Circuits involve active electronics and a dummy coil.

[Helmholtz]

Update: Mike Sulzer's Jfet buffer does not really have low output impedance. While typical textbook examples of the source follower give values of some hundred Ohms, a closer look at this circuit reveals that its output impedance increases noticeably with lower drain currents. In our case with Rs=27K, the output impedance will be around 3K (!) or even higher. (In can be measured directly with an LCR meter).

lnserting a series resistance of several k Ohms will damp the PU's resonance and might be audible.

[Helmholtz]

Update here...I had an interesting experience with this yesterday. I have a dummy coil i'd harvested from an old P90, and I had it wired in to a small PCB board to try this circuit. Wasn't working, so I detached it and put a connector inline that allowed me to insert the dummy coil, unbuffered, on the ground side of the actual pickup, tucked away behind the volume pots.

So now I have a P90 with a P90 dummy coil in series, no buffering. Didn't know what to expect....I was assuming it would be mud. But the guitar itself is a little bright, and the existing P90s (GFS Vintage) are not high-output, at least not for P90s. The result was:

1) Some reduction of hum, but highly directional. If I stand in the right spot it's almost silent, if i turn 90 degrees it's almost as bad as if the dummy coil weren't there. This is likely due to it being down in the control cavity, and parallel to but not on the same plane as the pickup. Might be able to move it a bit.

2) Significant darkening of tone, but highs are still there. Brings the bridge EQ closer in similarity to the neck, which doesn't have this dummy coil.

3) Here's the surprise - big increase in low-end punch through high gain. This thing is now way "chunkier" and crunchier than before and just feels really great to play. It's not more output overall; it's that the lows are louder and more dynamic in a way that differs from what an EQ pedal might do.

The low-end behavior is (I'm guessing) related to the increased inductance of the additional coil, which seems to have lowered the resonant frequency of the pickup in a pleasing way.

No real surprise, here.

You may achieve the same lowering of the PU's resonant frequency by wiring a capacitor of around 470pF (exact value depends on your PUs and guitar cable) in parallel with the PU - no noise reduction though.

The buffer avoids lowering of the resonant frequency.

Perfect noise cancelling via dummy coil would ideally require the dummy coil to be identical to the PU coil and being in the same place - or surround the PU as with low impedance frame shaped dummy coils. Results of real systems may not be completely satisfying if the noise source(s) are located in close proximity, as in these cases the magnetic interference fields vary strongly with position and orientation.

There is a problem with placing the dummy coil in the control cavity: The casings of the pots are typically made of ferromagnetic steel and thus change the noise fields close-by. This may prevent the dummy coil's signal to be identical to the PU's noise and consequently cancellation will suffer.

[cheezit]

Update here...I had an interesting experience with this yesterday. I have a dummy coil i'd harvested from an old P90, and I had it wired in to a small PCB board to try this circuit. Wasn't working, so I detached it and put a connector inline that allowed me to insert the dummy coil, unbuffered, on the ground side of the actual pickup, tucked away behind the volume pots.

So now I have a P90 with a P90 dummy coil in series, no buffering. Didn't know what to expect....I was assuming it would be mud. But the guitar itself is a little bright, and the existing P90s (GFS Vintage) are not high-output, at least not for P90s. The result was:

1) Some reduction of hum, but highly directional. If I stand in the right spot it's almost silent, if i turn 90 degrees it's almost as bad as if the dummy coil weren't there. This is likely due to it being down in the control cavity, and parallel to but not on the same plane as the pickup. Might be able to move it a bit.

2) Significant darkening of tone, but highs are still there. Brings the bridge EQ closer in similarity to the neck, which doesn't have this dummy coil.

3) Here's the surprise - big increase in low-end punch through high gain. This thing is now way "chunkier" and crunchier than before and just feels really great to play. It's not more output overall; it's that the lows are louder and more dynamic in a way that differs from what an EQ pedal might do.

The low-end behavior is (I'm guessing) related to the increased inductance of the additional coil, which seems to have lowered the resonant frequency of the pickup in a pleasing way.

