Leslie 215 switch question

[Brad1]

Have been given the task of converting a hand-controlled Leslie 215 speed control into an on/off fast/slow footswitch. It's got the Rotosonic (?) speaker that spins in the drum, and sounds pretty cool, actually. I have cleaned it well, and it's relatively quiet, mechanically.

Attached is a crude drawing (JPG) of the existing switch.

I figure I can get a Carling SPST to put in line with common black wire for on/off. That will then connect to the common of a Carling SPDT, with the red and white (fast and slow) wires connected to each side of that.

Put those in a box, and it should work? Maybe add some small 120V lamps? (Green for "on", and a red and orange for "fast" and "slow" to match up with the same color corresponding lighted toggle switch on the Leslie unit front).

Here's a weird thing. It appears that someone has added large .1uF/600V Sprague orange capacitors in parallel, like the drawing, from the black wire to each speed wire. No matter which position the switch is in (fast or slow...it's off when the switch is "off") 120VAC appears at both lugs as referenced from the black.

The thing works properly like that, but I can't figure out how. I can't seem to wrap my mind around this. It seems it should cut off the side that isn't engaged? I don't know who added those, or why...but they are just twisted together and crimped with those twist-on electrical caps. Any clues?

Does it look like this would work as I am thinking? Or, do I need to do something a bit different? I just want to confirm before I order parts. Any help will be appreciated.

Thanks,

Brad1

[52 Bill]

Here's a weird thing. It appears that someone has added large .1uF/600V Sprague orange capacitors in parallel, like the drawing, from the black wire to each speed wire. No matter which position the switch is in (fast or slow...it's off when the switch is "off") 120VAC appears at both lugs as referenced from the black.

Those caps are common in Leslie circuits. They are there to reduce the switch contact wear. I think that the voltage you are reading is caused by the fact that the black wire is the hot and the two other contacts are connected to the neutral side through the windings of the motors.

I'm surprised to see that much voltage on the speed switch, as normally most Leslies are under relay control. Has this unit been modified or "repaired"?

I really don't like the idea, but if you build the switch that you describe, be sure to ground everything that is metal and insulate all connections really well.

[Brad1]

Yeah Bill,

I was wondering about the grounding issue, and will have to find a way to address that. It is basically original, except for those caps, and the disconnected signal routing wires (from the Organ/Echo switch). So, I'll just wire as planned, with regards to those caps.

The original control box is plastic, as in attached page 5 pic, and it is wired directly to the circuitry in the cab with the 3-conductor wire, as shown in page 8 pic. I may have to get a 4-conductor wire capable of carrying these three 120V wires and ground, and make sure to ground everything, including adding a grounded power cord in place of the non-grounded one. And, I'll be sure to shrink-tube all voltage wires well.

It also contained an "Organ/Echo" push button that would interrupt the signal flow of the original speaker to run back through this thing, and you could switch from Hammond speaker to the Leslie, as in page 8 pic. Don't need that. Will connect a 1/4" jack directly to the speaker leads (that go to that weird stationary endcap to make contact with the rotating speaker).

I was thinking of an aluminum box, but maybe a good, solid plastic one would be better and safer? Where to find one?

I'd hate to have someone stomp on this thing with bare feet, and get buzzed!

I'm also going to print out warnings for him. Like that the footswitch DOES contain high voltage. And, "Use the speaker with a tube amp at your own risk. Because of the nature of the spinning contact to the speaker, there is no guarantee that contact will maintain constant continuity, and amplifier failure may be possible!"

I took a chance with it, and it sounded pretty good. Slow was like a very lush chorus. Fast had that "Cold Shot" sound down. That little rotating 6x9 seems to take some abuse, and pumps out a surprisingly wide frequency range.

I was just asked if I could make this work, and I think I can...with some cavaets stressed to the user.

Thanks, and if anyone else has any useful comments, please chime in?

Brad1

[Enzo]

The caps help keep the switch contacts from arcing, they extend the life of the switch. They also serve in doing that to reduce pops or other transient noises in the system when the switch is thrown.

If black is ground, then the AC reading is coming through the motor winding - sounds normal to me. Just as you can take open the switch on the wall for your ceiling light and find 120v on the switch coming through the bulb up top.

It is normal for a switch that turns power on and off to something for that power supply voltage to be across the switch in the off position. Think about it - classic battery, bulb and switch series circuit. Switch makes the bulb go off or on. In the off position, what voltage is measured across the open switch contacts? The battery voltage.

If you are concerned about the tube amp use, INCLUDE a safety resistor across the amp connections. 100 ohms or something will be sufficient to protect the amp and still not suck any appreciable power from the system if the speaker contacts fail in the rotary section.

DOn't obsess too hard on this, it really is the proverbial table lamp circuit. It just has motors instead of bulbs.

SOme Leslie switches switched relays, some switched the motors direct. Later ones used triacs instead of relays.

[Brad1]

Thanks Enzo,

The resistor across the speaker would be a good back-up safety feature, so that'll be easy to pop in there.

Yeah, i just couldn't wrap my head around that switch exhibiting voltage in either position, but it makes sense since you guys explained it.

Thanks,

Brad

[cowhands1130]

power and speed conversion on leslie

hello, i have a leslie motor and i am trying to hook it up to a wah pedal for power and speed. could anyone help explain this to me? i would really appreciate it. the motor has two wires coming out of it.

thanks so much.....

