the caps around on that diagram.
Those indeed, and all others .
  Reply With Quote
Old 28th May 2019, 09:53 PM   #12
renevoorburg is offline renevoorburg  Europe
diyAudio Member
 
Join Date: Mar 2019
I have some SB 631 PNP transitors available here. I assume they will work in stead of a SB 649A. The latter has somewhat higher voltage and current ratings (-180V C-B, -1.5 A vs -100V, -1 A) though.
If Q508 has gone open Emitter to Base that would explain the -29.5 V I am measuring. To be continued tomorrow...
  Reply With Quote
Old 29th May 2019, 07:21 AM   #13
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
NAD 3020i Hum
Those transistors sound as though they will be fine. I'd be surprised at this point if they fix the ripple but it has to be tried.
  Reply With Quote
Old 29th May 2019, 12:55 PM   #14
renevoorburg is offline renevoorburg  Europe
diyAudio Member
 
Join Date: Mar 2019
Quote:
Originally Posted by Mooly View Post
Those transistors sound as though they will be fine. I'd be surprised at this point if they fix the ripple but it has to be tried.
I changed Q508 but no impact indeed. Well, at least it provided a good opportunity to attach it to a bigger heat sink (see image).

Further, I experimented a little by doubling the capacity of both C526 and C523 but with no significant impact. Perhaps I should try to use bigger capacitors for both C517 and C516. These are now 330 uF but in older versions of the 3020 they used to be 470 uF.

Thanks! Ren

Click the image to open in full size.
  Reply With Quote
Old 29th May 2019, 01:22 PM   #15
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
NAD 3020i Hum
I kind of suspected as much. What is the voltage on the collector of that transistor? Is there enough headroom for it to operate correctly.
  Reply With Quote
Old 29th May 2019, 01:38 PM   #16
renevoorburg is offline renevoorburg  Europe
diyAudio Member
 
Join Date: Mar 2019
Quote:
Originally Posted by Mooly View Post
What is the voltage on the collector of that transistor? Is there enough headroom for it to operate correctly.
Will check that next time I open it up (for now it doing service again, swapped it for the Rotel RA-840BX4). In the mean time I found this posting: NAD 3020 recap and to quote from that

Quote:
Just finished replacing the caps in my 3020B.
...
I stuck to the original value, except for the caps around the preamp regulator - here I went 1000F 50V for C905 & C906 (originally 330F 50V), 220F 50V for C907 & C908 (originally 47F 50V), 22F 50V for C911 & C912 (originally 4.7F 50V), and 220F 50V for C913 & C914 (originally 47F 50V).
...
The result is pretty good. I'd assumed the slight hum this amp always had was normal - turns out it isn't - it's dead quiet.
which at least suggests that bigger sized caps C516 and C517 (the model i equivalent of the C905 and C906 in the B, it seems) might help to remove to slight hum it has.
  Reply With Quote
Old 29th May 2019, 01:42 PM   #17
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
NAD 3020i Hum
Interesting. Its a quick and easy thing to try. Good luck and lets hope its a quick fix.
  Reply With Quote
Old 30th May 2019, 05:44 AM   #18
Ian Finch is offline Ian Finch  Australia
diyAudio Member
 
Join Date: Apr 2010
Location: Coffs Harbour, NSW
As the -0.6V reference for the regulator is derived from its output, I'd take a look at what is happening around the zener and LED. I have no idea what their lifetime is but I know of another case where replacing them in a similar NAD 3020 model was the most likely reason that sound improved, according to the owner.
__________________
If only I had listened....
  Reply With Quote
Old 30th May 2019, 06:49 AM   #19
renevoorburg is offline renevoorburg  Europe
diyAudio Member
 
Join Date: Mar 2019
Quote:
Originally Posted by Ian Finch View Post
As the -0.6V reference for the regulator is derived from its output, I'd take a look at what is happening around the zener and LED. I have no idea what their lifetime is but I know of another case where replacing them in a similar NAD 3020 model was the most likely reason that sound improved, according to the owner.

To be sure, I replaced that zener, but without impact. About to order bigger caps now.
  Reply With Quote
Old 30th May 2019, 07:33 AM   #20
ubergeeknz is offline ubergeeknz  New Zealand
diyAudio Member
 
Join Date: Aug 2018
Before you start changing things, I would look to see if anything is drawing excessive current off that rail. Maybe a component downstream of it is bad causing excess draw, and therefore higher than normal ripple. Just a thought. I would start with any tantalums or electrolytics going from that rail to ground.

Last edited by ubergeeknz; 30th May 2019 at 07:40 AM.
  Reply With Quote

Reply


NAD 3020i HumHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
NAD 3020i repair help? wwenze Solid State 29 20th January 2012 07:48 AM
nad 3020i harsh sound mad_z Solid State 14 24th August 2007 04:45 PM
Stock NAD 3020i Upgrade path. dlarkin_dc Solid State 2 22nd April 2002 06:41 PM


New To Site? Need Help?

All times are GMT. The time now is 07:52 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki