Dummy Coil Experiment - Successful!

[gunther]

<EDIT:>
The topic of dummy coils comes up every so often, hence I have made an Executitive Decision to sticky this thread for easy future reference. gunther has done some positive research and posted his results in a way that most people will probably understand, and then be able to duplicate for themselves..... and that's a good thing.

If anyone else wishes to contribute, or ask questions because something is not clear, please do so here in this thread so that others can take advantage of the discussion.

UPDATE: Another thread, with a different method and explanation, can be found here: A successful attempt to low impedance dummy coils in an SSS
</edit>

Since reading lots on this forum i've become pretty anal about instrument noise...almost unhealthily so!

But My 5 string bass guitar had been REALLY irritating me.

It has a P pickup in the neck (which was pretty quiet of course), and a J pickup in the bridge (noisy as!). I liked the tone of the J pickup but never used it because it was so noisy

Was almost ready to pull the trigger on a stacked replacement pickup...but had a moment of inspiration after reading a couple of threads here about dummy coils.

I also remembered that i had a couple of guitar single coils that gfs were selling for cheap...the only reason i bought them really.

The J bass coil measured 5.36k ohms, and one of the gfs single coils measured 5.43k ohms....pretty good match i thought. Got a knife and pried away the bar magnet underneath. Then i had to cut off the mounting tabs so it would fit in the wiring cavity.

First i tried hooking up the dummy coil in parallel with the J...mainly because i'm lazy and i didnt have to solder it in this way....sounded a lot weaker, cutting out a lot of the bass frequencies.

Got out the iron and hooked it up in series the next time. The output was the same as the pure single coil..only problem was that there was still a bit of noise.

Spent some time just moving the dummy coil around in the cavity and listening, and eventually found 'the sweet spot' where it cut the most amount of hum.

Added a bit of tape to secure it in place (also the pressure of the cavity cover seems to hold it in tight)

Results: The bass isnt totally noiseless, but i'm quite happy with the signal to noise ratio now. The J pickup is almost as quiet as the p pickup, and just as loud. And the bass is even quieter when both pickups are on (and i like this sound the best)

As far as tonal change, i really cant detect any...but them again i'm not a bass connoisseur.

Hope that info helps anyone who's interested in this stuff.

[sumgai]

gunther,

+1 for ingenuity and then sharing with others. Thanks. ;D


sumgai

[UnklMickey]

^ Ditto. +1 from me too.

If you ever decide to put a switch in there so you can A/B the tone and hum content, with the dummy coil in series -vs- a direct connection to the Jbass pickup, we'd all be glad to hear the results. Either through a sound clip, or just your verbal evaluation.

Thanks for the info.

[gunther]

Mickey - too lazy to put in a switch + no room. But i can safely say that i dont find the tone to be any worse or any better than it was before.
In any case, being able to turn up just that little bit louder and have more dynamics in my playing makes it sound better to me

Love ya quotes BTW ;D

Just tried the same thing on my epi LP which has a GFS hum-sized p-90 in the Neck slot.

The coil mismatch was a bit greater this time (the p-90 was about 9k, and the dummy coil about 5.8k), + different coil shape, so the hum-cancelling wasnt quite as good this time.
But, with the coil in a very particular position, a similar result - A lot of the hum cut out (is actually as quiet as the humbucker in the bridge...but its a noisy bridge pickup i think).....and i can barely detect a difference in the tone. Cool! Dont get me wrong, it still makes noise...but its quiet enough to keep me happy

Now heres my problem: The mounting of the dummy coil. In the bass there wasnt much room for it to move around in the cavity plus the cavity cover was pushing down on it....so i dont think it will move. On the LP, the cavity is deeper and the dummy coil will move around when i move the guitar around. Plus, the 'sweet spot' of humcancelling is a lot smaller. Any ideas as to how to keep that coil fixed in the one spot for good? As fer now its just a very dodgy gaffa tape job
Edit: after a few solid test shakes, the gaffa seems to be working pretty nicely. Time to actually play the thing i think! ;D

Edit pt2: Neck pickup sounds great. Dream 90 they call it. Sounds like pure blues to me

Cheers, gunther

[sumgai]

gunther,

If gaffer's tape fails to hold the coil in place, you can use some RTV (Room Temperature Vulcanizing) silicone goop. This is the stuff they use on some circuit boards to hold components in place during times of expected rough transit. Probably the best known of these products is good ol' house caulking compounds. Manufacturers have access to lots of industrial grade compounds, but for your needs, I should think that window/door sealer would be sufficient. (It adheres to wood and most plastics or metal, painted or not.)

