Capacitor frequency - is there a chart?

[Whil57]

I was reading some websites on capacitors, and didnt really understand the volt/ohm input calculations that they used to get frequencies. Basically, what i was wondering, is that if you increased a caps value, at what value (on say a jazz or p pup) would you need to ground everything over the octave on the G string ? Almost like making it a low pass.

 

[tubestuff]

Roughly:

 

[Killed_by_Death]

You have to remember the treble cut pot is a R/C network, resistance & capacitance.
So the full value of the capacitor isn't realized until the resistance is eliminated (turned full counter-clockwise).

 

[Whil57]

Now i wondered why a .47 sometimes didnt do much, so according to tubestuff's chart, even though it affects it, its only a small gain reduction in db. And even a huge cap then wont completely kill a note.

 

[line6man]

There is no chart, because it's not universal. The frequency cutoff happens at different frequencies, depending on the impedance of the pickup. This is why lower impedance pickups tend to be paired with higher capacitances, and higher impedance pickups tend to be paired with lower capacitances. For example, you can use a 0.2uF capacitor with active EMG pickups, but the same capacitance gives you nothing but mud with a standard passive pickup.

 

[line6man]

Almost like making it a low pass.

A tone control IS a low pass filter.

 

[Whil57]

A tone control IS a low pass filter.

Yeah, i was thinking more in the scope of a larger db reduction. So you are correct, i just dont think of it that way. Could you get a cap to then reduce 100% of every frequency over 2K ?

 

[line6man]

Yeah, i was thinking more in the scope of a larger db reduction. So you are correct, i just dont think of it that way. Could you get a cap to then reduce 100% of every frequency over 2K ?

A capacitor is not like an on/off switch. There is a progression from fulling blocking to fully passing, as you move through the frequency spectrum. If you want everything above a particular frequency to be completely blocked, then there will be a range of frequencies below your target frequency that will be greatly reduced in amplitude.

 

[two fingers]

Yeah it's the whole circuit, not just the cap.

Think of it like a truck. How many tons you can tow is not just dependent upon horsepower alone. There's the horsepower of the engine, the gear ratios of the transmission, the ratio of the rear end, the size and grip of the wheels/tires, etc.

So you could put the same 450 hp engine in two vehicles and it will get two different results. One could go warp speed but not have enough torque to pull "a greased string out of a pig's behind". The other can pull Manhattan out of the ocean and you have to measure its 0-60 time with a calendar.

Short version: It's one component in a circuit. It alone will not get you where you want to be.

You have to remember the treble cut pot is a R/C network, resistance & capacitance.
So the full value of the capacitor isn't realized until the resistance is eliminated (turned full counter-clockwise).

There is no chart, because it's not universal. The frequency cutoff happens at different frequencies, depending on the impedance of the pickup. This is why lower impedance pickups tend to be paired with higher capacitances, and higher impedance pickups tend to be paired with lower capacitances. For example, you can use a 0.2uF capacitor with active EMG pickups, but the same capacitance gives you nothing but mud with a standard passive pickup.

 

[Whil57]

Thanks all.

 

[khutch]

Here is a chart of how a typical cap value works against typical pickup impedances:

The pickup impedance models used in the above are "typical" and do not necessarily match what is in your bass exactly. Obviously there are more than just the two different pickup models that I graphed out there on the market, there are dozens. And clearly you get a very different response when two pickups are active than you get when only one is. So it just is not possible to make a chart that shows you what a given cap value will do in your bass, there are way too many variables to plot. A listening test is your best guide to picking a cap value.

You can also see that as the others have said a capacitor does not act like a switch. It does not kill every frequency above some cutoff number. The attenuation with frequency varies and it never becomes 100% (which would correspond to negative infinity on a log/dB scale). On the other hand once the attenuation rises above some value then every frequency above that point is for all intents and purposes "killed". Various ears will disagree somewhat but most would find that any frequency attenuated more than 20 dB is essentially gone. Frequencies that are attenuated more than 0 dB and less than 20 dB are gone to some extent but various ears will disagree strongly on the exact cutoff.

I've noted the 20 dB cutoff frequencies for the single Precision, single Jazz, Precision + Jazz, and Jazz + Jazz pickup configurations on the chart above.

 

[micguy]

A capacitor doesn't have a "frequency" on it's own - it works in conjunction with the other things in the circuit. In the case of loading a pickup, the pickup has resistance and inductance, both of which can interact with a capacitor to resonate, have low pass or high pass characteristics, etc. - all depending on how things are hooked up.

Think of a capacitor as a spring, upon which you place an object with mass (your pickup's inductance). The heavier the object, the lower the resonance frequency of the combination. The lighter, the higher the resonance frequency. If you go measuring inductance, you will find quite a range of inductances - I've measured everything from half a Henry to 12 Henries, and I'm pretty sure mudbuckers are much higher than that (I haven't measured those). That's a range of 24 to 1 - like putting a one ton racing car or a 24 ton delivery truck on the same set of springs, things will work much differently depending on the mass involved.

Yes, this is an imperfect analogy - the spring's coils do have mass, so that physical object can have a resonance on it's own. In the audio range, capacitors don't act like that - they need something to work with/against.

 

[Whil57]

Here is a chart of how a typical cap value works against typical pickup impedances:

View attachment 2834769


You can also see that as the others have said a capacitor does not act like a switch. It does not kill every frequency above some cutoff number. The attenuation with frequency varies and it never becomes 100% (which would correspond to negative infinity on a log/dB scale). On the other hand once the attenuation rises above some value then every frequency above that point is for all intents and purposes "killed". Various ears will disagree somewhat but most would find that any frequency attenuated more than 20 dB is essentially gone. Frequencies that are attenuated more than 0 dB and less than 20 dB are gone to some extent but various ears will disagree strongly on the exact cutoff.

I've noted the 20 dB cutoff frequencies for the single Precision, single Jazz, Precision + Jazz, and Jazz + Jazz pickup configurations on the chart above.

Ok, this explains the results i hear when i toy with the caps. I dont own just a single P. But everytime i start with a .47, and it always ends up to seem like it doesnt do much. But i could see where it would make a difference in just the P.

 

[whatizitman]

There is no chart, because it's not universal. The frequency cutoff happens at different frequencies, depending on the impedance of the pickup. This is why lower impedance pickups tend to be paired with higher capacitances, and higher impedance pickups tend to be paired with lower capacitances. For example, you can use a 0.2uF capacitor with active EMG pickups, but the same capacitance gives you nothing but mud with a standard passive pickup.

I'm a noob at all this, and have been trying to wrap my head the last few days around impedance and capacitance. Kindly tell me if I have this right.

The active pickup in this case would be the one with lower impedance, right (output)? In which case a .2uf cap should not roll off as much higher frequencies as that same cap would with the passive pickup? But a lower cap, say .05, .02, should not roll off as much highs with the passive. Do I have this right?

 

[line6man]

I'm a noob at all this, and have been trying to wrap my head the last few days around impedance and capacitance. Kindly tell me if I have this right.

The active pickup in this case would be the one with lower impedance, right (output)? In which case a .2uf cap should not roll off as much higher frequencies as that same cap would with the passive pickup? But a lower cap, say .05, .02, should not roll off as much highs with the passive. Do I have this right?

Correct.