How much Noise Does a Rotary Switch Create?

[RobRed]

I am rewiring an HSS Strat-like Ibanez. In consideration of how to approach it, I came along discussions of using a rotary switch as a capacitor selector in order to augment the tone control options (I have found that this is frequently incorrectly described as being like a Gibson Varitone). Unlike other discussions I've seen, where only one of the two poles of the switch is used, I derived what looks like a nice clean way to wire the device that uses both poles of the 6 Position, 2-Pole rotary switch. I liked it and would prefer to use it because all the connections are clean, single, wire-to-terminal soldered joints, without the multiple wire connections and protective taping required of other modes of doing this (I have included an attachment in which my initial schematic is labeled "Figure A").

Then I came upon another discussion of the same topic on this site, that was initiated about a year ago. I figured if I added on to a thread that old I'd get no response, so I've started this new thread on the same topic. The fellow who started that original thread primarily wanted to assure his schematic demonstrated something that would work correctly. His question, aside from resulting in his being informed that his schematic was fine, started discussion of several points on the topic. Among them is the issue that I am interested in here.

One of the responders brought up the recommendation that a 1M resistor should be placed in the device between the outer lug on one pole of the switch, where each capacitor is connected in this plan, and the common lug that then leads off to ground (I have included my version of that schematic as Figure B), as means to limit noise arising from the switch, itself, as I understood the discussion. It will be obvious that the approach, on top of including the resistors in the second schematic, is quite different, but that it is otherwise electronically equivalent.

The problem is there is no way to utilize the resistors in my plan in this fashion. I certainly can change my plan to the other if this switch-induced noise is a major problem, but I have no experience with these switches, so I do not know how big a deal the noise is that these resistors are meant to diminish. In fact, the first discussion of this device I found on line made no mention of resistors or noise, whatsoever, so I feel fairly confident I'll be okay going without, but I'd like some more input before I actually set about wiring it all up. If the noise is constant even after the switch position is selected or if it is very obvious and annoying at the time of selecting the switch position, I would certainly want to change my plan, but if the noise is relatively quiet and a minor, brief passing issue only during the instant of setting the switch position, I'd sooner go with my original plan and not bother with the extra time, work, mess, space in the cavity, and expense of adding the resistors.

Does anyone know how big of a problem this switch induced noise is and have a strong sense, one way or the other, of how important the use of these resistors is in this device? Does anyone with experience with this think it would be a major error to leave the resistors off? Thanks in advance for consideration and any suggestions.

Rob Redden

[pdf64]

Fig A will tend to produce a click or pop as the switch connects to the next cap. Each cap would need 2 resistors to prevent that. Each plate of each cap needs ato be tied to a dc reference, otherwise it can drift to any Vdc, which then causes the click when it's selected and the dc discharges.
Fig B should be fine, that's the one to follow.
By the way, your caps are drawn to look like carbon comp resistors, which is a bit confusing at first. Pete.

[Steve Conner]

What Pete says is quite true. But in a guitar there is no source of DC voltage to charge the capacitors up, so I don't see how they can generate pops. The trick with the resistors is for amp circuits where the caps have considerable DC on them: you have to make sure the cap is already charged to the right DC voltage before you switch it into the circuit. In a guitar the right voltage is zero.

[RobRed]

What Pete says is quite true. But in a guitar there is no source of DC voltage to charge the capacitors up, so I don't see how they can generate pops. The trick with the resistors is for amp circuits where the caps have considerable DC on them: you have to make sure the cap is already charged to the right DC voltage before you switch it into the circuit. In a guitar the right voltage is zero.

Thank you very much. I must acknowledge, it is always easiest to hear what you wanted to hear in the first place, but I am left happy to understand from what you've said that I can go ahead with my own plan for the wiring of the rotary capacitor selector without worrying about noise.

I have a lot to learn--I've just recently become obsessed with guitar wiring. I am a longstanding guitarist and avid woodworker, and after recent early retirement due to a physical handicap, I've come to the conclusion I'd enjoy building (and then, of course, wiring ) guitars. Now I may have to consider amplifiers, too! Anyway, the problem is, despite immense effort, I find it difficult to locate adequately detailed information on the topics. I won't trouble you with that here, though. I am going to start a new thread on that topic, so it might be a resource for other folks with similar concerns and interest, when they wouldn't look for it under the heading of "Noise from a Rotary Switch".

[RobRed]

Fig A will tend to produce a click or pop as the switch connects to the next cap. Each cap would need 2 resistors to prevent that. Each plate of each cap needs ato be tied to a dc reference, otherwise it can drift to any Vdc, which then causes the click when it's selected and the dc discharges.
Fig B should be fine, that's the one to follow.
By the way, your caps are drawn to look like carbon comp resistors, which is a bit confusing at first. Pete.

Thanks, Pete. I had a bunch of questions for you, but Steve's response simplified the whole thing for me, and as I've spelled out in a response to him, I plan a new thread on the issue of finding good resources on the topic of electronics as it applies to guitar wiring. For that reason I won't trouble you with the specific questions your response left me with at this juncture. Hopefully I'll be able to find the answers for myself!

