[HAM] Leslie 147's

[David Anderson]

I think Scott and I agree--it's a matter of relative quietness. There  
will be a little noise from practically any audio amplifier, and it's  
especially hard to exclude noise from hi-gain preamp circuits. That's  
why some high-end preamplifiers have power supplies in a separate  
chassis.

The popularity of switching/switch-mode power supplies these days can  
be a problem, too. They are inherently noisy and, especially if  
poorly designed, can transfer this noise to other components via AC  
wall circuits or radiation. Many wall-wart supplies used to be linear  
supplies, which, while less efficient, are much quieter, but nowadays  
you have to search to find a linear supply. Switch mode power  
supplies are smaller, lighter, and cheaper, but there is a definite  
trade-off.

And, as Scott implies, the Leslie slow motors themselves radiate a  
substantial electromagnetic field that can be picked up by the  
matching transformer in the organ.

David


On May 26, 2008, at 11:34 AM, Scott Hawthorn wrote:

> At 07:45 AM 5/26/2008, you wrote:
>
>> I have a rebuilt AO-28...all caps are less than 6 months old.  Is it
>> normal to have some buzz and a little hum when  everything is  
>> turned all
>> the way up?
>
> I like David A.'s answer better than the one I'm about to give
> you.  :-)  He said yes, and I say, not really, if it's enough of a  
> hum/buzz
> to bother you.
>
> Based on my own experience when I started out working on these  
> things, I
> suspect that something isn't hooked-up right. It should be RELATIVELY
> quiet. And, are there cheap wall dimmers somewhere on the circuit?
> Flourescent lighting? Is your Leslie very near the matching- 
> transformer end
> of the organ? Any of these things can introduce noise.
>