Capacitors

[xhawk4]

Hi all.....

I recently rebuilt my '79 p-bass. New finish, fret dressing, Seymour Duncan QP's, wiring, pots and jack, etc.... It was a salt-water mess from Hawaii. Perfect now, except one thing....

I used the original capacitor on the tone pot and it has WAY too much treble!!

I have a few new capacitors and I need to know what they do to the tone. Here goes...

 

1 - 1 K-ohm

1 - 6.8 K-ohm

1 - 10 K-ohm

1 - 27 K-ohm

1 - .022 mfd

1 - .047 mfd

1 - 2.7 K-ohm

 

Again I have no idea what these do to the tone. I need to have less treble and a little more mid. I play blues and classic rock covers. My amp is an Ampeg SVP preamp and a Crown CE1000 through a Peavey 410 TVX. Great set-up for all interested. Lots of headroom.

Thanks for your help. This is a great forum.

[Tom Capasso]

Let's assume that the salt water damaged the capacitor, and that's why your sound is off (though I can't say for sure...). The best choice would be to replace it with the same value as what is in there. If you can't read the markings (salt will do that), try the Fender site to get that info (schematics).

 

Or you may be lucky and somebody here may know

 

Sorry, I can't be more help...

Tom

[Bob Gollihur]

This is a good resource for diagrams:

 

http://www.mrgearhead.com/faq/diagrams.php#BASSES

 

.05uF is the value given for an American Precision bass.

 

The capacitor tone control is not all that sophisticated, so don't expect a lot of ability to fine tune behavior. Given the simplicity of the circuit, you could easily use alligator clips or other temporary wiring solution to try the two values you have as well as others you obtain.

 

Seymour Duncan suggests .022 on their diagram: http://www.seymourduncan.com/website/support/schematics/standard_pbass.html

[Prague]

The parts you list with k-ohm values are resistors, so don't use them.

 

The .047uF cap (micro-Farrad, .000000047) is also used as a standard on a P.

 

To roll of more highs (less treble-y) try the .022uF that you have.

[hags2k]

So, a lower capacitance rating for the capacitor equals a darker sound? That's a place to start...

 

I would like to ask something, though, that may be related. I replaced the pickup in my P-bass with a Seymour Duncan Lightnin' Rod a while back, which is an active pickup. The controls are still passive, though, with a single volume and single tone pot, just like before. Now, I absolutely love the clarity and definition that this pickup adds, but one thing that I lost in the transition was the dynamic range of my tone pot. The stock pickup had a vastly different sound with the pot cranked full, and cranked down, and a wide range in between. With the new pickup, the range is reduced, and the overall effect of turning the pot full on or full off is much more subtle. I would really like to have some of that dynamic back (though it's not required, as it's quite easy to cut frequencies that are already there with my amps EQ). Basically, the sound is as bright as I want it with the tone on full, but not as dark as I'd like it with the tone down. The replacement kit came with new pots, though, that were both 100 kohm, replacing the 250 kohm pots that were stock, which I thought might be due to the reduced impedance of the active pickup. Would replacing the pot and/or capacitor help me? I really don't want to cut ALL the highs, I'd just like to have the range of tones from my tone pot back, but if I can't have it, it's really a small price to pay for the excellent tone.

[xhawk4]

Hags,

My P-bass came with the 250K pots. When I was rebuilding, I was advised to replace them with the same, so I did. If I'm not mistaken.... the higher the K-ohm,(ie 500K compared to 250K), the wider the range. If you left it passive, Then I'd suggest going back to the 250K.

[Ben]

The .05 / .047 value is more or less standard for Fender-style *bass* tone controls; the .022 is more or less standard for Fender-style *guitar* tone controls.

 

I tried different capacitor values in my '69 Precision, but went back to the stock value in the end.

 

I tried several different sets of strings until I found the sound I wanted. The strings seemed to make more difference overall than the capacitor.

 

(I use flatwounds. Fender flats these days are very twangy, ugh. I like TI Jazz Flats, myself, or Lakland flats.)

[jeremy c]

Larger capacitors roll off highs and can shift the midrange down. As the esteemed Mr. Gollihur said, use alligator clips and try them all out.

 

I've changed and added caps in some of my instruments. I had a nice discussion with Bill Bartolini once about this at a trade show where he started scribbling on a napkin. I still have the napkin...I'll sell it on EBay one of these days.

[xhawk4]

Thanks for all your replys. Quite a few different opinions. Just wondering why Fender suggests a .047 and Bartolini suggests a .022? Alligator clips is a pretty tedious way to go, with the pickguard and all in the way. Anyway....Thanks.

[Bill C from Nashvegas]

For experimentation, you can rig up a little box with an input and output jack and a potentiometer, so you can try different caps external to the guitar....nothing says it HAS to be under the pickguard.

 

Since I don't like a trebly sound myself, I prefer flatwounds. Then I leave the tone pot full up. Plus I like the feel of flats better.

[Edendude]

And a word to the wise, for anyone who might be taking apart an amp...

 

WARNING...capacitors store electrical charge!!!

 

I learned this the hard way, when I was in my teens. I took apart an old Traynor tube head to remove a screw that was rattling around in there. Although the amp was unplugged, and had been for hours, I was knocked across the room with the biggest jolt I have ever felt in my life, when I touched a 450 volt DC capacitor.

 

Word up!

