Taming A Bright Pickup

[guitar2005]

I have a Gibson 500T bridge pickup in my Explorer but I find it a tad bright. Its wired direct to a 500k volume pot.

Is there anything I can do to tame the high end and make it sound smoother - I mean noticeably smoother. I can try a 250K pot but I know I'll need more than that to tame it.

Any ideas?

[Prostheta]

Try the 250k first, then perhaps consider “biasing” your tone pot with a resistor to provide a degree of permanent treble roll off, perhaps. Is the ‘bucker wired in series or parallel?

[ToddW]

I'm not sure how much effort you want to put into this, but the easy thing to do, assuming going from parallel to series wiring isn't in the cards, is to use a small cap to shunt some of the high's to ground. If it's a 4 conductor PUP and you're worried a cap will shunt to much of the high end to ground when you have both pups on, you could try putting a .0047uf cap to ground between the coils. I don't know what that'd do, but it'd be very easy to test.

Another slighty more complicated option would be to put in a notch filter with a cap and an inductor in series. Mouser sells some tiny transformers, they're about 1 cubic cm, with various inductances. They're only a couple of bucks each, but you'd also wind up paying $7 for shipping and handling, maybe more to Canada.

I'll be interested to see what other options people suggest, besides changing PUPs

Todd

Edit PS) I think Prostheta meant to say bias your tone pot with a permanent Cap, not a resistor.

Edited June 17, 2008 by ToddW

[Prostheta]

Yes. I haven't needed to do it before myself, and i'm more than a little forgetful about my passive filter circuit design :-D

[WezV]

Try the 250k first

+1

[ToddW]

Hey, if you want to see if that'll be enough, just drop a 500k resistor across the pot and see how it sounds.

[Prostheta]

Good idea. I believe it would cause all kinds of weird stuff to go on in the middle of the taper though....!

For what it's worth, calculating parallel resistance uses the following formula:

1/Rp = (1/R1) + (1/R2)

1/Rp = (1/500) + (1/500)

1/Rp = 0.002 + 0.002 = 1/0.004 = 250

[Paul Marossy]

Use a slightly bigger tone cap...

[ToddW]

Use a slightly bigger tone cap...

I was shooting for something that would only knock the top off the bridge PUP. Why I suggested trying the cap between the coils. Voicing only the bridge PUP is easy if you only use one PUP at a time, but get's harder when both on is an option and you don't want to change the sound of the neck PUP.

Thinking about it a touch more, could he put a small inductor between the bridge hot lead and the switch (with or without a cap to ground before that). That'd stop most of the neck PUPs high end from shunting down the cap . . . Or between the bridge tone control and the switch?

I'd ask over at guitar nuts.

Todd

Edited June 18, 2008 by ToddW

[Paul Marossy]

Use a slightly bigger tone cap...

I was shooting for something that would only knock the top off the bridge PUP. Why I suggested trying the cap between the coils. Voicing only the bridge PUP is easy if you only use one PUP at a time, but get's harder when both on is an option and you don't want to change the sound of the neck PUP.

Thinking about it a touch more, could he put a small inductor between the bridge hot lead and the switch (with or without a cap to ground before that). That'd stop most of the neck PUPs high end from shunting down the cap . . . Or between the bridge tone control and the switch?

I'd ask over at guitar nuts.

Todd

Yes, it does get trickier when you want that on only one pickup. I think a small value cap to ground at the pickup switch could also knock of some of the highs. I'm thinking something in the picofarad range, nothing real big. Maybe like 300-500pF or something like that. Maybe it needs to be a bit bigger than that. I haven't done this before, I'm just thinking intuitively.

Anyhow, I was thinking about the original question when I made that post.

Edited June 18, 2008 by Paul Marossy

[ToddW]

Hi Paul,

I think the Explorer has individual tone controls for each PUP, so your answer is valid. Interesting little puzzle, maybe we should have said try heavier strings

Anyway, Guitar 2005 hasn't replied, so maybe he already solved this.

Todd

[Paul Marossy]

I think the Explorer has individual tone controls for each PUP, so your answer is valid. Interesting little puzzle, maybe we should have said try heavier strings

It looks like it's two volume controls and one tone control, at least on the one in this picture...

[guitar2005]

The guitar only has a volume per pickup. No tone controls to play with and its a 2 conductor pickup.

I already use 10 gauge strings.

The bridge pickup is closer to the bridge than usual. This, combined with a bright pickups makes for a bright sounding guitar. I don't have a big selection of resistors at home to try a 500k in parralel. I'll try to see if I can find something tonight.

[ToddW]

Is the guitar a gibson or something that you'd consider modifying? Because adding a tone control might be a nice thing.

Todd

[guitar2005]

Is the guitar a gibson or something that you'd consider modifying? Because adding a tone control might be a nice thing.

Todd

I never use tone controls. don't like 'em. I'd rather keep the instrument as is.

[ToddW]

Fair enough. Given you have individual volume controls, do what prostheta said first, put a cap across the bridge PUP. .oo47 is an ok place to start. I wouldn't change the Pot to 250k because then you'll change the relative max volume of each PUP. If you don't have any caps, let me know and I'll see what i have lying around. May be able to mail you a few to try as well as some resistors to try in series with them. From NC to you for would take a few days though.

