Simple Wiring for a Simple Mind

[RiffWildly]

I'm going to be doing probably one of the most simple wiring setups possible on my new build, but still have a couple of complete basic questions ...

See diagram below, found somewhere on the trusty old Interweb. Two P90s, one 500k volume, one 500k tone, one 3-way switch. I get most of the basic wiring; my questions are about the specific components.

The volume pot says "log" on it, which I take to mean that it is an audio taper. Conversely, the tone pot says "linear," which I take to mean a plain old pot. Is that correct? What is the "prefix" that is being referred to in the diagram (A or B)?

Also: I know different people like different cap values, but what would be a good range of values if I wanted to try out a few different caps? Say, .01, .022, .047?

And the caps themselves, are the "legs" polarized, or doesn't it matter which way you wire it? I've also heard that the voltage doesn't really matter for the low-voltage system of an electric guitar harness. True?

Anything else I am overlooking? Thanks all!  :redflag:

 

[stratamania]

log is short for logarithmic, but not sure on the other question.

 

[Cagey]

The volume pot says "log" on it, which I take to mean that it is an audio taper. Conversely, the tone pot says "linear," which I take to mean a plain old pot. Is that correct? What is the "prefix" that is being referred to in the diagram (A or B)?

"Log" is for "logarithmic", which is usually an audio taper. Linear means what it says. What they're talking about is how the resistance changes over the range of adjustment. On an audio taper pot, the resistance changes slowly at first, then increases rapidly. On a linear taper pot, the resistance changes in direct proportion to where the wiper is set. The reason you want an audio taper on the volume control has to do with how the human ear perceives sound pressure levels. Since the tone control deals with frequency response instead of loudness, it should ideally be a linear control. In practice, most folks use the same pot configuration for both.

Also: I know different people like different cap values, but what would be a good range of values if I wanted to try out a few different caps? Say, .01, .022, .047?

This is a matter of taste. But, the general rule of thumb is the larger the cap the muddier it gets and the less likely you are to use it. Personally, I think a .022 is size of choice to get a good range of response. Anything more or less than that just seems to take you into useless territory. .01 doesn't do jack, and .047 does too much.

And the caps themselves, are the "legs" polarized, or doesn't it matter which way you wire it? I've also heard that the voltage doesn't really matter for the low-voltage system of an electric guitar harness. True?

Caps are "polarized" to different degrees. On an electrolytic, they're almost like diodes. Put 'em in backwards and bare minimum they just won't work, and quite often they'll blow up. Others have a polarity marking, but what they're telling you is which leg is connected to the outside plate. Knowing that, you connect that side to common/neutral/ground to gain some shielding. In a guitar, the voltages and frequencies are low enough that it doesn't matter. But, noise rejection is often a game of inches, so you govern yourself accordingly.

 

[RiffWildly]

Caps are "polarized" to different degrees. On an electrolytic, they're almost like diodes. Put 'em in backwards and bare minimum they just won't work, and quite often they'll blow up. Others have a polarity marking, but what they're telling you is which leg is connected to the outside plate. Knowing that, you connect that side to common/neutral/ground to gain some shielding. In a guitar, the voltages and frequencies are low enough that it doesn't matter. But, noise rejection is often a game of inches, so you govern yourself accordingly.

Okay, on to polarization: I'm sitting here looking at an orange drop cap, and I don't see any indication of polarity. Obviously, there must be a way to tell, although it sounds like it doesn't really matter in this application. Nevertheless, I'd still like to do everything properly. So how can I tell?

 

[line6man]

I would not recommend using a linear taper pot on a tone control. Ideal tone control behavior is to have a very high resistance at the end of the sweep to give you a "bypass" setting, but to have that resistance quickly drop down into a considerably lower range as soon as you roll down from 10. Audio taper pots give you the steep drop off, but linear taper pots spread their resistance evenly throughout their sweep. The result of this is that the control has little effect throughout most of its sweep, until you get toward the end, and then everything comes in all at once like an on/off switch.

 

[Cagey]

Okay, on to polarization: I'm sitting here looking at an orange drop cap, and I don't see any indication of polarity. Obviously, there must be a way to tell, although it sounds like it doesn't really matter in this application. Nevertheless, I'd still like to do everything properly. So how can I tell?

They're not always marked, but when they are, it's usually a line marked next to the rest of the part#/value print to indicate the outside foil connection like this...

That black line on the right means that's the lead that you should treat as the negative/common/neutral/ground.

It's really a pretty minor thing, though, so you might not see any indication all.

 

[Jumble Jumble]

Any discussion of capacitor polarity is moot in the context of guitar wiring, because guitars are AC not DC. That is, the polarity changes rapidly (at the frequency of the signal in fact, what a coincidence!).

So wire your capacitor any way round you like.

 

[RiffWildly]

So this is a little off the wall, but as I look at my simple diagram above, it occurs to me ... it would be pretty easy, wouldn't it, to pop a small on/on switch into that yellow hot wire from the 3-way switch, with one line going out to the volume cap as shown, and another line going straight to the output jack, right? And then I could bypass the pots altogether, but still be able to choose pickups, correct? That might be a pretty raunchy option with two P90s, no?  :tard:

 

[Cagey]

Yes. And you wouldn't be the first one to do that. Even with larger (500K or 1M) pots, they still present some amount of load on the pickups. Getting rid of that puts more signal at the input of your amp. But, with modern amps, that isn't as necessary or useful as it used to be 100 years ago, before high-gain channels became as common as they are now.

Downside is, a volume control on the guitar is a very handy thing. You could do a variation on that idea where the tone control is a push/pull that would allow you to bypass it, but leave the volume in the circuit. Many players put the tone control on "10" and leave it there forever. Or, just not install one at all. But, if it was switched, you could use it if you started feeling Jeff Becky one day.

 

[line6man]

So this is a little off the wall, but as I look at my simple diagram above, it occurs to me ... it would be pretty easy, wouldn't it, to pop a small on/on switch into that yellow hot wire from the 3-way switch, with one line going out to the volume cap as shown, and another line going straight to the output jack, right? And then I could bypass the pots altogether, but still be able to choose pickups, correct? That might be a pretty raunchy option with two P90s, no?  :tard:

No, that won't work. The volume pot is still in the circuit via the connection to the jack. It will still control volume, because there is a variable resistance parallel to the jack. It just won't behave the same way as when there is also a series resistance.

If you want to bypass the pots, you need to use two poles of switching. One for the input side of the volume pot, and one for the output side. You can follow the wiring of an active/passive switch or a true bypass switch. Either works fine.

 

[KDC1956]

Okay, on to polarization: I'm sitting here looking at an orange drop cap, and I don't see any indication of polarity. Obviously, there must be a way to tell, although it sounds like it doesn't really matter in this application. Nevertheless, I'd still like to do everything properly. So how can I tell?

They're not always marked, but when they are, it's usually a line marked next to the rest of the part#/value print to indicate the outside foil connection like this...

That black line on the right means that's the lead that you should treat as the negative/common/neutral/ground.

It's really a pretty minor thing, though, so you might not see any indication all.

This is good to know thanks for posting.