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FDP Forum / The 'Pup' Tent / Custom Shop 69's with a Dummy Coil Question
(This message was last edited by Alan0354 at 01:21 PM, Mar 5th, 2012)
https://sites.google.com/site/stringsandfrets/Home/noise-reduction-for-sc-pickups
(This message was last edited by Alan0354 at 02:18 PM, May 26th, 2012)
(This message was last edited by Alan0354 at 03:16 PM, May 27th, 2012)
(This message was last edited by uneumann at 03:39 PM, May 28th, 2012)
(This message was last edited by Alan0354 at 11:37 AM, May 29th, 2012)
(This message was last edited by uneumann at 03:03 PM, May 30th, 2012)
(This message was last edited by Alan0354 at 07:37 PM, May 30th, 2012)
https://sites.google.com/site/stringsandfrets/Home/noise-reduction-for-sc-pickups
FDP Forum / The 'Pup' Tent / Custom Shop 69's with a Dummy Coil Question
Strat91
USA
Fender's are all I need!Feb 27th, 2012 08:43 PM Edit Profile Print Topic Search
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If I add a dummy coil to my CS 69's will the tone suffer that much? I like the tone & don't feel that the 69's sound brittle or ice picky. Will the dummy coil knock alot off & will it result in changing the 69's tone from good to bad? Thanks
Alan0354
Calif, USFeb 28th, 2012 01:47 AM Edit Profile Print Topic Search
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It will definitely change the tone as the dummy coil has 4000 or so turns of 42 gauge wires!!!! Even the Suhr coil has noticeable change in the sound with much lower inductance and resistance.
Strat91
USA
Fender's are all I need!Mar 4th, 2012 06:16 AM Edit Profile Print Topic Search
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Wow, tried the dummy coil & was not happy at all with the tone. Will the Shur have this effect also? I may just put a fat 50 in the middle position. Fender should RWRP the mid on this set. To good of a set to not feel confident at a gig. How would you control the noise?
Alan0354
Calif, USMar 5th, 2012 01:38 AM Edit Profile Print Topic Search
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Suhr is better, but it is expensive and does not cancel noise very well as seen in their own demo. You can hear that it does cut some highs.
stratcowboy
Contributing Member
*******
USA/Taos, NMMar 5th, 2012 08:13 AM Edit Profile Print Topic Search
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Suhr...
uneumann
USAMay 26th, 2012 08:50 AM Edit Profile Print Topic Search
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I recently made my own noise cancelling coil for a stock American Tele - its not as easy as popping in a "noiseless" but it works great and there is no impact on the tone that I can hear - except the noise is gone... I posted info and pics on my site if you're interested.
https://sites.google.com/site/stringsandfrets/Home/noise-reduction-for-sc-pickups
Alan0354
Calif, USMay 26th, 2012 02:10 PM Edit Profile Print Topic Search
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What you are doing is like Suhr using a large area coil. I can hear the difference in sound on the Suhr from their own demo.
I have experience on this, I did wound a coil on the strat back plate and it failed miserably. I am not convince you can match and cancel the noise well with a coil that is so different from the pickup. Suhr sure is not working that well from the demo and they have compensation. It is about a little over half noise reduction, that is not noise cancelling in my book.
I did a lot of experiment, noise source is very directional and very position dependent. You will find even using the identical coil like the Calif Strat ( I think) will not cancel noise like a humbucker because the dummy coil is farther away and don't "see" the same field. There is nothing, I repeat nothing you can do about it. I spent a lot of time on this. Any coil in series will change the sound, there is no way out.
Alan0354
Calif, USMay 26th, 2012 02:25 PM Edit Profile Print Topic Search
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To the OP, yes, adding a dummy coil will change the sound. a dummy coil is still over 1H inductance, and at higher frequency, it can be over 10K reactance and is frequency dependent. It is not the resistance of the dummy coil that matter like people think, it is the inductance that make the impedance change with frequency that really hurts.
uneumann
USAMay 26th, 2012 06:17 PM Edit Profile Print Topic Search
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Don't know about Suhr - the plate idea could work or not - making it so thin and small probably means the wire is thin and area is less than my coil. I didn't know about their product until I was done - probably good that way IMO.
