problem with leach amp

xxsmiffxx · 24th February 2005, 09:33 PM

I just got done seembling this amp, and I keep on blowing r51. I have thoroughly checked the board for solder bridges and things like this, but I am having no luck. Anyone have any idea what I might have done wrong to cause this problem? Thanks in advance!

David Smith

djk · 25th February 2005, 02:50 AM

R51 blows because you have a ground loop.

xxsmiffxx · 25th February 2005, 03:46 AM

thanks for the quick reply! So there is a problem with my ground path? I have everything grounded to a single point on my chassis. Could this be a problem on the board or is it likely a wiring issue? Thanks for your patience with me, I am new!

djk · 25th February 2005, 04:39 AM

"I have everything grounded to a single point on my chassis."

I hope you followed the instructions to the letter at Leach.

The input and output jacks do not make electrical contact to the rear panel.

Re-read all the instructions.

xxsmiffxx · 25th February 2005, 07:30 AM

My input and output jacks are isolated from the chassis ground. The only parts grounded to central point are the ones marked for central ground. Thanks again for any suggestions, and I will continue to re-read instructions to insure I haven't made obvious errors. Again, thanks for your patience!

djk · 25th February 2005, 07:50 PM

If the input jacks are floating, the only way R51 can conduct is if there is a difference in potential between the amp chassis and whatever you have driving it.

This is normally called a ground loop.

Replace R51 and add a pair of diodes in parallel, one reversed from the other, bypass the resistor with a 0.1µF film cap.

This will stop the resistor from blowing and give you a loud 'buzz' to tell you youhave a ground loop to troubleshoot.

The 'hot' and 'neutral' on and piece in your system may be backwards. The power supply of the amplifier may have high leakage current.

In the worst case an input transformer may be required.

24th February 2005, 09:33 PM	#1
xxsmiffxx diyAudio Member Join Date: Feb 2005 Location: Georgia	problem with leach amp I just got done seembling this amp, and I keep on blowing r51. I have thoroughly checked the board for solder bridges and things like this, but I am having no luck. Anyone have any idea what I might have done wrong to cause this problem? Thanks in advance! David Smith __________________ David Smith Custom Creations

25th February 2005, 03:46 AM	#3
xxsmiffxx diyAudio Member Join Date: Feb 2005 Location: Georgia	thanks for the quick reply! So there is a problem with my ground path? I have everything grounded to a single point on my chassis. Could this be a problem on the board or is it likely a wiring issue? Thanks for your patience with me, I am new! __________________ David Smith Custom Creations

25th February 2005, 07:30 AM	#5
xxsmiffxx diyAudio Member Join Date: Feb 2005 Location: Georgia	My input and output jacks are isolated from the chassis ground. The only parts grounded to central point are the ones marked for central ground. Thanks again for any suggestions, and I will continue to re-read instructions to insure I haven't made obvious errors. Again, thanks for your patience! __________________ David Smith Custom Creations

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25th February 2005, 02:50 AM	#2
djk diyAudio Member Join Date: Feb 2001 Location: USA	R51 blows because you have a ground loop.

25th February 2005, 04:39 AM	#4
djk diyAudio Member Join Date: Feb 2001 Location: USA	"I have everything grounded to a single point on my chassis." I hope you followed the instructions to the letter at Leach. The input and output jacks do not make electrical contact to the rear panel. Re-read all the instructions.

25th February 2005, 07:50 PM	#6
djk diyAudio Member Join Date: Feb 2001 Location: USA	If the input jacks are floating, the only way R51 can conduct is if there is a difference in potential between the amp chassis and whatever you have driving it. This is normally called a ground loop. Replace R51 and add a pair of diodes in parallel, one reversed from the other, bypass the resistor with a 0.1µF film cap. This will stop the resistor from blowing and give you a loud 'buzz' to tell you youhave a ground loop to troubleshoot. The 'hot' and 'neutral' on and piece in your system may be backwards. The power supply of the amplifier may have high leakage current. In the worst case an input transformer may be required.

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