nad 3020b cap replacement problem

[blrh93]

hi, i have a nad 3020b amp it recently developed a buzzing

i had a look inside and a few of the caps where bulging on the top

so i decided to replace 6 caps in total

here is what i replaced the originals with

and main psu caps

so after getting it back together, it has fixed the constant buzzin, but over around 1/3 volume the amp develops a noise that sounds like a record scratching, this starts with the bass

have i used the wrong tye of capacitors? i made sure to replace with the same voltage and capacitance ratings

any help appreciated

regards Ben

 

[rayma]

over around 1/3 volume the amp develops a noise that sounds like a record scratching,
this starts with the bass

Do you have a meter for checking voltage?

 

[blrh93]

i have a multi meter, what should i check?

 

[rayma]

i have a multi meter, what should i check?

Ok, set it to DCV. If not autoranging, set it to an over 40V range.
Connect the black lead to chassis ground and use the red lead to check voltages of -

1] red speaker outputs of both channels, for 0VDC.
2] main power supply voltages, both positive and negative, for 28VDC on either.
3] regulated voltages, both positive and negative, for 25.8VDC on either.

 

[padamiecki]

Hi!
I experienced similar issue, some caps should not have too low esr in 3020 model, especially those small ones, try solder back old caps, and try the sound after recaping again every single cap.

 

[jean-paul]

Best tip: buy industrial quality caps from a real distributor so you can be assured you buy the real thing. I would not use Sancon if I was given them for free.

 

[Welcome]

Indeed, it looks like you've used essentially fake caps. Those things might not work as intended. I recommend using the originals instead of those things.

 

[blrh93]

what brands should i look for? are the nichicon ones ok?

 

[jean-paul]

If you buy them from a distributor then: Yes.

 

[padamiecki]

what brands should i look for? are the nichicon ones ok?

I had the problems using original Nichicon FGs as C615, 616, 625, 626 https://www.elektrotanya.com/nad_3020_sm.pdf/download.html because the amp started to act like motorbike engine, and had back to factory mounted, then the amp began behavior like it should.

My guess was that they had too low esr...

All other caps you might to exchange with any you like but those four are enginestarter 😉

 

[jean-paul]

Then I think the caps were strange as they are not very low ESR...

Putting the old bulged (so defective) caps back in would be the worst advice really.

 

[Antana]

Can you post pictures the defective parts?

 

[blrh93]

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

 

[jean-paul]

Pictures don't load anymore but what I briefly saw of them is that it is an insult to the amp to solder those back in 🙂

 

[kevinkr]

Agree with Jean-Paul on this one, and in addition the PSU caps seem like a dodgy choice to me and I'd replace them with Nichicons, Rubycons, or similar.

You didn't state what source was in use when the problem was elicited or how loud the system was overall.

If the source used is a CD player it's output would be about 10dB hotter than was typical for analog sources available at the time that amp was first produced. This could mean that you actually are driving the amplifier into clipping due to insufficient power for the SPL you wanted to achieve with the speaker you are using, it could also mean that there is a problem with the amplifier itself, and that more electrolytic capacitors in the signal path have reached the end of their lives and the problems manifest at higher volumes.

Nichicon Muse are a reasonable choice for recapping as are Rubycon Silmic IIs, etc. You can also just use general purpose electrolytics for this task.

 

[blrh93]

ok, so new caps soldered in, im still having the same issue, i have realised it is only on the right channel

here is a video and some more pictures:

https://youtu.be/3RHGmuB5qxA

the only voltage i can find on my multi meter is 31.8v dc between main psu cap +ive and chassis the right channel cap i cant get a reading from

where should i meassure between exactly to find regulated and un regulated?

straight after the transformer and straight after main caps?

 

[jean-paul]

Sir you should have measured before replacing caps AND you have not replaced all caps. Either do it good or don't do anything 😉

* It was already buzzing and it had bulged caps. Measuring if all voltages are present would be first thing to do. When no active parts are defective i.e. 0V DC on the output then I would have replaced all electrolytic caps.

* Ok you replaced part of the caps and now have only 1 channel buzzing. Not all caps are replaced so....

* After it has been repaired I would remove those series JFETs in the outputs of the preamp section for a nice micro relay. Less impact on sound quality.

Question: what are the loose wires for ? To have a nice surprise when they short one day ?

 

[blrh93]

the original buzzing was very different from the issue i have now

the original buzzing was more of a hum even with no volume

now im just getting distortion over a certain volume on just one channel

by loose wires do you mean 2nd to lastphoto, p7 and p8, i dont know what these are

 

[jean-paul]

Wrong answer 🙂 I think you haven't found the cause of the defect yet. I know many will disagree but I would continue replacing all electrolytic caps as these are suspect anyway. Then try again to power it on with a bulb tester.

Questions:

1. Did you measure output DC offset ?

2. C905 and C906 have been replaced haven't they ?

 

[blrh93]

i have very limited experience testing audio eqipment with a multimeter

i had negative to chassis and positive to positive terminal of the big capacitors

on left i got 31.8v dc on the right i got 0v

this is looking at the amp from the front like in the first picture, i guess this corresponds to left and right channels?