Dummy coil question

[truetone]

I once found a posting on either this forum or the last one where somebody recorded a guitar with and without a dummy coil and showed its effect. Does anyone remember this and would you be able to post the link?

[truetone]

I found the site, my old computer went down and it had the link and I've been searching for a while.


http://www.blueguitar.org/new/mp3/sa...coil_strat.mp3

correct me if I'm wrong but it sounds like there's more output when the dummy coil is active.

[Dave Kerr]

Suhr's SSR system demo:http://www.prosoundcommunications.co...on2/rc_bb.html

[truetone]

I've seen that before, I just dont like the look of it. I never have the backplate on my guitar anyhow and I would rather have it in single coil form.

[David Schwab]

The real SSR doesn't put the dummy coil on the back plate. That's just the retrofit system.

The real SSR uses a large coil under the pickguard. The system works better than a small single coil size dummy coil because it has a large diameter, so it picks up more noise, and because of the large coil, it has less turns, so it doesn't impact the sound of the other pickups as much.

And why not back a back cover on your guitar. Do you adjust the springs often? I think they look unfinished with no cover.

But you can do it with a smaller coil... but it has drawbacks if you are running a passive system.

[truetone]

I use 15-58 and I do alot of bending, I keep the spring cavity open to adjust when needed. I dont know I think I like the tone you get from the single coil, its probably more of a tone thing than a hum reducer. I like heavy tone and from the sound of the clip it gives alittle more output, but I still would like to phase it out aswell. What do you think about a coil tapped dummy coil hooked up to the last tone pot to dial in the dummy to match the pickup. Would that work?

[David Schwab]

I use 15-58 and I do alot of bending,

Geeze! I'm mostly a bass player, and I like 9's on guitar! That's telephone pole wire!

What do you think about a coil tapped dummy coil hooked up to the last tone pot to dial in the dummy to match the pickup. Would that work?

I guess that would work. The Shur system has a trim pot to set the hum level.

I haven't tried any of this dummy coil stuff out with passive pickups. Give it a try.. you might discover something.

[truetone]

tell me about it, I used to play with 11 but it didnt have the tone I wanted.

[David Schwab]

tell me about it, I used to play with 11 but it didnt have the tone I wanted.

I actually like the tone of thinner strings.

[Mark Hammer]

Part of the trick is having the dummy coil be as sensitive to the source of hum as the actual pickups are. Remember that cancellation comes from having signals of identical strength/ampliltude that can cancel each other out as close to fully as possible. In the case of humbuckers, the two coils are so close together that turning your body in any direction will expose the two coils to the hum source to the same extent. Hence neither coil will dominate the other.

In the case of SC pickups, there is the question of where to situate the dummy coil such that it picks up as much hum (but no more hum) as the other pickups, irrespective of how the guitar is tilted or angled or facing. Both the under-the-pickguard and on-the-backplate solutions work nicely because the coil essentially surrounds the region where all the pickups are situated such that it isn't closer to one than to any other pickup.

Some 15 years ago, I wired up a dummy coil to a guy's Tele, and installed it in the control cavity because that was the only space available. It was a cheap polyethylene or polystyrene coil bobbin from a cheap japanese guitar with the metal slug and ceramic magnet removed. I have to confess that it did not remove ALL the hum, that it did not reduce hum equivalently for all pickups, and that its functioning varied with where you were facing. BUT...it knocked off at least 3-5db of hum most of the time, and that was appreciated by one and all.

The trick is to get the most hum-reduction in the least invasive and tone-changing manner possible. It doesn't have to be perfect to be considered as "working". All it has to do is reduce hum to a more acceptable level.

As an aside, with so many jurisdictions deciding to ban incandescent bulbs in favour of the energy savings of fluorescent bulbs, hum-rejection and hum-reduction is poised to be a real growth industry. I am hoping it will be as simple as walking into a Home Depot and saying "I'd like the shielded ceiling fixture, please".

[truetone]

let me run this buy you, could I figure out the reading of my largest pickup and hook a dummy coil up to a pot and than use the pot to change the value of the dummy to match each pickup or is that not possible?

[black_labb]

if you make the pickups yourlelf you could make split coil pups. i may do that for some pickups at somestage.

[Arthur B.]

If you made a single coil with balanced output, it would be a lot easier to null noise. If you want unbalanced output, use a balanced to unbalanced converter (most likely a transformer).

[Mark Hammer]

As I understand it, it is not the matching of turns or impedance that matters, but rather the matching of hum signal amplitude from the two sources (actual pickup and dummy coil). That's why the Suhr backplate, and a host of other things that are actually fairly low impedance, can work. If the dummy coil can be made/situated to consistently pick up lots of hum (hopefully at least as much as the actual pickup), then you've got it. The "tuning" simply lets you trim back the hum picked up by the dummy coil so that you have a perfect 50/50 balance resulting in cancellation.

Understand that for a long time, "dummy coils" were very often coils wound FOR a pickup but with the magnets and polepieces or slugs removed. That was merely done for convenience, though, and not because it HAD to be done that way. If I was farting around with dummy coils, simply taking the polepieces out, or winding up a bobbin I already had, presents the easiest starting point. It is not a necessary starting point though.

[Joe Gwinn]

As I understand it, it is not the matching of turns or impedance that matters, but rather the matching of hum signal amplitude from the two sources (actual pickup and dummy coil).

That's correct. The voltages must be equal and in phase, so subtracting one from the other yields zero (or at least a small signal).

That's why the Suhr backplate, and a host of other things that are actually fairly low impedance, can work. If the dummy coil can be made/situated to consistently pick up lots of hum (hopefully at least as much as the actual pickup), then you've got it. The "tuning" simply lets you trim back the hum picked up by the dummy coil so that you have a perfect 50/50 balance resulting in cancellation.

I think Suhr has his adjustment pot so he can match a variety of pickup outputs.

Understand that for a long time, "dummy coils" were very often coils wound FOR a pickup but with the magnets and polepieces or slugs removed. That was merely done for convenience, though, and not because it HAD to be done that way. If I was farting around with dummy coils, simply taking the polepieces out, or winding up a bobbin I already had, presents the easiest starting point. It is not a necessary starting point though.

In the absence of ferromagnetic cores (poles and magnets), one must match the area-turns products of the two coils (active plus dummy) to achieve cancellation.