[cheezit]

Your modified Jfet source amplifier circuit is critical with such low battery voltage and will work properly only with specially selected Fets having a very low pinch-off voltage. Also, to use it as an amplifier means to take the output from the drain. But the internal impedance at the drain is considerably higher than at the source. Thus you sacrifice one of the benefits of the simple source follower, namely inserting only little series resistance with the PUs.

BTW, in my searching around I consider this approach to be very similar in spirit to https://patents.google.com/patent/US5569872, which is the Dudley Gimpel patent for Ernie Ball. Take a look at Figure 5, which shows the same approach: a buffered noise-sensing coil inserted on the ground side of the pickup.

The circuits are much more complex, though, and I wondered why; your points about the sensitivity of the circuit to the characteristics of the JFET and the amplification problem may be it.

If I'm right, it's the same reason DIY fuzz pedals can be made out of 8 components but Boss equivalents have dozens and dozens; they have to design for consistency and low cost, and can't mess around with parts that are operating at (or beyond) the edge of their design parameters.

[Helmholtz]

Hi cheezit,
That is how I interpreted it.
For my application, the circuit wasn't working with unity gain. I was using a dummy in the neck position to cancel out hum from an overwound bridge. So I modified it slightly as per my post.

I have tried it on 3 guitars now:

1) Neck P-90 cancelling out hum from bridge P-90: Worked great. So much noise reduction.
2) Strat pickup under metal pickguard cancelling out hum from Jazzmaster pickup: Works so-so. It is a marked improvement though.
3) Strat pickup under pickguard cancelling out hum from other strat pickups: Also works fairly well, removes enough hum for me, but not as quiet as positions 2 and 4 with RWRP.

It sometimes gets overlooked that magnetic (interference) fields vary with position and especially orientation. The dummy coil needs to have its magnetic axis oriented parallel to the PUs' and should be placed as close to the PUs as possible.

When you remove the ferromagnetic core parts from a PU coil, it will produce less hum than the original PU. Thus it is advisable to use an overwound dummy coil or a coil with larger area than the PUs (e.g. P-90 dummy coil in Strat) in conjunction with the unity gain buffer circuit.

Your modified Jfet source amplifier circuit is critical with such low battery voltage and will work properly only with specially selected Fets having a very low pinch-off voltage. Also, to use it as an amplifier means to take the output from the drain. But the internal impedance at the drain is considerably higher than at the source. Thus you sacrifice one of the benefits of the simple source follower, namely inserting only little series resistance with the PUs.

Placing the duimmy coil under a metal pickguard not only reduces the HC signal but also changes its frequency content, as the conductive metal preferably absorbs the higher frequency components of the magnetic interference fields. But for perfect HC you want the dummy coil's signal to replicate the PUs' interference content as close as possible.

[cheezit]

Hi cheezit,
That is how I interpreted it.
For my application, the circuit wasn't working with unity gain. I was using a dummy in the neck position to cancel out hum from an overwound bridge. So I modified it slightly as per my post.

I have tried it on 3 guitars now:

1) Neck P-90 cancelling out hum from bridge P-90: Worked great. So much noise reduction.
2) Strat pickup under metal pickguard cancelling out hum from Jazzmaster pickup: Works so-so. It is a marked improvement though.
3) Strat pickup under pickguard cancelling out hum from other strat pickups: Also works fairly well, removes enough hum for me, but not as quiet as positions 2 and 4 with RWRP.

I'm doing this with P90s - I had an Epi LP with dual P90s, sold it to a friend because I couldn't take the hum, and he sold it back to me ... eight years later. So here I am with hum again.

Did you happen to note any voltages from your versions? I'm getting back to mine and trying to trace where things have gone wrong.

[Helmholtz]

Thanks Ethan - good catch - EM is not my strength so I used the terminology loosely. I've made the fix - and actually caught another in the process. Thanks again.

My site has my gmail address (uneumann@gmail.com) if anyone wants to reach me. As for signing, it seems like email is a sig these days. ;-)

-Ulrich Neumann

(To be precise, the term electromagnetic fields covers both : electric and magnetic fields. Conductive shields reduce electric fields/interference but can as well damp magnetic fields via eddy currents at high frequency, depending on conductivity of the shield. They are ineffective for low frequency magnetic fields though.)

