Hum when touching poles only with Strat-X wiring

[Max]

Hi,

I have a problem with my Strat-X wiring. I replicated it exactly as in the schematic diagram from the Phostenix Pages. I've attached the diagram picture for reference. I used an original Fender S1 pot and an original Fender superswitch with 24 contacts. My pickups are with RWRP middle. The overall switching does work normally, at least with S1 'off'.

Now, with S1 'off', when I touch pickup poles in certain superswitch positions there's hum. When I touch a grounded part at the same time, the hum stops (or greatly reduces). I tried to check if the culprit could be the pickups, for that I wired neck and bridge directly to output jack, bypassing any electronics, and there was no that hum. I've checked thoroughly the wiring like 5 times, everything is correct, for sure. There're no cold joints, nor unwanted joints.

It's worth noting that I get hum when I touch the common or the hot wire on a pickup. In the normal case, there should be no hum when touching the common pickup wire, as I understand.

I'm looking for any advices how to troubleshoot this issue.

[newey]

Max-

Hello and Welcome to G-Nutz2!

Sorry, I don't have any answers for you at first blush. But someone will be along.

My only thought is that perhaps your particular Strat pickups are grounded to the baseplate and thereby to the pole pieces somehow. That's not the usual way of Strat pickups, most have a fiber/plastic base which is non-conductive. But maybe it's more like a Tele, where the neck pickup has a metal cover that is grounded, you have to disconnect that to do series wiring. I dunno, that's all I got at the moment.

[Max]

Thank you, newey!

Sorry for telling nothing about pickups. They're are regular Strat pickups, custom built as replica of vintage Fender pickups. Nothing special in the design. They don't have any conductive parts on the base which is made of plastic. I suspect that it could be something wrong with S1 switch itself, although everything is brand new on the pickguard. I'm going to find a multimeter and check that. I'll write back.

[Max]

Can anyone tell if Strat-X2 wiring I use (see above) has inherently that hum? Maybe it is normal for this wiring? Symptoms seem as there's some phase flipping going on.

Meanwhile, I've checked everything I know but can't find the cause of the problem. I'm baffled due to trying to find it for several days without luck.

I replicated the same behavior with two different amps (tube vibrolux, digital processor) in two different locations. I've tested S1 switch for correct switching between contacts. I've inspected the super switch to see if blades and contacts engage correctly. Constructively, the pickups are a replica of Fender Texas Special, without any improvements. Wired with standard direction, the common terminal inward. The magnets are electrically floating (not grounded), without shielding.  Then I completely changed the pickups set for another exact copy. With old and new sets, the pickup poles are tested with a good multimeter for resistance against pickup output terminals, everything is fine. All that didn't help.

For what it's worth, here is some data.

A hum table, where 1 is bridge switch position and 5 is neck:

S1 is off

-------

1: N and M

2: N

3: N

4: none

5: none

S1 is on
-------
1: N and M
2: N
3: N
4: N and M
5: N

Pickups' resistance alone:

B: 6.08k

M: 5.83k

N: 5.64k

Resistance measured at output jack, where 1 is bridge switch position and 5 is neck:

1: 5.93k

2: 2.93k

3: 5.68k

4: 2.83k

5: 5.50k

[newey]

A hum table, where 1 is bridge switch position and 5 is neck:

S1 is off
-------
1: N and M
2: N
3: N
4: none
5: none

I'm not exactly clear on what this means. Position 1 should be the bridge pickup alone. Is that what you are getting at position 1? Does your notation of "N and M" at position 1 means that the neck and middle positions are producing hum at that position? And, if so, how did you ascertain that the hum was coming from both those pickups at position 1?

You resistance measurements look as expected, provided that the table "measured at output jack" was measured with the S1 switch in the "normal Strat mode", not in the series mode. Also, that V and T controls were maxed for the measurements.

I didn't see anything obvious in the diagram that would cause excessive hum. obviously single coil pickups do hum a bit, but what you're describing isn't that. I'm at a loss, max, we'll have to wait for someone who may be able to provide you with a better answer. Sorry.

[Max]

'1: N and M' means the neck and the middle pickups are humming in position 1.

I ascertain that the hum is coming from those pickups by touching their poles. As I described in my initial post, the problem is that there is hum when I touch pickup poles (magnets) by hand, and there's no hum when I don't touch the poles.

[Max]

Aug 31, 2022 11:43:50 GMT -5 newey said:

provided that the table "measured at output jack" was measured with the S1 switch in the "normal Strat mode", not in the series mode. Also, that V and T controls were maxed for the measurements.

Yes to all

[Max]

Thanks newey for trying to help me. I'm really starting to suspect that this hum is normal for this wiring. I would like that somebody with this or similar wiring chime in and tell whether it hums.

[ashcatlt]

I can’t speak to that wiring specifically, but I don’t find it unusual or surprising that touching an ungrounded pole piece would cause some noise. As we know, a lot of the noise we get from pickups comes from us. That’s why we have a bridge ground. When you touch a pole, you’re basically focusing all that noise right into the middle of the coil where it can do the most damage. Happens on several of my guitars. The fix is to not do that.

[Max]

You're right ashcatlt, a hum is expected sometimes. But in my case I see that hum abnormal because there's no such hum when I connect these pickups straight to the jack, bypassing all the controls. Also, I have another Fender Stratocaster with Fender Custom Shop '69 pickups, wired as standard, and there's no such hum when I touch the pickups. I think the CS '69 are constructively very similar to a Texas Special replica, and I expect similar behavior from both.

[unreg]

Perhaps your interesting hum situation is a result of your creation of a giant grounding spot on the back of your Tone 1 pot.


It may be a star ground of sorts, but you’ve attached a bunch of signal grounds to the back of a Tone pot. The back of pots should only be reserved for shield grounds.


At least, that’s what I was taught by ashcatlt; and fixing my ground system, so that shield and signal grounds are only combined after all electronics, helped tons with my hum problem. But, my hum problem was dependent on other factors which your guitar electronics amplifier doesn’t seem to be attacked by.


EDIT: You say that the odd hum problem isn’t present when connecting your pickups directly to your jack. Maybe that’s bc you remove the shield/signal ground combination on electronics before your jack AND your vol pot is removed too, so the signal can’t be as loud?

[ashcatlt]

To be clear, I don’t really care where you collect your grounds. IF they’re all actually well bonded and conduct properly, any place in the circuit is about as good as any other (with the caveat of watching for signal grounds which become signal hots from phase switches, series connections, etc). My objection to using a pot case for that is that they are difficult to solder to and get an actual solid connection that you can trust. Why make it harder on yourself than you need to? Find a lug that’s actually meant to be soldered and do it there if at all possible.

[Max]

Yes, I've used the Tone 1 back case as common ground point, like on the original picture. While I agree with ashcatlt that it's not perfect, while I agree with unreg that it could create some hum problems, though I doubt that this is the culprit in my case. I get very strong hum, like touching the signal wire, with loud pop. That doesn't seem like some hum. That is The Hum.

I conclude that a remedy would be grounding the poles. But it seems like surrender.

Edit: typo "Tone 1"