nad 3020i harsh sound

[mad_z]

Hi Folks!

I've just connected old NAD amp - 3020i into my loudspeakers and to my surprise one of the speaker give quite harshy, disturbed and unclean sound. I 've checked if everything is well with connections, speaker and cd-player and it's ok. Propably there is a damage in left channel and being a begginer in diy I ask for help - what part/parts may be damaged? I want to exchange bad parts and listen to this oldie.
Which parts I shall check first? Any hints?
Thanks for any help. mad_z

 

[jean-paul]

Bad transistors, capacitors or diodes ? Who knows ? Did you change the speakers from left to right on the amp to exclude the possibity of a bad speakercable/speaker ? And did you swap the left and right input cable to exclude a maybe broken cdplayer/tuner/inputcable etc. ?
Just to make sure it really is the left channel of the amp that's causing the problem

I think it is wise to download the schematic and compare the measured voltages of the bad channel with the good channel. Maybe it's even wiser that a more experienced person helps you repairing this amp.

I found a schematic of this NAD here:
http://steve.sky.net.ua/a_index.htm

And here:
http://www.gmweb.btinternet.co.uk/others.htm

 

[planet10]

I found a schematic of this NAD here:

Good advice on making sure it is the amp 1st.

Both the sites mentioned have schemas from the original 3020 (and there are at least 2 differenet versions of that). I have the 3020i Map 710 kB. A teaser is attached.

dave

 

[jean-paul]

Thanks Dave,

I wasn't aware of the small "i" behind the productname
Good reading is an art.

Jean-Paul

 

[Hamish]

mad_z,
i am undertaking a similar project (both amp and symptoms). i've found that the electrolytics and the transistors are the most likely suspects. i hope the guys here can help you as much as they have helped me

good luck, and don't give up.

 

[halojoy]

Old Electrolyt Caps

When we mention change of old electrolyts
we mostly think of the exchange of the BIG power caps.
They surely can have the toughest task
and maybe a higher temp during work.
So they dry out faster.

But all electrolyts gets bad with time.
More or less.
There are many Elyts in those old amps.

Even in signal's way.
Many of those can, nowadays be totally replaced by FILM caps.
Often with half the capacitance.
Because of the wide tolerance in elyts,
the designers probably selected more than needed,
to be sure to hit the value.

 

[jean-paul]

Probably ???

Because of the wide tolerance in elyts,
the designers probably selected more than needed,
to be sure to hit the value

Halojoy, I would never advise to use half the value when replacing electrolytics for film caps
You can always calculate the -3 dB point to be sure if you persist on doing so.

 

[mad_z]

Thanks Jean-Paul, Hamish, Planet10 and Halojoy. I've checked speakers and connectors by swaping left and right channel of cd and then the speakers - and the problem is still in the same channel.
I have suspected electrolytics an transistors. I've read on some article that it's often to hear such disturbances when there is a damage in caps.
Using the scheme I will check voltages, and maybe at once exchange electrolitics . I've already found e-supply with original motorala bipolars, and good caps are available too.

Thank You for hints. Let the story begin

 

[halojoy]

There is a reason .... ("Let your love flow")

Halojoy, I would never advise to use half the value when replacing electrolytics for film caps
You can always calculate the -3 dB point to be sure if you persist on doing so.

There is a reason for my advice.
We live in a big world, you know.
Reality is not the same for all of us.

Low Wth (Wallet-thickness) is only one reason,
that my advice is not for optimal audiophile high end upgrade.
Still it is an upgrade.

I often adjust my advices to suit "a worst case situation".
This is not my situation.
But it can be a potential friend's situation.

Lyrics: "Let Your Love Flow"

Let your love fly, like a bird on a wing
And let your love bind you, to all living things
And let your love shine, and you'll know what I mean
That's the reason

"Bellamy Brothers"
a superhit some time ago

 

[Orgonom]

Hallo mad_z,
i had the same problem with this amp.
Anybody tried to fix the problem in the finalstage
without success.
The real fault was a dirty switch!!!!!!
The output was distored in a way you see when one half of the finalstage is death.
After cleaning everything was ok.
Andreas

 

[mad_z]

Which switch do you think of Orgonom - the cd/aux switch??

I'll check it too. Thanks!

 

[Orgonom]

It was the Tape Monitor switch.
Andreas

 

[g n process]

Hallo mad_z,
i had the same problem with this amp.
Anybody tried to fix the problem in the finalstage
without success.
The real fault was a dirty switch!!!!!!
The output was distored in a way you see when one half of the finalstage is death.
After cleaning everything was ok.
Andreas

hi Andreas, im after advice on cleaning switches in my 3020i
im getting the strange feedback noise also,
do i need to dismantle or is there a majic spray for the switches.
many thanks neal

 

[gvalle]

I had a humming noise when the amp was switched on, but not in use. I thought the big filter caps was dried out and had them replaced.

The original caps was two 4700uF/35V. I replaced them with two 6800uF/50V. After the replacement, the humming was gone. I must then assume that replacing the caps was a good thing.

I didn't listen to it much before i changed them, since i recently bought the amp. But after the replacement i think i have the same problem as mad_z (who started this thread). The sound seems harsh and distorted, even at reasonably low volume (9-10 o'clock on the volum knob).

Is it a problem that i used larger caps than the originals?

 

[mad_z]

>gvalle

Changing these caps shall not do such a thing. In fact I have also changed these caps to get rid of the noise but it did not help. I have cleaned the switches and also it did not help - later on I got some better amp and did not 'fight' with the noise anymore. Hope you can find a solution.