Rotosonic Conversion

[Bobmann]

I thought you all would be interested in this project.
A customer requested me to convert a Leslie with a Rotosonic lower to use a standard 122 drum.
Actually, I have 3 of them to do, and if this is successful, perhaps several more.
I removed the entire lower shelf and made a new one that is an exact copy of one from a 122.
Since I did not have an upper bearing support bracket, and these are very rare, I made one of these as well.
The entire Rotosonic drum is in a different location than the 122 drum, so the lower bearing also had to be relocated.
The dimension of the drum shaft ended up needing to be a little shorter, so I just made a new shaft and pulley.
I had a spare drum to try it out, and it spins perfectly. The next thing I will do is to duplicate the drum itself.

[geoffbrown]

There's a video on YT of some doing this very thing ,they have turned a leslie 700 into a 770

[Sweet Pete]

Thanks for sharing bobmann! Nice carpentry!
Great idea if you have a 'Rotosonic' you need to make a traditional box from.
This 11 pin style HL722 is a good candidate for such a mod.It is in almost new condition.
Will be using an empty 122 box though!
Had one given to me a year ago that is quite beat up.....but the baffles are 'correct'.
Now that I have an 11 pin C2D 'clone' this makes sense!
Other than sorting out the x-over issues it's an easy swap me thinks?

[Bobmann]

I pretty much have the drum figured out, just a few adjustments to do.
One thing I did not anticipate was that the motor needs to be turned over; the 710 had it under the shelf, the 122 is on top. I need to get some springs to make the slow speed motor to work right.

[Sweet Pete]

The orientation is similar on the oldest (pre '63) and newest (post '83).
The ones built in the middle('63-'83)......such as 122/147/760/770 have different mounting and springs for sure.
My carpentry leaves much to be desired compared to yours......but this mod is quiet and works just like a 145!
Getting the upper idler quiet with the stack at the side instead of the middle? Once I had the correct height is quiet as well!
Had to shim the upper stack to match,works just like a 145.Used a 760 upper motor cover box!
Never was impressed by the 'inertia' difference of a single motor 'two speed mod'.
Those mods don't exactly nail the ramp time on the bottom IMO.

Quite sure Wes Garland has modded a 710 too!
Sold my 710 a long time ago,never got paid.....a deal I got burned on.
The guy still calls me inviting me to play for free.....must have dementia....

[shimoda]

Gotta follow this as I just picked up a pair of 715s that need a little work but I would love to convert one or both to be more 122 like. Would love more info on the changes to the pulley/shaft you had to make. Curious about having you make a couple more of these (and upper bearing maybe) while you are at it?

[Bobmann]

The Rotosonic motor has a different mounting bracket and different hole pattern as well as distance of pulley to the mounting surface is different. Rotosonic is on the left..
Rotosonic motor pulley is larger dia and shorter than 122.
Rotosonic on left.
Rotosonic drum pulley is larger, the pulley is in a different location in the shaft, and the shaft is longer.
Rotosonic on left.

Also the Rotosonic motor is designed to be hung on the bottom of the shelf, the 122 mounted on top so the upper spring is different.

As soon as I get all this documented and put together, we can talk about my making parts for others. I want to complete one from start to finish to make sure it all goes as planned.

Bob

[Sweet Pete]

Another caveat is the depth of lowboy (222/247) lower rotors.Shallower than 122/147.......and of course the corresponding motor brackets etc.
Wes says his turned out nice and quiet too!Getting the bottom plate squared up for the spindle is 'exact' type stuff!
Filling the old mount and drilling a new one seems easier and maintains structural integrity.

[Bobmann]

For the lower bearing, I routed out a pocket in the bottom of the cabinet to secure the bearing. I made a bearing holder out of oak that holds the bearing securely; it is a light press fit. I used the bottom half of the bearing holder that was in the cabinet. That bearing holder is glued and screwed to the bottom of the cabinet. To ensure alignment, I made a template that puts that bearing holder in the exact location and secures it while it is glued and screwed.
Note that all the screws are machine screws and T nuts.
I have the advantage of being able to design all this on AutoCad and the CNC to machine the parts to pretty close tolerances.

[shimoda]

The Rotosonic motor has a different mounting bracket and different hole pattern as well as distance of pulley to the mounting surface is different. Rotosonic is on the left..
Rotosonic motor pulley is larger dia and shorter than 122.
Rotosonic on left.
Rotosonic drum pulley is larger, the pulley is in a different location in the shaft, and the shaft is longer.
Rotosonic on left.

Also the Rotosonic motor is designed to be hung on the bottom of the shelf, the 122 mounted on top so the upper spring is different.

As soon as I get all this documented and put together, we can talk about my making parts for others. I want to complete one from start to finish to make sure it all goes as planned.

Bob

Notice you are in NC, might be able to visit some time and see this conversion in person? :)

[Bobmann]

Please PM me. I am always happy to have visitors. I am almost finished with this project, and the customer wants to pick it up probably the weekend of July 6. I have 2 others that I need to complete, but I have other projects before I get started on these so it will be several weeks before I get to them.

[Bobmann]

Finished!
Ready to start in the next ones. From what I have learned on the first one, these should get easier with each one.

The Leslie plaque was made from clear acrylic, carved and painted from behind.
Don't know why these pics turned sideways, they are right on my PC.:-P

Bob

[NittyRanks]

I think Wes did something like this to a 710 cabinet.

[shimoda]

Finished!
Ready to start in the next ones. From what I have learned on the first one, these should get easier with each one.

The Leslie plaque was made from clear acrylic, carved and painted from behind.
Don't know why these pics turned sideways, they are right on my PC.:-P

Bob

Looks great! Imagine the fit with the amp housing is tight but I bet it sounds great. Waiting on some 11 pin connectors to hook up my A-105 to the 715 to see A) if it works, B) how it sounds. Picked up a really nice M-101 this week for $30 that had not one but two LCC on it. While it's not ideal, I can use it temporarily. One kit is for a 122 or 147 and the other is for modern 11 pin cabs. He had a 710 hooked up to it. Dude put all new tubes in both AO-29 and AO-44 amps as well as new caps on the AO-29. Sounds really nice and the reverb is deluxe. I'll have to make it up your way in the future to get help with converting both of the ones I have.

[shimoda]

Finished!
Ready to start in the next ones. From what I have learned on the first one, these should get easier with each one.

The Leslie plaque was made from clear acrylic, carved and painted from behind.
Don't know why these pics turned sideways, they are right on my PC.:-P

Bob

That Leslie plaque is about as cool as it gets!