HTH


sumgai

[gunther]

Hooked the same coil i used for the p-90 up to my Ibanez hardtail strat today.

After much fiddling i managed to stuff it under the pickguard next to the bridge pickup, and i hooked it upto the switch to compare.

When turned on, It cancels most of the hum in the neck and bridge positions, but increases the hum in the other 3 positions.

Tonal change? In short, it takes away most of the great sounding characteristics of a fender single coil....all the sparkly single coil goodness is gone and it just makes it sound fairly flat and 'boring' for lack of a better word.
Also is just a tad quieter with dummy coil switched in.
Though i can see myself using the dummy coil when playing live or recording.....as i usually just use the neck or bridge

Recorded a clip just using the neck pickup.....first take with the dummy coil switched in and the second is just the neck pickup on its own....i'll let you decide which one sounds better.

martinrotolo.googlepages.com/dummycoil.mp3

Cheers

[CheshireCat]

I'm working on the same principle for my Utah. I'm ringing in my old Duncan Jeff Beck, and using the minibucker I got to replace it (pursuant to coupling it with a sustainiac) as a set of dummy coils for the split JB and the Duncan Antiquity Tele neck pickup, which is occupying the middle position.

The dummy coil is going into the back of the guitar, into a dedicated cavity. That way the magnet should be far enough from the strings that it won't pick them up, thus keeping me from having to pry the magnet out.

The splitter on the JB will, in fact, be a coil switcher, so the JB will be in humbucking mode all the time, whether it's the two adjacent coils, or a single coil coupled with a dummy coil.

More later . . .

Chesh

[ChrisK]

This is a difficult filter to design. For optimum passband response, a Chebyshev or Elliptical topology is in order due to their sharp cutoff. However, this comes at the expense of passband and/or stopband ripple.

For optimum phase response, a Bessel topology is in order, but this is most inefficient in the slope of the cutoff.

Either way, for optimum selectivity/Q (50/60 Hz vs 80 Hz), a multi-section filter of 4 to 8 poles is in order.

en.wikipedia.org/wiki/Active_filter

[sumgai]

Santa,

........a fully passive filter with a Hi Q to reduce the slope of the cutoff

That would depend on one's viewpoint, wouldn't it? Me, I'd describe a high Q filter as having a much steeper slope, not a more gentle one. Perhaps you meant to say, you're going for a sharper knee? This is what happens with a high Q filter - the knee itself remains at -3dB compared to the passband frequencies, but the frequency response from there to the peak (or dip) is much closer to vertical, when we look at it on a graph. Qualifies as steeper in my book.

But that's just one man's interpretation of the facts he was presented with, during his education in the pre-historic era of no innerweb. Of course, YMMV! ;D


sumgai

[sumgai]

Santellan,

The frequency of A# on a bass guitar is 58.27Hz, and for the B, it's 61.73Hz. Let's do some arithmetic, shall we?

Q is defined the center frequency divided by the bandwidth. The higher the Q, the narrower the bandwidth. So, at 60Hz, in order to avoid having more than a minimal effect on A# and B, we need to have a bandwidth of only 2.4Hz (58.8 - 61.2Hz). Remember, that's measuring to the -3dB down points. We may have to adjust our frequency figures later, but this is a good starting point. Anyway, that gives us a Q factor of 60/2.4, or 25.

But more important, that doesn't really tells us everything we'd like to know. It only tells us that we'll have a pretty steep slope, and that's about all. What we really need to know is, how many poles of a filter will we need to achieve this bandwidth.

First, we need to see how much attenuation is necessary in order to kill the 60Hz hum that we're getting. As a starting point, I'd pluck the number 24dB from the air. Why that one? Because it means that we'll need only 4 poles in a given filter configuration. In turn, that will offset the signal's phase an exact 360°, thus cancelling any phase distortion. And at the center frequency, the signal strength is 1/256th of the original signal. That's pretty low, no?

At that point, we need only stack up the filter poles (or sections) in a serial fashion, and we're done. Using two such filters, one a low-pass and the other a high-pass, will give us a notch filter. For a standard six string guitar, we only need a high-pass filter, that much should be obvious by now, but unless cost becomes an issue, then let's continue to build one device for both jobs.

All that's left is to tailor the components so as to reach the cutoff points we need (58.8Hz and 61.2Hz). We'll then make sure that the crossover between the two filters is so low, signal strength-wise, that we're actually knocking out the hum. If our components are somewhat shoddy in tolerance, we could actually be dropping the signal by as few as 6dB, and that would be a real waste of effort, no? In reality, even with perfect parts, we may not realize the whole 24dB, that's just the nature of the beast, in the hobbyist world. But using more filter poles re-introduces the problematic phase shift. For some folks, this is not an issue. I prefer to deal with it up front, so as to avoid getting bitten on the butt later on down the road.

