ubxf

Adding ac ground to a Hammond organ.
« on: October 13, 2020, 10:49:29 PM »
Hello,
Hammond organs are designed with a 2 pole ac plug. If i were to install a modern ac plug where should i attach the ground wire. I'm still not clear on earth safety ground and audio ground and how they should be connected or not.


JohnRoberts

Re: Adding ac ground to a Hammond organ.
« Reply #1 on: October 14, 2020, 12:18:33 AM »
The first guess is to tie it to the metal chassis if it has one.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

ubxf

Re: Adding ac ground to a Hammond organ.
« Reply #2 on: October 14, 2020, 12:26:43 AM »
in the preamp and the amp the high voltage H- is going to the chassis so is it ok to tie the ground from the wall to it as well ?

squarewave

Re: Adding ac ground to a Hammond organ.
« Reply #3 on: October 14, 2020, 12:42:39 AM »
The mains earth ground contact should be connected to the metal parts that a person could touch (so that if something shorts out to metal stuff, they don't get shocked) and to things like ground contacts of jacks (for shielding signals from electromagnetic noise) like the sleeve of 1/4" phone jacks for example. So if you check resistance between these sorts of things with your ohm meter, you should be able to find what it should be connected to. Figuring out how to connect it is a different matter. If you find some terminal strip with the desired continuity, that might not be the best option because the earth connection should not be something that can easily be undone by a reckless tech. It would be better to find some metal with a bolt (that cannot be unscrewed from the outside) or install one, use a toothed washer and maybe scrape away a little paint or oxidation to ensure really good contact. Even a few ohms could defeat it's benefits.

JohnRoberts

Re: Adding ac ground to a Hammond organ.
« Reply #4 on: October 14, 2020, 09:11:16 AM »
in the preamp and the amp the high voltage H- is going to the chassis so is it ok to tie the ground from the wall to it as well ?
The metal chassis if exposed to touch, should not be energized.

JR 
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

Speedskater

Re: Adding ac ground to a Hammond organ.
« Reply #5 on: October 14, 2020, 12:37:56 PM »
Don't have my mother's old Hammond to look at anymore.
But the Safety Ground wire should attach to the chassis, near where the AC cord enters the chassis.
Kevin

ubxf

Re: Adding ac ground to a Hammond organ.
« Reply #6 on: October 14, 2020, 01:12:48 PM »
Thank you for all the responses, here is a block diagram of the wiring. It shows that the ac at the lower left goes first to a line panel that connects to the start and run switches. Then goes to the different components preamp and amp that are not exposed to the user touch.
The metal parts exposed are the drawbars and misc switch panels.


 

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