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Old 23rd January 2004, 10:12 PM   #1
Kari is offline Kari  Sweden
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Default 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
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Old 24th January 2004, 01:22 AM   #2
SY is offline SY  United States
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Sounds like you've got yourself an oscillation.
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Old 24th January 2004, 01:28 AM   #3
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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.
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Old 24th January 2004, 01:32 AM   #4
SY is offline SY  United States
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Yes, it can. Also lead dress, grounding, and some flaky devices.
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Old 27th January 2004, 10:07 PM   #5
rchua77 is offline rchua77  Singapore
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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
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Old 28th January 2004, 06:59 AM   #6
Kari is offline Kari  Sweden
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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.
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Old 29th January 2004, 12:08 AM   #7
rchua77 is offline rchua77  Singapore
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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
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Old 29th January 2004, 06:57 AM   #8
Kari is offline Kari  Sweden
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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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Old 1st February 2004, 02:40 PM   #9
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Default 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

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