 

[jeremy c]

We're talking about caps in the range of hundredths of microfarads, I wouldn't worry about it.

[wraub]

If you are worried about messing with an amp, then don't go in there! However...

I have always been advised, when messing with higher voltage gear like amps, to keep one hand in my back pocket. Less likely that way to grab something with both hands, and complete the circuit.

You could also ground out the voltage to the chassis of the amp with a screwdriver or some such before you go in...

Otherwise, listen to Jeremy. Minimal risk at the lower voltages...

 

Peace,

 

wraub

p.s. Actually rewiring a p bass at the moment...

[fantasticsound]

First, it takes an instant to charge a capacitor by powering up your amp. It takes considerably longer for them to discharge when the power is turned off. The extreme involves capacitors used in Navy ships. Some of them are taller than a single deck, and must be turned off at least 24 hours, then fully discharged by wearing heavy rubber gloves and shorting the leads with a large wrench, before any work can be done on the system. A teacher of mine in college told us of a friend who made the mistake of asking someone at the controls (by comm on another deck) whether the circuit had been, in fact, off. The operator did what many of us do to ensure it was off. He turned it on, then off again. What followed killed my prof's friend.

 

Of course, most of us won't approach the voltage/amperage discharged by a cap of that size, but don't be fooled. Anything outside your instrument's electronics can still be hazardous or deadly. Act with caution.

 

Now, I have a question about your wiring. I'm not an electrical maven, so please excuse my ignorance if this is common. I was under the assumption you could not use active pickups without active electronics controlling the output. It seems logical that if you're using a low impedance, active pickup, then you must change the specs, maybe even the circuit design of the other controls to properly control your timbre and output. Can anyone shed some light on this?

 

(BTW - It occurs to me that some active pickup basses can be used in passive operation, but I have no idea if the signal from each mode uses the same signal path and circuit for volume and tone, or if two circuits and, perhaps, a double pot are called for to accomplish this. Anybody?

[Bill C from Nashvegas]

I dunno how the topic got shifted from guitar capacitors to amp capacitors

 

But as far as discharging the energy in capacitors: wrenches, screwdrivers, or other dead shorts ISN'T the proper way. Control the energy by discharging it through a resistor!!!

[Prague]

Originally posted by Yes There's Gas In The Car - FS:

Now, I have a question about your wiring. I'm not an electrical maven, so please excuse my ignorance if this is common. I was under the assumption you could not use active pickups without active electronics controlling the output. It seems logical that if you're using a low impedance, active pickup, then you must change the specs, maybe even the circuit design of the other controls to properly control your timbre and output. Can anyone shed some light on this?

At the time I wasn't smart enough to ask, but I was smart enough to rewire! I made a passive control plate for my Jazz bass (Am. Deluxe) and it works fine in either mode. I like both arrangements. I bought all the extra parts and wired it like a standard Jazz.

[Edendude]

I hi-jacked this thread to warn people of the danger of high-voltage capacitors, like the ones found in many bass and guitar amps.

 

The point is...

 

Just because it's unplugged, does not mean it can't hit you with a jolt that can send you flying, or could easily kill you. I didn't die, but I did learn that lesson the hard way, and thought this was a good time to share.

 

[fantasticsound]

I think Edendude was wise to temporarily hijack this thread. There are some who might think that instrument electronics and amp electronics are equally safe to work on. Hard as that might be for you to believe, there are people out there that believe this. Just watching out for our fellow forum members.

 

We also warn drummers not to play with Spinal Tap.. cause they all, eventually go BOOM!!!

[_Sweet Willie_]

xhawk4,

 

Did you make any decisions about which capacitor to go with? Are you going to test a couple out first? Let us know where you end up with this.

 

Originally posted by fantasticsound:

We also warn drummers not to play with Spinal Tap.. cause they all, eventually go BOOM!!!

No doubt.

[Tom Capasso]

Originally posted by Bill C from Nashvegas:

But as far as discharging the energy in capacitors: wrenches, screwdrivers, or other dead shorts ISN'T the proper way. Control the energy by discharging it through a resistor!!!

When we were kids, my cousin had a neon sign transformer, a huge hand-wound coil, and some big caps from old TV sets. The "resistor" we used to discharge one time was a worm. Instant carbon powder. Cousin went on to study physics and work for IBM. He still has the coil, though. The field would make flourescent lights light up (when not connected) and wipe out all radio reception in the neighborhood.... Ah the good old days....

 

Tom

[xhawk4]

With all regards to Edendude and others.... This thread was about Caps on the tone pot inside a bass cavity. Although I appreciate your info, My question was not about amps. I would never try to repain an amp.

Thanks to Bob G. and the links he posted, I found a solution.

[_Sweet Willie_]

What was your solution? What are you going with?

[rumpelstiltskin.]

hags2k -- check your PMs.

 

robb.

[xhawk4]

Willie,

I sold the '78. Just got in a '73 P-bass. I'm switching pups to Seymours SPB-2 Hots. The cap in here from the previous luthier(who did a sweet refin) is a 1k. It sounds the best so far. I'll keep it.

Funny, in my '74 P with a Kubicki j-p body, the cap is wired from the j volume to the tone? Don't know why its different, but I'm gonna leave it alone. I was told the EMG's in here were added from Kubicki's shop in the 80's. This bass has awesome R&B tone! And it's strung BEAD, Kinda cool, and it's all beat to hell but it's got THE tone and great playability!

Hawk