Rotary Switches: shorting vs non-shorting

[moro]

Hello,

I want to use a rotary switch to switch between several different input capacitors on a Rangemaster. There seem to be two types: shorting and non-shorting. It sounds like "shorting" means that contact is made with the next position before contact is broken with the current position. Vice versa for non-shorting. Do I understand this correctly?

Which one do I want to get? Does it matter? Thanks.

[CGDARK]

Hello,

I want to use a rotary switch to switch between several different input capacitors on a Rangemaster. There seem to be two types: shorting and non-shorting. It sounds like "shorting" means that contact is made with the next position before contact is broken with the current position. Vice versa for non-shorting. Do I understand this correctly?

Which one do I want to get? Does it matter? Thanks.

Yes, you are right. "Shorting" is "make-before-break" and "non-shorting" is "break-before-make"  and I would use non-shorting types.

CG

[moro]

Yes, you are right. "Shorting" is "make-before-break" and "non-shorting" is "break-before-make"  and I would use non-shorting types.

Great, thanks!

(What's the reasoning behind this?)

[Zben3129]

I'm not positive on this, just speculating, but I belive it is so you dont have 2 caps active at once. Im sure it would work either way, but I think having no caps for a split second is probably safer than 2 caps

Again, just guessing   

[Mark Hammer]

Whether you use a shorting or nonshorting switch, the net effect will be the same: currently unused caps will generate a "pop" when they are eventually placed in circuit.  For that reason, I tend to recommend one of two other strategies: caps in series, or a blendable-bypass path.

When caps are placed in series, their combined capacitance can be calculated by 1/Ca+1/Cb+1/Cn = 1/C.  So, .22uf in series with .22uf = .11uf.  Place .47uf, .22uf, and .1uf in series with each other, and you get .06uf.  It gets interesting when you shunt one of the caps with a straight-wire.  Shunt .47 and you get .068uf.  Shunt the .1uf instead, and you get .15uf.  By use of a 3-position SPDT toggle (center-off) you can use a couple of caps and shunt either none, this one or that one, and achieve three different capcitances.  The beauty of it is that all caps have a path to drain residual stored charge at all times, so you never get an audible pop the way you do with a rotary switch that leaves caps "hanging" and brings them into contact.  Toggles take less space than rotaries, freeing up plenty of chassis surface for other things.  The downside is that: a) you're limited to 3 choices, b) sometimes the math doesn't work out in your favour.  of course, is you want more than 3 choices, you can always use a rotary to provide selective shunt ing of more than 3 caps.

Alternatively, you can use an approach Joe Gagan use productively on a number of his pedals, which involves having two parallel input caps, one of which is a much larger value than the other.  The smaller one provides the default path for the signal, and the larger one is in series with a pot.  As the pot resistance is decreased, more and more signal can efficiently pass via the larger cap, letting more bass in.  Doesn't perfectly capture what selecting multiple caps does,but comes very close with less hassle and no popping.

[Gus]

Not going to give an answer but a HINT

look around the web for some switchable EQs.  Things like 1081 etc. look at the wiring

[joegagan]

there are upsides and downsides to the pot method you mention Mark.

it is nice to see the mentions of using this trick in my designs , but i have to say again, it came indirectly to me from Jack Orman.
I think it was Oscar Bruil who emailed it to me in 2000, he had seen it in one of the diy forums from Jack around '98(?)

About the only thing i can take credit for is seeing the potential of this control in a marketable series of fuzz and boost pedals, which as far as i know , did not exist in a widespread way in commercial pedals circa 8 yrs ago.

in the intervening years, a pretty impressive number of commercial pedals have a feature that is pretty obviously either using this method or something very similar. A half dozen are out there that I know for sure use the exact method i did.

the reason i liked it was that it shaped the tone at the front of the circuit rather than dragging gain down with a cap to ground at the end of  the circ. i just liked this direct sound. similar to the reason a tweed champ sounds so great, fewer places for the tone to bleed to ground!

one of the downsides was that my circuits got a lot of flack in the market due to 'too much treble'. in my rig they were awesome, and gave me that extra cut i needed to rise above my loud drummer. i guess a lot of the complainers had rigs that were inherently more trebly than mine, and/ or the treble bleed cap so common on most electric guitars sold nowadays were adding to the problem.

anyway, back to the pros and cons of the pot method to sweep a larger cap in series with a smaller one:

pros -  infinite variability  between the two extremes, rather than limited fixed positions; to my ears, having two caps in series usually adds a nice harmonic texture to the tone, especially at the early stage of the circuit; plus the lack of popping.

cons-  adding series resistance can possibly add noise, and in some cases you can hear static noise as you spin this control. also , the aforementioned 'too much high end' condition can be made worse because you are keeping that high pass cap in circ at all times.

