RAISING THE TONE
Jamie Dickson asks… On or off, what do pickup covers on humbuckers actually change tonally?
As we delve deep into the world of modding in this issue’s cover story (see page 68), it seemed appropriate to revisit one of the first mods for electric guitar to receive widespread attention. Back in the late 60s and early 70s, before replacement pickups were a thing, it was fashionable to remove the pickup covers from your Les Paul’s humbuckers. The theory was that it made them sound louder and hotter. In the retroobsessed present, however, avid modders will just as often seek to fit period-correct PAF-style nickel covers back on again to get the vintage look, even on more modern models from PRS, Suhr and so on. But what are the real pros and cons behind covers? Are they just a cosmetic detail or is your guitar’s sound significantly affected?
“There are many other companies that produce aftermarket covers of all shapes, sizes and designs these days,” explains Tim Mills, founder of Cornwall’s Bare Knuckle Pickups, one of the best-known brands in the business and a supplier of high-quality pickup covers.
“Actually fitting a cover is easy enough to do on your own. You do need to ground the cover to the baseplate. So, you’ll need to just solder on some tags, but most importantly, once that cover goes on you’re essentially trapping air underneath it [increasing the risk of microphonic feedback], so it does need to go into a wax bath. This is where it gets a little bit more tricky. Some people are quite happy to melt wax and have a go at wax potting themselves,” Tim continues, “but if you get the temperature wrong you can melt the coil formers and you can also melt the insulation. So, as a general rule, we always say to people, ‘Let us do that’, and then if we get it wrong the onus is on us.
“So, customers phone up saying, ‘I’d like a new set of nickel covers,’ ‘I want radiator covers,’ or, ‘I’d like something funky etched on them’. We always prefer them to send the pickups in and we’ll do that as part
“It would be a complete fallacy to say you get loads more drive if you take a cover off a humbucker”
of our service. So then we can install the covers, pot them, play-test them. That way, we know that they’re not microphonic and we know that then the customer is going to go away happy.
”What tends to happen, unfortunately, is when people put their own covers on, if they haven’t wax potted them they get very microphonic. If you go out on a gig like that it can be like trying to control a wounded animal when it comes to microphonics, and it can be quite unpleasant!”
Assuming you didn’t want to go down the route of wax potting the pickup but still wanted to fit your own covers at home, what could you do to suppress microphonic feedback?
“There are ways around it,” Tim says “You can pack under the cover with some
tape. A lot of vintage-inspired players like to do that because they like a little bit of microphony, they like that kind of onthe-edge feel. So, if you line the inside of the cover with some paste tape; and also line over the top of the bobbins with it; and then securely clamp the cover on so that you really are minimising how much movement there can be inside; and then solder it down. That can work as well, but I generally would steer away from it if the player is using a lot of gain or a lot of volume, because any benefits that you’re going to get are completely outweighed by the problems you’re going to get with microphony. So, it’s just a question of applying some common sense to it.”
Metal Matters
So much for the ‘how’ and on to the crucial ‘why?’. Does the metal of the cover influence the performance and tone of the pickups to any tangible degree – or is this classic mod based on myth?
“This comes down to the integrity of the materials that are used in the cover,” Tim explains. “At Bare Knuckle, we only use very pure nickel silver for the covers. So, that’s as sonically invisible as you can get, I suppose. It has as little effect as possible on the actual tone. Some covers can be made out of a deep-drawn brass, for instance, because you can draw brass into a cover shape quite easily. These will then have a coating applied to them, like nickel or a chrome or something. Brass is a very good conductor, however, so that creates an eddy current effect going right round the pickup and that can roll off quite a lot of high-end. So, a pure nickel cover is going to have the least effect, sonically. There will be a very slight warming of the high-end, and I mean slight. It’s very subtle, but it is audible.
“We’ve produced a range of videos on YouTube that show the difference, where we’ve got the same sets of pickups but we popped covers on some and not others. Then play the same sorts of track to A/B them so you can get a rough idea. I think the majority of people go, ‘Yes, I can hear a little bit of a difference, but it is quite subtle.’ I think in the 60s you had lots of players, like Clapton and Page, all popping the covers off their PAFs, and claiming that they’re getting a lot more drive and a lot more clarity out of it.
“They probably did notice that little bit of extra zip in the high-end,” Tim concludes. “But I suspect they were probably also turning up a bit more as well, inadvertently. That was a very funny time because there were huge strides in the power of amplifiers running alongside with that. So, if I was to say, ‘Yes, if you take a cover off a humbucker you’re going to get loads more drive,’ that would be a complete fallacy. You don’t. You’ll notice a little bit of extra articulation, probably in the high-end, but it’s very subtle.”