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Forum: Analog Circuits Burnt subwoofer amplifier Nubert AW 850 _ HELP


Author: Max 2. (vanzan)
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Hello

I am looking for a subwoofer amplifier scheme Nubert AW 850. Can someone 
have such a scheme?
Thank you in advance

: Moved by Moderator
Author: Luca E. (derlucae98)
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Hi,

I had a similar problem with a AW 1000. Could you show us the whole PCB? 
I've reverse engineered the PCB. Maybe you can also use it for the AW 
850.
Beitrag "Nubert AW 1000 Endstufe abgebrannt; Ruhestrom"

Apparently those Nubert amp modules burn up quite often...

Author: Max 2. (vanzan)
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Luca E. wrote:
> Hi,
>
> I had a similar problem with a AW 1000. Could you show us the whole PCB?
> I've reverse engineered the PCB. Maybe you can also use it for the AW
> 850.
> Beitrag "Nubert AW 1000 Endstufe abgebrannt; Ruhestrom"
>
> Apparently those Nubert amp modules burn up quite often...


Hello
I added some PCB photos
Some elements are the same

Author: Luca E. (derlucae98)
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Looks quite similar. My amplifier module even had the same blown 
capacitor ;-).
I've replaced the whole module. That's the easiest and safest way to 
repair the subwoofer. It would probably burn up again if you manage to 
repair it with the same parts.

Author: mudman (Guest)
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Hello, this PCD looks really burned (out). Although thats' only
the case at some small areas, that's really bad... you'd have to
cut out the coaled PCB base material wholly, and don't you dare
to forget a little bit of it - that material tends to conduct
current, just like coal for heating, or like some metals.

I'd not use this PCB any more, but eventually other users do
know other ways to handle that.

My choice would be making a whole new PCB or switch to class d.

Author: Luca E. (derlucae98)
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mudman wrote:
> My choice would be making a whole new PCB or switch to class d.

But use a different circuit instead. Class D would be appropriate these 
days.

Author: Max 2. (vanzan)
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Luca E. wrote:
> Looks quite similar. My amplifier module even had the same blown
> capacitor ;-).
> I've replaced the whole module. That's the easiest and safest way to
> repair the subwoofer. It would probably burn up again if you manage to
> repair it with the same parts.



where I can get such a module because it is hard to find

Author: Lothar M. (lkmiller) (Moderator)
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Max 2. wrote:
> where I can get such a module because it is hard to find
Try this:
https://www.google.com/search?q=class+d+amp+module+200w
And for example you'll get that:
Ebay-Artikel Nr. 111655568658

Author: mudman (Guest)
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Luca E. wrote:
> Class D would be appropriate these days.

That's right, class D already has many advantages.
The days class D was't as good as AB are past.

But for subwoofers, even the very first class D amplifiers
would have done so, as such low frequencies are far less
demanding to reproduce.

Today there is not the slightest sensible reason to operate
any Subwoofer not with (even with cheap or "bad") class D amps.

For fullrange speakers it's slightly different, a DIY amp
built from a TL494 as PWM Modulator wouldn't do that right. :)

Max 2. wrote:
> where I can get such a module because it is hard to find

You can't find class D modules with 250 watts at 4 ohms
(i think that's the absolute maximum rating of the AW850)?

That's impossible.

You only have to search for that ones, which work with the
symmetrical supply that you have in your active woofer also.
(Would be "halfbridge" topology, and "+ xxV / -xxV" could
(SHOULD, to see) be mentioned at the article description.


Search for some examples (the specified wattage could also
be a little higher than 250W, but not too much, and a little
lower also, but maybe better not unter 200-220W to get it
richt with specified input volts).

And present them here - we can tell you, which are good.

: Edited by Moderator
Author: Luca E. (derlucae98)
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You won't be able to find the exact same module. You could replace the 
PCB with a Class D module. For example: 
https://www.soundimports.eu/de/aa-ab32291.html?gclid=CjwKCAjw0N3nBRBvEiwAHMwvNuTwQQ3wJOfzKkXQSfrHtqFvtK-Q9aSoe1nHzECKQBt9pHQLZ54tIRoCZNwQAvD_BwE
You need a power supply though. You can either build one based on the 
components on the current PCB (I did that) or you can buy one. The 
transformer produces around 62V DC after rectification.
I can give you the pinout of the signal connector, if you need further 
information on that.

: Edited by User
Author: Max 2. (vanzan)
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Thank you for the tips. I would like to first fix the amplifier and I 
would need a schematic. As is the case for the AV1000.
If I can not fix it, I will definitely use class D modules

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