Dang HUM!

[No Treble]

New member, first thread!
Troubleshooting a problem with a Spector Performer 4 bass.
I just rescued this thing 3 weeks ago from the Guitar Center ab-used instrument section for a great deal! Very clean, passive EMG SSD pickups, nice looking. It's still inside the 30-day window, but I don't want to return it. The thing sounds great, I love it.

Problem is this:
Dang hum! The 60 Hz type. Barely noticeable at first, but over the last 3 weeks, it has gotten progressively worse, and achieved "intolerable" status today. Touch anything bare metal from the bridge, strings, the cord shell, or the bare metal of my amp, and it would stop. Leave the guitar alone, and it would hum. Not loud, but it was there. I took it back to guitar center today, to the oracle of all things "electric guitar", and the man was rather uncooperative. I knew what I'd have to do.

I tried a few things, and have troubleshot it to either a bad pot, or a bad cap.
The potentiometer is for the neck pickup volume control, a 500K audio taper pot.
The cap goes between the neck pickup tone pot center terminal and the volume knob pot center terminal where the green wire for the first neck pickup winding is also soldered. Maybe a pic would help here. While troubleshooting, I have developed a new problem where the neck pickup produces no output at all. Great.

I jumpered in another pot of equal Ω rating, and restored control. So, I can have a bad pot, but what if that cap goes out? I jumpered it on the bridge pickup and got the same result as the other pickup that is now inop. It went dead.
What does this cap do? Is this for tone control?

 

[NigelD]

Sounds like a ground issue or a bad connection somewhere. Start fresh. Rewire the circuit v/ v/ t (basic j bass).Diagrams on Stew-Mac ,Best Bass Gear,and here on TB (pickups & electronics).

 

[Turnaround]

Yes the cap is for tone control - it's bleeds higher frequencies to ground through the tone pot. Just how much is bled to ground is controlled by the pot. Jumpering the cap shorts ALL of the signal to ground, so no output.

From your description it sounds like there is a bad volume pot on the neck pickup or a bad solder connection to it. That could introduce a lot of hum. You may also need a proper shielding job.

 

[DiabolusInMusic]

New member, first thread!
Troubleshooting a problem with a Spector Performer 4 bass.
I just rescued this thing 3 weeks ago from the Guitar Center ab-used instrument section for a great deal! Very clean, passive EMG SSD pickups, nice looking. It's still inside the 30-day window, but I don't want to return it. The thing sounds great, I love it.

Problem is this:
Dang hum! The 60 Hz type. Barely noticeable at first, but over the last 3 weeks, it has gotten progressively worse, and achieved "intolerable" status today. Touch anything bare metal from the bridge, strings, the cord shell, or the bare metal of my amp, and it would stop. Leave the guitar alone, and it would hum. Not loud, but it was there. I took it back to guitar center today, to the oracle of all things "electric guitar", and the man was rather uncooperative. I knew what I'd have to do.

I tried a few things, and have troubleshot it to either a bad pot, or a bad cap.
The potentiometer is for the neck pickup volume control, a 500K audio taper pot.
The cap goes between the neck pickup tone pot center terminal and the volume knob pot center terminal where the green wire for the first neck pickup winding is also soldered. Maybe a pic would help here. While troubleshooting, I have developed a new problem where the neck pickup produces no output at all. Great.

I jumpered in another pot of equal Ω rating, and restored control. So, I can have a bad pot, but what if that cap goes out? I jumpered it on the bridge pickup and got the same result as the other pickup that is now inop. It went dead.
What does this cap do? Is this for tone control?

How is the shielding? In most cases that is the culprit if you have a hum that stops when you touch metal/strings/bridge.

 

[No Treble]

Thanks for all the suggestions! This has to be the first forum I've visited where everyone was actually helpful, rather than condescending.

I've learned something about this particular racket: I have my rig set up in half of the "dining room", and the chandelier has a dimmer switch on the same circuit. When I use it, it changes the dang hum, and is therefore the big jerk here. It never goes away, but changes intensity as I change its brightness.
After sitting under it rewiring the whole dang bass, with new pots and input jack, I plugged in the bass to test it, and it worked great, but the dang HUM was STILL THERE. This chandelier makes me hot under it, as more of my scalp is exposed to light every year due to age, so I turned it down, and whizbang magic happened. It changed! I now know that either the dimmer must go, or I get to negotiate another room. Either way, I win.

Another handy lesson learned: there is no schematic online for the Spector Performer. There is something posted here in one of the threads, but it is incorrect. I learned this today. I'll try to remake it as it was/is in my bass, as a contribution to the tech dept.

Thanks again for the help. I now gather that I should look more into the shielding issue...

 

[guy n. cognito]

Sorry for some of the terrible advice above. When you have a hum that goes away when you touch the strings or metal, that is shielding issue. The ground is fine. Have the bass properly shielded and star grounded.

 

[vaesto]

Sorry for some of the terrible advice above. When you have a hum that goes away when you touch the strings or metal, that is shielding issue. The ground is fine. Have the bass properly shielded and star grounded.

