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Hammond L100 ground noise DIY Hardware
Old 2 weeks ago
  #1
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Hammond L100 ground noise

Hi everyone, I hope this is the right section.
I have a Hammond L100. The problem is the 60 Hz ground noise coming from the speaker. The organ also has a TRS plug that takes the signal from the preamp (added from the previous owner I think) for recording it directly or for put it into an amplifier. And, of course, the hum is still there. So I think it comes from the preamp or something before.

How can I add a sort of shield ground or something to reduce this hum? I don't want to burn something.

Thanks.
Old 2 weeks ago
  #2
It could be a lot of things from capacitors going bad to the electronics having problems. You might want to read this hammond l100 mods - Google Search

Best of luck!
Old 2 weeks ago
  #3
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Quote:
Originally Posted by Thomas W. Bethe View Post
It could be a lot of things from capacitors going bad to the electronics having problems. You might want to read this hammond l100 mods - Google Search

Best of luck!
Thank you!

I will check some of the results (the first one is a website that has some interesting mods and troubleshootings) hoping to get something useful for my cause.

But I'm still curious to know how to manage ground wirings in L100.
Old 2 weeks ago
  #4
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Does the source (Hammond L100) hum on its own? (When NOT connected to anything else.)
By "the speaker." do you mean a vintage Leslie cabinet with the original interconnection to the console?

When you say And, of course, the hum is still there." does that mean that you hear the same hum when listening to the audio from that added output?
Solving problems with ground loops and similar problems will take much more precise explanation of all the details.

Since the original design did not hum, it seems counter-intuitive to have to ADD something to make it quiet.
As Mr. Bethel suggested, one possible source of hum would be the vintage capacitors simply drying out.
Especially the large electrolytic capacitors that are supposed to block the hum from the power supply.

Another potential source is that after-market connector.
That will require some serious investigative work to figure out how it was connected.
And whether the modification contributes to the hum.
Old 2 weeks ago
  #5
While I was in the Army I completely rebuilt a Hammond B-3 organ with a Leslie speaker cabinet. It was a daunting task but I did it in my spare time and it was located in a hospital radio studio that I was also rebuilding. There were LOTS of filter caps, there were lots of coupling caps, there were a lot of tubes and it took a long time to get the tone wheels operating since they had not been run for years. It was a fun project and this was back in the 60's so high voltage caps were still available from the local radio repair shop. The government paid for all the parts so their was no out of pocket expenses. The biggest problem was getting the Hammond oil for the tone wheels as it is not a normally stocked item in the Army's supply chain. Anyway enough history. When I started the rebuild there was lots of hum and the tone wheels would not spin and the Leslie had a multitude of problems. I got it all working and it sounded great. I would say that the hum is from maybe two sources. Aged filter caps on the power supply and or someone messing with the grounding when they put in the external jack. It is going to take some very detailed trouble shooting to isolate the problem. Best of luck and let us know how things progress.

FWIW
Old 1 week ago
  #6
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Quote:
Originally Posted by Richard Crowley View Post
Does the source (Hammond L100) hum on its own? (When NOT connected to anything else.)
By "the speaker." do you mean a vintage Leslie cabinet with the original interconnection to the console?
On its own. This Hammond has a built-in speaker and the hum comes out also from it.


Quote:
Originally Posted by Richard Crowley View Post
When you say And, of course, the hum is still there." does that mean that you hear the same hum when listening to the audio from that added output?
Solving problems with ground loops and similar problems will take much more precise explanation of all the details.
Yes, I hear the same exact hum from the built-in speaker and from the TRS out in direct recording. I measured both situations with an analyzer (analyzing the mic recording and the direct signal) and that's it, 60 Hz.


Quote:
Originally Posted by Richard Crowley View Post
Since the original design did not hum, it seems counter-intuitive to have to ADD something to make it quiet.
As Mr. Bethel suggested, one possible source of hum would be the vintage capacitors simply drying out.
Especially the large electrolytic capacitors that are supposed to block the hum from the power supply.
I tought a similar thing too... If the instrument was built like this, of course it hadn't any hum at the time. So I think that looking for a dry or broken capacitor will be the right solution, in the end.


Quote:
Originally Posted by Richard Crowley View Post
Another potential source is that after-market connector.
That will require some serious investigative work to figure out how it was connected.
And whether the modification contributes to the hum.
This was the first thing I checked. The TRS connector seems to be connected properly, all the solders are good and solid and the wire is a quality one, as of the connectors (Neutrik). Well, I tried to disconnect it and re-wire the original connection between preamp and amplifier using a good RCA cable. The hum was still there, so the problem can't be the added TRS.



Quote:
Originally Posted by Thomas W. Bethe View Post
While I was in the Army I completely rebuilt a Hammond B-3 organ with a Leslie speaker cabinet. It was a daunting task but I did it in my spare time and it was located in a hospital radio studio that I was also rebuilding. There were LOTS of filter caps, there were lots of coupling caps, there were a lot of tubes and it took a long time to get the tone wheels operating since they had not been run for years. It was a fun project and this was back in the 60's so high voltage caps were still available from the local radio repair shop. The government paid for all the parts so their was no out of pocket expenses. The biggest problem was getting the Hammond oil for the tone wheels as it is not a normally stocked item in the Army's supply chain. Anyway enough history. When I started the rebuild there was lots of hum and the tone wheels would not spin and the Leslie had a multitude of problems. I got it all working and it sounded great. I would say that the hum is from maybe two sources. Aged filter caps on the power supply and or someone messing with the grounding when they put in the external jack. It is going to take some very detailed trouble shooting to isolate the problem. Best of luck and let us know how things progress.

FWIW
Woah, very interesting story. I love rebuilting and restoring, and you were lucky to find the original components.

Anyway, as written above, the hum is present also without the external jack, so I will definitely check all the capacitors, because I'm pretty sure the problem is related with them.


Thank you all for the precious help.
Old 1 week ago
  #7
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Richard Crowley's Avatar
 

If you temporarily unscrew the added 1/4 inch jack from the chassis, does it still hum?
Specifically to break any connection between the 1/4 inch sleeve terminal and the (presumably metal) chassis.
This tests to see whether there is an inadvertent ground loop was formed by the added connector.
Old 1 week ago
  #8
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Quote:
Originally Posted by Richard Crowley View Post
If you temporarily unscrew the added 1/4 inch jack from the chassis, does it still hum?
Specifically to break any connection between the 1/4 inch sleeve terminal and the (presumably metal) chassis.
This tests to see whether there is an inadvertent ground loop was formed by the added connector.
As I already said in my last post, I tried to completely bypass the 1/4 jack. I basically restored the original connection between the preamp and the amp, via a good RCA cable. And the hum was still there. So the added connector isn't the origin of the problem.
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