NAD 3020i Hum - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

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
Reply
 
Thread Tools Search this Thread
Old 25th July 2006, 11:41 PM   #1
diyAudio Member
 
Join Date: Jul 2006
Location: Edinburgh
Default NAD 3020i Hum

Hey guys,

Besides trying to build my own chipamp i have a NAD 3020i, i'm quite sure many of you know that amp it's a very common model. It's quite an old one around 15 years of age. It was on storage for a while and about 3 years ago i started using it again. It's no fantastic sound but also not bad.

Since the "revival" of it it has a constant hum on the speakers, this is quite static, it doesn't change with volume change or input, it's always there, not extremely loud but enough to annoy.

Today i got an oscilloscope from work to check out the frequency and shape of this noise. Frequency is around 100-110Hz and shape of a sine (well not exactly but close) amplitude is around 60mV p-p with another 60mV DC offset. As i suspected it's possibly from the psu since fully rectified 50Hz beomes double if not smoothed correctly (very very ballpark). I tried changing the large caps which are 4700u/50V with some brand new ones 10000u/63V and not much changed. I also tried bypassing them with smaller values (1u, 10u, 1n, 100n) but nothing changed.

Any ideas how can i reduce this huuuum?

If you need more details let me know.

(As far as i can tell the output stage is a pair of MJ2955/MJ3055)

Thank you very much
  Reply With Quote
Old 26th July 2006, 04:34 PM   #2
diyAudio Member
 
Gold_xyz's Avatar
 
Join Date: Dec 2005
Location: Italy
if you have already replaced all the cap on psu you can be tried
to short-circuit the inputs and to see from where noise produces him.

and then with the oscilloscope to go up again step by step to
the input that produces the noise...

also check all ground connection points.


(sorry for my terrific english... )


bye
  Reply With Quote
Old 26th July 2006, 05:57 PM   #3
ash_dac is offline ash_dac  United Kingdom
diyAudio Member
 
Join Date: Jan 2005
Location: UK
Hi,

I had a nad 3130 before I gutted it. These things really don't last.

1. dry solder joints absolutely everywhere on mine

2. corroded rca jacks, and rusty transformer.

3. bulging capacitors everywhere!

Have you tried connecting source equipment to different rca sockets ?

I would look for bulging caps.
  Reply With Quote
Old 26th July 2006, 08:57 PM   #4
AKN is offline AKN  Sweden
No snake oil
diyAudio Member
 
AKN's Avatar
 
Join Date: Aug 2005
Location: In the middle of Sweden
Send a message via MSN to AKN
otherside,

How is things progressing for you?

You may check +43V and -28V voltages that comes from regulators built around Q507 and Q508. These regulators have feed from separate winding on transformer and powers pre amp and voltage amplifying stages in power amp.
Caps C516 and C517 are smoothing caps after rectifier and should be candidates to check.
__________________
/ Anders
  Reply With Quote
Old 26th July 2006, 09:52 PM   #5
diyAudio Member
 
Join Date: Jul 2006
Location: Edinburgh
Thanks a lot guys for the replies

I'll look into it on more detail,

does anyone know if/where i can find the schematics of this model ?

I tried to follow the noise and see where it's generated, it quite a wild guess without the schematics but from what i can see it's not comming from the pre-amp section, most likely the decoupling near to the output stage is damaged or just the components past their lifetime. Anyway a schematics or component ref would help a lot.
  Reply With Quote
Old 26th July 2006, 10:05 PM   #6
AKN is offline AKN  Sweden
No snake oil
diyAudio Member
 
AKN's Avatar
 
Join Date: Aug 2005
Location: In the middle of Sweden
Send a message via MSN to AKN
Mail me and I send schematic in return.
__________________
/ Anders
  Reply With Quote
Old 27th July 2006, 06:56 PM   #7
diyAudio Member
 
Gold_xyz's Avatar
 
Join Date: Dec 2005
Location: Italy
i have found a schematics here
  Reply With Quote
Old 27th July 2006, 07:08 PM   #8
diyAudio Member
 
Join Date: Jul 2006
Location: Edinburgh
thanks a lot guys, the schematics help a lot, i'll let you know how it goes.
  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
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 05:48 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