What the heck is wrong with my Leslie 145?

[Juan]

I have an A-102 Hammond organ that I use with a Leslie 145. I have controls that allow just the A-102 speakers, Just the Leslie or both together. The Problem.... When the Leslie is on (or the organ and Leslie together) there is an intermit, very loud raspy, buzz noise.... ONLY when playing the C# just above middle C. This does not happen on any other notes. It sounds as if some dirt is stuck in the driver diaphram. I assumed there was some kind of problem with the driver itself although I have never had a problem with this driver before.
I replaced the driver with a known good one. The exact same problem occured. There is no way this issue can simply be two bad drivers. However, I don't think it is the organ either. This sound never happens when only the organ speakers are being used.
It is an odd problem and I'm stumped. Could this be a cross over problem in the Leslie?
Also, Please note... this problem started recently, just after I hooked up the Half moon switches and the control box to my A-102. Up to that point I only used this 145 with my M3. I never had a problem when using the M3. Currently the M3 is apart for modifications so I can't use it as a test.
Let me know what you think.

[Charlie Metcalf]

I once had a distorted tone that was only on one note. Turned out to be a bad tube, and not the speaker. I'd never had that before, and never since. But changing that one tube ended the problem that one time. It's been so many years I can't recall whether it was a power tube or one of the little ones.

[Juan]

Testing information update - I have discovered that the buzz noise occurs only on the C# just above middle C, on both the upper and lower manual. Also, it only occurs when the 16' drawbar is used. However, it happens with all four of the 16' drawbars (two on each manuel). No other keys or draw bars cause the buzz.

[torea]

Even on the other drawbars when adjusted to the same note? Strange.

[bossbandbob]

I have been getting a similar or rattling noise on my solid state Leslie and A101 but only on C's and F's in some octaves! Does not happen at all when just the organ's speakers are being used.

[Juan]

OK! After yet further testing based on the question from Torea... THe buzz occurs on other drawbars when adjusted to the same note (meaning the same octave of the C# just above middle C with the 16' bar)
It seemed to take a few minutes with the Leslie on before the buzz came back.
Thanks to Torea for asking the correct question. What do I check next??

[torea]

Glad I could help :-B If only my help could extend beyond asking questions :embarrassed:

[johnny b3]

Are you certain it isn't a mechanical buzz/resonating frequency going on inside the leslie cabinet? does it happen on all volumes?

[Juan]

It does not happen at low volume. I don't think the buzz is a resonating frequency unless it is being amplied. The noise is very loud. Perhaps "buzz" is not a good description. Very loud, raspy, grating noise is closer. Ever time I hear it I jump as if I am getting shocked by a big jolt of electricity.

[johnny b3]

disconnect the treble driver from the crossover and see if the noise happens through the woofer. If not, you have a damaged driver, as slim as the odds are... If you want to narrow it down even further, remove the driver from the cabinet but leave it plugged in. This will remove any chance of resonance vibration occurring from the horn hardware.

[Tim_at_Jonas]

I've had that on a number of Leslies. Usually it's the box around the upper motor. I lay the Leslie on it's face and take a large bottle of thin superglue to all of the joints of the box, and where the box mounts to the cabinet. Sometimes I hit all of the joints in the cabinet while I'm at it. It takes a whole bottle (which I get from StewMac.com).

Warning: Noxious fumes! Wear eye protection!

I also had the reverb amp in a 122R do that. I had to drive a wedge between the two transformers to shut it up.

[Juan]

At first I suspected the driver was damaged. I replaced it with a known good driver. Same problem happened again with the replacement driver. I will disconnect the driver from the crossover and check for the noise through the woofer.

[Hamman]

I just had this exact same problem with one of my 122's. I would be just playing along when all of a sudden this loud...like feed back sound. Turned out to be one of my 6550 tubes going south on me. But boy did it ever send me and my dogs through the roof when it went off!

[weslan]

Echoing Tim's sentiments -- I had tiny phillips screw hidden in the bottom of my upper motor box once. It rattled around and drove me crazy when I played certain notes. Took me forever to figure out what it was. Check to make sure there's nothing stuck in there.

Also I've had my plastic horn assembly bounce around and dance to certain frequencies and make some noise. Haven't figured a way around that one. Part of "the sound."

[torea]

I accidentally left an eyeglass screwdriver in the back once. It was small enough that I couldn't find it but it rattled on C#. Was doing a different fix up job and found it, felt like an idiot...