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Thread: suhr and dummy coil...

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    suhr and dummy coil...

    So what's the final conclusion?. Anybody tried to wind something that likes, works, or anything?. What about wire gauge, etc? Thanks a lot for any reply!

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    I missed the previous discussion, and I have not tried to build one yet. However, I think it makes sense and could be useful for several applications.

    For example, I would like to try something like this on my outboard reverb tank, since it picks up hum and radio signals when my band has performed in radio stations or near a powerful station.

    I understand the design as an AM antenna coil (out of phase with the pickup coils) terminating to a resistance and/or capacitance pad. The pickup grounds are terminated to the same pad. Probably, the resistance is very small, like 10-20 ohms. The Suhr has adjustable pots to fine-tune the 'noise-canceling'. I would think these could be in series with the pickup and/or antenna grounds. Again, probably a low resistance.

    The information I have read indicates you would NOT use RWRP setups with this approach. So, I would have to make some changes on my stock Fender pickup configurations.

    The antenna coil may be difficult to make neatly and unobstrusive. It seems like I could experiment though with an old AM antenna from a transistor radio with a single pickup.

    BruceB

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    Pickup Maker David Schwab's Avatar
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    Quote Originally Posted by BruceB
    For example, I would like to try something like this on my outboard reverb tank, since it picks up hum and radio signals when my band has performed in radio stations or near a powerful station.
    Craig Anderton has a reverb tank setup that uses two sets of springs and is set up for hum cancelation.

    Here's info, and the schematic too:

    Hot Springs Reverb



    .

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    Pickup Maker David Schwab's Avatar
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    Here's something interesting... I was reading the archives at www.mimf.com, and found this post about dummy coils by Rick Tuner from November, 2000:

    Dummy coil area counts, too. You can enlarge the area picked up by the dummy coil and reduce the number of turns..... A series dummy coil made the same size as the perimeter of a control cavity and wound with fairly large wire might cancel a fair bit of hum with minimum effect on tone.....Just a thought.
    Hmmmm, sound familiar? Seems like Turner invented Suhr's dummy coil!

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    I tried out a Suhr guitar with dummy coil at a recent trade show and was reasonably impressed. Of course standing right beside the power transformer in the amp introduced very audible hum, but when you realize what the gain of the amp was, it was not surprising or unreasonable hum.

    The area thing is important in a couple of ways. First, it does allow for a modest number of turns to acquire sufficient hum to be useful for cancellation purposes. But beyond that, it accomplishes the neat trick of not being that much closer to one pickup than to any other. If the Strat was a two-pickup instrument like the old Alembics, with a dummy coil in the middle, that would be one thing. But when you have 3 pickups, just where do you put the coil so that it is equidistant? Suhr's solution, using the backplate, was brilliant: make it surround all of them!

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    Senior Member madialex's Avatar
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    Quote Originally Posted by Mark Hammer View Post
    I tried out a Suhr guitar with dummy coil at a recent trade show and was reasonably impressed. Of course standing right beside the power transformer in the amp introduced very audible hum, but when you realize what the gain of the amp was, it was not surprising or unreasonable hum.

    The area thing is important in a couple of ways. First, it does allow for a modest number of turns to acquire sufficient hum to be useful for cancellation purposes. But beyond that, it accomplishes the neat trick of not being that much closer to one pickup than to any other. If the Strat was a two-pickup instrument like the old Alembics, with a dummy coil in the middle, that would be one thing. But when you have 3 pickups, just where do you put the coil so that it is equidistant? Suhr's solution, using the backplate, was brilliant: make it surround all of them!


    I too have seen the whole system. It is made on the strats back plate which is slightly wider around to make up for the 1/4 inch coil. The coil I think is fairly low in resistance as it is very flat and only 1/4 inch wide and the whole backplate is covered by some black sprayed on material, maybe sheilding paint?? It also comes with a small PC board that has 2 or 3 very tiny trim pots to adjust the frequencys of each pickup to the noise signal generated therefore making them vitually noiseless. The one for the telecasters are made right in the guitar on the Suhr guitars. Pretty darn neat idea, my hats of to Mr. Surh.

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    And while it has been said many times over (on the old Ampage), it bears repeating: Even knocking 12db of hum level off, without changing the tone of single-coils that one has grown sentimentally attached to, and plans one's pick attack around, is, if not perfect, nevertheless a good thing.

