When swapping a capacitor with a resistor while testing some components, I noticed that, to my ears at least, resistors and caps seem to have the same effect on the sound. Is there any disadvantage using a resistor for tone control?
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Resistor vs. Capacitor
- Thread starter subdude67
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A resistor passes all frequencies.
A capacitor's ability to act as a filter is dependent on it's value AND the frequency of the signal.
Google capacitive reactance for a full explanation. Also, check out inductive reactance for some additional knowledge.
A capacitor's ability to act as a filter is dependent on it's value AND the frequency of the signal.
Google capacitive reactance for a full explanation. Also, check out inductive reactance for some additional knowledge.
If you were getting the same results from a resistor and a capacitor in a typical tone circuit there's either something wrong with the resistor, the capacitor or the circuit. These components do not, and should not, behave the same.
They are 100% not interchangeable..
The initial tone change when turning down a passive tone control comes from the increased loading of the variable resistor AKA tone pot. The capacitor value doesn't come into play until the last 1/2 or 1/4 of the tone pot travel.
Just to be sure we all (well...maybe just me LOL) understand, did you remove the cap in a regular passive tone control and replace it with a fixed value resistor? This is how I interpret what you said:
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Like others have said, the two are very different electronically, do different things, and aren't interchangeable. Either there's something wrong in the circuit, or you're conflating the slight tone rolloff heard in any pot (volume or tone, they're the same) with the actual high end bleed in a proper tone circuit.
Like @Matt Liebenau said, the potentiometers used for tone and volume are variable-resistors. Rolling off either Volume or Tone will cause some "tone" rolloff. That's why they say 500K pots are brighter and 250K pots are warmer. But they're only brighter or warmer when they've rolled off an amount. They should sound exactly the same when they're wide-open because the signal isn't going through any of the resistive material.
With the tone wide-open, the pot is essentially shorted around or skips any of the resistor material inside. It's acting just like a wire. As you turn them counter-clockwise, it goes into the resistance material, and some signal goes through the circuit and some bleeds to ground. The tone pot is the same exact thing as the volume pot, except there's a capacitor between the pot & ground to actually give proper high end rolloff.
A resistor just limits electrical flow.
A potentiometer is just a variable resistor.
A capacitor has two internal plates a small distance apart. One plate will build up charge until it's high enough to jump across the gap to the other plate and continue along the circuit. At that point the first plate's charge is depleted and has to build up again. It has a certain "capacity" for charge.
Like @Matt Liebenau said, the potentiometers used for tone and volume are variable-resistors. Rolling off either Volume or Tone will cause some "tone" rolloff. That's why they say 500K pots are brighter and 250K pots are warmer. But they're only brighter or warmer when they've rolled off an amount. They should sound exactly the same when they're wide-open because the signal isn't going through any of the resistive material.
With the tone wide-open, the pot is essentially shorted around or skips any of the resistor material inside. It's acting just like a wire. As you turn them counter-clockwise, it goes into the resistance material, and some signal goes through the circuit and some bleeds to ground. The tone pot is the same exact thing as the volume pot, except there's a capacitor between the pot & ground to actually give proper high end rolloff.
A resistor just limits electrical flow.
A potentiometer is just a variable resistor.
A capacitor has two internal plates a small distance apart. One plate will build up charge until it's high enough to jump across the gap to the other plate and continue along the circuit. At that point the first plate's charge is depleted and has to build up again. It has a certain "capacity" for charge.
Yes. It will eliminate your tone control's ability to roll off only high frequencies and make it roll off all frequencies, essentially turning your tone control into a second volume control. Depending on the value of the resister used, the tone control will fully turn off all signal to the output jack, or will just reduce the signal to some degree. Use of a resistor in place of a capacitor won't function to reduce only high frequencies, which is the design purpose of a tone control.
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G&L adds an additional resistor to their SB-1 tone control, but a capacitor remains within the circuit running parallel with the potentiometer's wiper arm and one end of the resistive lug.
See attachment.
But as others have mentioned, you cannot replace a resistor with a capacitor and expect the same results.
