[HAM] Popping problems with a home made Leslie

[Timothy Broms]

Hi Doug, 

 

Sorry to take so long to reply, I have not checked this in a while.  

 

Here is what I did:  

 

For the lower rotor unit, I got most of my parts from Ebay.  I found an
internal Leslie unit from a Lowry organ (one with a foam rotor).  It had a
single speed motor, so I also found an original 2 speed Leslie lower rotor
motor on Ebay, and replaced the single speed motor with that.  Then I bought
a 12” woofer with a decent frequency response, cut the hole on the board so
it would fit, and mounted the speaker.  Finally, I built a cabinet out of
plywood to house the lower rotor unit.  I made it as small as I could.  The
top portion that houses the speaker is lined with acoustical foam, and is
all enclosed.  The bass response it not bad.

 

For the upper horn unit, I actually use an old Motion Sound Pro 3.  I found
it on Ebay also.  I made sure to get the older Pro3 that does not have the
12ax7 tube in it.  The newer Pro3T has the tube, but I use a separate amp
(which I will describe below) so I did not want the tube.  The advantage was
that it was very cheap, because most people nowadays want the newer Pro3T.
The only other thing I did was to upgrade the driver in the Pro3 to the
newer phenolic diaphragm.  This is the driver that is found in the newer
Pro3T, and it is a much better design, so I wanted to switch to that.  I got
it directly from Motion Sound.  This motion sound unit sits right on top of
the lower rotor cabinet.

 

To drive everything, once again I searched Ebay for a nice old stereo tube
amp.  I found an old WICO stereo tube amp that sounds great.  I also had to
build some crossover units.  Leslie speakers had a crossover point of 800
Hz, and had a slope of 12 dB/octave.  This is known as a 2nd order
crossover.  I used this website to help design and build the crossovers:
http://www.colomar.com/Shavano/crossover12db.html.  I just built the
crossovers in some project boxes.  So, I just run my organ (I have a Korg
CX3) into the tube amp, and then I take one channel of the tube amp out to
the lower crossover and then to the lower rotor cabinet, and I take the
other channel of the tube amp out to the upper crossover and then to the
Motion Sound unit.  I disconnected the driver in the Motion Sound unit from
the solid state amp that is in there, no need for that!  I just go from the
upper crossover directly to the driver in the Motion Sound unit.  This amp
sits right on top of the Motion Sound unit.

 

I control everything with a double pole, double throw switch mounted in a
project box.  One side of the switch powers the slow motor in the lower
unit, the other side powers the fast motor in the lower unit.  This all
works great for the lower unit because it is all AC, but the Motion Sound
unit is a DC unit, so I had to figure out how to control the speed on that
too.  I ended up putting a ¼ inch jack in the box that has my DPDT switch,
and hooked it to a pole that was not being used (It was trial and error to
see which side of the switch to use).  Then I run a ¼ inch patch cable to
the speed control input of the Motion Sound.  This works well, I am able to
switch both units between fast and slow speed with one switch, no problems.
I also used the advice I got on this site and used snubber circuits for the
switch, which has totally eliminated the popping sounds.

 

Well, that is the quick version.  It was a lot of trial and error, and I was
always going back and changing things as I though of better ways to do
things.  I also have left out many details, but I can tell you more.  I am
very happy with the sound.  I’m sure it doesn’t sound as good as the real
thing, but I think it is very close.  It was also a lot of fun to build.
Plus, it is in 3 pieces that are very lightweight, so it is super easy to
carry around.  I play out with it a lot.  If you have any more questions or
you want to see some pics, please e-mail me at tbroms at hotmail.com

 

Tim  

 

 

 

 

       

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