Bartolini Pups Wired to Jim Williams Pre question

[skb5string]

Hello All!

Got a question regarding the Bartolini Pups in My Roscoe skb6. They are the stock pups Roscoe uses. Here is my problem:

I just installed a New Jim Williams Audio Upgrades pre into this bass. All of the wiring (pots and pups) connect right to the circut board, meaning it does not use a traditional "Blend" pot. The pre chip is a "Pan" chip.

I have sheilded both pickup cavities and the control cavitiy. All is well with this.

My question is concering the Pups, let me explain....

The barts have a Red, Black, White, Green and sheild wires. I found a diagram of the Bart pups on line and it shows:

Red-Hot
Black-Hot
White-Ground
Green Ground
Shield -Sheild

Now, the original pre-amp was a Aggie OBP-1. When I removed the Pups, the Red and White wires on each of the pups were tied off together under some heat shrink tube. The only wires that were soldered were the Black-Hot, Green-Ground and Sheild-Sheild

When I rewired the pups to the Jim Williams chip, I left the Reds and whites tied together under the heat shrint and wired the Blacks (Hot) to the In-A and In-B of the Circut board as instructed. On the Bartolini pickup Diagram it shows the Shields and Grounds (green) both going to ground for each pick up, so... the black wires went to the pre and the shelids and ground went to "Ground". I grounded them to the volume pot, and yes, the volume pot is grounded. Here is what I get:

1.) When I have the sheilds going to ground (like the diagram says) I get NO GROUND BUZZ but ALOT of RF freq noise.

2.) When I cut the sheilds away from the ground and tape them back away using electrical tape. The RF Freq Noise is GONE but I GET GROUND BUZZ that only go's away if I touch something metal (Bridge, Knobs, strings, etc..) on the bass.

So..anyone have some experience with the Bart pups to help explain whats going on? Am I missing something with those Red and white wires being tied off together? Is this a Series, Vs. Parallel issue that I'm having?

Thanks for looking and assisting

 

[skb5string]

Any suggestions?

 

[bongomania]

No suggestions, but I will be interested to see other peoples' responses since I had the exact same problem with a Glockenklang pre, and Glock was not able to resolve the problem.

 

[skb5string]

No suggestions, but I will be interested to see other peoples' responses since I had the exact same problem with a Glockenklang pre, and Glock was not able to resolve the problem.

Yeah, I called Jim Williams and he had not idea either. It seems that its only the bridge pickup...I think. I know the sheilding is good. When I left the neck pickup sheild grounded and just cut the bridge one away I get a little ground noise and a bit a buzzy HUM when my finger is near the bridge pickup without touching the strings...so strange. Man, I just want this over. I'm so close and the Pre sounds great. I just want it silent. Anybody??

 

[GeoffByrne]

Try reversing the polarity of the connections ie currently hot to ground & vice versa - I know it sounds counter-intuitive, but sometimes during construction mistakes are made, and if it doesn't work, there'll be no harm done.

 

[skb5string]

Try reversing the polarity of the connections ie currently hot to ground & vice versa - I know it sounds counter-intuitive, but sometimes during construction mistakes are made, and if it doesn't work, there'll be no harm done.

Hmm, not sure. I did not seem to get this issue when the Aggie was installed. Jim Williams said it should make no difference whether it was in series or paralle. is this correct? Should I have these in paralle? Any other suggestions?

 

[skb5string]

Bump

 

[David Jayne]

Not a series/parallel issue-leave the reds and whites tied. Now, is there a place on the new pre where you could attach the greens? In other words are you NOT using terminals on the pre? If so try putting the greens on those terminals, and the bare shields to ground(vol pot), as you have already done.

 

[SGD Lutherie]

Should I have these in paralle? Any other suggestions?

You do have it in parallel:

Red-Hot
Black-Hot
White-Ground
Green Ground
Shield -Sheild

Series would be:

Black-hot
red & white connected together and taped off
green-ground
shield-ground

When you say "Shield -Shield" do you mean you have the shield wire from the pickup connected to anything other than ground? Solder it to a ground point.

