Emu XL-7 & MP-7 User's Group

Did you have hum before? because if the socket is causing a ground loop, 
it should hum regardless of the type of lamp or even no lamp at all......

The LED lamps are great though.

On 2/15/2012 1:35 PM, Bob S. wrote:
> Years ago I found an LED replacement for the bayonet bulb on the 
> gooseneck....no hum on my XL-7 !
>
> Bob
> El Segundo, CA
>
> Sent from my iPad
>
> On Feb 15, 2012, at 12:36 AM, "Boris" <bgutman@... 
> <mailto:bgutman@...>> wrote:
>
>>
>>
>> Thanks Ricard, this is very useful info! I've always been annoyed by 
>> the hum from my Command Station. But I don't quite understand - do 
>> you disconnect the BNC from the top board completely? Is the problem 
>> is different ground between the two halves, wouldn't it make sense to 
>> connect the BNC connector to the lower chassis?
>>
>> Sorry for the stupid questions, I'm not to knowledgeable in 
>> electricity matters...
>>
>> --- In xl7@yahoogroups.com <mailto:xl7@yahoogroups.com>, "Ricard" 
>> <ricard2010@...> wrote:
>> >
>> > Here's a solution to an issue that has been mentioned here in this 
>> group and elsewhere: if the XL-7 is not securely mounted screwed 
>> together, you get hum and noise in the audio. This has sometimes been 
>> attributed to insufficient shielding, but the root cause is something 
>> completely different.
>> >
>> > As it turns out, the bottom half of the XL-7, where the main board 
>> and the power suppply are mounted, is grounded via the main board. 
>> This is as it should be. However, as it turns out, the top half is 
>> grounded via the 12V lamp BNC connector on the top. Due to a small 
>> but still significant voltage drop along the internal power supply 
>> lines, there's a small voltage difference between the metal of the 
>> top and bottom halves. That means that when they are screwed 
>> together, quite a lot of current flows in the chassis, creating a 
>> ground loop. If the two halves are not in proper contact with each 
>> other, you get a lot of current flowing in the ground wire(s) of 
>> internal power supply lines between the top and bottom halves, in 
>> effect, forming a ground loop.
>> >
>> > The solution is to isolate the BNC connector. For my part, I don't 
>> need the light anyway, so I just unsoldered the connector from the 
>> volume/headphone board where it is mounted, turned it 90� so it 
>> wouldn't make contact with the board, and put it all back together. 
>> Voila, no noise at all. I don't know if there are isolated BNC 
>> connectors out there which would fit, that would be the final 
>> solution to this problem.
>> >
>> > There are still other reasons that the top and bottom halves should 
>> be securely mounted together, but at least this eliminates the noise 
>> one gets if the connection is not 100%.
>> >
>> > /Ricard
>> >
>>
>