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Old 30th November 2002, 05:13 PM   #1
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Question nad 3020i harsh sound

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
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Old 1st December 2002, 12:18 AM   #2
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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
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Old 1st December 2002, 07:44 AM   #3
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Quote:
Originally posted by jean-paul
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
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File Type: gif 3020i_schematic-tn.gif (25.6 KB, 814 views)
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Old 1st December 2002, 09:55 AM   #4
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Thanks Dave,

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

Jean-Paul
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Old 1st December 2002, 10:14 AM   #5
Hamish is offline Hamish  Australia
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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.
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Old 1st December 2002, 10:45 AM   #6
halojoy is offline halojoy  Sweden
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Default 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.
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Old 1st December 2002, 01:31 PM   #7
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Default Probably ???

Quote:
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.
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Old 1st December 2002, 02:44 PM   #8
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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
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Old 1st December 2002, 03:17 PM   #9
halojoy is offline halojoy  Sweden
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Default There is a reason .... ("Let your love flow")

Quote:
Originally posted by jean-paul

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
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Old 1st December 2002, 04:35 PM   #10
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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
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