Paralllel configuartion LM3886 - adjusting variable resistors

jmillerdoc · 25th May 2009, 09:38 PM

I am looking for some assistance with adjusting the variable resistors on a LM3886 parallel configuration. I recent purchased a prebuilt amp PCB from Nemo-e-store on eBay and I was very impressed with the sound from this configuration. I subsequently purchased the PCB's to DIY the design but, although the PCB came with a schematic it did not explain how to balance the 3 chips by adjusting the 3 variable resistors. I have come up empty handed searching the web and asking the guy I bought the PCB from.

The PCB I bought is here:
http://cgi.ebay.com/lm3886-3-Paralle...3A2%7C294%3A30

Can anybody help me with this problem?
Thanks for all y'alls help.
Sincerely,
Jeff M.
Lawton, USA

pacificblue · 25th May 2009, 10:07 PM

Without a schematic it is guesswork, but they are probably there to adjust the DC offset to zero.

deepthrob · 26th May 2009, 03:09 AM

I purfed up a 3*3886 non inverting and balanced it by lifting the three output resistors and adjusting each chip individually to the lowest dc offset. Then I adjust the two lowest to match the highest (8 mv).

Frank
http://www7.taosnet.com/f10/

deepthrob · 26th May 2009, 03:39 AM

Ooops, meant to write 'inverting'

jmillerdoc · 26th May 2009, 04:08 AM

Where exactly do you take the measurements? Across pin 3 and GND on each chip? Or is there another way to measure the DC offset? Also, how do you put a load across the output and GND of each individual pin or is it even neccessary?
Jeff

deepthrob · 26th May 2009, 04:14 AM

A load is not necessary and yes, from 3 to ground but the resistors must be lifted so the outputs are isolated.

jmillerdoc · 26th May 2009, 06:44 AM

i am sorry but this is a first for me....which resistors must be lifted? What is the general value of the resistor you are speaking of? There are several resistors, I am not certain which you are speaking of.
Thanks,
Jeff

pacificblue · 26th May 2009, 08:17 AM

The big ones R2, R5, R11 on the PCB you linked to.

jmillerdoc · 26th May 2009, 12:21 PM

I got it, thanks! Anybody know of a source to buy similar PCB's. I have tried to email www.Shine7.com several times with no response. I would love to get a few of the PCB's found at their website!

Thanks again for all of your assistance!
Sincerely,
Jeff

AndriyOL · 1st June 2009, 11:02 PM

Quote:

Originally posted by deepthrob
I purfed up a 3*3886 non inverting and balanced it by lifting the three output resistors and adjusting each chip individually to the lowest dc offset. Then I adjust the two lowest to match the highest (8 mv).

Frank
http://www7.taosnet.com/f10/

Sorry, but I can't understand. Could you explain how exactly you adjusted each chip individually to the lowest dc offset.
Thanks.

25th May 2009, 09:38 PM	#1
jmillerdoc diyAudio Member Join Date: Mar 2009 Location: Lawton, OK, USA	Paralllel configuartion LM3886 - adjusting variable resistors I am looking for some assistance with adjusting the variable resistors on a LM3886 parallel configuration. I recent purchased a prebuilt amp PCB from Nemo-e-store on eBay and I was very impressed with the sound from this configuration. I subsequently purchased the PCB's to DIY the design but, although the PCB came with a schematic it did not explain how to balance the 3 chips by adjusting the 3 variable resistors. I have come up empty handed searching the web and asking the guy I bought the PCB from. The PCB I bought is here: http://cgi.ebay.com/lm3886-3-Paralle...3A2%7C294%3A30 Can anybody help me with this problem? Thanks for all y'alls help. Sincerely, Jeff M. Lawton, USA

25th May 2009, 10:07 PM	#2
pacificblue diyAudio Member Join Date: May 2008	Without a schematic it is guesswork, but they are probably there to adjust the DC offset to zero. __________________ If you've always done it like that, then it's probably wrong. (Henry Ford)

26th May 2009, 08:17 AM	#8
pacificblue diyAudio Member Join Date: May 2008	The big ones R2, R5, R11 on the PCB you linked to. __________________ If you've always done it like that, then it's probably wrong. (Henry Ford)

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26th May 2009, 03:09 AM	#3
deepthrob diyAudio Member Join Date: Jun 2008 Location: Taos, New Mexico	I purfed up a 3*3886 non inverting and balanced it by lifting the three output resistors and adjusting each chip individually to the lowest dc offset. Then I adjust the two lowest to match the highest (8 mv). Frank http://www7.taosnet.com/f10/

26th May 2009, 03:39 AM	#4
deepthrob diyAudio Member Join Date: Jun 2008 Location: Taos, New Mexico	Ooops, meant to write 'inverting'

26th May 2009, 04:08 AM	#5
jmillerdoc diyAudio Member Join Date: Mar 2009 Location: Lawton, OK, USA	Where exactly do you take the measurements? Across pin 3 and GND on each chip? Or is there another way to measure the DC offset? Also, how do you put a load across the output and GND of each individual pin or is it even neccessary? Jeff

26th May 2009, 04:14 AM	#6
deepthrob diyAudio Member Join Date: Jun 2008 Location: Taos, New Mexico	A load is not necessary and yes, from 3 to ground but the resistors must be lifted so the outputs are isolated.

26th May 2009, 06:44 AM	#7
jmillerdoc diyAudio Member Join Date: Mar 2009 Location: Lawton, OK, USA	i am sorry but this is a first for me....which resistors must be lifted? What is the general value of the resistor you are speaking of? There are several resistors, I am not certain which you are speaking of. Thanks, Jeff

26th May 2009, 12:21 PM	#9
jmillerdoc diyAudio Member Join Date: Mar 2009 Location: Lawton, OK, USA	I got it, thanks! Anybody know of a source to buy similar PCB's. I have tried to email www.Shine7.com several times with no response. I would love to get a few of the PCB's found at their website! Thanks again for all of your assistance! Sincerely, Jeff

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