Successful Dummy Coil?

[Natman]

Hey all, I know there have been some attempts at using a dummy coil in passive circuits to calm 60HZ hum, but something tells me that everyone would use it if it really worked.

Has anybody managed to get a dummy coil to work properly? The Illitch BPSS was popular some 10 years ago but again why isn't it more common?

Thinking of making my own and my strat has the swimming pool rout which helps. I read somewhere (probably this forum) that it's best to use a different gauge wire from your pickups.

Pls discuss...

 

[JB_From_Hell]

I did this on a MIM Strat a few years ago. It worked really well, but darkened the tone a bit. That’s the part most people dislike, and why the Suhr and Illitch are pricey (they don’t color the tone).

 

[Mincer]

The best I've heard was an active one: the Music Man Silent Circuit.

 

[ICTGoober]

Alembic has been doing it for decades. Fender did it in the 80's on their Elites.

 

[idsnowdog]

I did it recently in combination with heavy shielding and it does work. Since the dummy coil I used was not the same strength as the others it only canceled about 80% of the hum.

 

[Natman]

Huh, never saw this before:

https://blog.music-man.com/instruments/what-is-the-silent-circuit/

You can clearly see the inductor is wound like a sewing machine bobbin. I would have guessed larger? Maybe the battery is used to amplify the noise signal to match the hum put out by the pickups.

I know about the Nighthawk and some that use a regular coil. I still think a thinner coil with wide surface area in the same plane as the pickups would be ideal like some old TV antennas.

I'd be pretty happy with 80% reduction. If it darkens the tone, maybe higher value pots would be in order?

 

[ICTGoober]

That's pretty clever - induce another source of hum and then use it to cancel hum in a pickup.

 

[freefrog]

Hey all, I know there have been some attempts at using a dummy coil in passive circuits to calm 60HZ hum, but something tells me that everyone would use it if it really worked.

Has anybody managed to get a dummy coil to work properly? The Illitch BPSS was popular some 10 years ago but again why isn't it more common?

Thinking of making my own and my strat has the swimming pool rout which helps. I read somewhere (probably this forum) that it's best to use a different gauge wire from your pickups.

Pls discuss...

The Ilitch coil is not more popular because it's awfully expensive and because it's a large air coil, difficult to place in a guitar. If we want it to be not too directional, ideally, it should be around the pickups, which forces to route the body under the pickguard or under a giant backplate.

The ultra-low inductance of an Ilitch air coil has also a tendency to generate HF noise. It's possible to filter it but it requires added components & some tweaking.

All that being said, it DOES work and is easy to wind since it includes only a few turns of thick wire.

More conventional small dummy coils "really work" too but as they bring a non negligible amount of sonically useless DCR and inductance, they need a careful wiring based on unusual solutions, possible additional components, and some extensive tests (reason why "everybody" is not digging this idea: most players haven't the materials, tools and lab gear needed to make it work properly)... Now, personally, I have custom made dummy coils + filters paired with Strat, P90 and Dynasonic single coils in various guitars and they ALL work well enough for my humble needs : I use them periodically on stage, as much as the noiseless SC's mounted in some of my other instruments.

Last but not least and for the record, rumors say that SRV had a dummy coil in a Strat. Here is a discussion about that, involving several famous contributors and some ideas to think about (page 3) : https://www.thegearpage.net/board/index.php?threads/srv-seen-this.2067224/

FWIW. Good luck in your experiments if you decide to try dummies...

 

[beaubrummels]

Pot values won't help you. If you had no pots at all, the dummy coil would darken the sound, if it's the same geometry as the pickup. The coil has to be calculated to be the right dimensions. Larger area with fewer turns and thicker wire reduces the inductance and the resistance, which keeps the coil from affecting the sound.

Here's a couple good articles on the topic.

https://sites.google.com/site/stringsandfrets/noise-reduction-for-sc-pickups
https://sites.google.com/site/stringsandfrets/noise-reduction-for-sc-pickups/s-500-hum-cancellation
http://diyegp.blogspot.com/2015/04/dummy-coil-for-danelectro.html

 

[Natman]

FWIW. Good luck in your experiments if you decide to try dummies...

Great info Frog, it's not IF but WHEN!

Thanks brummels, going to look into all this before I start winding!

 

[ThreeChordWonder]

Off the wall thought.

What happens if you put a cap in parallel across the ends of the dummy coil like a treble bleed? Would higher frequencies short through the cap instead of going through, and attenuating in, the dummy coil?

 

[Mincer]

Huh, never saw this before:

https://blog.music-man.com/instruments/what-is-the-silent-circuit/

You can clearly see the inductor is wound like a sewing machine bobbin. I would have guessed larger? Maybe the battery is used to amplify the noise signal to match the hum put out by the pickups.

I know about the Nighthawk and some that use a regular coil. I still think a thinner coil with wide surface area in the same plane as the pickups would be ideal like some old TV antennas.

I'd be pretty happy with 80% reduction. If it darkens the tone, maybe higher value pots would be in order?

Yeah, and it works really, really well.

 

[freefrog]

Off the wall thought.

What happens if you put a cap in parallel across the ends of the dummy coil like a treble bleed? Would higher frequencies short through the cap instead of going through, and attenuating in, the dummy coil?

Yes. That's how HF frequencies can be filtered. Hence the presence of a RC network parallel to the air coil in the Ilitch patent. See the figure 5, where the variable resistor and cap (components 20 and 22) are litterally a tone control for the dummy coil (while the variable resistor 18 works like a volume control for it): https://patents.google.com/patent/US7259318B2/en

The tricky part with this patent is to find the proper value for parallel resistors 19 & 21.

Parallel RC networks are also a way to deal with the messed resonant frequencies due to dummy coils, for reasons that I won't dig here (since it has to do with "sensible information")... but there's no rule there, since it depends on the actual LRC specs of the coils used. That's where it becomes necessary to measure Rz with lab gear and to tweak the circuit accordingly.