Can I move the pole pieces?

[sanrafael]

Re: Can I move the pole pieces?

theodie,

I do not have access to a powerhouse. There were some pictures of the inside at FDP, but cannot get access to them now. However, the description that is still there says that there are slugs in the outer holes in the dummy coil. Here is why:

1. We need to make a coil with the same sensitivity to stray magnetic fields as the single coil pup, but without the sensitivity to the strings. It needs to have the same orientation as a pup to pickup the same fields.

2. It is necessary to throw out the magnets to eliminate the sensitivity to the strings completely. (One could use magnets, but put the dummy coil further from the stings, but that would not be as good.)

3. But it is necessary to use some ferromagnetic material to increase the sensitivity to stray fields over what an "air core" coil has.

4. A magnet used as a core does not have as high a permeability (sensitivity to magnetic fields) as a material such as soft iron that does not support permanent magnetism. We do not need as much soft iron as alnico to get the sensitivity.

5. Therefore, one can use just enough soft iron in the dummy coil to get the proper sensitivity. Apparently this means put slugs in just the outer holes.

6. It might also be necessary to adjust the amount of wire on the dummy coil.

The result is a coil which can be used to cancel magnetic hum, but does not see the strings. It is a clever idea and can give great results when properly executed.

 

[Thames]

Re: Can I move the pole pieces?

I think my Powerhouse strat dummy coil has 2 magnets (1 and 6) I can verify this tonite.

 

[sanrafael]

Re: Can I move the pole pieces?

Thanks, Thames. Check to see if they are really magnets; I would expect them to be unmagnetized iron (or steel) slugs, but I guess you could do it with magnets, too.

 

[Artie]

Re: Can I move the pole pieces?

Artie,

This is getting a bit complicated, but let me try again . . .

Remind me not to "correct" you in the future. I have a feeling that you know a heckuva lot more about this than I do. :smack:
I'll try to stick to "connecting point A to point B".

BTW - Great information. This info is vault-worthy.

 

[brandobean]

Re: Can I move the pole pieces?

So riddle me this:

I unwound a RWRP coil to be the same K ohms as the "active" coil I am using.

It still hums. I tried it hooked up in series and parallel and I reversed the leads and tried it again. What gives? The gague of the wire is relativley similar if not identical.

It holds true when the magnets are in or if they are not.

brando

 

[sanrafael]

Re: Can I move the pole pieces?

Artie, no problem. I am kind of professional at the engineering and amateur at the guitars, so I learn a lot hanging out around here.

Brando, Is this the LP project?
Let give an example that has to work. May be it will help show what could go wrong. Suppose one has a humbucker pickup, one using all slugs and no adjustable pole pieces; instead of using one big bar magnet, let us put small magnets on the back of each slug. (I have done this in my guitar, I use very small neodymium magnets, small so the field does not get too strong.) Suppose you verify that it works as a humbucker. Now take it apart and take the magnets off the slugs of one coil. Put it back together and you have a pup that puts out about half as much voltage but still cancels hum. You could now move the "dummy" coil somewhere else, not too far away, and it would still cancel hum, but you must have it pointing in the same direction. It works because the dummy coil has the same sensitivity to magnetic fields as the active coil.

If you start out with two different kinds of pups, getting the number of turns the same is just one step. If the magnets on the two pups are different, these magnets might have different sensitivities when used to sense magnetic fields.

Was there any change in the amount of hum with the magnets in place with any of the wiring configurations?

 

[theodie]

Re: Can I move the pole pieces?

I think my Powerhouse strat dummy coil has 2 magnets (1 and 6) I can verify this tonite.

Thames, I think you may be right!! It has been about two years since I had a powerhouse. I thought it didnt have any but, You have refreashed my memory.

 

[Jester700]

Re: Can I move the pole pieces?

I'm sure there are many slightly different ways of doing this. I know that the DiMarzio stacks I have do not have any magnets in the dummy coils. But those are older designs, and maybe one of the improvements in the newer VV line is the addition of magnets or other ferromagnetic material in the coil.

That is not to say that they're *required*; the DiMarzio HS-2 and HS-3 are still on the web page and in the catalog, and they work as Brando & I have described.

I'd love to hear from a more pickup-specific engineer on this (no offense meant to you, Sanrafael).

 

[sanrafael]

Re: Can I move the pole pieces?

No offense taken, Jester. I made my first guitar pup when I was about 14; playing with electric guitars was one of the things that got me into engineering and science. I will try to figure out how those DiMarzios work. There has to be some method of getting the sensitivity up over an "air core coil". Altough I have seen a few bad reports on DiMarzios in this forum(!), I believe that they are reputable, and work as described.

 

[brandobean]

Re: Can I move the pole pieces?

Hey guys. I gave up on the dummy project for the LP....for now.

I got a set of Ibanez pickups: a V7 and a V8. They seem to be low output humbuckers. I like the sound so they stay for this month.

If the Duncan Jazz humbuckers are like these, I may just get a set. They are very balanced and are not hard or dark. I miss the dirty sounds that my 59, Distortion and my JB made in bridge position, but the V8 sounds loads better clean (in a mahogany body set maple neck, rosewood fretboard Schecter PT).

I am not totally happy with the V8 because it is a bit thin through my Marshall, but maybe a clean booster would help it.

The V7 almost sounds like a single coil (as close as I have ever heard a humbucker sound like one), so it will do me for now.

I am putting my SSL1 back in my other guitar. I covered it with a chrome cover so it fits in a humbucker space but it is a strat neck pickup. A similar idea to the Phat Cat.

I'll have to post a pic somewhere.

San Raf: One coil is from a Fender (RWRP) the other looks like an Ibanez...wait a minute... it is probably the middle coil that was with the V7 and 8 I got for $10 for all of them.... anyhow. The series hookup yielded some hum reduction, but actually just changed the pitch of the hum. Parallel did almost nothing. All coils are good because I had to get another as one of my previous coils was bad.

I had to unwind the Fender coil to make it match the Ibanez coil. I am sure the Duncan coil is hotter than all of them. Since the Duncan and the Ibanez coils are both shielded, I think I will just leave them alone.

In the future if I decide to stick with the Snark, I will order a RWRP and go from there.

....but it shouldn't have to be that difficult!

 

[sanrafael]

Re: Can I move the pole pieces?

Brando,

"....but it shouldn't have to be that difficult!" But i think it really is not so easy to get it right!

I have found out a little about the more modern Dimarzio stacked humbuckers. This article has a brief explaination (http://www.soundonsound.com/sos/nov98/articles/pickup.htm). It says that the top and bottom coils are separated by a magnetic shield to prevent interaction, and that the bottom coil uses its own set of steel cores. Also, the bottom coil needs only about 20% as much wire.

I think that this implies that the steel cores have a much higher permeability than the magnets in the single coil as expected. The idea is to be able to put the dummy coil in series without affecting the sound from the single coil. Thus it should have both a lower resistance and a lower inductance while keeping the same sensitivity to stray magnetic fields. This works because the sensitivity to fields is proportional to the number of turns, while the inductance is proportional to the square of the number of turns, and so the ratio of the inductances will be proportional to the ratio of the number of turns when including the effect of the different permeabilities.

The powerhouse is an active guitar, and so the dummy coil can be added in electronicly. This makes the exact characteristics of the dummy a lot less important.