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Permalink Reply by petey twofinger on July 30, 2010 at 10:55am

i had the same problem , in my case the bridge is metal , i drilled a tiny hole next to the bridge , soldered some solid core copper wire around it and ran that to the ground side of the jack .

does the cap really make a difference ?

i monkeyed with a few on mine and couldnt hear it so i left it out .

i also had to make a preamp cause my amps didnt like the piezo .

id love to see some pics of your bass , im planning on trying to make one someday soon .

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Permalink Reply by pi_r_squared on July 30, 2010 at 11:48am

pics from an earlier post are here:

http://www.cigarboxnation.com/forum/topics/first-build-and-hi-from-a

Since those pics, I've added the switch, volume control, and strap buttons, changed the lightest string (A-string) from 0.095" to 0.080" nylon trimmer line, seems to work better for the "A" at this scale length.

and yes, the caps worked. They have to be in series with the output, and .1 micro-farad did almost nothing, .2 seemed to work ok, I might try a .3 or .4 if i get the chance


petey twofinger said:

i had the same problem , in my case the bridge is metal , i drilled a tiny hole next to the bridge , soldered some solid core copper wire around it and ran that to the ground side of the jack .

does the cap really make a difference ?

i monkeyed with a few on mine and couldnt hear it so i left it out .

i also had to make a preamp cause my amps didnt like the piezo .

id love to see some pics of your bass , im planning on trying to make one someday soon .

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Permalink Reply by Outhouse Instruments on July 30, 2010 at 1:40pm

You need to run a ground from the volume pot to the jack. Just a simple wire soldered to the case of the volume pot to the jack should work.
Try to google a wiring diagram for a single pick-up and a vol.

Never mind, go HERE.
Do this and just ignore the bridge ground.

Shielded wire might help, but twisting the two wire around each other will do about the same thing.

Matt

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Permalink Reply by pi_r_squared on July 31, 2010 at 2:47am

Thanks for the help.

I think I might need a new volume pot. Rad Shack was out of the 500k audio taper pots, so I picked up a "500k volume control". The body is all plastic, and I've had a terrible time finding any place on it that will act like a ground. If someone knows the major difference between a "500k audio taper pot" and a "500k volume control" I'd love to know what is is.

I'll try a different pot, I did notice that the hum gets worse when I switch the caps into the circuit, and there are actually 2 hums at different frequencies. They both go away it get really good contact and touch the ground side of the jack.

If the new pot doesn't do it, I suppose I could get one of those "static control" grounding clamps for working on a computer, and clamp it to my......um......yeah.

Thanks again.

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Permalink Reply by Skeesix on July 31, 2010 at 5:28am

The volume pot might possibly be a linear taper, vs. an audio taper.

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Permalink Reply by pi_r_squared on August 1, 2010 at 4:40am

It seems that, since a pot can have linear and non-linear (audio) taper, if they call it a "volume control" I would hope it's audio taper. When I adjust it, it acts like it's audio taper. I still have no idea why they have "500k audio taper pots". "500k linear taper pots", and "500k volume controls", all side by side :S

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Permalink Reply by petey twofinger on August 2, 2010 at 6:56am

my last two visits to the shack they didnt have any 500k pots , not even a bin for them ! (cell phone hut) .

just that goofy "volume control" thing , luckily for me there is a frys near by , but man i am getting sick of shelling out $$$$ for little stuff , like 5 bucks for a switch ! the 3 scrap yards by us w oob , i used to do an all day raid there and return with a bag full of goodys . :(
there is a resale store one block away , they really only sell clothes , so i hit their dumpster weekly and get stuff , but , , ,

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Permalink Reply by Outhouse Instruments on August 2, 2010 at 7:38am

So .... did you get rid the hum?
Did you try the ground wire?


Matt

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Permalink Reply by pi_r_squared on August 2, 2010 at 12:52pm

Matt,

The volume control I was using is an all-plastic body. Th 2 Rad Shacks near me are out of "traditional 500k pots" and 250k as well, which is why I bought this 500k plastic one. I need to get a pot that I can ground to.

Also, the hum is MUCH worse when the caps are switched into the circuit. Does this still jive with what you were thinking?

Matt Towe said:

So .... did you get rid the hum?
Did you try the ground wire?


Matt

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Permalink Reply by Outhouse Instruments on August 2, 2010 at 1:07pm

Without seeing the circuit or the actual wiring .... I'd still say that grounding the pot/jack/whole she-bang is the issue.
I was misunderstanding the pot issue tho'. Replace that, you troubles might be over. But even in replacing that I would still use the diagram I linked.


Matt

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Permalink Reply by pi_r_squared on August 3, 2010 at 2:43am

Matt,

Here's the circuit. I'm sure in needs to be grounded, and as soon as I get a 500k pot with a real case to ground to I'll try it.

In the mean time I do have a 100k pot left over from another project. It doesn't attenuate the volume enough, but I may wire it in and ground to it just to see if it kills the hum.

Attachments:

• cbbcircuit01.JPG, 26 KB

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Permalink Reply by Outhouse Instruments on August 3, 2010 at 10:22am

Yeah, I think the pot is the problem. Replace it, making sure to ground the case, pot, and the jack together.


Matt

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