Just to respond to your last comment. I did not draw those caps. I copied them from the ad on the web site where I purchased them to paste them into my schematics. They are called "Bumblebee Work-alike" caps, and I presume they were named after the stripes on the cylindrical body that make them look sort of like a bee. As I made the purchase, I said to myself, "These sure look like resistors!" As I understand it they are a recent re-creation of an ancient cap that was appreciated for its sound qualities but went out of favor because the materials it was made out of caused it to crumble over time. The new version is designed to mimic the sound qualities of the originals but is made of more modern materials that are purported to last. I was a bit panicked when after I made the purchase I ran into Bumblebee caps on line produced by Gibson at a ridiculous price and with very poor reviews. However, the ones I've purchased are different--they do not come from Gibson, the price was very reasonable, and I ordered them from a small German company operated by a fellow who I understand to have a long, good relationship with the guitar wiring community. I communicated with him before the purchase, and he expressed belief that they were the best, most natural sounding caps of the several varieties that he had in stock, so I am pretty excited about putting these caps that look like resistors in my guitar!

Thanks, again Rob Redden

[big_teee]

My friend and I are looking for a 5 or 6 way Rotary switch, with a long bushing.
I find Pots made that way, but all the switches I find have a 3/8" threaded bushing.
Any Ideas, It's going in a PRS Single Cut Guitar.
It must have a thicker top.
Thanks,
Terry

[RobRed]

Terry--I was looking for a special rotary switch (actually a concentric stacked one--I won't go into that, but I gave up on it). However, I did find a site where they design rotary switches to your liking using what they call their Rotary Switch Configurator. As you've responded to a bunch of my ridiculously long questions ( ), I took the time to call them. Some of the switches that they have to make special would be unreasonably expensive to buy in small quantities, but they have a standard 2-pole, 6-position rotary switch with a 1" shaft (I hope that is not too long, but the 3/4" would be a special design deal). The sales person I talked with said he could direct you to a distributor that could sell it to you if your interested. The part no. is D2D0206N. He didn't know the going retail price but thought it would be "twenty odd dollars)." The URL for the site is Electroswitch - Rotary Switch Configurator.

If you just can't do with a 1" shaft, I found a 2-pole, 3-position rotary switch with a 2" long shaft that can be snapped off to 3/4" at Rotary Switches: All Other. I've attached an image of the ad for the switch (just so you'll know what you're looking for, as there are a bunch on the page). If you can't find anything else that works, you could separate the two poles of this switch and use a mini-switch to go from pole-to-pole, and that would give you 6 positions.

If neither of those work for you and you would be comfortable doing it with whatever instrument you're working on, and if you had access to a drill press and could set the guitar body up very carefully and soundly on the drill press table, you could use a Forstner bit slightly larger than the diameter of the rotary switch, in the drill press, to decrease the thickness of the guitar face centered on where the switch goes. Then you could get away with a readily available rotary switch, say from Stew-Mac, with the usual, shorter shaft.

I hope one of those ideas helps.

Rob R

[big_teee]

Rob:
It's not the Shaft that is the issue, its the threaded bushing part.
Most switches have a 3/8" threaded bushing.
If your guitar body is 1/2" or more thick, when you stick the switch in the hole, there is no threads sticking through to thread the nut on.
I'm going to suggest that he gently do some hand routing to the area that is too thick for a regular switch.
Thank you for checking.
Terry

[RobRed]

You know, I read the word "bushing" and my brain didn't click...of course I know the length of the shaft is not the issue when I stop to think about it! I understand exactly what you're talking about. I'd just say, I called that first company that I mentioned predicting that they'd deal only with big outfits, and it turns out they'll deal with anybody if they have a product you can afford. You might just call the number on the web page and ask if they have or can not too expensively make rotary switches with the longer bushing. I don't think that is any more outrageous a question than mine, as to whether they had one with the longer shaft. The fellow who answered the phone was actually quite pleasant and helpful.

There is a bigger issue from my point of view. I am a woodworker, and to me the idea of using a router for this purpose is scary. It strikes me you'd have to make quite a fancy jig to sit on the back of a guitar with an irregular surface in order to assure you don't go tearing into something you don't mean to (including yourself as well as the guitar). That's why I would recommend, if you don't have access to a drill press, hunting down someone you know who does--you might even talk to a local high school shop teacher. If the guitar is clamped securely in the right position, you can use a Forstner bit in the drill press with much more control than you could use the router, the depression would be exactly the right shape (i.e., round and cylindrical!) and diameter, and it would not be hard to make it about exactly as deep as you want it. Aside from whatever you needed to clamp the guitar body in position on the drill press table, all of which you could certainly pad or cover in a way that it would not damage the guitar's finish, no part of the drill press other than the cutting bit would come in contact with the instrument, whereas with a router, you would need to do some pretty nifty work to create a jig that would allow you to cut the depression in the cavity without representing a significant risk of damage to the finish. I would think most router work on a guitar body is best done early in production, when it is still a flat piece of board and it is nowhere near being finished yet.

I hope that helps...Rob R

[big_teee]

I said route by hand, I really had in mind hand tools.
No to the Router.
I would probably use some hand chisels, and perhaps a hand drill with some severely taped up bits, to control depth.
I'm a retiree also. I usually know my limitations.
I take things slow and thorough.
I installed Electronic Phone offices for 42 years, used to doing a lot with nothing.
If it were my guitar I would rather work on making the guitar where it would use standard parts, vs. Having to put High dollar parts, on a cheap guitar.
I will pass the info on to my friend.
Terry

[RobRed]

Language is funny. When you said "rout by hand", I presumed you meant to use a router by hand! Again, I'm just suggesting calling those folks on the possibility that they have a part that is not too expensive as a standard part that would save the work of altering the control cavity on the guitar. I certainly don't mean to suggest you should buy some ridiculously expensive piece of hardware. At the same time, I am confused with your saying, "on a cheap guitar." I thought you had mentioned a PRS. How cheap do they get?

I take things "slow and thorough" in my own way, too. That's why I'm driving everybody crazy with all these questions before I dive in.

Rob R

Rob R