I have exactly the opposite opinion: if hum goes away when you touch the metal parts it is grounding issue. Your body becomes "ground" that way. Although, poor shielding may result in a greater hum and instrument will just pick more noise. In any case the shielding MUST be grounded as well.

 

[guy n. cognito]

I have exactly the opposite opinion: if hum goes away when you touch the metal parts it is grounding issue. Your body becomes "ground" that way. Although, poor shielding may result in a greater hum and instrument will just pick more noise. In any case the shielding MUST be grounded as well.

The only reason the humming stops when you touch metal is because the grounding is intact. It's not an opinion, it's scientific fact.

 

[vaesto]

The only reason the humming stops when you touch metal is because the grounding is intact. It's not an opinion, it's scientific fact.

If it is scientific fact can you share the link to it?

Because IMHO the only way grounding may be intact is if it were no grounding when you touch metal parts and your body becomes that "ground" due to its capacitance. The other way if we have good ground connection: touching metal parts would do nothing because planet Earth has greater capacity and metal wires have less resistance to pass the "ground" electricity.

In some case the shielding is left ungrounded (i.e. not electrically connected to any ground wire). In that case it becomes a noise pickup/magnifier.

Please, correct me if I'm scientifically wrong.

 

[guy n. cognito]

If it is scientific fact can you share the link to it?

Because IMHO the only way grounding may be intact is if it were no grounding when you touch metal parts and your body becomes that "ground" due to its capacitance. The other way if we have good ground connection: touching metal parts would do nothing because planet Earth has greater capacity and metal wires have less resistance to pass the "ground" electricity.

In some case the shielding is left ungrounded (i.e. not electrically connected to any ground wire). In that case it becomes a noise pickup/magnifier.

Please, correct me if I'm scientifically wrong.

Just prove it to yourself: disconnect your bridge ground, then touch the strings while the buzzing is occurring. It won't stop.

 

[guy n. cognito]

There's also a ton of great info in this thread:

Jazz Shielding Pictorial (Big Images Warning)

 

[Turnaround]

If it is scientific fact can you share the link to it?

Because IMHO the only way grounding may be intact is if it were no grounding when you touch metal parts and your body becomes that "ground" due to its capacitance. The other way if we have good ground connection: touching metal parts would do nothing because planet Earth has greater capacity and metal wires have less resistance to pass the "ground" electricity.

In some case the shielding is left ungrounded (i.e. not electrically connected to any ground wire). In that case it becomes a noise pickup/magnifier.

Please, correct me if I'm scientifically wrong.

You actually have it backwards. You are a noise source. When you touch the strings or any other part of the instrument that is grounded you ground yourself and that drains away the noise.

 

[testing1two]

Thanks for all the suggestions! This has to be the first forum I've visited where everyone was actually helpful, rather than condescending.

I've learned something about this particular racket: I have my rig set up in half of the "dining room", and the chandelier has a dimmer switch on the same circuit. When I use it, it changes the dang hum, and is therefore the big jerk here. It never goes away, but changes intensity as I change its brightness.
After sitting under it rewiring the whole dang bass, with new pots and input jack, I plugged in the bass to test it, and it worked great, but the dang HUM was STILL THERE. This chandelier makes me hot under it, as more of my scalp is exposed to light every year due to age, so I turned it down, and whizbang magic happened. It changed! I now know that either the dimmer must go, or I get to negotiate another room. Either way, I win.

Another handy lesson learned: there is no schematic online for the Spector Performer. There is something posted here in one of the threads, but it is incorrect. I learned this today. I'll try to remake it as it was/is in my bass, as a contribution to the tech dept.

Thanks again for the help. I now gather that I should look more into the shielding issue...

Sounds like you may have less of a bass problem and more of a household dimmer problem. Dimmers are a fantastic source of EMI/RFI noise for your pickups to amplify. Cheap dimmers do the bare minimum to filter these noises since most folks don't have sensitive transducers hooked to amplifiers in their house.

A quick test would be to turn the dimmer completely off and see if the noise subsides or at least reduces.

A little info on noise and dimmers - Kill Studio Hum and Buzz at the Source

 

[BlueTalon]

I don't like thinking of shielding and grounding as two different things. They are essentially the same thing -- if done properly, the shielding just becomes an extension of the ground.

(If not done properly, i.e., if the shielding is not grounded, it becomes a nice big noise antenna.)

 

[vaesto]

You actually have it backwards. You are a noise source. When you touch the strings or any other part of the instrument that is grounded you ground yourself and that drains away the noise.

Hmm. Maybe. But then explain me why my bass has hum when I'm away from it and it doesn't change when I take the bass (not touching metal parts)? And why the hum disappears then I actually touch any metal part? And by the way we don't have grounding wire (green-yellow) in our house. So I guess my instrument doesn't get grounded through the amp.
P.S. I did an experiment - connected the amp's body to the water pipe using a piece of wire. That way I've got good ground and my bass has become dead silent. Regardless me touching the metal parts or not.

 

[vaesto]

If not done properly, i.e., if the shielding is not grounded, it becomes a nice big noise antenna.

Exactly!