Talk to me about capacitors

[scuz]

So I just got my new UltraJazz pickups and I need to rewire the whole thing, including pots and shielding. I've ordered the $.49 .047 uf cap from warmoth.com (where I ordered the rest of the electronics), and I'm not so sure that it'll do the trick for me. I read Lyle Caldwell's thread on shielding and proper wiring, and he mentioned in there something about not using the "cheap ceramic" capacitors, which is apparently the one that I have purchased.

Now while looking for new grill cloth for the cabs I don't have yet (I'm obsessive like that), I stumbled upon these from mojomusicalsupply.com. These are filled with mineral oil. Does this REALLY affect the tone enough? I'm not whining about the price (it's only $5), I'm just wondering if it's worth the effort.

Also what's uF @ 600v? How do they measure the capacity of capacitors? Why would I go with a .047uF instead of a .1uF or a .47uF capacitor?

[4StringTheorist]

[physics knowledge incoming... I knew this degree would have 101 uses!]

I want to give you an idea of how a capacitor works, not just what it does. I'm going to do this through an analogy, but I hope it gives you some info to work with and a basis for you to do some experimentation.

As it relates to bass playing, think of a capacitor in this way:

If you've ever seen a spectrograph representation of music (the sort of thing that a lot of digital audio programs will represent music as), picture that. The squiggly line is a representation of the vibrations that make up the music. In air, the vibrations are sound that we can hear. In the wire, the vibrations are an alternating electric current.

Imagine that squiggly line of music is a road and you're riding in a car over it. There are long bumps like hills and tiny quick bumps like pebbles. The long bumps are bass frequencies and the short bumps are treble frequencies.

A capacitor stores charge. What this means in terms of my road analogy is that a capacitor is like the shock absorbers on your car. Ride with no shocks and you feel every little bump in the road. The better the shocks, the more energy they can absorb and the less you feel the bumps, starting with the little ones, right? This is because there's not much energy in the little bumps to absorb. (Similar to how we crave 400+W amps to be heard with the guitarist who levels the club with a 15-30W amp)

A capacitor works on your musical signal in the same way. The higher the rating on the capacitor (measured in capacitance) the more energy it can store, and thus the more high frequency signal it will absorb. So on a tone control rolled off fully (maximum cut to the highs) the capacitance of the cap on the tone pot tells you what frequencies are being cut. The higher the capacitance, the larger the swath of your high frequencies get cut.

About your question regarding the capacitor material affects the tone. The material in a capacitor (if any) is called the dielectric. Do different dielectrics have a different sound? Here we enter the realm of the subjective. Different dielectrics in caps with equivalent capacitance might build up a charge at different rates. Think about doing 1-30 in a Ferrari vs. 1-30 in a Model-T.. the end result is the same, but how quick you get there is a whole different experience. However, I'm not sure if that's even the case. ULtimately, I'd be impressed by anyone who could hear any kind of difference in a double blind hearing test.

I'm heading out for an evening with the wife. I'll think about it. If you want to do some digging, see if you can find a difference in Δq/Δt (possibly also labeled dq/dt or δq/δt) for different dielectrics.

Hope this gave you some idea of what a cap does and how it can influence your tone. Use this knowledge, and experiment with it!

Take care,
-T

[scuz]

Hells yeah! That's exactly what I was looking for; a guy with a degree who knows things

Ok, so that learned me quite a bit. If I were going with a .47cF versus a .047cF capacitor, I would get a more drastic high roll-off. Does that mean it will absorb frequencies in a wider range, or just more the frequencies within the same range?

[niftydog]

Originally Posted by scuz

Does that mean it will absorb frequencies in a wider range, or just more the frequencies within the same range?

A higher capacitance moves the corner frequency of the filter down, meaning a wider band is attenuated.

Just bear in mind that 0.47 is ten times as big as 0.047, so the difference between those two caps is of course very dramatic. But there's a lot of territory between (and around) those values to be explored.

The various, more subtle differences between types of capacitor are very real phenomenon, and they most definitely have an affect on sound. The extent of the effect can be debated, but the effect is real, no question. Otherwise, why would there be so many different types of capacitor? Why use a ceramic here and the same value polyester there? Well, because they ARE DIFFERENT.

[RyreInc]

Great post from 4StringTheorist! I just wanted to make a small correction: The corner frequency is determined by the RC constant, not just the C value. Of course, in a particular bass R is a constant anyways, so only C needs to be determined. But the same C value in two different basses might give a different corner frequency, due to differing resistances. For a given frequency, as R increases, C decreases, and vice versa.