A resistor allows for direct current (DC) to pass through it whereas a capacitor blocks direct current.
Two different electronic components with two different functions.
See attachment.
But as others have mentioned, you cannot replace a resistor with a capacitor and expect the same results.
A resistor allows for direct current (DC) to pass through it whereas a capacitor blocks direct current.
Two different electronic components with two different functions.
Capacitors and resistors are two very different things. There may be some circuits where you hear a similar result, but that would be a rare occurrence, not the norm. In most guitar or bass tone circuits, the value of the capacitor doesn't make much difference until you are below "half tone". There, if you run your tone control on the high side, you may hear a similar result.
If, however, you swap a resistor in place of a power supply capacitor in an amplifier, it might hum and then catch fire ( I have designed a lot of circuits in my career, I know these things). The capacitor won't do either of those things, unless you put it in backwards, in which case....it can explode (but probably not catch fire). Context matters.
If, however, you swap a resistor in place of a power supply capacitor in an amplifier, it might hum and then catch fire ( I have designed a lot of circuits in my career, I know these things). The capacitor won't do either of those things, unless you put it in backwards, in which case....it can explode (but probably not catch fire). Context matters.
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What's the point of exploding if you don't then immediately catch fire?
Killjoy….
Killjoy….
For anybody reading this thread -- the above statement is incorrect.
@sheltjo6 alluded to this, above, but resistors allow both DC and AC / RF to pass. Electron flow is resisted (mostly) independent of frequency.
Inductors only affect AC/RF signals -- the magnetic field that's generated in the inductor impedes a quick reversal of polarity, but DC flows just fine.
Capacitors can be thought of as physically separated plates, but the only time anything "jumps" the gap is at dielectric breakdown -- and failure of the component. Capacitors allow current to flow only until the plates are maximally polarized for a given voltage -- then the capacitor blocks DC. In an AC or RF circuit, it's possible to have a circuit where a capacitor poses no impediment to current flow.
The magic of a capacitor on a tone pot is setting up a variable, passive R-C network. Changing resistance of the pot alters the shoulder frequency of the low pass filter -- ranging from "let a lot of highs through, too" to "dump high frequencies to ground (through the capacitor) and let only low frequencies through".
The lower the capacitance, the higher the shoulder frequency for a given resitance. At the extremes, an extremely small capacitance is like a disconnected path to ground. An infinitely high capacitance can let even a super-low-frequency signal have an effective path to ground. Variable capacitors were a staple of radio tuners. It just turns out that changing the R component by a potentiometer is easier and more compact in a guitar.
In any case, there are no arcing plates unless you want the magic smoke to be released.
FullumMusic
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When that happened in our factory (mislabelled capacitors), the people working there got an exhilarating experience, but.....were able to go to work the next day, because the factory was still there. It's a good balance of fun and responsibility.
Actually, in some cases, explosives are used to put out fires - it's like blowing out a candle, in that you deprive the fire of oxygen. If that's what you find fun, I'm sure you can find a job where you do that for a living. Let us know how it goes when you explain what you do for a living to your spouse and/or parents.
TL ; DR direct answer:
If you put the fixed value resistor where I think you put it (post 6), you can adjust the treble tone. The only 'disadvantage' is you won't get as bassy as when using a cap when control is off (ccw). Personally, I see that as an advantage because sometimes (with cap and the pot turned off), it's just bassy, tubby, indistinct, mud. I'd rather avoid that useless area. Your resistive tone circuit would prevent the mud area from happening while still providing a range of tone adjustment.
For anyone else interested, grab a snack LOL:
How can the tone change without a cap?
Super easy, and players have probably already experienced that behavior with a volume control. When you lower the volume from 10, you've heard the treble start disappearing. Changing resistance changes the tone. Other examples of a purely resistive component changing the tone are swapping a tone or volume pot for a different value. Swap to a higher value tone or volume pot = increased treble. Swap to a lower value tone or volume pot = less treble. Technically, you're hearing the effects of "resistive loading" on the entire circuit. Any change of resistance will change the tone.
But what about the cap in a tone control?
