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Old 28th May 2006, 12:57 AM   #1
dfro is offline dfro  United States
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Default DIY Leslie speaker cabinet crossover questions

I would like to build a Leslie speaker cabinet for an organ from scratch, including the crossover, and a DIY tube amp. What I want to do is split the cabinet into two pieces so that I don't break my back hauling it around to gigs. I also want the tube amp visible so that the red glow of the tubes can contribute to the vibe on stage!

The original values for the 2nd order crossover are 3.2 mH and 5.2 mH, 12.5 uF and 7.8 uF. I think they mean uF, since no unit of measure is provided in the schematics I downloaded for a Leslie 145. I know I am really revealing my ignorance at this point.

How would anyone suggest I match those values, since there are no components for sale that exactly match. Could I, for example, run a 5.0mH and a .20mH air coil inductor in series to get an inductance of 5.2mH? Or should I buy a higher value inductor and peel away some of the windings? Is there a cheap way of measuring these inductances without buying an expensive LRC meter?

Could I run a 8.2 uF and a 4.3 uF cap in parallel to get the 12.5 uF value I need? Other threads have mentioned this as a possibility. Are there any considerations I should know about?

I did not lurk for very long before jumping in with some questions, so I apologize if they have been asked and answered many times before.

Thanks for any advice.
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Old 28th May 2006, 07:33 AM   #2
dfro is offline dfro  United States
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This thread answers my question about tweaking the inductance values:

OK to wire 2 inductors in series?

I think I will get a $50 lcr meter on ebay.

Being new to audio electronics, I still wonder, how critical is it to tweak inductance and capacitance values to exact calculations. Is there a margin, + or -, that designers accept?
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Old 28th May 2006, 11:58 AM   #3
lndm is offline lndm  Australia
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In my opinion, to within 10 percent will be OK in many cases. The differences are not as severe as they may seem, especially for a musical instrument. And I'm not downplaying that, I use one myself. Still though, it warrants checking.

Though it is not that severe, I do have an issue that serves to illustrate. When I play a D in the octave above middle C, it plays a few dB louder. It makes me feel you'll have no problem finding problems. Much easier than Hi Fi speakers
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Old 28th May 2006, 09:41 PM   #4
dfro is offline dfro  United States
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Quote:
It makes me feel you'll have no problem finding problems.
With all of the spinning cones and baffles, the louvres, motors, etc, it is a very uncontrolled setup from a dampenning and resonance standpoint. But, all of that stuff bouncing around is part of the leslie sound - which I know is what you are saying. Breaking the cabinet into two pieces is also going to change it's resonance characteristics.

If there are some glaring resonance problems, what might I do to improve things?

Thanks.
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Old 28th May 2006, 10:19 PM   #5
poobah is offline poobah  United States
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dude...

It's the Hammond that breaks your back. The Leslie feels like a twinkie after moving the keys...

Have you considered buying a smashed up Leslie? Then you can build a new box the way you want and have all the mechanicals and electronics for rebuilding. Just the amp will cost you 400-500 to scratch build.

I just got done rebuilding my 122. Ask if you need any leads on repair parts etc...



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Old 28th May 2006, 10:38 PM   #6
lndm is offline lndm  Australia
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My Leslie has a nice wooden enclosure with a cedar looking rear panel. It does resonate quite a bit, but at least it was made that way.

I did play with a blanket inside. Now thats an easy way to kill the sound. I ended up putting it against a couple of the walls just to lower the resonances, but left the main volume free.

I would guess that if you built a modern audiophile style braced enclosure, the sound would be so different, maybe even unsuitable, possibly critical sounding.

One thing I would recommend is cleaning/servicing the tremolo horn motor.
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Old 30th May 2006, 06:22 AM   #7
dfro is offline dfro  United States
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For starters I want to run a B3 clone like the B4 program through a leslie cab. I do not have a B3. There are some great diy leslie blogs on the net especially:

http://www.users.bigpond.com/johnacollins/hammond.htm

His solution for getting the scalloped louvres is brilliant. I am interested in making the speed of the rotor rotation more controlable - most likely I will use PWM (pulse width modulation).
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