DOZ smoking?

Kari · 23rd January 2004, 10:12 PM

Hi,
i've got a problem with DOZ smoking. While i'm setting the current, R10 starts to smoke. This happens when current is about 0.5A. As i understand this R10 (10ohm) and C7 (100nF) are a zobel network? They are connected over SPKR out and GND. Any one have any clues?

Thx

SY · 24th January 2004, 01:22 AM

Sounds like you've got yourself an oscillation.

5th element · 24th January 2004, 01:28 AM

Lucky you Ive never had one before I dont think.

Now the hard part, fixing it

If you have used a PCB design thats proven to work and we know the amp design does, then check for any brakes in the copper, or see if any solder is accidentally touching where it shouldnt. I hope thats right, in that a faulty PCB could cause oscils, im not entirely sure.

SY · 24th January 2004, 01:32 AM

Yes, it can. Also lead dress, grounding, and some flaky devices.

rchua77 · 27th January 2004, 10:07 PM

I have encountered the same problem with R10 smoking and burning to a crisp. The other channel works fine and is able to bias properly.

Does anyone know why? I have checked for broken tracks on the PCB and wire connections and they're all good. Any solution or insight would be helpful.

Regards

Kari · 28th January 2004, 06:59 AM

What i did was to put a 100uF cap over ve+ and gnd at the pcb. This did still not fix the issue. I also shorted the input. After this i got it to work. I know i have a issue with my powersupply leads but this will get fixed as soon as i get my enclousure parts. I also read that twisting the leads from the transistor to pcb should help, especially when using MJ15003 transistor. Hope this helps.

rchua77 · 29th January 2004, 12:08 AM

Hi Kari,

What do you mean by shorting the inputs?
Did you manage to find out what was causing R10 to smoke and burn out?

Regards

Kari · 29th January 2004, 06:57 AM

By shorting the input i mean connecting input to gnd. Apparantly we've got oscillations. So please check that your psu wires are not longer than needed and that they are thick enough. When i get my enclousure parts, and while assembling i will twist the wires from the transistors to the pcb. Mine are approx 10cm long.

I still need to find a inrush currentlimiter solution, getting tired of changing the main fuses......

1st February 2004, 02:40 PM

@Kari

How about using a negative temperature coefficient thermistor in series with the primary winding of the power transformer?
Should solve this issue

And it's also inexpensive

Regards

23rd January 2004, 10:12 PM	#1
Kari diyAudio Member Join Date: Jan 2004 Location: Stockholm	DOZ smoking? Hi, i've got a problem with DOZ smoking. While i'm setting the current, R10 starts to smoke. This happens when current is about 0.5A. As i understand this R10 (10ohm) and C7 (100nF) are a zobel network? They are connected over SPKR out and GND. Any one have any clues? Thx

24th January 2004, 01:22 AM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Sounds like you've got yourself an oscillation. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

24th January 2004, 01:28 AM	#3
5th element diyAudio Member Join Date: Oct 2002 Location: England	Lucky you Ive never had one before I dont think. Now the hard part, fixing it If you have used a PCB design thats proven to work and we know the amp design does, then check for any brakes in the copper, or see if any solder is accidentally touching where it shouldnt. I hope thats right, in that a faulty PCB could cause oscils, im not entirely sure. __________________ What the hell are you screamin' for? Every five minutes there's a bomb or somethin'! I'm leavin! bzzzz! Droggon Attack!

24th January 2004, 01:32 AM	#4
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Yes, it can. Also lead dress, grounding, and some flaky devices. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

1st February 2004, 02:40 PM	#9
Vek Guest	inrush current limiting @Kari How about using a negative temperature coefficient thermistor in series with the primary winding of the power transformer? Should solve this issue And it's also inexpensive Regards


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27th January 2004, 10:07 PM	#5
rchua77 diyAudio Member Join Date: Jul 2003 Location: Back in Singapore	I have encountered the same problem with R10 smoking and burning to a crisp. The other channel works fine and is able to bias properly. Does anyone know why? I have checked for broken tracks on the PCB and wire connections and they're all good. Any solution or insight would be helpful. Regards

28th January 2004, 06:59 AM	#6
Kari diyAudio Member Join Date: Jan 2004 Location: Stockholm	What i did was to put a 100uF cap over ve+ and gnd at the pcb. This did still not fix the issue. I also shorted the input. After this i got it to work. I know i have a issue with my powersupply leads but this will get fixed as soon as i get my enclousure parts. I also read that twisting the leads from the transistor to pcb should help, especially when using MJ15003 transistor. Hope this helps.

29th January 2004, 12:08 AM	#7
rchua77 diyAudio Member Join Date: Jul 2003 Location: Back in Singapore	Hi Kari, What do you mean by shorting the inputs? Did you manage to find out what was causing R10 to smoke and burn out? Regards

29th January 2004, 06:57 AM	#8
Kari diyAudio Member Join Date: Jan 2004 Location: Stockholm	By shorting the input i mean connecting input to gnd. Apparantly we've got oscillations. So please check that your psu wires are not longer than needed and that they are thick enough. When i get my enclousure parts, and while assembling i will twist the wires from the transistors to the pcb. Mine are approx 10cm long. I still need to find a inrush currentlimiter solution, getting tired of changing the main fuses......

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