Using Caps to Soften a Bright HB

[PlayItAll]

I have a Les Paul with Burstbucker Pro's in it. I always felt the bridge pu was way too bright. I installed a 300k pot which helped a little, but it was still too shrill for my tastes. I had the control plate off and just started messing around with strumming the guitar and listening to the tone when touching a low-value capacitor (.006 uf) between the input of the pot (where the pup is connected) and ground. It seemed to mellow it out so I soldered it in. I really like it!

Can anyone explain to me what is happening here? I only know enough about these things to be dangerous


Thanks,
Ed

[SWRing]

The capacitor bleeds off high frequencies

Without getting into too much math or physics, the simplest answer is that capacitors act like a short cicuit to high frequency signals. This shorts them to ground and prevents them from flowing out to the amplifier.

The actual impedance of the capacitor (impedance is the tendency of a device to NOT allow electrical current to flow through it) is given by the following equation: Z = 1/(2*pi*i*f*c) where
Z = impedance
pi = the number pi (3.14...)
i = imaginary number (sqrt(-1))
f = frequency of the applied signal
c = value of capacitance (i.e. 0.006uF)

Without worrying about why 'pi' and 'i' are in the equation, it can be seen that the impedance depends on the capacitor value and signal frequency. If either the frequency of signal or capacitor value is increased, the impedance of the capacitor decreases, allowing more of the applied signal to flow through it.

In your situation, you have connected the capacitor between the output of the pickup and ground. This provides a low-impedance path to ground for higher frequencies. Therefore, you can imagine that higher frequency signals from the pickup are now flowing directly into ground (through capacitor) instead of flowing out into the amplifier.

Fun things to try:
Bigger capacitors: Bigger capacitors will essentially allow more current to flow through, and at lower frequencies. This will result in losing more highs (and maybe even mids depending on capacitor). The guitar will sound darker.

Smaller capacitors: Smaller capacitors will allow less current to flow through, except at the higher frequencies. This will result in only cutting higher frequencies, and therefore the guitar will sound brighter (but not as bright as with no capacitor).

What would happen if you connected the capacitor in series (between the pickup and the input of the pot)? Again, since the capacitor only allows higher frequencies to flow through, this would cause the pickup to lose most of it's lower frequency output. Essentially, it would lose all bass and maybe mids, sounding extremely shrill. You probably wouldn't want to do this, but it just illustrates a point.

It sounds like you've already found something that works for you. Hope this satisfies your curiousity about why the 0.006uF helped.

[black_labb]

when dealing with the values of the tone pot, turning a 500k down will get you to 300k. i know it seems that the highest value on the tone pot sounds the best, but may be too bright, but thats just the high end comig through, and using a smaller value pot will just make the pot less sensitive. if you wont use anything over the 300k, thats fine but i prefer the increased diversity of tone. good to see you have found the right fix for your problem.

[PlayItAll]

Thanks!

Wow... This is great info. Thanks so much to you both.

I experimented more today and ended up going with just a slightly lower cap (.001 uf) and it's "just right". Took away the brittle top end but left enough sparkle.

Thanks again for the replies - much appreciated.
Ed

[Steve A.]

Wow... This is great info. Thanks so much to you both.

I experimented more today and ended up going with just a slightly lower cap (.001 uf) and it's "just right". Took away the brittle top end but left enough sparkle.

Thanks again for the replies - much appreciated.
Ed

Another way to smooth out a "too-harsh" humbucker is to replace the magnet. I'll replace an Alnico 5 magnet with Alnico 2, 3, or 4 to mellow it out a bit. FWIW I just put in a BB Pro #2 at the bridge of my brand new PRS SE Singlecut and I love it. I put in a regular BB (another #2, I believe) on the neck and they work well together.

But I'd done the cap trick you mentioned on an Antiquity tele bridge because it was just too darned bright for my tastes.

Another tip for the cap trick: you can temper the effect by wiring a resistor in series with the capacitor, rather than just changing the value of the capacitor. Like the circuit that Kinman recommends on volume pots to retain trebles at low settings... You can also try mixing two different types of caps in parallel- like ceramic and mica, or ceramic and poly.

[kevinT]

This is a really good thread. i needed a good lesson on capacitors.

I have a few questions that i hope someone could address. It would be greatly appreciated.

1. What value of capacitor do you usually start with to reduce the brightness, or is it just a guestimate based on what you're hearing? ie.,.022 or .047?...or something lower?

2. I've heard of bubblebees, malory, spreagues (sorry about spelling)... is there a tonal difference among them? Is it a quality difference?

3. What about materials...e.g., ceramic... and what would be the benefit of the different materials?

4. How and where do i go about purchasing some? can i get them at a regular electronics store? (e.g., Mouser) Is there a specific type that you would use just for guitar electronics or could you use any type that are used in all types of electronics?

[Rosewood]

Anything smaller than .02 starts to sound like a midrange boost to me. One of my favorites was a .004 to .005 on the bridge pu tone control but was really only good for distorted lead work, sounds kinda honky for chord work. I've never been pleased with a cap from pu to ground full time to tame the highs, it just sounds funny to me, I'd rather use a smaller value volume pot with a larger tone cap. As far as the type caps go I never thought it mattered in a guitar but a lot of smart guys swear by it so it's worth a try. Even high dollar caps are cheap compared to the other gear we own.