Regards,

Todd

[guitar2005]

Fair enough. Given you have individual volume controls, do what prostheta said first, put a cap across the bridge PUP. .oo47 is an ok place to start. I wouldn't change the Pot to 250k because then you'll change the relative max volume of each PUP. If you don't have any caps, let me know and I'll see what i have lying around. May be able to mail you a few to try as well as some resistors to try in series with them. From NC to you for would take a few days though.

Regards,

Todd

I think I have a couple of caps lying around. So is the cap supposed to be wired from hot lead to ground?

0.0047 is 4700mF. That's pretty big. did you mean 4.7pF or 4.7uF?

[Paul Marossy]

0.0047 is 4700mF. That's pretty big.

It's really a pretty small value. I would start with that and tweak it from there. You might even find that it's not quite big enough for your taste.

Edited June 18, 2008 by Paul Marossy

[Prostheta]

Different pickups would be a tempting option in my opinion.

Question is - why is the bridge position sounding too bright to start out with?

[guitar2005]

Different pickups would be a tempting option in my opinion.

Question is - why is the bridge position sounding too bright to start out with?

Its a 500T by Gibson. Its really bright to start with. I might try a different PU but I'd like to see if I can tame this one first. Its output matches well with the neck pickup.

The fact that its a little over 1/4" closer to the bridge (compared to a Real Gibson Explorer) doesn't help with the brightness.

[guitar2005]

0.0047 is 4700mF. That's pretty big.

It's really a pretty small value. I would start with that and tweak it from there. You might even find that it's not quite big enough for your taste.

4700mF is HUGE - That's mili, not micro

I guess that what is being proposed is a low pass RC filter where the capacitor is in series with the pickup's hot lead and the pickup's output is taken in parallel with the cap.

As for the volume pot value... I was thinking... will it really make a difference if I run it wide open? When its wide open, the pickup sees 0ohms from the pot, as if it was connected directly to the guitar cord, no?

Edited June 18, 2008 by guitar2005

[ToddW]

Halt, stop, desist . . . LOL

I meant .0047uf. .0047 would be huge.

Sorry, I assumed you'd just interpret it as a standard tone cap size. My bad. Use the .0047UF cap to shunt the highs to ground. So basically wire it from the hot lead to ground.

Todd

[ToddW]

0.0047 is 4700mF. That's pretty big.

It's really a pretty small value. I would start with that and tweak it from there. You might even find that it's not quite big enough for your taste.

Hmmmm, you must be building some JUMBO guitars there Actually, you were wearing guitarspeak goggles when you saw .0047, and turned it into mf. Guitar2005 actually read what I wrote like an engineer would. I have no idea how you'd fit a 4700uf (4700mf) cap inside a guitar, but I hope Guitar2005 reads this before he tries. The 12w ones I have upstairs are 3" tall and 1.5" across!

Todd

[guitar2005]

0.0047 is 4700mF. That's pretty big.

It's really a pretty small value. I would start with that and tweak it from there. You might even find that it's not quite big enough for your taste.

Hmmmm, you must be building some JUMBO guitars there Actually, you were wearing guitarspeak goggles when you saw .0047, and turned it into mf. Guitar2005 actually read what I wrote like an engineer would. I have no idea how you'd fit a 4700uf (4700mf) cap inside a guitar, but I hope Guitar2005 reads this before he tries. The 12w ones I have upstairs are 3" tall and 1.5" across!

Todd

Ok - So I tried a couple of values.

The lower the cap value, the more high end you lose i.e 68pf make the guitar sound real thin as it not only removes high end, it also removes a lot of bass.

I tried 10nf and that kept much of the bass but didn't remove enough high end to get rid of the ice-pick treble.

4.7nf isn't too bad but still, ice-pick still there.

3.3nf seems to roll off enough high to make the guitar sound better and all of the bass is there. Really smooths out the frequencies.

Then, there's this unknown value I tried (I think I prefer the 3.3nf though) which sounded pretty good. Its marked 100v, 68cp, 8821, 682k. Not sure what value it is but I'm curious.

I don't have many more values... but I think I'll stick with the 3.3nf for now, live with it for a while and see how I like it.

In the process, I found this interesting site:

http://buildyourguitar.com/resources/lemme/

[ToddW]

That's actually backwards Guitar2005.

The cutoff frequency formula is 1/2*pi*r*c. If we assume a 10k resistance for the PUP, using the 4.7nf I suggested as a start point, gives a cut off frequency of 3386hz. If you go to 3.3nf, it goes UP to 4823hz. Not down. Remember, the cap is essentially a short to ground for very high frequencies, but won't pass DC. To the cap, lower frequencies look more like DC. Bigger caps will move the cut off freqency down.

http://en.wikipedia.org/wiki/Lowpass_filter

However, we don't hear sound in a linear way, the formula is probably not very accurate, and since you're ear can use harmonics to create a perceived fundamental tone, the math is only a starting point. So 4.7pf or 3.3pf, or 10pf . . . it doesn't matter. All that matters is what sounds good to you.

Regards,

Todd

Edited June 19, 2008 by ToddW