DC offset 20V!!!

jmillerdoc · 27th June 2009, 08:23 AM

Hi,
I have built several of Brian Bell's LM3886 Chipamps in the past. He was running a special where he was giving away a fre set of LM1875 PCBs with each purchase. I had collected several of these so I thought I would try one. After collecting all of the parts and using the build thread here, I had it all complete....so I thought. Tonight I finally got everything wired in the chassis (extremely tight fit, unique wooden chassis) and powered her up. Immediately from both channels I am getting the same voltage as my rectified voltage....20V! I am scratching my head and re-tracing everything and I cannot figure it out. Any stupid oversights I may have done? What would be a straight forward answer to why I am getting 20v as if there where no amp in between the speaker outs and the rectifier? Both boards are seperated in two small wooden eclosures on either side of the PSU. the only thing connecting them (really not a connection) is the 3 power leads + GND - . I must have done the same thing wrong on each side. I am pretty sure I followed the directions. Ant thoughts?
Thanks,
Jeff

Zigis · 27th June 2009, 01:10 PM

You have disconnected one power leg or wire.
Measure +20 and -20 direct on chip power legs, check all connections.

jaudio · 27th June 2009, 05:54 PM

Check input resistor to ground ,make sure ikt is connected

27th June 2009, 08:23 AM	#1
jmillerdoc diyAudio Member Join Date: Mar 2009 Location: Lawton, OK, USA	DC offset 20V!!! Hi, I have built several of Brian Bell's LM3886 Chipamps in the past. He was running a special where he was giving away a fre set of LM1875 PCBs with each purchase. I had collected several of these so I thought I would try one. After collecting all of the parts and using the build thread here, I had it all complete....so I thought. Tonight I finally got everything wired in the chassis (extremely tight fit, unique wooden chassis) and powered her up. Immediately from both channels I am getting the same voltage as my rectified voltage....20V! I am scratching my head and re-tracing everything and I cannot figure it out. Any stupid oversights I may have done? What would be a straight forward answer to why I am getting 20v as if there where no amp in between the speaker outs and the rectifier? Both boards are seperated in two small wooden eclosures on either side of the PSU. the only thing connecting them (really not a connection) is the 3 power leads + GND - . I must have done the same thing wrong on each side. I am pretty sure I followed the directions. Ant thoughts? Thanks, Jeff

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27th June 2009, 01:10 PM	#2
Zigis diyAudio Member Join Date: May 2005 Location: Riga, Latvia	You have disconnected one power leg or wire. Measure +20 and -20 direct on chip power legs, check all connections.

27th June 2009, 05:54 PM	#3
jaudio diyAudio Member Join Date: Oct 2004	Check input resistor to ground ,make sure ikt is connected

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