4xLM3886 fuse blow-out - diyAudio
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Old 10th September 2014, 05:01 PM   #1
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Default 4xLM3886 fuse blow-out

what wrong with this schematic?

Click the image to open in full size.

I found this diagram to this forum site:
w w w .elab.ph/forum/index.php?topic=45229.40

the thread starter also put a link for pcb
w w w .4shared.com/file/yMDRO11oce/bpa200.html

I follow everything but I guess there is something wrong.
I recheck the pcb and I'm 100% sure that there's no shorted traces.
I put 5A fuse and it's always blow in a negative side of the rail.

Last edited by Brilliantes; 10th September 2014 at 05:43 PM.
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Old 10th September 2014, 07:15 PM   #2
ericj is offline ericj  United States
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I don't see anything wrong with the schematic but the power supply isn't shown?

That file sharing site is annoying and i'm not going to log into it to download the pcb info.

Double check that you installed all parts correctly.

See if the psu alone blows the fuse with just a dummy load.
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Old 10th September 2014, 07:38 PM   #3
AndrewT is online now AndrewT  Scotland
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Is this another Member that does not understand how a SINGLE chipamp operates and yet he/she jumps headlong into a multi-chipamp implementation?

Why call it a 4x3886 when National's name for it is BPA200?
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Old 10th September 2014, 07:39 PM   #4
AndrewT is online now AndrewT  Scotland
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Please attach pics.
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Old 10th September 2014, 08:05 PM   #5
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I attach the power supply I used and the schematic.
Attached Images
File Type: png powersupply.png (41.3 KB, 103 views)
File Type: jpg eagleground_zpsab5ab34a.jpg (304.8 KB, 102 views)
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Old 10th September 2014, 08:40 PM   #6
Art M is offline Art M  United States
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The +15V/ -15V have no reference to ground as shown on the schematic ? If you are going to run the OpAmps with a single voltage of 30V, you are going to need to bias the OpAmps with additional parts and use AC coupling capacitors ?
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Old 10th September 2014, 09:26 PM   #7
mzperx is offline mzperx  Hungary
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Try to remove components C4,C8,... in order to deactivate the Mute function. During the muting the servo loop is broken and the outputs of opamps can rich opposite voltages to force current between LM3886 after stepping out from mute mode.
It's better to not apply the delayed muting in case of parallel tied setup, because the timing can be an issue between chips:
https://docs.google.com/file/d/0BzbI...w4MG5jQWs/edit

On the other hand the resistors seem to be too high value around the NE5534s otherwise use JFET input opamp or bipolar type with bias current cancellation.
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Old 10th September 2014, 10:35 PM   #8
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by Art M View Post
The +15V/ -15V have no reference to ground as shown on the schematic ? If you are going to run the OpAmps with a single voltage of 30V, you are going to need to bias the OpAmps with additional parts and use AC coupling capacitors ?
The power supply ground is on J2.

I question the need for the DC servo circuitry at all, the offset of the 5534 with a 2.2M input resistor is going to be a lot worse than the LM3886. The 5534 is not unity gain stable and probably needs to be compensated for integrator use. If you want to use the servo choose a low offset fet input unity gain stable op-amp instead. (It does not need to be fast)
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Old 11th September 2014, 02:14 AM   #9
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Quote:
Originally Posted by mzperx View Post
Try to remove components C4,C8,... in order to deactivate the Mute function. During the muting the servo loop is broken and the outputs of opamps can rich opposite voltages to force current between LM3886 after stepping out from mute mode.
It's better to not apply the delayed muting in case of parallel tied setup, because the timing can be an issue between chips:
https://docs.google.com/file/d/0BzbI...w4MG5jQWs/edit

On the other hand the resistors seem to be too high value around the NE5534s otherwise use JFET input opamp or bipolar type with bias current cancellation.
do you mean sir I try to remove all mute caps c4,C8,c12,c13.
I have also doubt with the NE5534s
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Old 11th September 2014, 02:39 AM   #10
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Quote:
Originally Posted by kevinkr View Post
The power supply ground is on J2.

I question the need for the DC servo circuitry at all, the offset of the 5534 with a 2.2M input resistor is going to be a lot worse than the LM3886. The 5534 is not unity gain stable and probably needs to be compensated for integrator use. If you want to use the servo choose a low offset fet input unity gain stable op-amp instead. (It does not need to be fast)
thanks to all response...

try to test again, I remove the ne5534 and the fuse dosn't blow-out but there's an a "zzzz...." sound on the board. and also base on the data-sheet of ne5534, 5534 is Fast opamp NE5534 10mhz than opa134 8mhz. the problem is opa134 is not available in the Philippines.

any good substitute?
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