BPA300 & PA150 setup on the bench

Ted205 · 27th November 2009, 01:35 PM

Hi all

I've finally got round to populating my PA150 boards (Alexw88). I'm testing them using a bench power supply.

i started by installing one chip and it tested with no problems. When i added the second chip (2 in parallel) i can't get the power supply stable. When i increase the current limit on one power line (-ve) then adjust the other line (+ve) up the opposite line current limit kicks in.

Now i'm not sure if its operator error on my part but i can't seem to figure it out and i'm very reluctant to let the current rise to 1amp (the input is shorted to ground, no load connected)

can anyone please prod me in the direction of what i may be doing wrong

Mark Allen · 28th November 2009, 02:56 AM

Take a look at this thread and when you get yours going let us know if yours also does this....

Parallel LM3886 problem

shmulik · 28th November 2009, 09:07 PM

what else is already installed (filter capacitors, mute, smd parts of all LMs, input network, output network, power resistors, trimmers)?
maybe you made a short when soldering the bypass capacitors below (somewhat crowded there)?
it is harder to identify a short with DMM while the filter capasitors are installed.
I had one LM suspect to be faulty right out of the tube. it blew up with no apparent reason when I first conneted the power. placing another one in the very same position did reiterate the fireworks. there is always of course the option I had a hidden short there of which I somehow caused and miss in the visual inspection.

Ted205 · 30th November 2009, 09:51 AM

thanks for the replies guys.

I've removed the bypass caps and the reservoir caps. I have installed everything else and i've checked it on two boards but they are both doing it.

i'll keep at it

Mark Allen · 30th November 2009, 02:55 PM

See this thread... You need to bypass the three pots on each board.
Parallel LM3886 problem

Ted205 · 12:56 PM

well i've not managed to get much further. With only one lm3886 in place the voltage and current is perfectly stable. When i add another chip the current from the -ve side is over 1amp

how have your guys wired up the power ?

Ted205 · 1st December 2009, 03:20 PM

ok so I have removed the output resistors and the chips are all working well individually. I take it this is a case of each chip fighting each other ?

Which leads me to the question what values are you using ?

i have 1% 0.2OHM Dale surface mounts at the ouput of each chip.

i notice the Jeff Rowland on the shine7 site is using .5ohms while Mr.Shine7 himself is using the 0.2ohm

shmulik · 1st December 2009, 07:28 PM

what is the dc each LM's output (with no output resistors)?

Ted205 · 1st December 2009, 10:03 PM

well i've adjusted the dc down with the trimmer pots to around 3mv on each chip.

Ted205 · 4th December 2009, 10:35 AM

can anyone help me out with alittle bit of theory.

When i put in place the output resistor the amp becomes unstable and draws more current. What could be causing this. What would a larger resistance cause on the output as compared to a lower resistance?

The chips are perfectly happy with out the output resistance though.

thanks

27th November 2009, 01:35 PM	#1
Ted205 diyAudio Member Join Date: Jun 2008	BPA300 & PA150 setup on the bench Hi all I've finally got round to populating my PA150 boards (Alexw88). I'm testing them using a bench power supply. i started by installing one chip and it tested with no problems. When i added the second chip (2 in parallel) i can't get the power supply stable. When i increase the current limit on one power line (-ve) then adjust the other line (+ve) up the opposite line current limit kicks in. Now i'm not sure if its operator error on my part but i can't seem to figure it out and i'm very reluctant to let the current rise to 1amp (the input is shorted to ground, no load connected) can anyone please prod me in the direction of what i may be doing wrong

1st December 2009, 12:43 PM	#6
Ted205 diyAudio Member Join Date: Jun 2008	well i've not managed to get much further. With only one lm3886 in place the voltage and current is perfectly stable. When i add another chip the current from the -ve side is over 1amp how have your guys wired up the power ? Last edited by Ted205; 1st December 2009 at 12:56 PM.

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28th November 2009, 02:56 AM	#2
Mark Allen diyAudio Member Join Date: Jan 2008 Location: Bountiful, You-Taw	Take a look at this thread and when you get yours going let us know if yours also does this.... Parallel LM3886 problem

28th November 2009, 09:07 PM	#3
shmulik diyAudio Member Join Date: Aug 2004 Location: country side	what else is already installed (filter capacitors, mute, smd parts of all LMs, input network, output network, power resistors, trimmers)? maybe you made a short when soldering the bypass capacitors below (somewhat crowded there)? it is harder to identify a short with DMM while the filter capasitors are installed. I had one LM suspect to be faulty right out of the tube. it blew up with no apparent reason when I first conneted the power. placing another one in the very same position did reiterate the fireworks. there is always of course the option I had a hidden short there of which I somehow caused and miss in the visual inspection.

30th November 2009, 09:51 AM	#4
Ted205 diyAudio Member Join Date: Jun 2008	thanks for the replies guys. I've removed the bypass caps and the reservoir caps. I have installed everything else and i've checked it on two boards but they are both doing it. i'll keep at it

30th November 2009, 02:55 PM	#5
Mark Allen diyAudio Member Join Date: Jan 2008 Location: Bountiful, You-Taw	See this thread... You need to bypass the three pots on each board. Parallel LM3886 problem

1st December 2009, 03:20 PM	#7
Ted205 diyAudio Member Join Date: Jun 2008	ok so I have removed the output resistors and the chips are all working well individually. I take it this is a case of each chip fighting each other ? Which leads me to the question what values are you using ? i have 1% 0.2OHM Dale surface mounts at the ouput of each chip. i notice the Jeff Rowland on the shine7 site is using .5ohms while Mr.Shine7 himself is using the 0.2ohm

1st December 2009, 07:28 PM	#8
shmulik diyAudio Member Join Date: Aug 2004 Location: country side	what is the dc each LM's output (with no output resistors)?

1st December 2009, 10:03 PM	#9
Ted205 diyAudio Member Join Date: Jun 2008	well i've adjusted the dc down with the trimmer pots to around 3mv on each chip.

4th December 2009, 10:35 AM	#10
Ted205 diyAudio Member Join Date: Jun 2008	can anyone help me out with alittle bit of theory. When i put in place the output resistor the amp becomes unstable and draws more current. What could be causing this. What would a larger resistance cause on the output as compared to a lower resistance? The chips are perfectly happy with out the output resistance though. thanks

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