The trade-offs here are many. How much ripple outside of the notch can we tolerate (there will be some, make no mistake)? How much will the whole thing cost, in terms of materials and efforts? How much space will it consume - will it be small enough to be viable? And if it's passive, there's no power consumption, but what if we need to reduce the parts count (to fit within a given space), and we can do that only by going active..... can we afford the power source for that?

Lot's of "bullet points" to think about, eh? ;D I don't wanna discourage you on this, but I also don't want you to walk down to your local Radio Shack with your checkbook in hand, thinking that you will soon have the World's Ultimate Solution for preventing hum.

Wikipedia is full of articles on this topic, go grab a cold one out of the fridge, and take a look.

HTH


sumgai

[ChrisK]

Ok, this gets real involved for a filter like this. The thing that defines the topology and order of a filter is the steepness factor (Fpass/Fblock) and rejection ratio (dB).

Using the curves for an elliptic-function filter* with a steepness factor of 1.3 (60 vs 78 Hz), a rejection ratio of 60 dB, and a passband ripple of 0.18 dB** (which requires a total rejection factor of 73.9 dB), an order 7 filter is required.

This is not all that bad when one realizes that a Butterworth topology for the same response requires order 27.

To realize this filter actively, anywhere from 4 or 5 or more OPAMPS will be required. A passive topology will have substantial signal loading as well as insertion loss, rendering it unusable.


*R Saal, Der Entwurf von Filtern mit Hilfe des Kataloges Normierter Tiefpasse, Telefunken GMBH, 1963.

** Even if the ripple is allowed to increase significantly, only about a 10 dB less total rejection factor is required.


Attempting a notch filter amidst desired notes/frequencies is even more difficult. While one can realize significant steepness curves with digitally derived analog filters (decimation filters), significant artifacts result (why "everyone" hates DSP-based modeling).

[jj]

gunther said:

Now heres my problem: The mounting of the dummy coil. In the bass there wasnt much room for it to move around in the cavity plus the cavity cover was pushing down on it....so i dont think it will move. On the LP, the cavity is deeper and the dummy coil will move around when i move the guitar around. Plus, the 'sweet spot' of humcancelling is a lot smaller. Any ideas as to how to keep that coil fixed in the one spot for good?

here's a few ways you could try.
Hot Melt glue,
Epoxy Glue (eg:araldite)
Neutral-Cure RTV silicone Caulk (Never use acid cure/acetic cure silicone on electronics)
or just fill the void with Expanded polystyrene scraps (styrofoam)

[David Schwab]

If we are going to go through the trouble to put an active notch filter in, which is not a good way to get rid of single coil noise, then we can go ahead and make a dual buffer set up, one for the dummy coil, and the other for the string sensing pickup(s). Then you actively mix the two.

This way the dummy coil will not load down the string sensing coil, and you wont get that dull tone.

One way to do it passively is based on the idea behind both the Suhr BPSSC System, and stacked pickups like those made by DiMarzio (Virtual Vintage) and Kinman.

With the Suhr/Ilitch system, you use a large diameter coil of heavier gauge wire than used in the pickup. The larger the gauge of the wire, the lower the resistance. That will help produce less loading and less of an increase in inductance. The large are covered by the coil makes it more sensitive to picking up noise, which is what you want.

The DiMarzio method uses a smaller bottom coil, wound to a lower resistance (8.53k on the top and 2.45k for the bottom coil on the Solo Pro), and then they add extra steel slugs to raise the inductance to make the coil more sensitive to noise.

So you don't need the dummy to be the same DC resistance, and you actually want it lower. If it's a Strat type coil that uses steel poles with ceramic magnets on the bottom, pull off the magnets and glue a piece of steel bar on the bottom on the coil.

Then either wind, or even unwind the dummy to 1/4 the resistance of the sensing coil. You should keep the outside diameter of the coil as large as the real pickup if you can.

If you want to try winding you own, go to Radio Shack and pick up the magnet wire they sell. It's very large gauge.... much larger than used in pickups. Use the thinnest of the three. it's easy to work with, and will give you a low resistance coil. You can use an old pickup bobbin, or just make any kind of form to wrap the wire around. If you make a large size coil, like the BPSSC System, you can use a hundred turns or so of the heavy wire.

