NAD 3020 problem

[vubkevin]

I have a problem with my NAD 3020a , it seems that the woofer on the left channel moves bigger than the one on the right channel. but both sides seems to have the same volume.
I have tried, the problem comes from the pre-amp part, what could possibly cause this problem?

 

[Mooly]

Hi, Does it sound wrong. Lacking in Bass etc. What tests have you done. Are you sure it is Pre-Amp. Are all inputs affected.
Regards Karl

 

[vubkevin]

yep, less bass than the other channel, I've tried to connect the pre amp out to another amp. so I know it's the pre amp's problem

 

[Mooly]

Hi, It can only be a capacitor that has gone low in value.Have you got a schematic ? IF you have no test equipment get a 47mfd 63volt capacitor (or anything thereabouts 10 mfd 100mfd it dosent matter) and bridge any coupling caps in the Pre-Amp one at a time (Keep volume low and connect right way round).If you have circuit can tell you which ones to check.Just a thought, nothing like an open circuit pot on the tone controls ?
Regards Karl

 

[vubkevin]

hi, yes, I have the circuit , which one should I check?

 

[vubkevin]

An externally hosted image should be here but it was not working when we last tested it.

 

[rdf]

Hi vubkevin. For 6 electrolytic caps just replace them all and enjoy it for another 20 years. I recently did the same to a Rotel RX-980 bought cheap and it was worth the effort. Don't forget the PS caps, electrolytics have advanced spectacularly since that amp left the showroom. Worth the minimal cost.

 

[vubkevin]

which 6 electrolytic caps should I replace? just want to narrow where is the problem, I donno how to read the circuit, and donno which cap effects the bass

 

[rdf]

C401, C402, C409, C410, C417 and C418. If you're new to this make sure the negative sign on the replacement caps are in the direction as the ones you remove. Is the bass problem only on records? The schematic you posted is for the phone pre.

 

[vubkevin]

oh? then does anybody has the pre-amp schematic for NAD3020a?

 

[rdf]

Sorry, didn't see the pre section. Wide images can't be scrolled in reply mode. Change C513, C514, C515, C516, C517, C518, C523 and C524 if it affects all source components, the caps in the earlier post if just phono. But honestly, just replace them all for best performance.

 

[vubkevin]

another problem is that, I use 3020 as pre-amp, when I turn on the 3020, the left channel(the one has more bass) has sound first, only after half a second, the sound comes out of the right channel.
maybe this has something to do with the difference in the 2 channels?

 

[vubkevin]

maybe it has something to do with the delay? which cap effects the delay?

 

[Leolabs]

Sounds like output coupling caps problem too.

 

[vubkevin]

which one is the output coupling caps ?

 

[Mooly]

Hi again, change caps as per rdf's component refs.As others say, having seen circuit just change them all, 16volt or 25volt rating is fine.Let us know how you get on.
Regards Karl

 

[vubkevin]

after exchanged all the cap , and no use. but finally find out that it's the bass Potentiometer's problem, I changed a new one, and now it works perfectly fine, Thank you for all your guys help.