Multi-capacitor tone control

[Flux Jetson]

Originally Posted by Stealth

The inductor basically works opposite a capacitor - in series it inhibits high frequencies, in parallel it inhibits low frequencies.
As you know, depending on the rest of the circuit, capacitors have a cut-off frequency that shows you which frequencies will get passed (for a standard tone control, below cut-off) and which get attenuated (above cut-off). The exact opposite works for inductors - if you had an inductor instead of a capacitor on your tone control, you'd have a variable high-pass filter, and that too would have a cut-off frequency.

If you have a capacitor and an inductor in a circuit together, they form a so-called resonant circuit. Normally, if those two components were in series, this'd mean any signal with a frequency close to their gets a slight boost. The closer their cutoff frequencies are, the more pronounced the effect is with a higher gain and narrower bandwidth (i.e. range of frequencies where the effect is noticeable). The resonant peak frequency, gain and Q-factor (a central-frequency versus bandwith ratio) can all be calculated from the inductance, capacity and resistances of the above two components, the pickups themselves and the rest of the circuit.

Now, since those components are in series with each other, but as a unit parallel to the signal going from the pickup to the output jack, what happens is that instead of getting boosted, those frequencies will get shunted to ground and thus attenuated. On an amplitude/frequency graph you'd see a dip at the frequency, which would be narrow and deep if the Q-factor was high or shallow and wide if the Q-factor was low.

In real life, what you'd hear is a change in the midrange with a slight hollowness to it - again, depending on the selected capacitor, the exact frequency that'd get "hollowed out" varies. Since you usually change only the cap and keep the inductor the same, the Q-factor would also change so you'd either lose a lot of high midrange or you'd have a wide dip throughout half the low mids.

TL;DR: inductors in varitones make dips and notches in the sound depending on which cap and inductor are selected.

Excellent descriptions (per normal Stealth-age!) .. copied, and stored!

So, essentially this is close to creating a parametric band, with a fixed Q?

Are wahs constructed using these same priciples?

[tonebrulee]

Originally Posted by TJBass

but my issue is that it seems the switch doesn't effect the tone until I roll the treble all the way down. Should I swap the two connections at the tone pot?

Not quite sure what you mean by swap the two connections at the tone pot, but if you look at my drawing and trace the leads, the switch doesn't do anything but change which cap is in line between the middle lug on the tone pot and ground. When the switch is in the middle position, it's the .047 cap in line which is the P-Bass standard and it acts no differently than the tone pot on a P-Bass. In general I've always found the majority of a passive tone pot's effect ends up in the last third or so of the roll-off. If it's more extreme than that for you maybe the taper on your pot is off, or maybe you have a linear rather than audio taper.

[TJBass]

I just finished swapping the leads to the tone pot from the switch, made no difference. With the tone rolled all the way off I can hear differences in the switch position. When the treble is turned all the way up I cant hear any discernible difference in any of the three positions on the switch.

The caps do affect the tone when the tone knob is turned all the way up....right?

[TJBass]

A few months ago I switched the stock pots out for alpha A250k pots.

[Southway]

Originally Posted by TJBass

The caps do affect the tone when the tone knob is turned all the way up....right?

Technically, yes, as long as the pot and capacitor(s) are in the circuit there will be a difference in tone. But with the pot all the way up it will be very slight and you may not hear the difference. I know I can't, but many people can. That's really how it's supposed to work. With the knob full up you're supposed to get full tone, effectively no highs being bled off. You can use a smaller pot, so that the cap(s) have more effect when you're all the way up.

[T-34]

I too cannot hear the difference with the tone pot full on...
(And I don't expect to hear any difference)

[tonebrulee]

Originally Posted by TJBass

The caps do affect the tone when the tone knob is turned all the way up....right?

Well.. technically yes, the caps are still part of the circuit, but with a 250k or 500k resistor in front of them so only a tiny fraction of the signal is hitting the cap. The net effect might be something like 95% of the signal going straight to the jack and 5% having it's highs rolled off before being mixed back in with the unaffected 95%. The effect is negligible so you're unlikely to hear any difference between the three caps, even when you're listening hard for it.

[TJBass]

Originally Posted by tonebrulee

Well.. technically yes, the caps are still part of the circuit, but with a 250k or 500k resistor in front of them so only a tiny fraction of the signal is hitting the cap. The net effect might be something like 95% of the signal going straight to the jack and 5% having it's highs rolled off before being mixed back in with the unaffected 95%. The effect is negligible so you're unlikely to hear any difference between the three caps, even when you're listening hard for it.

Thanks for explaining that, I was expecting to hear a significant difference in tone even at the treble side of the pot. I roll back a lot to get any significant change in tone, I may look at getting some higher quality audio taper pots to get a more even sweep.

[James Ridener]

I love this post! I'm modding my P bass and would like to do something similar, but I don't want to make a new hole for the switch. How would one wire up a push/pull DPDT switch to toggle between two caps? I haven't seen this while searching, but I assume it must be possible. I'm guessing the top two posts would be for one cap, the bottom two for the other, and the middle two would go to the tone pot?

James

[James Ridener]

Bump.