@Matt Liebenau said it best in post 5. "The initial tone change when turning down a passive tone control comes from the increased loading of the variable resistor AKA tone pot. The capacitor value doesn't come into play until the last 1/2 or 1/4 of the tone pot travel." In other words, the cap isn't used until pot is close to off. Resistive loading is the majority of tone change you hear while turning tone control down.
So, the OP's purely resistive tone control, assuming it's a pot and fixed resistor, will change the tone by the effects of resistive loading. The fixed resistor (assuming a high enough value) will, besides not allowing the 'mud' area to happen, also stop the modded tone control from becoming a second volume pot. I hate it when that happens LOL.
I intentionally kept out heavier tech stuff. If you wanna go into a fuller explanation of what's happening, see @micguy's excellent sticky post How Tone Controls Work. His first post gets the idea across that the cap isn't a factor until rolling the pot towards off position. The rest of the thread is a learning experience.: https://www.talkbass.com/threads/how-tone-controls-work.1644471/
I'll point out in the same thread above, @Jerry Catanescu also suggested replacing the cap with a resistor (post 11), same idea as what I think the OP has done. "One unorthodox thing I would suggest is replacing the tone cap by a...resistor. Perhaps around 20 to 50k or so. This will turn the tone pot into a variable resistive load for the pickup. Before you call nonsense, just try it. You might like its effect better than a cap. I, for one, enjoy the resulting lack of "tubbyness" (that half-cocked wah sound) with the tone nearly or completely off. Others might actually crave it, so YMMV."
Great video (about 13 minutes long) from TB member @RobbieK live demonstrating that resistive loading is a major portion of tone controls and that the cap only comes into play towards end of rotation.:
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One thing work pointing out is that this is a minor issue on a P bass (the volume control is wired as a potentiometer - the load on the pickup does not change much with change in volume. Yes, the resonance is damped a bit by taking the volume off 10, but that's farily minor, and below 9 or so, the tone stays quite constant.
On a J bass (with VVT controls), the volume controls are wired backwards - they shunt the pickups (the resistive load on the pickup changes substantially). This means the tone changes a lot more than it does on a P.
Thanks a lot to all who have taken time to reply 
I should clarify something. I am finishing a build and want a no pot setup with only a on-off-on toggle switch selecting 2 caps for each PU. So all tone shaping is fixed, on or off without pots.
When trying different resistors, which I have never used in bass wiring, I noticed a decrease in high frequencies very similar to when a cap is hooked up. This lead to my question if they can be used for tone shaping, why is it not done?
I should clarify something. I am finishing a build and want a no pot setup with only a on-off-on toggle switch selecting 2 caps for each PU. So all tone shaping is fixed, on or off without pots.
When trying different resistors, which I have never used in bass wiring, I noticed a decrease in high frequencies very similar to when a cap is hooked up. This lead to my question if they can be used for tone shaping, why is it not done?
Ahh, thanks for clarifying.
Caps will maintain volume better than resistors when selecting a different tone.
A resistor passes any and all frequencies (Bass, mids, treble), which is the full audio spectrum of your pickup's output. Used by itself as a tone selection, all frequencies get passed to ground. This lowers your volume. How much lower depends on value of resistor. With switching, you'd have a switchable volume selection. The large volume changes that might happen when a player selects their favorite tone might not be appreciated. "I got my tone, but the frakkin' volume dropped alot?" LOL. This is why a resistor isn't used as a tone selection.
A capacitor passes only treble frequencies. Used by itself as a tone selection, only the treble frequencies from the pickup's output get passed to ground, while the bass and mids (not passed by the cap) are retained on the main signal path. That means most of your volume is maintained, which is why caps are used.
I hope this helps.
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I meant to get back with you concerning the extra resistor (R1) of the tone control in the diagram you posted.:
It's a good idea if a player's tone control starts sounding muddy and indistinct when almost dialed all the way off (ccw). The resistor electrically (not mechanically) prevents the mud portion from happening, even when control is dialed full ccw.
Here's how a player can tailor their own Mud-Be-Gone Resistor to suit themselves.:
It's a cool idea if the player wants the full rotational range of the pot without that bullpoopie mud.