[mattumbi]

I used the 2 caps & a pot Joe & Mark described on the input of my rangemaster circuit. I really like the variety of tones it provides.

[joegagan]

or, to keep the highs a little less intense - I haven't tried this but I should: (diagram is for a pos ground circ)

[moro]

Wow, thanks for all the responses.

Mark, is this what you meant? (sorry for the sloppy drawing)



Joe, I really like the idea of having a continuous control. Thanks for the schematic!

[moro]

Oh also, why such a large value on the second input cap? I was just reading RG's Rangemaster article and he says that an 0.15uF input cap should give you full gain across the entire frequency range. Before reading that, I was thinking 0.1uF, apropos of nothing, so I was a bit surprised to see the 2.2uF cap in there.

[joegagan]

i wasn't specifically referring to the rangemaster, although a 2.2 input cap might make it a nice fuzzy tone.
i generally like the way gainstages react when i hit them with a 2.2uf up to 10 uf input cap. I use telecasters, so this is a nice way to round them out.

you also don't hear as drastic tone control effect when a 1.0 uf is the larger in the sweep cap/ pot application.

[moro]

i wasn't specifically referring to the rangemaster, although a 2.2 input cap might make it a nice fuzzy tone.
i generally like the way gainstages react when i hit them with a 2.2uf up to 10 uf input cap. I use telecasters, so this is a nice way to round them out.

you also don't hear as drastic tone control effect when a 1.0 uf is the larger in the sweep cap/ pot application.

Cool, thanks for the clarification. I'm itching to try this now. I just need to find some transistors.

[Mark Hammer]

Wow, thanks for all the responses.

Mark, is this what you meant? (sorry for the sloppy drawing)



Joe, I really like the idea of having a continuous control. Thanks for the schematic!

Yup, that's exactly what I meant (nice drawing BTW).  The values were just ones I pulled out of the air without reference to the actual Rangemaster schematic, not recommended values.  Sorry for the misleading impression.  The same math applies to the "proper" values too, though.

I don't think Joe's method or the one drawn should be put in competition with each other.  Some folks like the predictability of presets, and some like the flexibility of continuous dials.  Six of one, half dozen of the other.  But BOTH can be one heckuva lot quieter, simpler, and less problem-ridden than a rotary switch.

Inidentally, one of the things I've never seen discussed or alluded to is the possibility of sticking a cap and inductor in series in the bypass path, so that a selected resonant band can be blended into the input signal.  Could be interesting.

[moro]

I don't think Joe's method or the one drawn should be put in competition with each other.  Some folks like the predictability of presets, and some like the flexibility of continuous dials.  Six of one, half dozen of the other.  But BOTH can be one heckuva lot quieter, simpler, and less problem-ridden than a rotary switch.

Good point. The Rangemaster seems like a fun build so I will probably make one of each.

Inidentally, one of the things I've never seen discussed or alluded to is the possibility of sticking a cap and inductor in series in the bypass path, so that a selected resonant band can be blended into the input signal.  Could be interesting.

I'm having trouble picturing this. What would it look like?

[Mark Hammer]

Inidentally, one of the things I've never seen discussed or alluded to is the possibility of sticking a cap and inductor in series in the bypass path, so that a selected resonant band can be blended into the input signal.  Could be interesting.

I'm having trouble picturing this. What would it look like?

Simple.  A cap, followed by an inductor, followed by a variable resistance.  Normally, that alternate path provided by the larger cap lets everything above freq X through, and if it is a much lower frequency than what the primary cap would let through, then you've provided a path for bass content to reach the transistor base.  The inductor in series with the cap would simply make that alternate path a route for content within a specific band with upper and lower bounds, rather than simply everything above X.

[moro]

Simple.  A cap, followed by an inductor, followed by a variable resistance.  Normally, that alternate path provided by the larger cap lets everything above freq X through, and if it is a much lower frequency than what the primary cap would let through, then you've provided a path for bass content to reach the transistor base.  The inductor in series with the cap would simply make that alternate path a route for content within a specific band with upper and lower bounds, rather than simply everything above X.

So, like Joe's schematic but with an inductor + pot after the 2.2uF cap?