Then try wiring that up in series with the pickup. You will need to experiment with it a bit, but you shuld be able to come up with something that should remove most of the hum and not mess with the tone too much.

[djd100]

I did something similar to an old 66 Strat, though I wired the dummy coil (old MIJ SC sans bar mag and pole pieces) in series with the output through a 250K pot.

In this way you can vary the amount of noise reduction and high-end roll-off, which can be effective in giving your SC pups a little more of a humbucking freq response vibe.

[D2o]

Jul 15, 2008 11:32:09 GMT -5 djd100 said:

I did something similar to an old 66 Strat, though I wired the dummy coil (old MIJ SC sans bar mag and pole pieces) in series with the output through a 250K pot.

In this way you can vary the amount of noise reduction and high-end roll-off, which can be effective in giving your SC pups a little more of a humbucking freq response vibe.

Hi djd100, and welcome to GN2!

This sounds good. I am glad you brought it to us - thanks!

It appears that you took the time to check out and validate this idea too. Excellent!

Depending on what you mean by the following, you may have also hit on another topic that has been discussed around here; that of disconnected coils acting as antennae. In the thread via the link to thefenderforum below, you wrote: "This is a great idea (I just wired mine to be on all the time so I could still have two tone knobs), thanks again!"

I suspect you mean that the dummy coil is always on but, by chance, do you mean all your pickups are always connected? If so, we'd love to hear more.

Anyway, good stuff - and, again, welcome!

For anyone else interested in some background discussion on the mod - take a look via the link here. (I've copied the original post too)

www.thefenderforum.com/forum/showthread.php?p=458369#poststop

"I really like my Stock pups on my 62 AVRI but hated the Hum. Was looking into installing a Suhr Backplate but then started tinkering and came up with this Mod.


Using stock 250k Pots.

Dummy coil is a Old Plastic Bobbin Fender Japan pup with magnets removed.

Bottom Tone Pot is wired to Roll off Treble on just the Bridge Pup, personel preference.
I Could have wired it as a Master Tone for all pups but I often ride on the Bridge pup at a gig with the Tone on 8.
I never need to roll off tone on the Neck and Middle pup so...

Stock pups are about 6k and the Dummy Coil is about 6k. If you measure at the output jack you'll measure 6k.
Roll back the Middle pot and the resistance will increase up to 12k and the Hum just goes away, AWESOME !

I must note with this setup I noticed there was a considerable amount of hum still until I flipped the dummy coil.
I imagine that I could have just flipped the Dummy coil wires on the Middle pot to achieve the same result.

Such a useful MOD especially for guys that love there stock vintage Pups but need to take away the Hum when needed.




Tell me what you think ?"

[angelodp]

Very interesting. Are there any great pics on either strat or dano implementation ??

ange

[D2o]

Very interesting. Are there any great pics on either strat or dano implementation ??

ange

Not yet, but so far I like your great pics ... I suspect you will see a serious increase in your karma points if you do it.

D2o

[steveb]

My Magnatone Typhoon uses a dummy pickup in the middle position. One of these days I'll have to take the pickguard off again and draw out the circuit, it's very advanced for a '60s guitar.

[JohnH]

Hi steve - thanks for posting that. There were nutz before we were nutz! And welcome to GN2.

John

[rabidgerry]

Are there any diagrams for this I could follow?

Is it best to have a pickup with the same resistance as the pickups?

How could I use the same coild for say 2 single coils in a HSS?


Is this mod better than sheilding? Who can vouch for it?

[newey]

RG-

Welcome back!

You're resurrecting an old topic here, and we haven't had any further input from the author(s) recently. So, essentially, what you see here is what we got.

I haven't ever experimented with a dummy coil, so no real input for you. I do not think that matching the coils resistances exactly would be a big issue.

Ideally, someone would do this experiment with an "A-B-C" switch to compare the dummy coil with shielding and with neither one present.

[rabidgerry]

Ok I realise I resurrecting this once again, but please advise me if I should just start my own thread on the matter guys.

I'm going to try this out.

I've been reading a few approaches online and I really fancy trying it.

I had an idea on trying to save some room.

Could I perhaps use a tele neck single coil for the job?

I am reading this link BTW

link

[newey]

Could I perhaps use a tele neck single coil for the job?

Sure, why not? The article you linked to mentions using one-half of a P-bass pickup. You could save space with one of those, too. Buy an Asian-made cheapie off EBay for about $10 and you can do 2 guitars. . .

One question I would have with the Tele neck pickup is if it would make a difference, for better or worse, whether the chrome cover was either removed and/or disconnected. Some experimentation might be in order; I suspect you could do so external to the guitar before wiring it in place permanently, although Gunther felt that placement of the dummy was an important factor.