[Brad1]

Cowhands...

You really should have started a new post for your question since it has nothing to do with this thread.

You also didn't post any info on model or anything else that would help answer your question. Most Leslies are either fast or slow, and can't be speed-controlled by a pot, unless you do some fancy electronics...if it's even possible then. The speed is usually controlled by simply turning it on or off, and/or switching from fast to slow and back.

Anyway...about my project. I hate the idea of running 120VAC through this, but I have found some 4-conductor wire, and I'll ground it. I also found some "Performix Plasti-Dip" rubber-coating spray that I'm going to apply several coats to the inside and bottom plate (inside) of the chassis. With careful soldering, careful heat-shrink lead covering, rubberized internal insulation, and grounded...this pedal should be about as safe as I can make it. The most worrisome part would be the wire from the pedal to the cab getting abused and shorting out.

I may even research the idea of installing relays in the cab, with lower-voltage wires controlling them. I suppose if I mounted them in an enclosure, then they shouldn't make too much clicking noise.

Brad1

[Brad1]

Enzo...

Everything finished except finding a small metal plate for the bottom to mount the 1/4" speaker jack on, and constructing a right-angle speaker cord to use with it.

Enzo. I have a 110 ohm, 10W ceramic resistor. Would that work to buy time in case the speaker path is interrupted...for a tube amp? Is it safe to use that if someone runs a solid state amp...or is that another story? (Something in the back of my scattered brain tells me I should to ask that).

Footswitch turned out pretty good. 8 layers of rubber spray inside, grounded, graphics and sprayed on the outside with a clear enamel. Was a tight fit with those large Orange Drop caps, but I made it work.

Also put some new rubber grommets on the motor and drum mounts. The old ones were a bit squished.

Thanks,

Brad1

[Enzo]

Solid state amps do not care if they have a load or not.

If an amp puts out 20v of signal into 8 ohms. that is 50 watts.

If that 20v is across a 100 ohm resistor, that is 4 watts. A 10w resistor should be fine if the amp output falls within the specs.

[Enzo]

But such a resistor would go in the amp, not the speaker cab. Unless I missed the premise.

[Brad1]

OK, Enzo. Now I'm confused. I can't put a resistor in an amp because I don't know who will end up with this thing, or what amp they will use.

So, no resisitor on the cab, (which is what I was going to ask next...is how, for sure, if I did?), but just a warning that it might be possible to lose connectivity, and to shut off amp immediately if no sound?

Thanks,

Brad1

[Enzo]

OK, rereading: your rotating speaker has the moving contacts which might fail. is that the issue? As opposed to the common Leslie arrangement with the mounted speaker facing a moving baffle.

I could see your resistor in that I suppose. I was thinking the hard wired Leslie speaker and there would be little point in adding a resistor to that.

[Brad1]

OK, rereading: your rotating speaker has the moving contacts which might fail. is that the issue? As opposed to the common Leslie arrangement with the mounted speaker facing a moving baffle.

I could see your resistor in that I suppose. I was thinking the hard wired Leslie speaker and there would be little point in adding a resistor to that.

Exactly. It's actually got two places where it could potentially fail, even though I've taken steps to minimize the possibility. Would I just put that resistor on the speaker input jack (- to+)? And, that resistor is safe in case a SS amp was plugged in?

Thanks,

Brad1

[Enzo]

The resistor is going to extract its percentage of power regardless. The resistor has no idea what kind of amp is producing that power. As to the SS amp. All it knows is hte total impedance of hte load. That 100 in parallel with 4 or 8 won;t alter things much.

[Brad1]

The resistor is going to extract its percentage of power regardless. The resistor has no idea what kind of amp is producing that power. As to the SS amp. All it knows is hte total impedance of hte load. That 100 in parallel with 4 or 8 won;t alter things much.

OK. Everything's connected, and working great. The thing is probably safer than it was before...except it has 120VAC running through the footswitch...which I've grounded directly to the AC plug ground pin. But, I've written out a "DON'T" list for whoever uses this thing.

I'm not sure I've got the theory behind that resistor right in my head. I attached it across the input jack, it's an 8-ohm speaker...and it measured ~6.4 ohms at the jack. Not much difference than normal.

The signal will obviously take the path of least resistance, so only a tiny percentage may be soaked by the resistor while the majority goes through the speaker...right?

If the connection to the speaker fails, the amp will then see a 110-ohm, 10W resistor load...not exactly an ideal load. Obviously this will keep the amp from seeing a complete open. But, what effect can a 110-ohm load have on a tube amp? Is this in there just to buy a bit more time to turn the amp off before the tubes or output transformer fry? Tell whoever that "if it fails to produce sound, turn the amp off IMMEDIATELY"?

The initial connecting cap (which remains stationary) that fits onto the spindle of the drum was just hanging loosely, and may have been subject to gravity originally. I tied the wires down close to the hole to keep it from moving, and stretched a nylon zip-tie over it and stapled that down to keep it held in place. Should minimize the chances of disconnect. Now, it should only be the point of the spinning contacts that may fail.

This thing actually took a BF Bandmaster dimed. Had to back off the bass a BIT, but, it took more than I thought it might, with that little 6x9 speaker. Actually, voiced pretty good for guitar...better than the 825's I did in Denver.

Thanks,

Brad1