Cap Mod

pflash4001 · Post by **pflash4001** » Sun Jul 31, 2005 9:46 pm

Hi, guys. I just tried the .0047 cap mod on my '79 4001. Just a question, though. The individual pickups sound really rich and full, but if I have the pickup selector in the middle position, the sound gets really thin. Is that supposed to happen with this mod? Another thing is that I keep hearing about the orange capacitor. Mine didn't have that. Mine has a yellow barrel shaped one labeled .0047 mfd. Did I bypass the right part? I think I did. Anyone seen this before? Here's a pic of my bass.
Thanks a lot!

javier

rickenbrother · Post by **rickenbrother** » Sun Jul 31, 2005 9:52 pm

Javier, you should have removed the cap, then added the wire in it's place. You seem to have both.

It's hard to see in the pic if you've soldered the wire to the correct two lugs. They should be the same ones the cap is/was soldered to.

I do still have the cap in my '79 even though I did the mod, but I have a SPDT mini switch to select the bypass wire or the cap.

heinpete · Post by **heinpete** » Sun Jul 31, 2005 9:55 pm

Dear Javier,

your mod seems o.k. though you should definitely hear a difference. However the thin sounding of the middle position raises the suspect of a phase error in the PU circuit. Just change the "+" and "-" of one PU and check out whether it sounds fatter now?

Best regards
Peter

pflash4001 · Post by **pflash4001** » Sun Jul 31, 2005 9:56 pm

Is that what's causing the thin sound? Where can I get the switch and instructions for the installation? I was hoping to just bypass it with the short length of wire leaving the mod reversible. Is this not possible?

pflash4001 · Post by **pflash4001** » Sun Jul 31, 2005 9:58 pm

Let me give that a try.

pflash4001 · Post by **pflash4001** » Sun Jul 31, 2005 11:12 pm

Peter, that solved that problem, but raised another. Please be patient with me, as I am new to doing this stuff and am only praying I don't really jack something up. Now that the + and - were reversed and the phasing issue has been solved, there is a buzz on the front p/u, like a ground loop. It is there, but very low when playing, but becomes much more pronounced when I touch the p/u. What should I do? Any suggestions? I have already looked back to see if anything is crossed or making any contact that shouldn't be happening, but I don't see any. HELP, PLEASE!

lars · Post by **lars** » Sun Jul 31, 2005 11:28 pm

I have had hum caused by bad contact in the stereo output jack. There are some switches there that may be bent slightly, enough to cause hum.

charlyg · Post by **charlyg** » Mon Aug 01, 2005 3:16 am

FYI, You can leave the cap in place as the wire effectively shorts out the cap. You should notice no difference leaving the cap in or out with the wire in place.

ken_j · Post by **ken_j** » Mon Aug 01, 2005 5:20 am

Javier,
When changing the polarity of the pickup did you leave the sheilded wire to ground? If not that could cause the buzz or a hum. Only switch the insulated wires.

syncop8r · Post by **syncop8r** » Mon Aug 01, 2005 8:01 pm

Leaving the cap in, even if disconnected one end if you want, means you won't lose it should you ever want to use it again. I think that's what I did. Either that or I lost it.

heinpete · Post by **heinpete** » Mon Aug 01, 2005 11:05 pm

Hi Javier,

great that you solved the phase issue. The hum is of course also enhanced if the PU are in right phase, as they now act as real single coils. The hint form Ken might be right, check the ground shielding of the PU cables. Other than that you could check if the middle position of the PU-selector gives less hum, then you proved my second sentence above: The single coil hum is a 4001/3 specific issue. You can improve the noise/signal ratio by applying "shielding paint" in the body cavity and cupper foil for the back of the scratchplate(check out you local luthiers and stores). Hope this helps!
Best regards
Peter

ken_swearingen · Post by **ken_swearingen** » Mon Aug 01, 2005 11:27 pm

Also is the ground wire still attached to the tailpiece,if not this can cause hum.

martyr · Post by **martyr** » Fri Aug 05, 2005 11:06 am

wow, just did the cap mod. i can't believe how much of a difference it makes!

david_schwab · Post by **david_schwab** » Mon Aug 08, 2005 5:33 am

If you have hum with the two pickups on, and they are in phase, you can try flipping one of the magnets over, providing you can do that. I know the treble PUs on my 4001 had a large ceramic magnet under the coil that probably could be flipped over. After flipping the magnet, you would most likely have to reverse the phase of that PU again.