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    Quote Originally Posted by David Schwab View Post
    Here's something interesting... I was reading the archives at www.mimf.com, and found this post about dummy coils by Rick Tuner from November, 2000:



    Hmmmm, sound familiar? Seems like Turner invented Suhr's dummy coil!
    This might be worth some research. If one can legally establish a prior date at which the innovation was "anticipated", no patent.

    Chilliachki filed what became application number US 2005/0204905 A1 on 14 March 2005, so it seems possible to likely that he was anticipated.

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    Pickup Maker David Schwab's Avatar
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    Well the post by Turner is dated and all, and obviously precedes Chilliachki's filing by 5 years!

    I know if I had read that post, and there wasn't this patent, I'd be trying out ideas myself.

    Could be parallel discovery... but that seems unlikely.

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    Senior Member madialex's Avatar
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    either way

    He is getting 325.00 each for the system. Wish I could have been the one to come up with it.

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    ...

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    Quote Originally Posted by David Schwab View Post
    Well the post by Turner is dated and all, and obviously precedes Chilliachki's filing by 5 years!

    I know if I had read that post, and there wasn't this patent, I'd be trying out ideas myself.

    Could be parallel discovery... but that seems unlikely.
    I looked around the MIMF website, but could not find the posting you quoted. Where should I look?

    I don't know if the USPTO accepts web dates or not, but if it's that long ago, five years, enough other sites will back the date up, perhaps sufficiently.

    Parallel happens a lot, but in the US only the first to invent gets to patent the invention. In the rest of the world, it's first to file. In the entire world, if something has been publically known for five years, it cannot be patented, even by the true original inventor.

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    Quote Originally Posted by madialex View Post
    He is getting 325.00 each for the system. Wish I could have been the one to come up with it.
    I'd pay $80, which I think is fair. At an MSRP of $325, I'll wait until Steve A. comes out with a perfected design....

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    Pickup Maker David Schwab's Avatar
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    Quote Originally Posted by Joe Gwinn View Post
    I looked around the MIMF website, but could not find the posting you quoted. Where should I look?

    I don't know if the USPTO accepts web dates or not, but if it's that long ago, five years, enough other sites will back the date up, perhaps sufficiently.

    Parallel happens a lot, but in the US only the first to invent gets to patent the invention. In the rest of the world, it's first to file. In the entire world, if something has been publically known for five years, it cannot be patented, even by the true original inventor.
    Here's the whole post...

    I'm going to try and find it again and submit the URL...

    Rick Turner - 09:51am Nov 2, 2000
    Resawing and Tonewoods
    Jeez, I hate to come off like the old fart I am, but we did the dummy coil thing 30 years ago at Alembic. The pickups were relatively low impedance---1500 to 3000 turns of # 40, and at first, we series wired a dummy coil (wound the same physical size but with a plexi core)in series with each pickup. Then Ron Wickersham designed a preamp which could use a single smaller dummy coil and subtract the hum from each string pickup. On the classic Alembic preamp there are four trim pots: gain controls for each pickup and hum cancelling controls for each pickup. The closer the dummy coil is to the pickup coil, the more complete the hum cancellation will be; of course if it's so close that it's picking up the same string section read by the pickup, you'll get phase cancellation of signal. Dummy coil area counts, too. You can enlarge the area picked up by the dummy coil and reduce the number of turns..... A series dummy coil made the same size as the perimeter of a control cavity and wound with fairly large wire might cancel a fair bit of hum with minimum effect on tone.....Just a thought.
    [EDIT] Here's the URL

    Reinventing phantom ("dummy") coils to decrease hum in single coil pickups

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    well this is an interesting reading...is it possible to get rid of the trimmers and just go for the dummy coil, for a partial but usable hum reduction??. i will experiment and research a little more...i have some old radio books 'round here...

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    Yes, it is possible to just guesstimate or eyeball or go for a shot in the dark. Obviously a professional touring musician who desperately needs zero hum may require the precision of trimpots to dial in optimal cancellation, but every db less of hum is a db less of hum. I'd like 0db of hum myself, but I'll happily settle for 12db less. So, yeah, you can just whip up a dummy coil that's somewhere in the ballpark and expect to hear some sort of benefit, even if it isn't as much as a Suhr system would get you.

    I guess the other way to look at it is that every db less of hum makes it easier for more aggressive noise-reduction methods like noise gates or downward expanders to be set in less aggressive ways. Traditionally, we've hated noise gates as a solution because the threshold would often have to be set so high that you'dlose the initial attack of the note and lose some of the decay. If you can afford, by means of modest hum-reduction, to set the gating threshold much lower, then the noisegate's behaviour may interfere with the naturalness of the sound and instrument's dynamics much less.

