NAD 314 problem (fading channels) - 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 1st January 2007, 05:20 PM   #1
Juko is offline Juko  Netherlands
diyAudio Member
 
Join Date: Jan 2007
Default NAD 314 problem (fading channels)

Hi all,

I picked up a NAD 314 for little money. The right channel was dead. The first quick examination learned that the pushing (not turning) the bass-control had an effect. It was not tightly connected to the metal case, so I screwed the nut on. Both channels worked now, but after a while it sometimes still fades and becomes then louder again. Strange, because the outside of the bass-control potentiometer should not have influence on the circuit (I suppose). But when I move the metal 'turn-pin' of the potmeter against the metal case you can hear it on the speakers.
So I thought it was a grounding problem and I made sure the outside of the tone-control potontiometer was connected with the grounded case by soldering. This helped away the fading, but now I hear a very loud click when I activate the tone circuit by pressing the tone defeat button.
When I click the button in (bypass tone circuit) I hear nothing, but when I click it again (turn on tone-circuit) I hear a click. The longer I wait, the louder. This makes me think there somewhere is a DC-current which shouldn't be there. But where?

This all makes me think the problem is bigger as I thought. The amp works fine now, great sound also. The fading is almost over, but not at all.

Can somebody help me? What could this problem be? I include the schematic of the line amp part (and tone-control circuit), which I got from Etsang (thanks again).

I have basic experience an knowledge with electronics and amplifiers and I like to learn, so any help would be greatly appreciated.
Attached Images
File Type: gif line amp-3.gif (29.2 KB, 523 views)
  Reply With Quote
Old 1st January 2007, 07:38 PM   #2
diyAudio Member
 
unclejed613's Avatar
 
Join Date: Dec 2006
looking at the circuit, i can see 2 places where DC leakage could cause the popping you mention. C148 near the line amp output, and the 47uf electrolytic near the tone defeat switch. if either of those caps were leaky, you could get the popping you mention. put a voltmeter at the wiper of the switch and see if you have dc there (switch the tone control in and watch for dc, then switch the controls out and watch for dc) , then check at the junction of r 160 and r170 for dc. it most likely is at the switch. if you find dc at either place replace the cap causing it.

also it sounds like you should rebuild that noisy pot. how to do this is shown here:
http://www.geofex.com/Article_Folder...s/potscret.htm
__________________
Vintage Audio and Pro-Audio repair ampz(removethis)@sohonet.net
spammer trap: spammers must die
  Reply With Quote
Old 3rd January 2007, 12:51 AM   #3
Juko is offline Juko  Netherlands
diyAudio Member
 
Join Date: Jan 2007
Thanks for the advice. I think i traced the 'pop'-problem now. It was in the right channel of the pre/line amp. My multimeter couldn't find any DC at the points you told me, but I think that's because it's a digital meter (maybe to slow to catch the pop).

Unfortunately my fade-problem is not solved. Both channels are still fading/cracking/dead sometimes. I disconnected the pre-amplifier from the main-amp and connected a cd-player (with adjustable volume) to the main-amp. Still cracking and fading. Not sure if this is a right method, but I think this isolates the fading-problem to the main-amp. Am I right?

And again my question is, what could be the problem?
  Reply With Quote
Old 3rd January 2007, 07:47 AM   #4
diyAudio Member
 
unclejed613's Avatar
 
Join Date: Dec 2006
try checking the collectors on the diff amp (LTP) and see if the voltages are drifting there...... also check the emitters (could be the current source) if you have any zeners in your input stage, replace them. any problems with the diff amp will cause changes in gain. zeners get noisy (so do some diff amp transistors)
__________________
Vintage Audio and Pro-Audio repair ampz(removethis)@sohonet.net
spammer trap: spammers must die
  Reply With Quote
Old 3rd January 2007, 08:58 AM   #5
diyAudio Member
 
EchoWars's Avatar
 
Join Date: Dec 2002
Location: Left of the Dial
Does it use relays in the speaker protect circuit? Dirty relays can do what you describe too.
  Reply With Quote
Old 3rd January 2007, 04:27 PM   #6
diyAudio Member
 
unclejed613's Avatar
 
Join Date: Dec 2006
if it does use relays, tap on the relay with a screwdriver handle.
if the relay is bad, replace it, or if you feel you can do it, burnish the contacts with a piece of brown paper bag.
__________________
Vintage Audio and Pro-Audio repair ampz(removethis)@sohonet.net
spammer trap: spammers must die
  Reply With Quote
Old 3rd January 2007, 11:29 PM   #7
Juko is offline Juko  Netherlands
diyAudio Member
 
Join Date: Jan 2007
I tapped the relay, which indeed seems to be the problem. I will try to burnish the contacts. Thanks guys!
I will let you know in couple of days if it worked.
  Reply With Quote
Old 6th January 2007, 02:10 PM   #8
Juko is offline Juko  Netherlands
diyAudio Member
 
Join Date: Jan 2007
Problem solved! I have a very nice sounding amp now, for very little money.
Thank you guys!
  Reply With Quote
Old 3rd February 2008, 04:44 PM   #9
aes is offline aes  Canada
diyAudio Member
 
Join Date: May 2007
I just discovered this thread.

I have had a NAD 314 since new (Nov 97) and in past few years it has been exhibiting symptoms similar to what the OP describes. In my case, the unit would operate fine for about an hour or so till it warmed up, then the left/right channels would fade in and out randomly. If I adjust the volume up or down from the source input (eg TV), not using the volume pot on the amp, the problem temporarily goes away (few seconds). I pretty sure its not a dirty pot problem since I don't get the characterisic crackly sound when I turn any of the pots.

I suspect a bad solder joint/ground or something similar that loosens up when things get warm.

Interesting to read that the OP found that the speaker relays were a major contributing factor. A while back I did a similar test using a source direct into the power amp and found that things were working properly. I suspect my problem is in the preamp.

Anyway, all this to say thanks for sharing your experience, it may help me.

Alan
  Reply With Quote
Old 29th February 2008, 04:19 PM   #10
Elvalys is offline Elvalys  France
diyAudio Member
 
Join Date: Jul 2007
Send a message via MSN to Elvalys
Hello,

I discover this threat with a lot of pleasure because I also have a NAD 314 and start to have some similar problem.

Therefor there is a little different, I only have the prob on the right channel. So it shouldn't be coming from the pot...

May someone have an idear to help me ?

I precise that I am not really use to electronic testing and just created a preamp in my life... I am full of good will so with appropriate explainations I will manege the best I can

Thks

Fabrice (from France)
  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 304 integrated amp one channel fading problem dima2ooo Solid State 59 17th November 2014 04:01 PM
Marantz SR7200 receiver - problem with front 2 channels willick Solid State 1 28th July 2008 04:20 AM
Paint fading on speakers? Glowbug Multi-Way 3 17th July 2007 08:32 AM
NAD CD C541 display is fading hreiff Digital Source 8 13th November 2006 11:00 AM
guitar pickup fading ThSpeakerDude88 Instruments and Amps 4 31st January 2006 07:15 PM


New To Site? Need Help?

All times are GMT. The time now is 06:33 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