Gibson Ultratone Lap Steel P90 - question regarding tone

[ZRGuitarPickups]

Hey there, I've got a customer with the original p90 in their Gibson Ultratone Lap Steel. They are complaining that no matter what, this thing is just too trebly for them. I'm not sure if it's the normal sound they don't like, or if there's something wrong with the pickup. They do have a bit of 60 cycle hum coming from their home, so I'm likely going to recommend a few tips for fixing that first. The amps sound fine without anything plugged into them.

I'm wondering what could be causing this in their lap steel. The electronics in this thing look brand new and seem to be original, so I'm thinking it's NOT a cold solder joint or anything on that end. There seems to be some aluminum foil wrapped around it though - I'm guessing someones attempt to lower the hum? I'll recommend adding a bit of copper tape to the backplate just in case.

If it is a short in the pickup, I'll only be able to tell once they bring/send it in to me. From what I've read, I should be winding this with about 10,000 winds of 42PE, is that correct? Are there any other steps I should be taking to help eliminate this rogue noise from their guitar, hopefully without replacing their original wiring?

Also, I'm thinking it's possible that they could have a bad capacitor somewhere. In his lapsteel, there are two capacitors and three knobs. Maybe i'm wrong but, what would the third knob do in a guitar with 1 pickup? Is it a bass rolloff?




Any help would be appreciated!

Thanks,
Zach

[big_teee]

A P90 is a single coil pickup, and will pickup 60 Hz hum.
Loose ungrounded foil can be microphonic.
Test the pickup to see that is not open and you get the 7.5-8.5k ohms.
Check that each Pot is good by reading them with a VOM.
If the guitar has always been to bright, you can put larger value caps in it.
Here's some good info on the tone circuit.
https://www.google.com/url?sa=t&rct=...XxGjuHRHyAXcnB
T

**Anyone have any thoughts or ideas?
Please jump in!

[ZRGuitarPickups]

Hey T,

Thanks for that advice. I wasn't too sure when I saw the aluminum in there - looked pretty sketchy for sure. I'm seeing now though that the same material is in that picture you showed me, must've been something gibson did?

I'm not sure what his experience with a lap steel is, but what I've seen is that people tend to start with the tone knobs on '0', then bring it up until they have the tone they're looking for. I'm wondering if he's tried this or not. I'll write back here when I hear back from him.

'Till then, on the very off-chance he DOES want a rewind (I'm pushing for him to keep that thing as original as possible, unless something is totally off with the electronics), does anyone have any info regarding the size of these pickups? I haven't seen any info here on an Ultratone specifically (just the BR-2 and BR-6, not sure how different they are from the Ultratone), but looking at the other similar models, it seems that these may have had a slightly different shape and spacing than a regular p90.

Also, I saw in an earlier article that some people have fixed the noise issue just by replacing the coax ground wire with something else. Any way I can test this to see if it's his wire causing issues?

Thanks,
- Zach
ZRGuitarPickups

[rjb]

Steve A. has posted a wiring diagram. Yes,the "third" knob is a bass rolloff.
http://music-electronics-forum.com/s...ad.php?t=20045

[big_teee]

Steve A. has posted a wiring diagram. Yes,the "third" knob is a bass rolloff.
http://music-electronics-forum.com/s...ad.php?t=20045

The diagram calls it a treble bypass.
I referred to the same diagram, in my post 2 pdf.

[rjb]

The diagram calls it a treble bypass.
I referred to the same diagram, in my post 2 pdf.

I believe you. The pdf reader on this borrowed computer is whacked out.
In the thread I linked to, Steve sez he "doesn't know why" he originally called the circuit a treble bypass.
At any rate, its just a bass-blocking cap in series with the pickup, with a variable resistor across the cap.

[big_teee]

I wonder what the end result and outcome was?
T

[ZRGuitarPickups]

Just heard back from him

He was able to fix the issue by replacing the ground wire connecting the bridge to the rest of the circuit and giving his output jack a more solid ground connection.
"Voila, no hum"

Now hoping he's still thinking of replacing his p90, but given the weird sizes on those things I'm a little hesitant to offer.

[ZRGuitarPickups]

Here are some images of his temorary fix:



He said the pickup sound 100x better now.

I've got another customer coming in with a 50's Lap Steel that has gone completely dead. I had no idea that these things were this common, I guess I'll have to pick one up myself so I can start offering pickups for em.

Thanks again for the info! Will post