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pat allen 29th December 2004 09:26 PM

JBL PB12 subwoofer, Class D amp, dead.
One of my friend just gave me a blown PB12, there is a class D module amp, where everything seems to be in.
The circuit seems to be repaired and looks like there was a lot of rework from factory. I know this unit never been opened by a redneck or so, my friend dont even have screwdrivers.

So, is there some schematics that i could get, or some inputs. I do think that the source of the problem is the module, wich is a small heat sink and some urethane molded behind it. When i turn it on, the woofer pops in with huge hummmmmm. Dead for sure.

Sources for this part?

It seems that there is a lot of bad coments on this subwoofer.


Pat Allen

classd4sure 29th December 2004 10:57 PM

hmmmmmm Big pop and big hum huh? Check for blown output devices, sounds like they're toasted. Why they're toasted, I do not know.

pat allen 29th December 2004 11:11 PM

There is no output devices, it is a monolithic device, and is a class D amp.
So, i f i want ot repair it, i have to change the whole unit (sealed)
What fears me is all the mess around it, wich dont seems good.
So i want to see a valid schematic before spending money in it.

Pat Allen

classd4sure 29th December 2004 11:41 PM

Good news and bad news:

I've done some searching about this thing, I see what you mean about other users, basically 99.99893719% of everything I've read about it are users saying "it blew, loud hum, can't fix, known problem, faulty part"

.. ouch.

The rest of the % of what I read on it were of course manufacturers sales adds.

I've hunted down the likely name of your class d wannabe module "S64AMI power module" made by harman karding I think.

It looks to me like they're only willing to sell you a replacement woofer.

It looks like this is certainly a faulty amp that should not be on the market, and like they're unwilling to replace it with anything that does work. It looks to me like they're still selling this scrap, and not fixing it.

It looks to me like I'll never be dealing with them!!

Based on all that, if the box /woofer itself is something you want to make use of, I think you can get it working by ripping out the electronics that are in there and replacing it with a good class d module, or plate amp.

Out of what is in there, you may only want to keep the cross over, and replace everything else with decent products, because I really don't think even if you could find a working S64AMI power module to replace it with, that you'd want to spend the time money and effort when it seems it will only blow again.

BTW, most users said it blew while idle playing no music, this is when most class d amps are switching fastest/more heat, maybe being in epoxy doesn't suit them well.

Hope that's more helpfull.


pat allen 30th December 2004 02:59 AM

Wow ! that is a lot of information !
I did try to deal with the company, they offered me another module under some waranty and some fees, but i did ask to de guy how long will it survive, since they all blow.
I didnt get response from the guy then. Guess why.

The woofer in it is a 12inch one, big magnet, but a 2 ohm single voice coil. There is an electronic cross over in it (op amps TLO64), as well as the muting circuit.
The power supply is a very high voltage type, with a very small transfo wich is normal for a D amp. So, if i want to use any of its inards, i am stuck with a lot of issues, especialy the 2 ohm sub and the very small power supply.What is a plate amp?

The cabinet is in top notch condition.
Maybe it will find some use...for now it resides along with all my scrap amps and speakers.

thanks a lot for the info !!

Pat Allen

classd4sure 30th December 2004 03:58 AM

You know, there's other "unhappy customer" alternatives, if being a nice guy about it fails.

Take it into the store with you, (hope your buddy kept the receipt) during peak time when it's full of people (saturday afternoon?) and scream your head off until they give you something new of equal value :)

Orrrr, get the email address of whoever is in charge at JBL, mention the vast amount of unhappy users you've found all over the internet, and the possibility of a class action lawsuit if the situation isnt' rectified.

Yeh, it's low and dirty, but so is selling garbage equipment for over a thousand dollars and not supporting it while hanging their customers out to dry.

The small transformer is not normal for a class d amp in itself, it is normal for a switching power supply, which as far as I know, is not the optimal set up for any amp as far as high end audio is concerned. It is a way for them to make alot of them very cheaply and maximise profits while quality suffers.

A plate amp, is just an amp on a plate :) Used for making powered speakers, cut the hole and screw them into the back of the speaker, pretty easy.

Go to and check out their DS1.2, run your mouse over the picture of it and you'll see it has a real power supply attatched, can hardly go wrong, it is also using cutting edge class d circuitry (so good it's almost a waste using it just for a sub), and the guy stands behind his products.

Shop around though and compare it to others you can find.
Anyway, I wouldn't worry about keeping their wimpy switching supply in it either, it's probably junk too.


JohnW 30th December 2004 12:47 PM

Pat Allen,

I consulted for a company once that had a connection with JBL / HK - there Class D amps (nothing to do with me) where based on the Harris solution :(

Can you post a photo of the module - I have some spare modules here that MIGHT be the same.


pat allen 30th December 2004 01:34 PM

2 Attachment(s)
Here is the complete board.
I meant by a small tranfo that is it small for a 250w amp, even D mode.

Pat Allen

classd4sure 30th December 2004 01:35 PM


I did more reading on these,

Either uses the S64AMI and S53AMI output modules, (both had problems) made by Analog Modules, Inc (the AMI in the serial #) they've been discontinued and JBL "was" making accommodation deals.

John, nice offer but considering all the problems people have had with these.. would you really want to replace it with a like unit, unless you wanted to fix it and sell it to someone you didn't like right away.

So is it a flaw in the harris design, if so, what, or the fact they encased the whole thing in epoxy?

Curious about this now :)


I meant by a small tranfo that is it small for a 250w amp, even D mode
Got ya.

pat allen 30th December 2004 01:36 PM

2 Attachment(s)
here the other side...

Pat Allen

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