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JL Audio 300/4 BIAS
JL Audio 300/4 BIAS
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Old 6th June 2020, 04:10 PM   #1
DerSamoaner is offline DerSamoaner
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Default JL Audio 300/4 BIAS

Hi

Can anyone tell me how high the BIAS must be at the JL 300/4?

After changing the output section the BIAS is to high.

I've read in an other Thread (JL Audio 300/2) that the BIAS must be around 4mv. Maybe for the 300/4 it is the same?

Thx!
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Old 6th June 2020, 05:34 PM   #2
Perry Babin is offline Perry Babin  United States
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I've mostly seen 4mv across the bias headers but I think that's too high. I generally set it to where it just starts to increase the idle current like this:
http://www.bcae1.com/temp/ausettingbias.swf
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Old 6th June 2020, 08:27 PM   #3
DerSamoaner is offline DerSamoaner
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Thank you!

This amp has many cold solder joints on the driver boards. Some I have found and all LED's on the driver boards light up.

But I cant set the BIAS on the right rear channel. The trim potentiometer has no function. First I have to search this issue.
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Old 6th June 2020, 09:42 PM   #4
Perry Babin is offline Perry Babin  United States
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With the exception of the 47k resistors that have a significant problem with solder connections, if you found any others that had bad solder connections, that will likely lead you to other problems with components connected to the components with bad connections.
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Old 7th June 2020, 09:28 PM   #5
DerSamoaner is offline DerSamoaner
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I tested the 47k resistors, they are ok.

All trim potentiometer now works, but I have another problem.

If I move the two driver boards in the picture slightly, the BIAS goes up and down. Same problem with both boards.

The other two work fine.

I thought the pin header has bad connection to the circuit board. I resoldered everything but the problem persists. Sometimes the LED's dont light up when I move the board too.

I think I have no choice but to lay patch cables?

Do you have another idea?

Best regards.

Click the image to open in full size.
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Old 7th June 2020, 09:52 PM   #6
Perry Babin is offline Perry Babin  United States
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Did you properly resolder the 47k resistors (add solder, desolder and resolder)?
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Old 8th June 2020, 05:19 AM   #7
DerSamoaner is offline DerSamoaner
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I had only checked it. When resoldering I noticed directly a resistor had no connection. I order new resistors because at least one has no contact area to solder. I'll get in touch. Thank you!
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Old 14th June 2020, 12:12 PM   #8
DerSamoaner is offline DerSamoaner
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Thanks for the tip Perry.

I replaced the 47k resistors and resoldered many parts of the driver boards. Now it works without issues.

I set the BIAS to 0,5mV per channel and it works great. I read the 0,5mV in another thread.
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