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    This is an idea I had quite some time ago. I have no time to build such a thing right now, but I will soon.

    Cheers,
    Lucas

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    Quote Originally Posted by LVS View Post
    This is an idea I had quite some time ago. I have no time to build such a thing right now, but I will soon.

    Cheers,
    Lucas

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    Be aware that inductance varies as the square of turnscount unless the individual coils are well separated. This is unlike the behaviour of resistors and capacitors.

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    Thanks for the answer, Joe, though it confuses me somewhat.

    What I have in mind is a dummy coil like this :

    - air core
    - 0.2mm dia wire
    - large area compared to a pickup, possibly rectangular shaped
    - wound together as one coil package with several taps connected to a switch array
    - connected in series with a pickup.

    The switches would make it possible to dial "any" number of coil turns.

    I assumed a linear relation between the number of turns and the hum field caused voltage.

    The large area would involve lesser turns, making the coil inductance quadratically smaller for less impact on tone.

    Is there anything I am overlooking? Influences from coil segments that are switched off?

    Cheers,
    Lucas

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    Last edited by LVS; 09-06-2006 at 07:42 PM.

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    Quote Originally Posted by LVS View Post
    Thanks for the answer, Joe, though it confuses me somewhat.

    What I have in mind is a dummy coil like this :

    - air core
    - 0.2mm dia wire
    - large area compared to a pickup, possibly rectangular shaped
    - wound together as one coil package with several taps connected to a switch array
    - connected in series with a pickup.

    The switches would make it possible to dial "any" number of coil turns.
    So far, so good.

    I assumed a linear relation between the number of turns and the hum field caused voltage.

    The large area would involve lesser turns, making the coil inductance quadratically smaller for less impact on tone.
    For a given coil shape and size, induced voltage will be directly proportional to turns count, while inductance will vary as the square of the turns count.

    The actual rule is that given a uniform hum field, the induced voltage is proportional to the area-turns product of the dummy coil. This is the area of the average turn multiplied by the number of turns.

    Is there anything I am overlooking? Influences from coil segments that are switched off?
    Not that jumps out at me. Open coils are invisible in this setup.

    If you have a good voltmeter, you can figure out the correct number of turns. Take a dummy coil with a known number of turns and the pickup to be cancelled. Put both in the same hum field, and measure the resulting hum voltages. The objective is to make these two voltages the same.

    Compute the correct turns count using the following formula:

    NewDummyTurnsCount= (MeasuredPickupVoltage/MeasuredDummyVoltage)*OldDummyTurnsCount

    Make a new dummy coil with the exact size and shape as the old dummy coil, but with the computed number of turns. No switch needed.

    This should allow for near perfect hum cancellation.

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    Understood, thanks - it's reassuring you confirm my assumptions, which I expressed in a somewhat unstructured way. I was aware of the Area-Turns product : I was gonna start from an estimation of Area x Turns of a P-90 to apply to the dummy, and then increase the dummy's calculated number of turns to a number satisfying that powers-of-2 formula.

    The method you describe to use voltage ratio to build a new coil is more simple, I must admit.

    This er, "binary" dummy coil idea is actually a spinoff of a few guitar pickups I made in the same manner. I'm gonna give it a go anyway. For the experience, and as a tryout alternative to Mr. Suhr's pot-adjustable coil.

    Cheers,
    Lucas

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    Supporting Member Dave Kerr's Avatar
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    How about the gauge of the wire in the dummy coil? For a given area and turn count, what would the effect be on the induced voltage by substituting 37 AWG wire (.0068" dia) for 43 AWG (.0036)? Assume that the size of the coil is rather large, so the increased thickness of the wire doesn't contribute appreciably to the outside diameter of the coil.

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    Quote Originally Posted by Dave Kerr View Post
    How about the gauge of the wire in the dummy coil? For a given area and turn count, what would the effect be on the induced voltage by substituting 37 AWG wire (.0068" dia) for 43 AWG (.0036)? Assume that the size of the coil is rather large, so the increased thickness of the wire doesn't contribute appreciably to the outside diameter of the coil.
    Won't make the slightest difference, and #37 is far easier to handle.

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    I had a Kramer Classic (their answer to a 62 reissue at that time - mid-to-late 80s). It had three duncan alnico single coils with a 4th reverse wound one mounted inside the cavity but underneath the pickguard. It was used to noise cancel the 3 pickup that were mounted normally. It worked well, but took a little bit of the top end off of the pickup in my opinion. But I do think it worked better than most solutions or humbucking replacements.

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