[warnergt]

Ceramic capacitors may be cheap but there is certainly nothing wrong with them - absolutely nothing wrong with them for a bass or guitar tone control circuit. They are probably the most reliable electronic components you can find. Furthermore, they work extremely well far up into radio frequencies. At audio frequencies, they perform virtually the same as a theoretically ideal capacitor. You're not going to find a better capacitor type for the application.

[Busker]

Originally Posted by warnergt

Ceramic capacitors may be cheap but there is certainly nothing wrong with them - absolutely nothing wrong with them for a bass or guitar tone control circuit. They are probably the most reliable electronic components you can find. Furthermore, they work extremely well far up into radio frequencies. At audio frequencies, they perform virtually the same as a theoretically ideal capacitor. You're not going to find a better capacitor type for the application.

I have some vintage caps that I stripped out of an old cheapie tube guitar amp. They are small cylindrical caps dipped in wax. Are those oil-filled most likely? I know some are .1uF.

Should I experiment with those?

[jwymore]

While I love the technical stuff (I'm an engineer) I have done some back to back testing of a few different caps in bass applications.

While the ceramic caps work fine for bass I did find by upgrading to a $.99 Orange Drop I got a smoother and more linear tone rolloff as I rotated the tone knob. For lack of a better description I will say it made the tone control more useable. As I went from there to Hovlands and Vitamin Q's I can say I did get a bit different effect but not nearly as drastic as going from the ceramic to the Orange Drop. IMHO, going to the slightly more expensive Orange Drop was worth it. Going to the $10 to $12 Hovlands and Vitamin Q's was not (at least for bass).

[4StringTheorist]

Originally Posted by jwymore

While the ceramic caps work fine for bass I did find by upgrading to a $.99 Orange Drop I got a smoother and more linear tone rolloff as I rotated the tone knob. For lack of a better description I will say it made the tone control more useable. As I went from there to Hovlands and Vitamin Q's I can say I did get a bit different effect but not nearly as drastic as going from the ceramic to the Orange Drop. IMHO, going to the slightly more expensive Orange Drop was worth it. Going to the $10 to $12 Hovlands and Vitamin Q's was not (at least for bass).

You bring up an interesting point, and I've got a question, seeing as you have the capacitors there to test, and you're an engineer. Is there a dramatic difference in the resistance between the Orange Drop and a cheapie ceramic cap of the same capacitance?

RyreInc is right that the resistance plays a part in the bass circuit. The pickup is also an inductor, to technically, a passive bass is an RLC circuit where the inductor is the source of the emf thanks to Lenz's Law. And in AC instead of DC. Never mind what happens on the amp end of the circuit. Talk about weird!

I'd be curious to know if the resistance of the two caps that you can hear the difference between is different. That can account for a difference in the sound.

Take care,
-T

[warnergt]

Originally Posted by jwymore

While I love the technical stuff (I'm an engineer) I have done some back to back testing of a few different caps in bass applications.

While the ceramic caps work fine for bass I did find by upgrading to a $.99 Orange Drop I got a smoother and more linear tone rolloff as I rotated the tone knob. For lack of a better description I will say it made the tone control more useable. As I went from there to Hovlands and Vitamin Q's I can say I did get a bit different effect but not nearly as drastic as going from the ceramic to the Orange Drop. IMHO, going to the slightly more expensive Orange Drop was worth it. Going to the $10 to $12 Hovlands and Vitamin Q's was not (at least for bass).

I'm not trying to be confrontational but I just don't buy this. I'm an electrical engineer (BSEE and MSEE) with 30 years of engineering experience. As I mentioned above, at audio frequencies, ceramic capacitors are virtually ideal capacitors. The are almost perfect in every significant electrical way (e.g. negligible resistance and inductance). Actually, most capacitors -- even those that are not ceramic -- fit this description at audio frequencies. If one capacitor sounds better than another, there must be another explanation because it's not the capacitor.

[4StringTheorist]

Originally Posted by warnergt

I'm not trying to be confrontational but I just don't buy this. I'm an electrical engineer (BSEE and MSEE) with 30 years of engineering experience. As I mentioned above, at audio frequencies, ceramic capacitors are virtually ideal capacitors. The are almost perfect in every significant electrical way (e.g. negligible resistance and inductance). Actually, most capacitors -- even those that are not ceramic -- fit this description at audio frequencies. If one capacitor sounds better than another, there must be another explanation because it's not the capacitor.

What effect would it have if the two caps has very different internal resistances?

[warnergt]

Originally Posted by 4StringTheorist

What effect would it have if the two caps has very different internal resistances?

