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Topic: Microphonic pickup -- how is it fixed? |
Jack Hanson
From:
San Luis Valley, USA
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Posted 19 Apr 2018 5:57 am |
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| The pickup in one of my lap steels apparently is extremely microphonic. The pickup itself sounds fine, but whatever physical contact is made with the body of the instrument is amplified too, to the point of distraction. I've read that this malady can be cured by a process known as "repotting." Can someone explain what that means in words a neophyte can understand? Is this a procedure that someone could attempt at home? |
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Dave Mudgett
From:
Central Pennsylvania and Gallatin, Tennessee
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Posted 19 Apr 2018 6:11 am
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Potting a pickup generally means immersing the pickup and its windings into some type of liquid which, when cooled or dried, solidifies the windings to keep them from sympathetically vibrating with sounds coming from the amp or other sources such as physical contact with the guitar.
A lot of guitar pickups are potted with some type of wax, or something similar. For example, wax is heated in a pot to a temperature where it's liquid but not so hot that it melts the bobbin. Then the pickup is dipped long enough to permeate the windings.
There are other variations, such as dipping the pickup in lacquer.
Yes, it can be done at home. I probably wouldn't recommend someone without experience do this to a valuable pickup like a vintage Gibson PAF, vintage Strat/Tele, or something you really don't want to mess up - it is possible to short/open the coil. |
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Jack Hanson
From:
San Luis Valley, USA
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Posted 19 Apr 2018 7:43 am
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| Thank you, Dave. Great info. |
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Michael Maddex
From:
Northern New Mexico, USA
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Bob Hoffnar
From:
Austin, Tx
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Posted 19 Apr 2018 8:34 am
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The problem might helped by remounting the pickup so it doesn’t come in as much direct contact with the body.
Can you talk into the pickup and hear your voice through the amp ? That is when the problem is that the pickup is microphonic.
_________________
Bob |
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Jack Hanson
From:
San Luis Valley, USA
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Posted 19 Apr 2018 9:00 am
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| Michael, thanks for the Stew-Mac link. I should have known they would have something relevant to the problem. I will be sure check it out. |
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Jack Hanson
From:
San Luis Valley, USA
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Posted 19 Apr 2018 9:09 am
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| Bob Hoffnar wrote: |
| The problem might helped by remounting the pickup so it doesn’t come in as much direct contact with the body. |
The pickup itself does not come into direct contact with the body as far as I can tell. It's suspended by a pair of machine screws from a relatively thick plastic mounting plate. The plate itself is attached to the body with four wood screws.
| Bob Hoffnar wrote: |
| Can you talk into the pickup and hear your voice through the amp ? That is when the problem is that the pickup is microphonic. |
No, not really. The problem is that virtually any contact with the wood body itself is amplified to the extreme. It sounds like the piece of plywood with a contact mic that John Hartford used to dance on when he played his fiddle. Could it be that the pickup is not microphonic at all, and that there's some other issue?
The instrument in question is branded "American." It's virtually identical to the Kalamazoo KEH that Gibson manufactured between approximately between 1948 and 1952. The odd thing is that I also have a Kalamazoo with virtually the identical setup, and it's quiet as a church mouse.
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Paul Arntson
From:
Washington, USA
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Posted 19 Apr 2018 12:21 pm
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Could there be a backing plate that has come unstuck?
_________________
Excel D10 8&4, Supro 8, Regal resonator, Peavey Powerslide, homemade lap 12(a work in progress) |
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Carl Mesrobian
From:
Salem, Massachusetts, USA
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Posted 19 Apr 2018 1:39 pm
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Try using a short piece (1/4 inch or so)) of rubber tubing over the screw before it attaches the pickup.
Edit Ignore this paragraph -- So, if the pickup is mounted onto the deck, put the rubber between the deck and the bottom of the pickup.
(If it's mounted to a pickguard), use the lower half of the drawing. it might help - the rubber tubing will have some springiness to it.
