STK4050V and it's use in Definitive Tech PF15TL subwoofer

[duratothemax]

Here is the second pdf file of the low-level side.

[at1receptor]

Duratothemax, my apologies to you but the sound stage of your sub amp is definitely different from the PF15TL. No it doesn't use the STK4050v but uses pairs of MOSFETS. Thanks for sharing the schematics- this is actually the same amp they use for their newer SUPERCUBE III, rated at 700 watts but uses a 36 ohm driver. Again, sorry, can't help you with this one. Surely, someone out there is more knowledgable and will probably give a helping hand. Or you can purchase a replacement amp from Def Tech... might turn out to be more frugal.

[duratothemax]

well looks like Im screwed... took apart the 'real' part of the amp and found this. Surprised the darn thing didnt catch on fire.

I will pull it out tonight and clean it off to try to figure out where the problem started and maybe with ANY luck at all I can replace that one component and be good to go again. No simple resistor will fix this one.

If anyone feels like tackling this, Ill gladly pay them to fix it!!!





thanks
Ben

[at1receptor]

Duratothemax, I suggest you write to Stuart Easson, one member who posted a reply in this thread. He can help you. Or you can buy a good amplifier from Rhythmikaudio.com but you might have trouble with your driver...remember this is 36 ohms.

[duratothemax]

It says 75 ohms on a sticker on the voice coil tho???

I talked to Definitive, they said they can replace just the high level output stage board (im assuming the input stage and low level processing board is still good because the amp clicks on and the LED lights up as normal) for 175$ with a one year warranty. Its a fair chunk of change, but not really THAT unreasonable in my opinion, especially with the 1 year warranty.

Ben

[at1receptor]

u are absolutely correct. yes your preamp may still be functional but just be careful when you put in the replacement output stage from Def Tech bec you haven't really determined the reason why your output got fried. check to see if there are any wires that may have caused a short circuit specially in the speaker (driver) area. $175.00 is still a lot of money!

[duratothemax]

Is there ANY possibility that a problem with the input stage can fry something in the output stage? I mean I know anything is possible, but I would think the probability would be low...

From looking at the schematics it looks like everything is centered around the positive and negative output stages, moreso on the negative output stage.

Most everything is so burned I cant even see the markings and designations on the PCB, but the destroyed components I can tell are:

the "U1" LM324 op amp has a huge section blown out of the center

Id say half of the resistors are blown/melted

blown resistors:
R38
R39
R49
R46
R4
R70
R16
R37
R38
R36
R72
R2

blown transistors:
O18
O19

Blown IC's
U1 (LM324)
ISO1

I think 4 of the 6 FETs might be blown too, but Im not sure.

Massive catastrophic failure for sure, there is no fixing this. There are some good holes blown right through the board.









thanks again for all the advice!

Ben

[duratothemax]

OK I feel totally stupid I didnt notice this before...but am I understanding the schematic correctly in that the input stage basically does all the processing, then encodes it into a PWM signal, sends it to the output stage/amp and the amp decodes the PWM and then obviously amplifies it.

Seems kind of odd and a lot of extra circuitry, expense, and work for nothing...whats the point? Because the high voltage might induce some noise if it was transferred as an analog low level signal????

so U3 on the input/processing board looks like its what generates the PWM signal and, so hopefully the output stage going nuclear didnt backfeed a voltage spike across the PWM data signal line and break something in the input board/processor.....

Or maybe im all wrong???

Ben

[at1receptor]

This damage can be due to shorted wires goin to your driver (speaker). It is so badly damaged even the board might not be salvageable! You must remember the parts you listed are the obviously and grossly burned ones but the other resistors and capacitors which look ok may not be ok. It will be best and frugal that you get the amp being offered to you by Definitive Tech. I do not believe your preamp or the low level part where the inputs and volume control is is at fault. This burned amp can only result from a short circuit. Please check that your driver is not burned too. If you so decide to fix this, you can go to Mouserelectronics.com for parts.

[jyhfeei]

Sorry for resurecting this thread once again, but I am looking at converting the PF-15TL to a sealed box arrangement (less boomy)and I want to extend the low frequency response of the internal amplifier.

As an electronics layman, I measured the voltage output of the amp with a constant voltage input of varying frequency (10 to 100 hz) to the low level inputs. There seems to be quite a drop off from the amp below ~35Hz.

Any easy way for flat amplifier response down to ~10Hz or so?

I see there is a bandpass filter which can be part of the problem, but I'm really not sure this is what I should attack. The low frequency fall off is really steep. Any help would be appreciated.

Attached is the schematic.


http://www.diyaudio.com/forums/attac...amp=1173815791