First of all, I reject the premise of two caps having very different internal resistances. In reality, they just don't. There is just not much resistance in a capacitor.

But it's still a good, valid question that we can look at hypothetically. What if the resistances were very different?

Consider the tone circuit in a bass. Typically, it is a potentiometer (pot) in series with a capacitor. A typical capacitor value is 0.05 microFarads (uF). A typical pot value is 250,000 ohms. Because the pot is variable, it has a range of 0 to 250,000 ohms.

If the capacitor used had an internal resistance, it would be the equivalent of adding another resistor in series with an ideal capacitor (meaning a capacitor with zero resistance) and potentiometer.

Let's take an example to see what would happen. Let's say the capacitor has an internal resistance of 5,000 ohm (an extremely high and unrealistic value that is 100 to 20,000 times higher than what you would find in a real capacitor). This would be the equivalent of putting a 5000 ohm resistor in series with a potentiometer and an ideal capacitor. The resulting circuit looks like an ideal capacitor with a pot that goes from 5,000 to 255,000 ohms instead of 0 to 250,000 ohms. The net effect is like turning your tone pot a very few degrees -- a tiny effect that is easily cancelled out by turning the pot the other direction by those few degrees.

This example was with an unrealistically extreme case of resistance (5000 ohms) in a capacitor. For any real capacitor, the resultant change from resistance would be like a microscopic adjustment to the tone pot.

By the way, all components have some tolerance. Typically, it is 5%. So, for example, when you buy a 0.05 uF capacitor, the actual value can be anywhere between 0.00475 and 0.0525 uF. This tolerance alone could affect the tone more than any realistic variation of resistance you will find between capacitor types. But again, the difference would be tiny and easily compensated for with a tiny adjustment of the tone pot.

[staindbass]

oh boy. one guy says there shouldent be a difference in sound. remember, we are in the realm of subjective oservation, things you cant measure. if you cant hear a difference, it could be your system is not transparent enough for you to tell the difference. ever wonder why those bumblebee capacitors are so expensive? partly because they go in vintage guitars, partly because they sound better and different. i mostly do capacitor stuff in speakers, but i a circuit i will guess they perform similar. a good high quality cap is solen.maybe 3-6 $. hi end -super pure-add no sound of thier own caps like mundorf from germany (i use em) are like 49$. before you snort, if u dont have somthing like a jbl 075 tweeter which will show you the difference, dont say there is none because you cant notice it. i started with the normal electrolytic bi polars from radio shack, then i noticed a definite difference with military grade audio caps. then i had to try the mundorfs. im not sugesting the expensive ones, because i dont know the ratio of performance vs caps in electronics, just speakers. the problem is, you would have to wire a switch between to two and flip back and forth instantly to hear differences. wether you would notice them or not is another matter. maybe the difference would be too small to be worth the extra $. if i were you, i would be happy that i bought a higher quality part than needed and be satisfied completely. on the other hand, if you happen to notice a difference, then you will wonder what a 8$,$14,$20 cap would sound like. johnny a

[staindbass]

another note, if its a passive bass, you would only notice differences with the tone/caps when the tone is control all the way down, with the tone control on full treble, the cap is not in the circuit. so, if you play with the tone up, you wont notice a difference. johnny a.

[cybersnyder]

The ultimate tone control:

Stellartone.com

I have one on my P-Bass and really like it. Is it worth the price over a standard tone control? Dunno.

[Jim Breece]

Scuz- I'd recommend getting a few different value caps and playing with them to see the difference. You don't have to solder them in- hook them up with alligator clip test leads (I think Radio Shack still sells them) and go to town. Get the el cheapos and when you decide what you want you can decide whether to spend more for a more expensive one of the same value. You may also find that it does affect your sound a little even with the pot on 10. I've got switches on a couple basses and guitars to eliminate the cap from the circuit completely and it does add a tiny bit more brightness with it out on most of the instruments I've done that way. They're all passive fwiw, and on one guitar at least it makes no difference, but if you pick a really big value cap you may feel like your tone control only goes to 8 or 9. And you may have figured out already that the 600v part of the spec doesn't matter in the teensy voltage world inside the bass.

[4StringTheorist]

Originally Posted by niftydog

The various, more subtle differences between types of capacitor are very real phenomenon, and they most definitely have an affect on sound. The extent of the effect can be debated, but the effect is real, no question. Otherwise, why would there be so many different types of capacitor? Why use a ceramic here and the same value polyester there? Well, because they ARE DIFFERENT.