My coils run 60-100 ohms since I used thick (relatively) gauge wire. Doing the physics...(http://www.66pacific.com/calculators/coil_calc.aspx) the calculator for inductance says I have ~1.76 millihenries of inductance. So compare my coil resistance and inductance to the pickup (7k ohms and ~4 Henries) and you can see I'm at ~1% of the PU specs on resistance and 0.1% on inductance. That's probably within the tolerance of factory or hand winding. I suspect you're right - the inductance is the bigger issue for tone impact.
As for directional and exact cancellation - you also have a point. If I'm near the amp, the mag field is very non-uniform so I still get a buzz (although much less than before). If I'm relatively far from a transformer (5-10 feet) the field is pretty uniform and the cancellation works great. There is no trick to this - it's physics. If done properly and carefully it works.
As for matching coils - you don't want to match them like a humbucker or regular dummy coil. That's the point - you want a large area coil to change the coil parameters so it picks up hum but doesn't impact the tone. Bigger is better in this regard. I think l% parameter change is pretty small IMO. I'm guessing that changing my cable can make that much difference.
RicOkc
Nicoma Park, OK.
"Let the music do the talking"May 26th, 2012 10:15 PM Edit Profile Print Topic Search
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When using the Suhr plate it says not to have a rw/rp middle pup.
I think Peegoo has used them before, ask him.
Alan0354
Calif, USMay 27th, 2012 03:14 PM Edit Profile Print Topic Search
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uneumann
I cannot speak about you coil as I have not listen to it. I can only speak about the suhr. I don't think larger area and less turn implies lower inductance. If you look in any electromagnetics book, self inductance is about the total flux linking to the coil divided by the current it produce. The larger the area, the higher the inductance per turn. You might have less turn and bigger wire, you lower the resistance, but not necessary lowering the inductance proportionally. On cause there are the shape of the coil that affect the inductance, but in general, the larger the area, the more inductance per turn. That's the reason why the Suhr coil has noticeable affect on the sound.
uneumann
USAMay 27th, 2012 06:05 PM Edit Profile Print Topic Search
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Alan
You comment “I don't think larger area and less turn implies lower inductance" got me thinking.
Sorry for the long answer...
One issue is inductance – I’ll get to that in a minute, and the other is sensitivity to a magnetic field. Let’s start with that. Faraday’s law is that the voltage generated in a coil due to a varying mag field is = -N A dB/dt. Ignore the db/dt since the mag field change is out of our control and the same for all coils. However, this formula clearly says that the voltage a coil produces is proportional to N (# of turns) time A (area of coil). (see http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html#c1) So it’s clear that Suhr and other dummy coils can have proportionally larger area and fewer turns and still produce the same hum voltage as a normal pickup. Let’s take an example where we increase the area of the coil by 4 and decreased the number of turns by 4. The larger coil will give us the same noise (hum) voltage as the original PU coil. Keep this change factor of 4 in mind.
Now to inductance… L = N2 A u/l (see http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/indcur.html#c2) Ignore u and l for the moment. Since Area went up by a factor of 4, and the number of turns is down by a factor of 1/4, so N2 = 1/16. The total change in L is 4/16 or 1/4. Note that one term (A) is multiplied by the change factor (4), while the N term causes division by the square of the change factor, or 16. This is where the big-area win comes from. The A term increases linearly with the change factor, while the N2 term decreases with the square of the change. The bigger the area change, the bigger the win, in terms of reducing inductance. My coils and Suhr coils have about the same area where the change factor is about 30. So if all else is fixed (u/l), then the inductance changes factor is 30/900 = 0.03 or to about 3% the original PU inductance.
Now consider u/l. The big coil has an air core so u is much lower than for the PU where the coil is iron or magnetic core. The metal core increases u by anywhere from 10 to 10000 or more depending on material. (see http://en.wikipedia.org/wiki/Permeability_%28electromagnetism%29 for values of ur) So using an air core reduces inductance by that same factor – let’s use ur = 100 as a very conservative factor for steel. Now the inductance of the air coil comes down to 0.03% of the PU coil. There may also be a difference in l, which is the length of the coil. The PU coil is taller (bigger l) than the Suhr coil (which is flat) so there is a slight increase in L of the Suhr coil due to that. My coils are not flat, they are about 0.3 inches around so l for my coils is about the same as for the PU.
Anyway, this is probably way more than you wanted to know, but your question is a good one and it got me to dig up all this material cause I wanted to know the answer too.
