Non-Alembic passives PU questions

[pauldo]

For my recent b-day my son gifted me a Jazz Bass.  It is an older MIM fretless model he stripped the paint off, sanded, stained and added a coat of poly to it.  It looks cool, but more importantly he did this with his two hands for me and it certainly makes me proud.


It also came with single coil pickups, there is a noticeable hum/ buzz, seems dependent on orientation/location of the instrument in an environment (60hz interference?).*


I want to shield the cavity first.


Then I was wondering what other things I should look at.  Putting in a set of humcancelling pu’s is an obvious answer but the instrument has a unique voicing that I particularly enjoy and am concerned about altering its tone with new pu’s. 


I am curious if there are other options for noise reduction with the current pu’s?  Is there any benefit to reconnecting all the soldered connections?  Any tips for troubleshooting circuits, pots, capacitor etc for good continuity?



Electricity is magic to me so ‘grade school level’ replies would be appreciated.


* current research indicates that single coil noise is a characteristic of the machine and it will always be there. And in a band environment it is only noticeable during silent parts/ between songs.  I am not dong any ensemble, band work these days so pretty much noodle alone or play along with stuff, so ‘noise’ is less than desirable.


TIA

[gtrguy]

First make sure that the bridge has the ground wire hooked up!

[StephenR]

If everything checks out with the wiring maybe put a noise gate before the amp. There appear to be a number of pedal options available. Shielding the cavity is a good first step, though. The silver paint Alembic uses is very effective but expensive and you may not be able to buy a small quantity.

[lbpesq]

Shielding is definitely the first step.  While I might use shielding paint (the usual Stewmac stuff, not silver),  for the pickup routes for asthetic reasons, I'd use copper tape in the control cavity.  I'd also use copper tape on the underside of the control plate. 

If, after shielding, there is still too much hum, the next step would be shielding the wire from the pickups to the controls.  Also, does the bass behave the same in all different environments or just in your house or other specific places?  Some houses seem to just have wiring that disagrees with single coil instruments.  Also things like dimmer switches and other rheostats are notorious for interfering with SC PUs. 

The next step you might consider is adding an internal dummy PU, (coil with no magnets), not unlike Alembic's hum canceler on Series instruments.  I haven't looked for basses, but there are several youtubes on how to do this with a Strat.

Bill, tgo

[edwin]

I like Bartolinis for fretless. Alembic pickups, of course, sound wonderful.

[cozmik_cowboy]

Shielding is definitely the first step.  While I might use shielding paint (the usual Stewmac stuff, not silver),  for the pickup routes for asthetic reasons, I'd use copper tape in the control cavity.  I'd also use copper tape on the underside of the control plate. 


Bill, tgo

As the control panel on a Jazz is metal, the tape on it shouldn't be needed; be sure, however, to put tabs of the cavity tape over the edge to contact the panel (easiest to do it at the screws).

Peter

[pauldo]

Thanks for the quick replies.

I did check the ground wire to the bridge and it looked good.

I will get some copper tape and make sure it touches the metal cover.

On the volume pots there are three tabs, on-line schematics show a variation of what is on the bass.  Do the three tabs have unique functions or are they simply connecting points?

I have not tried the bass other than at home (someone call me for a fill-in!  ). There is a noticeable “hot spot” in my practice area...


Thanks again and an early Merry Christmas to all.

[lbpesq]

I would definitely try the bass in a different environment before I did anything else.  And I would also do all the shielding before I'd even think about messing with the wiring to the pots.

Have a great holiday, everyone. And a happy belated Festivus to all (yesterday).

Bill, tgo

[gtrguy]

I would check the bridge ground wire with a VOM as well, just in case.

[pauldo]

I would check the bridge ground wire with a VOM as well, just in case.

You mean verify there is good continuity traveling through it? 
Incase there is a break somewhere in the hidden hole?

[elwoodblue]

You mean verify there is good continuity traveling through it? 
Incase there is a break somewhere in the hidden hole?

Sometimes if the ground wire is just clamped between the body and bridge with the bridge screw pressure, the wood can settle around the wire end and contact becomes iffy.
 The fix there would be to just move it over 1/8" or so.

[cozmik_cowboy]

You mean verify there is good continuity traveling through it? 
Incase there is a break somewhere in the hidden hole?

Sometimes if the ground wire is just clamped between the body and bridge with the bridge screw pressure, the wood can settle around the wire end and contact becomes iffy.
 The fix there would be to just move it over 1/8" or so.

Or put a small washer under it.

Peter

[keith_h]

Thanks for the quick replies.

I did check the ground wire to the bridge and it looked good.

I will get some copper tape and make sure it touches the metal cover.

On the volume pots there are three tabs, on-line schematics show a variation of what is on the bass.  Do the three tabs have unique functions or are they simply connecting points?

I have not tried the bass other than at home (someone call me for a fill-in!  ). There is a noticeable “hot spot” in my practice area...


Thanks again and an early Merry Christmas to all.

The three tabs each have a purpose. The pots are variable resistors. The two outer tabs would be at each end of the substrate and would measure the full resistance. The middle tab is the wiper and will measure different resistances depending upon where it is set and which outer tab you are measuring from. Basic passive bass volume wiring would be pickup/s go to one of the outer tabs and then out the middle tab to the 1/4" connector or tone control. A rudimentary pan or blend control would have each pickup going to its own outer tab and the middle tab going the 1/4" jack or tone control. I say rudimentary as signal levels would not be very consistent but this give you an idea of why three tabs.

[pauldo]

The control cavity is shielded and the noise is less noticeable.  Still there but not as prominent.

Keith thanks for the tab explanation!