Dual ganged rheostats?

[Enzo]

SO you can find the rheostats with through-shafts. Then mount them one behind the other and couple the shafts. If it is an L-pad circuit, watch the one up while the other down thing, or at least watch the legs.

But keep in mind this, a 50w rheostat is rated for 50 watts across the whole thing. If you plan to dial down a lot, make sure you get a part rated for the power dissipated in the amount of resistance used.


Are you planning to replace what would be a commercial L-pad with your homade one directly? I don;t see how a L-pad made from two discrete rheostats would function any different from a L-pad which is two of them in one package. Or are you putting other parts in the middle of it?

Typically, ganged high power components like that would be custom orders. I would just hunt up 50w rheostats and see which ones accommodate connecting their shafts.

And if you are handy, instead of on the same shaft, you could place them side by side with a crank on each shaft - the way old Steam railroad locomotives connected the driving wheels together. SOmewhere around here I have a rig like that from some old radar set. You turned on dial and it cranked three pots around. Actually, a rack and pinion steering works sorta like that.

[Chuck H]

Thanks guys. In truth I know that most L-Pads are just ganged rheostats. But my only experience with a comercially available inductive model really turned me off to such units. Besides, look at those things. How in the world do they rate those tiny rheostats so high in power capacity. I have to assume they are saying their unit will handle a system of a particular "peak" wattage. It's really poor how there are so many poorly regulated standards for rating output and power capacity in audio gear. As Enzo said:

But keep in mind this, a 50w rheostat is rated for 50 watts across the whole thing. If you plan to dial down a lot, make sure you get a part rated for the power dissipated in the amount of resistance used.

Exactly. I designed my attenuator to handle the actual overdriven output of a clipping tube amp. ie: A pair of EL84's producing 16 clean watts in one of my designs actually puts out closer to 27 watts clipping with peaks that go even higher. I use a 25 watt rheostat with that model but:

Are you planning to replace what would be a commercial L-pad with your homade one directly? I don;t see how a L-pad made from two discrete rheostats would function any different from a L-pad which is two of them in one package. Or are you putting other parts in the middle of it?.

Yes, I am replacing the L-Pad with my own thingy. It does function a little differently and there are other parts sharing the load.

SO you can find the rheostats with through-shafts. Then mount them one behind the other and couple the shafts.

Right. Thats the observation I mentioned above. Looks easy enough.

I would just hunt up 50w rheostats and see which ones accommodate connecting their shafts.

The Ohmite products do have a through shaft design, but you do need to have a sort of chuck that joins them. It won't be hard to make it.

And if you are handy, instead of on the same shaft, you could place them side by side with a crank on each shaft - the way old Steam railroad locomotives connected the driving wheels together. SOmewhere around here I have a rig like that from some old radar set. You turned on dial and it cranked three pots around. Actually, a rack and pinion steering works sorta like that.

Fortunately my design doesn't require an elaborate setup like that. I probably could fabricate it. But I really wouldn't want to. It is an interesting idea though if you needed to adjust for a specific taper. You could use cammed gears or pullys. I'll tuck that away in my "how'm I gonna solve this" file in my head.

Thanks for always stepping up guys.

Chuck

[Enzo]

What I meant was, if you have a 50w rheostat of for example 100 ohms, and you dial it down to 4 ohms, you cannot still crank 50 watts across that 4 ohms. The rating is only for the entire resistive winding.

I don;t know how much inductance they might have, but 50w rheostats are going to be wire wound.

[Chuck H]

Thanks Enzo. I do know that. My system shares the current proportional to the attenuation level between the speaker, other components and the rheostat. I never bothered with exact figures but I haven't had any excessive heat or failures.

I read here that the inductance on a wire wound resistor is really insignificant as it applies to guitar amps and speaker loads. The post made enough sense that I never researched it for myself. I did have a problem during development of this attenuator with one of the inductors EMF "talking" to my single coil pickups. I solved that one. I suppose it's possible that a resistor, or rheostats inductance could do the same since this phenomenon isn't speaker dependant for frequency reproduction. But no problems so far.

Chuck