Alan0354
Calif, USMay 29th, 2012 11:36 AM Edit Profile Print Topic Search
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uneumann
The inductance is proportion to area of the coil. Inductance is defined as total flux generated by current through the coil:
http://en.wikiversity.org/wiki/Inductance
This agree with all EM books that L=Φ/I=BA/I where Φ is the total flux.
For a round coil, the formulas are:
B=μNI, Φ=BA, L=Φ/I = BA/I = μNA
Where N is number of turns, I is current, B is flux density, A is area.
Granted this is for round shape and is different from your coil. But you can see the relation of the area to the inductance.
Inductance is the one that degrade the sound, and a bigger area coil still have significant inductance. Case in point that there is a distinct difference in sound from the demo of Suhr.
uneumann
USAMay 30th, 2012 02:01 PM Edit Profile Print Topic Search
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Alan
Hi – your application of these formulas seems to omit a factor of N in your initial equation L=Φ/I. See http://en.wikiversity.org/wiki/Inductance where inductance of solenoid is defined as L=NΦ/I. It appears your eq’s do not account for multiple turns of the coil. The geometry of the coil also matters, and different approximations have been derived for common cases like loops and solenoids. But in all cases I see a factor of NNA (N squared x Area) to the final inductance. See examples below.
http://en.wikiversity.org/wiki/Inductance (note NNA for inductance of a solenoid)
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/indcur.html#c2
http://emclab.mst.edu/inductance/ covers many geometry options and more specifically
http://emclab.mst.edu/inductance/circular/ show NNArea relationship for a coil of wire like my coils
http://www.technick.net/public/code/cp_dpage.php?aiocp_dp=util_inductance_circle again shows the NNA factor
http://www.eeweb.com/toolbox/coil-inductance/ points out that inductance of N turns is related to inductance of 1 turn by factor of N squared.
So, I’ll stand by my reasoning that for a constant NxA factor, a larger area coil inductance will be lower. With the change from iron core to air core, the big coil inductance is reduced even farther.
To your point about the Suhr coil affecting the PU tone, I can’t argue that one way or another since I don’t have one to try and I don’t know their actual specs. I believe you hear the difference, and others have posted similar opinions. If anyone has one of their coils and could measure its resistance and inductance, that could be of great help in figuring out why it impacts tone.
As for concluding that a hum cancelling coil MUST affect the PU tone, I disagree. The physics argues that the inductance (and resistance) of a hum-cancelling coil can be made very low (< 1% of PU parameters) to the point that it’s within PU winding tolerances and arguably negligible (or unnoticeable) in terms of tone impact. Given the equations and my tele-experiment results, I have to consider that the Suhr coil design or construction is somehow sub-optimal, since its impact is so noticeable. The community should press Fender to route a channel in its guitars so Suhr or Ilitch can sell *optimized* coils for those guitars. I suspect the back-plate design is too limiting. Note that Ilitch already sells a big flex coil if you have a channel routed. http://www.ilitchelectronics.com/products.htm
Alan0354
Calif, USMay 30th, 2012 07:36 PM Edit Profile Print Topic Search
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I just respond to the first part as I am busy, I'll come back on the rest.
Read my post, I did not omitted the N. This is what I gave: L=Φ/I = BA/I = μNA which is the same as yours. As in formula, L is linearly proportional to N and A. So if you have a bigger area, you have more inductance per turn. So even you have less turn, you get more inductance because A is big. Unless the formula has the square of the N, you are still dealing with the linear proportion.
Yes, I am using a general case of a round long solenoid. The exact shape make a difference. BUT as a rule of thumb, you don't deviate a lot from a simple round coil.
As I repeat, I did not test your design, I just pull out formulas.
uneumann
USAMay 31st, 2012 01:36 AM Edit Profile Print Topic Search
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Not sure this is going anywhere.
You say L = Φ/I and the citations I list say
L = NΦ/I. Seems like a simple mistake to me.
Alan0354
Calif, USMay 31st, 2012 02:42 AM Edit Profile Print Topic Search
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Yes, I double check the book, you are right.
L=μN^2A so you have the square of N.
uneumann
USAJul 21st, 2012 03:03 PM Edit Profile Print Topic Search
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FYI - I've now done the hum cancellation on a stratocaster-like guitar (a G&L S-500). Details are at https://sites.google.com/site/stringsandfrets/Home/noise-reduction-for-sc-pickups
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