As dmusic148 said, check the wiring to thew preamp and check all your grounds.

 

[skb5string]

You do have it in parallel:



Series would be:

Black-hot
red & white connected together and taped off
green-ground
shield-ground

When you say "Shield -Shield" do you mean you have the shield wire from the pickup connected to anything other than ground? Solder it to a ground point.

As dmusic148 said, check the wiring to thew preamp and check all your grounds.

Hello, thanks for responding

Actually, I have it in series right now. I was just re-stating the Bart Wire diagram in that comment. The Red and Whites are tied off and taped back. This is how it was connected to the old Pre. So the only HOT wire going to the Pre CHip is the BLACK per pickup.

Here is what is happening:

When I have the shield wires from the pickups going to ground, which it shows on the Bart diagram I get ALOT of RF type of noise. Not 60 cy hum, no radio stations, just alot of static and it changes as I move around.

When I cut the shields away from ground and just tape them back, all that RF feq Static goes away but then I get a ground buzz that will only go away when I touch something metal, strings, bridge etc..But, when I am touching something metal the Pre is dead quiet and sounds great.

If I take the sheilds to ground, Static noise, if I cut them and tape them back, Static gone but Ground Buzz when nothing metal is touched?

On a side note it sounds like most of this is coming from the bridge pickup. There is NO traditional blend pot. The "Pan" happens in the pre. My pan Pot is a 10k Linear Center Detent pot. I have all the right pots installed. Jim gave me a list of the pots to use with his pre.

 

[SGD Lutherie]

Hmmmm. Where do the pickup grounds attach? At the pre, or somewhere else? And where do you have the shields attached?

 

[skb5string]

Hmmmm. Where do the pickup grounds attach? At the pre, or somewhere else? And where do you have the shields attached?

The pickup grounds go the casing on the volume pot. The sheilds are wrapped with the pickup ground wires and ground to the pot.

 

[SGD Lutherie]

The pickup grounds go the casing on the volume pot. The sheilds are wrapped with the pickup ground wires and ground to the pot.

OK, and I assume the back of the pot is also connected to ground?

If it's only connected to ground by touching some foil shielding, try running a real ground wire from the back of the pot to the output jack ground lug.

 

[skb5string]

OK, and I assume the back of the pot is also connected to ground?

If it's only connected to ground by touching some foil shielding, try running a real ground wire from the back of the pot to the output jack ground lug.

The volume pot goes to ground using one of the solder lugs, but that wire just grounds to the copper foil sheilding. So, I'll try and take that ground to the output jack lug. But as far as the pickups go, should I be having the sheild wires go to ground? Again when they go to ground RF static, when they dont, buzz. Is it common and normal practice to have the sheilds grounded?

 

[bongomania]

Just for clarity, what's "common and normal" is not always what's "correct", and I have found this to be agonizingly true with onboard preamps. The Audere and Glock pre's, for example, have specific grounding requirements that are quite different from what is common and normal.

 

[SGD Lutherie]

The volume pot goes to ground using one of the solder lugs, but that wire just grounds to the copper foil sheilding. So, I'll try and take that ground to the output jack lug. But as far as the pickups go, should I be having the sheild wires go to ground? Again when they go to ground RF static, when they dont, buzz. Is it common and normal practice to have the sheilds grounded?

Pickup shield wires must go to ground. This grounds the internal shields, and often other metal parts inside the pickup. If shields are not grounded, then they are not shields, but in fact noise antennas.

You must have a solid ground connection throughout the circuit, so the backs of the pots have to attach to the circuit's ground point, usually at the output jack, even if they are sitting on foil. And of course that foil has to be grounded also. I'd run a wire to the back of every pot to ground.

I had a similar problem in one of my basses that required me to run a redundant ground wire from the pots, and that cleared up the electrostatic noise. Don't worry about having multiple grounds... the myth about having ground loops is just that, a myth, since there is only one ground in a bass, there can be no loop.