This is true. Capacitors with different construction but the same capacitance value are different. But in what way? Here are a few:

voltage rating
temperature tolerance
chemical composition / reactivity / toxicity
size
weight
density (because of the previous two)
price

Any of these could matter to an engineer for a host of different reasons. I was bit by the first one in my list there a few weeks ago. I teach high school physics and chemistry. My students were building electric motors from scratch (nails, wire, a plywood board, tape, that's it) and the digital power supply I was using wouldn't hold onto it's constant voltage mode while supplying these hand built motors: it kept cutting out because it thought it was seeing a short. So I wired up a capacitor in parallel with the students' motors to smooth out the current spikes that the power supply was seeing. Worked like a charm, until I turned the voltage a bit too high to get one group's motor turning. I turned the voltage up higher than the cap's rating. Smoke started coming out the top of the cap I went to Radio Shack and got a cap that had a similar capacitance, but could handle 3x the voltage. It was bigger, heavier, more expensive and it worked like a charm.

The thing that's relevant here is that different types of caps exist for tons of different reasons. From the standpoint of what a cap does in an audio circuit (i.e. at frequencies from 20 Hz to 20,000 Hz) warnergt has a solid argument that there should be no human detectable difference between two caps with the same capacitance and different construction. I'm inclined to agree.

So an electrical engineer and a physicist are skeptical here. I'm betting that both of us are willing to be enlightened by a properly controlled double-blind test. I know I am.

Originally Posted by warnergt

***extremely good "back of the envelope" style proof deleted for space***

Great line of reasoning!

Originally Posted by staindbass

if you cant hear a difference, it could be your system is not transparent enough for you to tell the difference.

It might be that, or it might be that there is no difference there to be heard.

Originally Posted by staindbass

ever wonder why those bumblebee capacitors are so expensive? partly because they go in vintage guitars, partly because they sound better and different.

Perception of quality can drive price up just as much as actual quality.

Originally Posted by staindbass

the problem is, you would have to wire a switch between to two and flip back and forth instantly to hear differences. wether you would notice them or not is another matter. maybe the difference would be too small to be worth the extra $. if i were you, i would be happy that i bought a higher quality part than needed and be satisfied completely. on the other hand, if you happen to notice a difference, then you will wonder what a 8$,$14,$20 cap would sound like. johnny a

It'd be really interesting to try out your idea! Wire up a pair of caps with a switch to alternate between them. Put the switch where you cannot see it. Have a third party switch back and forth between the caps and see what % of the time you can correctly tell the difference.

For proper experimental design: The person you have working the switch should not know which switch position engagages which cap until after the experiment is concluded. That's the double in double-blind. Also, there should be a "dummy" switch that they can and do throw so that you can't assume that hearing a switch click means you're hearing a different cap than you were hearing a moment ago. The person using the switch should use a random number generator to generate the sequence so they don't use any patterns that you can pick up on consciously or subconsciously. Then, afterward, the results can be compared with reality and you can see whether you really could tell the difference.

Whether with speakers or with the tone controls in a bass, I really would love to see a well done double blind on this one!

[Bassamatic]

Boy, there are a lot of smart guys on this forum! I am also an EE and Audio engineer since the 70's (hoo boy - that dates me).

I agree that the type of cap should not make any difference, but I do know that our design engineers usually picked mylar film caps instead of ceramics for our audio equipment. One of the reasons is for better stability over temperature (not so important inside an instrument), but perhaps some better electronic parameters as well - I will check on this.

I would venture to say that at the frequencies of a bass pickup, and because it is a shunt to ground, you probably cannot hear a bit of difference.

As I have gotten back in to playing again and have a couple of project basses in the works, I have developed a theory that bass players (at least me) might prefer to change the frequency of the high cut instead of the amount - a low pass filter. I find that ANY tone control that I have used cuts off too much useful stuff while rolling off the high end. This is because the simple cap circuit is not very steep.

In my current bass in the works I am installing a rotary switch in place of the tone control with 5-6 different caps to select from. SO - as I rotate the control, I cut off more and more of the high end, but always at the same maximum slope.

I'll let you know how it goes.

[Bassamatic]

After looking - I see that this is what the Stellartone device is doing - sliding the cut frequency up and down instead of just changing the amount of cut at a set frequency.

I'll make my own instead of spending $100, but it is an easy drop-in, and I'll bet it sounds better than any passive and many active tone controls.

Are there any active preamps with a tunable hi-frequency? I see tunable mids, but not highs.

[mongo2]

Originally Posted by Gio S

After looking - I see that this is what the Stellartone device is doing - sliding the cut frequency up and down instead of just changing the amount of cut at a set frequency.

I wonder if the Q varies as the cutoff frequency changes.