[TimWatson]

Bump for the same reason James bumped.

[chapito]

Originally Posted by James Ridener

How would one wire up a push/pull DPDT switch to toggle between two caps? I haven't seen this while searching, but I assume it must be possible. I'm guessing the top two posts would be for one cap, the bottom two for the other, and the middle two would go to the tone pot?

James

you'll only need to use "one side" of the switch.

top — cap 1
center — to pot
bottom — cap 2

See attached. I use the green chiclet caps and the larger caps can be thick. As a result I mounted each cap on opposite sides (In my first mod I mounted them to the same side, see pic.)

–the caps can go to ground at the push-pull casing.

[Flux Jetson]

Originally Posted by chapito

you'll only need to use "one side" of the switch.

top — cap 1
center — to pot
bottom — cap 2

See attached. I use the green chiclet caps and the larger caps can be thick. As a result I mounted each cap on opposite sides (In my first mod I mounted them to the same side, see pic.)

–the caps can go to ground at the push-pull casing.

Neat install. Looks like that blue thing got a little pen-fry at some point. Sometimes it can be tough to solder without scorching surrounding components in tight quarters, it can be a pain to do now and then.

I've never used the green chiclets. How close do they stick to their rated capacitance? In other words, if you measure one, how much tolerance do they typically show from factory rating?

I've found some of the ~cheaper~ caps can be pretty far off from their specs at times (more than 20%). That can be good or bad depending on what I'm doing. That is not to say that what you've used are "cheap parts", I'm just saying that I've noticed that sometimes cheap parts can be far from their specs many times. So ya gotta think about how "worth it" it is to you just to save a few cents when buying project parts.

I've seen those green chiclets in a lot of phase shifters.

[T-34]

Tight tolerance capacitors are more difficult to manufacture than, say, resistors. That's why in the same price range the resistor will have 5% tolerance while capacitor - 10% or even 20%.

[chapito]

Originally Posted by Flux Jetson

Neat install. Looks like that blue thing got a little pen-fry at some point. Sometimes it can be tough to solder without scorching surrounding components in tight quarters, it can be a pain to do now and then.

I've never used the green chiclets. How close do they stick to their rated capacitance? In other words, if you measure one, how much tolerance do they typically show from factory rating?

I've found some of the ~cheaper~ caps can be pretty far off from their specs at times (more than 20%).

yeah, i fried it! I use the blue screw terminals while I'm mocking up the control plate so that I can quickly swapout pickups I want to try.

I use the terminal for temporary cap auditions too. (with a lead extending outside of the control plate so that I can plug in different cap values)

I can't speak to tolerances. The J rated ones should be ±5%. Ultimately I go by ear, once I've narrowed down the value I want, I'll plug in 3 or 4 of the same value to test for consistancy.

[Flux Jetson]

Originally Posted by T-34

Tight tolerance capacitors are more difficult to manufacture than, say, resistors. That's why in the same price range the resistor will have 5% tolerance while capacitor - 10% or even 20%.

Well, I have noticed that caps by Nichicon (aluminum electrolytic) measure within 2% of spec even though they are rated at 10% +/-.

[Charley Umbria]

Originally Posted by chapito

you'll only need to use "one side" of the switch.

top — cap 1
center — to pot
bottom — cap 2

See attached. I use the green chiclet caps and the larger caps can be thick. As a result I mounted each cap on opposite sides (In my first mod I mounted them to the same side, see pic.)

–the caps can go to ground at the push-pull casing.

Chapito,

I've been thinking about doing this exact thing on a P/J I'm rebuilding. It looks like you're using .047uF and .027uF caps. I'm looking at .047uF and .1uF to switch between new and "vintage" P-Bass specs.

Do you notice enough difference between the two caps to make the mod worthwhile?

[T-34]

I do. I hear a lot of difference between 0.1 and 0.047 caps when tone pot fully closed.

[Flux Jetson]

Originally Posted by T-34

I do. I hear a lot of difference between 0.1 and 0.047 caps when tone pot fully closed.

THere's twice as much capacitance (mathematically speaking) between the two, I'd imagine there would be a noteworthy difference in sound.

It wouldn't be difficult to put together an off-bass test circuit to test various caps and tone circuits. You may wish to think about constructing something of that nature to help with making choices. A small project box (or even just a board with a small piece of angled metal, such as aluminum angle or a piece of flashing, heck just about anything really that could be used to mount a pot too). You could even get way with just putting together parts as a loose assembly ... a tone pot and some caps ... that are put in-circuit between your bass and whatever it is you use right after your bass (direct in to amp, or tuner, or compressor, or whatever). You could use an old guitar cord, cut it in half and wire in a pot/cap setup between the two male plugs, to be able to test various tone control ideas. Thay way there's no drilling, no mods to the bass itself until you are certain about whatever it is you want to do.

Just a thought ...

[JimmyM]

I figured that if I did something like this, I'd just butcher it and have to go through 3 of each part before I got it even close to right, so I just ordered a Tonestyler Bass 10 in a pre-wired assembly and saved myself a lot of money and aggravation. Hats off to those who can solder well. I'm not one of them.