Bongomania also has a valid point that certain preamps have a floating ground (balanced inputs) for the pickup common returns (in this case the green wires) that is separate from the shield grounds. If you have followed the wiring instructions for the preamp exactly, then you have to start checking for wiring other issues. I'm thinking you have an inadequate ground somewhere.

Also is your bridge grounded?

Also, since the hum goes away when you connect the shields, the buzz you are then hearing is being picked up by the pickups. Is the shielding in the pickup cavities connected to ground? You really don't need that for humcanceling pickups anyway. Something changed between the old preamp and the new, and it sounds like the shielding you added might be the problem.

 

[skb5string]

Pickup shield wires must go to ground. This grounds the internal shields, and often other metal parts inside the pickup. If shields are not grounded, then they are not shields, but in fact noise antennas.

You must have a solid ground connection throughout the circuit, so the backs of the pots have to attach to the circuit's ground point, usually at the output jack, even if they are sitting on foil. And of course that foil has to be grounded also. I'd run a wire to the back of every pot to ground.

I had a similar problem in one of my basses that required me to run a redundant ground wire from the pots, and that cleared up the electrostatic noise. Don't worry about having multiple grounds... the myth about having ground loops is just that, a myth, since there is only one ground in a bass, there can be no loop.

Bongomania also has a valid point that certain preamps have a floating ground (balanced inputs) for the pickup common returns (in this case the green wires) that is separate from the shield grounds. If you have followed the wiring instructions for the preamp exactly, then you have to start checking for wiring other issues. I'm thinking you have an inadequate ground somewhere.

Also is your bridge grounded?

Also, since the hum goes away when you connect the shields, the buzz you are then hearing is being picked up by the pickups. Is the shielding in the pickup cavities connected to ground? You really don't need that for humcanceling pickups anyway. Something changed between the old preamp and the new, and it sounds like the shielding you added might be the problem.

Thanks!

Yes the bridge is grounded. Yes I did add sheilding to the pickup cavities. I tried removing the pickup sheilding out of the BRIDGE Pup cavity and it made no difference. I can try removing it from both cavities

 

[SGD Lutherie]

Thanks!

Yes the bridge is grounded. Yes I did add sheilding to the pickup cavities. I tried removing the pickup sheilding out of the BRIDGE Pup cavity and it made no difference. I can try removing it from both cavities

Did you ground the backs of the pots?

Also have you taken the bass to a different location or used a different patch cord?

 

[skb5string]

Did you ground the backs of the pots?

Also have you taken the bass to a different location or used a different patch cord?

I have not grounded the back of the POTS. The Volume POT and PAn pot go to ground on via the lugs. The MID pot and Stack Treb/Bass pot have wire leads to all the lugs from the PRE chip so no lugs on those to go to ground. The Pre amp Chip has a ground wire and it just grounds to the copper foil.

I've used at two different locations and tried multi cords, same response.

 

[SGD Lutherie]

I have not grounded the back of the POTS. The Volume POT and PAn pot go to ground on via the lugs.

You said earlier "The pickup grounds go the casing on the volume pot."

But now you say "I have not grounded the back of the POTS."

So how is the ground connection to the pickup grounds being made?

And when you say "go to ground on via the lugs", do you mean that the lugs are soldered to ground, or soldered to the back of the pot? If the lug is soldered to the back of the pot, but you are relying on the copper foil for ground, you should instead solder ground wires from the pots to ground.

The Pre amp Chip has a ground wire and it just grounds to the copper foil.

Why are you soldering the ground connection to the shield foil? Solder the ground to the ground at the output jack.

Do not use the foil as a ground plane. If you are soldering your ground connections to the foil instead of a more solid ground point, that is likely the problem.

This is why the backs of pots is usually established as ground points, with all the grounds then connected together.

Try soldering some real ground connections and see if the noise doesn't go away. I bet it will.

As I mentioned earlier, I had an issue like this once and adding new ground wires fixed the problem. I was also using the foil for the ground connection.