Pwm Class D Issues

packer · 28th February 2009, 09:23 PM

I have an FBT MAXX 4a powered speaker which keeps blowing FETS (Q3).
Even with a lamp in series with the AC Line it shorts Q3, D5 & U2

SCHEMATIC HERE

All help would be be most appreciated

infinia · 1st March 2009, 12:45 AM

MOVED FROM CLOSED THREAD IN SOLID STATE FORUM

Hi
It looks like a Class D amplifier output stage.
It's basically a pulse width modulated power switch with a low pass filter.

U2 is a MOSFET driver with high side and low side gate drive.

Check Q4 and then ohm for any low impedance or shorts on the output.
If OK, check with O-scope after disconnecting the 60V drain supply.
EDIT>If the otherside is working, use it for a reference.

Cheers

packer · 1st March 2009, 10:59 AM

@infinia Thanks very much for the assistance :-)

If i am understanding the PWM theory part correctly.
If the amplitude of the audio signal increases or decreases to the mark/space ratio of the waveform, do higher frequency's dictate the amount of on time and lower frequency's the amount of off time on the wave form?

b15075 · 17th March 2009, 05:34 AM

Anyone know where I could find a schematic for an FBT MAXX 6a
I tried the 4a but it is a lot different. Any help would be greatly
appreciated.
Thanks

packer · 17th March 2009, 08:28 AM

Morning,
Let me make a call to FBT today, I should be able to get that for you.

packer · 23rd March 2009, 04:39 PM

OK,
Finally got that schematic from FBT send me your email addy if you still need it. :-)

b15075 · 24th March 2009, 03:32 AM

Hi, if you could e-mail it to me at jt2130@yahoo.com that would be great . Thanks so much, really appreciate it.

fredos · 24th March 2009, 01:47 PM

Me too please..I have 3 on a tablet for at least 6 weeks...fredos666@hotmail.com

packer · 24th March 2009, 01:54 PM

Sure thing,
I will do it when i get back to the workshop tonight!

packer · 24th March 2009, 07:13 PM

OK Guys,
Just emailed you both the Schematic. And if you need anything else let me know.

28th February 2009, 09:23 PM	#1
packer diyAudio Member Join Date: Oct 2006	Pwm Class D Issues I have an FBT MAXX 4a powered speaker which keeps blowing FETS (Q3). Even with a lamp in series with the AC Line it shorts Q3, D5 & U2 SCHEMATIC HERE All help would be be most appreciated

1st March 2009, 12:45 AM	#2
infinia diyAudio Member Join Date: May 2005 Location: Californication	MOVED FROM CLOSED THREAD IN SOLID STATE FORUM Hi It looks like a Class D amplifier output stage. It's basically a pulse width modulated power switch with a low pass filter. U2 is a MOSFET driver with high side and low side gate drive. Check Q4 and then ohm for any low impedance or shorts on the output. If OK, check with O-scope after disconnecting the 60V drain supply. EDIT>If the otherside is working, use it for a reference. Cheers __________________ like four million tons of hydrogen exploding on the sun like the whisper of the termites building castles in the dust

17th March 2009, 05:34 AM	#4
b15075 diyAudio Member Join Date: Mar 2009	FBT MAXX 6a Anyone know where I could find a schematic for an FBT MAXX 6a I tried the 4a but it is a lot different. Any help would be greatly appreciated. Thanks

23rd March 2009, 04:39 PM	#6
packer diyAudio Member Join Date: Oct 2006	Schematic request. OK, Finally got that schematic from FBT send me your email addy if you still need it. :-)

24th March 2009, 03:32 AM	#7
b15075 diyAudio Member Join Date: Mar 2009	FBT MAXX 6a Schematic Hi, if you could e-mail it to me at jt2130@yahoo.com that would be great . Thanks so much, really appreciate it.


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1st March 2009, 10:59 AM	#3
packer diyAudio Member Join Date: Oct 2006	@infinia Thanks very much for the assistance :-) If i am understanding the PWM theory part correctly. If the amplitude of the audio signal increases or decreases to the mark/space ratio of the waveform, do higher frequency's dictate the amount of on time and lower frequency's the amount of off time on the wave form?

17th March 2009, 08:28 AM	#5
packer diyAudio Member Join Date: Oct 2006	Morning, Let me make a call to FBT today, I should be able to get that for you.

24th March 2009, 01:47 PM	#8
fredos diyAudio Member Join Date: Mar 2005 Location: Quebec	Me too please..I have 3 on a tablet for at least 6 weeks...fredos666@hotmail.com

24th March 2009, 01:54 PM	#9
packer diyAudio Member Join Date: Oct 2006	Sure thing, I will do it when i get back to the workshop tonight!

24th March 2009, 07:13 PM	#10
packer diyAudio Member Join Date: Oct 2006	OK Guys, Just emailed you both the Schematic. And if you need anything else let me know.

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