Hammond C-3 has hum when sigle keys are depressed on slow speed

[johnieappel]

Hey Folks, I'm really hoping I can get a little advice from some of you on a problem I'm having with a C-3. It has had a 120hz hum that I cant quite figure out. It happens when the Leslie 147 is on slow speed, no notes played.It is almost acceptable but when you play a note, it gets much more noticeable. The Leslie amp has been re-capped, tubes checked out on my tube tester and are fine. The Hammond AO-28 pre amp has been re-capped & re-tubed. I'm tearing my hair out on this one - any help would be very much appreciated. Thanks & Happy Holidays!

[CEB]

If you unplug the slow motor does it go away?

[Wes]

Is the Leslie on the left side of your organ?

[CEB]

Yeah. I've seen old Synths sitting on top of Hammonds start talking to each other if the transformer is too close. A piece of sheet metal fixes that.

[johnieappel]

Thanks for your responses - so the Leslie is on the left side of the organ. No synths or anything on top of the organ. The organ is in my friends studio so i cant uplug the slow motor at the moment to see if the hum goes away. If it does would it be the slow motor?

[CEB]

There is a big old matching transformer on the left side of the organ. Our theory is the slow motor is generating an electric field that is being picked up by the matching transformer..... well that is my theory at least.

It is an easy fix just move the leslie further away or move it to the right side and try that.

[Wes]

My theory, too. :)

This happens a lot. You need to move the Leslie. Or the organ. Or both.

Alternatively you could try encasing the matching transformer in mu metal. Or at the very least, make sure the ground to the matching transformer can is good.

Wes

[David Anderson]

There's no theory involved. Because of their open construction, the Leslie slow motors radiate a much stronger magnetic field than the fast motors. Any of the audio transformers in the organ can pick this up, but the matching transformer (at the back left as you're sitting at the organ) seems most vulnerable. You can't position a Leslie close to this corner of the organ. This is not the first studio situation where this has been a problem. People often position the organ and Leslie next to each other without knowing this Hammond/Leslie 101 fact.

Years ago, I got a halogen reading lamp to put on my C3, right over the matching transformer, without thinking about the fact that it had a power transformer in the base. The hum through the organ when I turned it on was pretty impressive.

[CEB]

Or unplug the slow motors because it sounds way cooler. :D

[jdoc]

just like real estate, location, location, location...move stuff, sometimes a couple of inches, check the cable routing and condition of connectors for bonus points