[rabidgerry]

pardon the stupid question newey, bu those p bass pickups are actually two seperate pickups right?

Yeah good idea on bagging one of them. on can get them for dirt on ebay.

I'll scout about for a suitable candidate.

I wonder if there would be anyway to just have the dummy coil on for two single coils in neck and middle and exclude a humbucker in the bridge without having to imploy a switch. I'll have to get thinking about that.

[newey]

those p bass pickups are actually two seperate pickups right?

Yes.

I wonder if there would be anyway to just have the dummy coil on for two single coils in neck and middle and exclude a humbucker in the bridge without having to imploy a switch. I'll have to get thinking about that.

If you are using a regular 5-way switch, you could move the tone controls off the second pole of the switch and use that pole for the N and M pickups, dummy coil would then go in series off the common for that pole of the switch. The bridge pup would reside on the other pole of the switch, including the coil cut (if you have that set-up).


.

[rabidgerry]

I have been looking at p bass pickups. I can't find any that would split into two and give the right kind of ohms. I seem to only see p bass pickups around 8 0r 9 which splits into 4. I needs 5-6ohms.

So the new candidate is link

Newey when you say remove the tone controls from second pole, you mean I'd have no tone controls then?

No coil tap set up currently but I am interested in doing that also.

Think I'll just go for a simple dummy setup currently before making things any more complex.

[newey]

What I meant about the tone controls was to move them over to the pickup side of the switch, rather then having them use their own pole. So, if you wanted the regular Strat setup where the tones are for the neck and middle pups, the tones are wired to the same lugs as their respective pickup "hot" wires.

If you wanted to put a tone on the bridge pup, which is a common Strat mod, then that tone would move over to the bridge side of the switch, sans dummy coil.

If you wanted the HB to be coil cut, the "series junction" between the pickups would get wired to the center lug on the bridge side of the switch. Bridge "hot" goes to lug #1 on that side. This then connects the bridge pup's "series junction" to output in position 2, shorting one coil to hot and giving you the other coil (i.e., the one that's permanently grounded at one end). It also connects the series junction to output at positions 2 and 3, but this is meaningless as the bridge "Hot" is disconnected at those positions.

[rabidgerry]

Dec 4, 2015 6:06:40 GMT -5 newey said:

If you wanted to put a tone on the bridge pup, which is a common Strat mod, then that tone would move over to the bridge side of the switch, sans dummy coil.quote]


Yes I normally perform that mod. Actually now I think about it the strat I am thinking of doing this with only uses one master tone pot (its a sort of rare KV98 squire made for the southern American Market).

Ok I get ya on the pole swapping on the switch. This should be fairly easy to test out I think. I just have to wait on the pickup arriving now

Thanks newey for helping.

[reTrEaD]

Dec 4, 2015 6:06:40 GMT -5 newey said:

What I meant about the tone controls was to move them over to the pickup side of the switch, rather then having them use their own pole. So, if you wanted the regular Strat setup where the tones are for the neck and middle pups, the tones are wired to the same lugs as their respective pickup "hot" wires.

I agree with this, as the "tone" side of the switch doesn't really accomplish anything that won't happen by wiring the tone controls directly to the pickups. But I don't think you can accomplish all the desired tasks with that side being free-up.

The Fender Standard Strat (Mex) uses that side of the switch to split the bridge pickup in a method similar to what you described. The series link is connected to the "bridge" lug. The "middle" lug is connected to ground. The neck and common lugs are not used.
support.fender.com/service_diagrams/stratocaster/013-4700_02C_SISD.pdf

This results in one coil of the bridge HB being shunted to ground, only in the #2 (B+M) position. So the #4 selection becomes one coil of bridge in parallel with the middle pickup. Life is good.


But if you are to connect the middle and neck pickups in series with the dummy coil, you could indeed shunt the dummy in just the #4 position.
5 - Neck in series with dummy.
4 - Neck + Middle (no dummy).
3 - Middle in series with dummy.

Good so far, but what happens in the #4 position?
You can't shunt both the dummy and one coil of the bridge at the same time.
(at least I can't see how to accomplish it)
It's either/or, or no shunt at all.

Your choices:
[Middle (shunted dummy)]in parallel with full HB.
[Middle in series with dummy] in parallel with one coil of the bridge.
[Middle in series with dummy] in parallel with full bridge HB.

[newey]

RT-

Here's what I was thinking (numbered with the neck as #1, bridge as #5):



Would this not work? Or, is it problematic to have the (N + M) X dummy at Position 2?