Swapping Pickup Magnets

barnsleyboy

Hi all, hope you are all doing ok!

A quick question, following John Robson's lead on youtube, I'm swapping out the ceramic magnets on my HB-35 rather than changing the whole pickup. I ordered the same size magnets as the video (58mm x 3.2mm x 12.5mm) in Alnico II, IV and V so I can do a bit of experimentation.

Either John made a mistake when he measured the original pickups, or the chinese factory sourced a different pickup on my model, The ceramics appear to be 5mm thick and not 3.2mm. The obvious answer is to return the Alnicos and get the correct size. This is a bit of a faff as I've had them a little while. Would it make that much difference if I put the thinner magnets in? or does the magnet have to have full contact with the pole pieces and the brass pickup plate?

Any advice appreciated!

Winny_Pooh

It'll work fine but you'd need to cut down the spacer so it fits tightly and remove the gap.

CasperCaster

3.2mm or 1/8th inch is the standard thickness for vintage PAF style humbuckers. Everything should be in contact and reasonably firm to avoid microphonic feedback. Some plastic spacers are rectangular in cross section so may be 5mm tall but 3.2mm across....if you're lucky. Of course, it also depends on everything else below the coils - how far the slug polepieces protrude, and if they pass through the baseplate/ or if they could if required; the thickness of the metal keeper if the pickup has a screw coil etc. If the only problem is the plastic spacer just replace them - you can get 3.2mm or 1/8th inch strip wood from model shops and Hobbycraft for very little. 

Roland

@Alegree @OilCityPickups ;

Funkfingers

Erm, is a 5mm thick alnico magnet a good idea?

Alegree

You need to swap over to 3.2mm spacers like these
https://www.alegree.co.uk/collections/pickup-building/products/humbucker-plastic-spacer?lshst=collection

Funkfingers

barnsleyboy said:

ceramic magnets on my HB-35

Ceramic magnet humbuckers on a 335-alike? Highly unusual.

The 5mm thickness implies either a high output “Heavy Metal” pickup or the magnet power is balancing a very low coil output - in the manner of a Filter’Tron.

For the neck/Rhythm position, I suggest A4, under a proper nickel silver cover, not too much wax inside the cover.

For the bridge/Treble position, Alnico 5 will provide clarity. Rough/sand cast unoriented A5 sounds a bit more interesting than the polished type. I cannot remember the “science bit” explanation for why this is.

HINT: As you remove the stock magnets, mark which way around they were. Try to maintain the same polarity orientation when you insert a replacement magnet.

barnsleyboy

barnsleyboy

@Alegree @OilCityPickups ; There doesn't seem to be a plastic spacer! I think I'll bung them in and see what happens.

ICBM

The magnet doesn’t need to be in contact with the brass baseplate, so if there’s a gap just cut a piece of cardboard of the right thickness to the same size as the magnet. Cardboard has slight give in it under compression so it will help to keep everything tight when you do the screws up.

barnsleyboy

Cardboard shims - Yep, that sounds like an ideal solution! I'll give it a try, thanks @ICBM and thanks everyone else for taking the time.

One last question, I'm probably going to swap out the magnets a few times between all 2's, 4's. 5's or different combinations on neck and bridge. The pickup covers have a blob of solder on each side to fix them in place and stop them dropping out. I don't want to keep soldering then unsoldering the covers and risk melting something in the process, so I'm going to use a bit of masking tape/ electricians tape to secure them as a temporary measure. Do I need to maintain ground continuity between the brass base plate and the cover with say a piece of shielding tape? Or are the blobs of solder purely to fix the covers, and not used for grounding purposes?

ICBM

barnsleyboy said:

One last question, I'm probably going to swap out the magnets a few times between all 2's, 4's. 5's or different combinations on neck and bridge. The pickup covers have a blob of solder on each side to fix them in place and stop them dropping out. I don't want to keep soldering then unsoldering the covers and risk melting something in the process, so I'm going to use a bit of masking tape/ electricians tape to secure them as a temporary measure. Do I need to maintain ground continuity between the brass base plate and the cover with say a piece of shielding tape? Or are the blobs of solder purely to fix the covers, and not used for grounding purposes?

The cover does need to be grounded to provide a shield, but you usually find there's enough contact around the edges of the plate - it's rare that there's a gap all the way round. It's also common for the height springs to touch the sides of the cover, which does the same thing.

You find this out when you're trying to *deliberately* leave the covers ungrounded, to preserve the appearance but remove the treble-cutting effect of the cover capacitance .

barnsleyboy

Awesome, big Free-time thumbs up!

OilCityPickups

Funkfingers said:

Erm, is a 5mm thick alnico magnet a good idea?

Gretsch thought so ... that's what proper Filtertrons have. Low winding count and a stonking big magnet produces a unique sound all of its own.

barnsleyboy

A quick update on the magnet swap, at the moment I'm liking a 2 in the neck, and a 5 in the bridge. One thing I'm noticing is in the middle position there is a definite drop in output. When I back off one of the volume pots a tad the overall volume increases, I was very careful to keep the polarity of the magnets the same, so I don't think it's the old Peter Green out of phase thing. Could it have something to do with two different strengths of magnet?

Funkfingers

Alnico 2 will have a weaker magnetic field than Alnico 5. 

The volume drop when two pickups are selected together in parallel occurs because their overall resistance is then divided rather than summed.

The magnetic poles of bar magnets run along the long edges, not the flat faces.

The proportional increase in volume as one volume pot is rolled off is what would be expected to happen as the phase reversal notch filtering effect reduces.

barnsleyboy

The magnetic poles of bar magnets run along the long edges, not the flat faces.

Hmm, I've had another play on the guitar and I wonder if maybe I might have inadvertently switched the polarity of one of the magnets! I'll open her up again and see if it makes a difference. Does it matter which pickup I rotate the magnet on?

The proportional increase in volume as one volume pot is rolled off is what would be expected to happen as the phase reversal notch filtering effect reduces.

I have a Chapman ML-2 Classic (don't snigger) which admittedly has a matching set of Seymour Duncans and a phase reversal switch for the neck pickup. With no phase reversal the middle position doesn't experience the volume drop, but obviously when engaged, it gets quieter with both volume controls on full. Could explain a lot!

CasperCaster

To me it does sound like a phase issue. Given phase is relative, it doesn't matter which pickup you flip the magnet on, but do only do it to one of the pickups. 

Funkfingers

barnsleyboy said:

Does it matter which pickup I rotate the magnet on?

No but, in your position, I would use this opportunity to try the Alnico 4 magnet in the neck position pickup.

barnsleyboy

that's not a bad idea @Funkfingers .... I feel some more tinkering under the hood coming on!!

barnsleyboy

CasperCaster said:

To me it does sound like a phase issue. Given phase is relative, it doesn't matter which pickup you flip the magnet on, but do only do it to one of the pickups. 

Now here's the thing about my previously mentioned ML-2, The push pull tone pot reverses the phase of the neck pickup, so when both pickups are on you get the PG tone when it's engaged. If I have just the neck pickup on (to my ears) there is a difference in tone when I switch the phase switch. I can't quite put my finger on what the difference is, maybe it gives a more open sound. With this in mind, I'm toying with the idea of installing a phase reverse switch on the bridge pickup too, which could potentially give me a wider palette of tones. If anyone has any thoughts or observations I'd appreciate your views