 [/img]
_________________
--carl
"The better it gets, the fewer of us know it." Ray Brown |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 19 Apr 2018 3:33 pm
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| First, you should remove the strings to see how bad the microphonic problem really is. If tapping the body makes noise (with the strings removed), you can be sure the pickup is the culprit. If there's little or no noise with the strings removed, then isolating the pickup somewhat (with spacers or foam rubber) may fix the problem. |
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Jack Hanson
From:
San Luis Valley, USA
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Posted 19 Apr 2018 3:39 pm
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| Paul Arntson wrote: |
| Could there be a backing plate that has come unstuck? |
I don't think so, Paul. But I'll be sure to check once I open it up. Thanks for the suggestion. |
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Jack Hanson
From:
San Luis Valley, USA
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Posted 19 Apr 2018 3:45 pm
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| Carl Mesrobian wrote: |
| Try using a short piece (1/4 inch or so)) of rubber tubing over the screw before it attaches the pickup. |
Like they used to do (and probably still do?) on Stratocasters. That's an excellent suggestion, Carl. I'll give it a try. |
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Jack Hanson
From:
San Luis Valley, USA
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Posted 19 Apr 2018 3:56 pm
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| Donny Hinson wrote: |
| First, you should remove the strings to see how bad the microphonic problem really is. If tapping the body makes noise (with the strings removed), you can be sure the pickup is the culprit. |
It's bad. Any little jostle is amplified. Sounds like a kick drum through a PA when you thump on the body with your fingertips. The thing is, it sounds fine when you play it. It's a single coil, and there's little if any 60-cycle hum, so it doesn't appear to be a shielding or a grounding issue. |
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Bob Hoffnar
From:
Austin, Tx
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Posted 20 Apr 2018 5:05 am
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It’s a pretty cool looking guitar. I would be be very careful modifying it. The fix might be worse than the cure.
_________________
Bob |
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Jack Hanson
From:
San Luis Valley, USA
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Posted 20 Apr 2018 6:34 am
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| Bob Hoffnar wrote: |
| It’s a pretty cool looking guitar. I would be be very careful modifying it. The fix might be worse than the cure. |
Thanks, Bob. This style of instrument is not particularly uncommon; it's the fourth one I have come across. Two were branded "Kalamazoo." One is unknown because it was just a body missing everything aside from its nut and bridge, and it had been stripped to bare wood. Then there's this one -- the "American." All were purchased on eBay and they were all inexpensive.
These instruments originally were hardwired, so I removed the cable, drilled a hole, and installed a jack and jack plate. The three that still had tuner strips all had disintegrating or missing plastic buttons, which I replaced. So, they have already been modified -- the tuner buttons were a necessity and I consider the jack an upgrade.
Austin's own Carolyn Wonderland made a video a while back featuring her KEH:
https://www.youtube.com/watch?v=bsVMfARmqaI |
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Jim Palenscar
From:
Oceanside, Calif, USA
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Posted 21 Apr 2018 6:13 am
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| If you'd like some help potting/re-potting the pickup- I'm happy to do it for you |
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Michael Brebes
From:
Northridge CA
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Posted 21 Apr 2018 6:51 am
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An inexpensive wax melting/potting unit can be something as like a small mini crockpot about 6 inches in diameter. The heat is controllable enough as to not overheat the wax. I make a mixture of beeswax and paraffin.
_________________
Michael Brebes
Instrument/amp/ pickup repair
MSA D10 Classic/Rickenbacher B6/
Dickerson MOTS/Dobro D32 Hawaiian/
Goldtone Paul Beard Reso
Mesa Boogie Studio Pre/Hafler 3000
RP1/MPX100 |
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Jim Palenscar
From:
Oceanside, Calif, USA
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Posted 21 Apr 2018 7:15 am
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Me too  |
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Godfrey Arthur
From:
3rd Rock
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Posted 21 Apr 2018 7:39 pm
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Yes the days of pickup potting ala Van Halen.
Not that Eddie invented it he may have just made it popular.
Edison's engineers used to wax/resin pot electronics long ago to cure hum and feedback on electronics.
The wax, seeping inbetween helps the windings to go deaf a little so they don't start resonating next to a loud amp.
Some pickup makers followed suit.
Lacquer and epoxy potting was tried as well.
_________________
ShoBud The Pro 1
YES it's my REAL NAME!
Ezekiel 33:7 |
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Jack Hanson
From:
San Luis Valley, USA
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Posted 22 Apr 2018 7:39 am
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Thanks for your replies, everyone.
First, I'm gonna try isolating the pickup from the mounting plate with rubber tubing (as soon as I can locate the chunk I have sitting around here somewhere).
If that doesn't do the trick, I may give potting a shot. I have an old glue pot I bought about 40 years ago that looks exactly like the one in the Stew-Mac tutorial. Need to get a kitchen thermometer and the wax. Pretty certain my local grocery would have paraffin. Where does one obtain beeswax, aside from a beehive? |
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Jim Palenscar
From:
Oceanside, Calif, USA
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Posted 22 Apr 2018 7:57 am
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| Amazon |
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Jack Hanson
From:
San Luis Valley, USA
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Posted 22 Apr 2018 8:40 am
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| Thanks, Jim. |
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