Seems you have reinvented the patented Ilitech system:
HUM CANCELING SYSTEMS ? ILITCH ELECTRONICS

This is probably the best passive humcancelling system known.

[harry]

Hi - I'm trying this out, no luck so far - but I took the PDF and created a more detailed view of how this works for an actual guitar circuit.
[ATTACH=CONFIG]47650[/ATTACH]

Mike, if you are still reading this thread, could you confirm that this is correct?

I included a 'defeat' switch to eliminate the circuit - may not be necessary.

Hi cheezit,
That is how I interpreted it.
For my application, the circuit wasn't working with unity gain. I was using a dummy in the neck position to cancel out hum from an overwound bridge. So I modified it slightly as per my post.

I have tried it on 3 guitars now:

1) Neck P-90 cancelling out hum from bridge P-90: Worked great. So much noise reduction.
2) Strat pickup under metal pickguard cancelling out hum from Jazzmaster pickup: Works so-so. It is a marked improvement though.
3) Strat pickup under pickguard cancelling out hum from other strat pickups: Also works fairly well, removes enough hum for me, but not as quiet as positions 2 and 4 with RWRP.

[cheezit]

I made a new pdf file. That seems to work.

[ATTACH]43692[/ATTACH]

Hi - I'm trying this out, no luck so far - but I took the PDF and created a more detailed view of how this works for an actual guitar circuit.


Mike, if you are still reading this thread, could you confirm that this is correct?

I included a 'defeat' switch to eliminate the circuit - may not be necessary.

[harry]

Many thanks Mike!
That circuit is brilliant in its simplicity. I like the individual pickup trimpots. Looks like it could be powered with a very small battery. Any recommendations on a specific J-FET?

Just did this with a K117. I have a guitar with 2xP90s but only use the bridge, so I pulled the magnets off the neck. I had to modify the circuit to provide some gain, because the bridge is overwound wrt the neck. I used a 6.8k on the drain and 2.2k on the source - maybe a bit high res but wanted to keep current draw low as just using a CR2032. Flipped + and - pickup wires and took output from the source thru 10uF. It works brilliantly. No discernable effect on tone, and just pop the battery out to see what it would be like with all the noise!

Thanks again Mike. I wish I had done this years ago!

[AlDiMeowla]

I made a new pdf file. That seems to work.

[ATTACH]43692[/ATTACH]

Many thanks Mike!
That circuit is brilliant in its simplicity. I like the individual pickup trimpots. Looks like it could be powered with a very small battery. Any recommendations on a specific J-FET?

[harry]

I made a new pdf file. That seems to work.

[ATTACH]43692[/ATTACH]

Thank you very much, Mike.

[Mike Sulzer]

I made a new pdf file. That seems to work.

bufferedDummy.pdf

[Steve A.]

Hello and sorry for necrobumping the thread. I am very intrigued by this FET-dummy coil buffering, that Mike was talking about. But it seems the schematic has disappeared. Would anyone of you happen to have a copy of it to post again? Thanks

I am having trouble getting it to attach.

Maybe PM me, or upload and link to an external imagehosting site?

Al: Perhaps if you include the Post # [this post is #52] the original schematic can be retrieved. Or not.

Mike: Can you try attaching the schematic again? I just checked and was able to attach an image file here. Or PM/email it to me and I can try to reattach it to the original post (I'd need to know Post # to do that.)

Al: If you have run across a good imagehosting site still around let us know. Photobucket used to be great but the last time I checked I could not link directly to 100's of images I had uploaded there (links went to an HTML page that included the image- along with tons of ads! )

%=%=%=%=%=%=%

Most people seem to be using cloud host sites like DropBox these days. DropBox gives you 2GB space for free*** but the code generated to share files includes "dl=0" as the last entry which disables downloading.

Change the 0 to 1 (or delete the entry) for a direct link to the file.

There are other cloud host sites but DropBox has been around forever and is well-integrated on most platforms, programs and mobile apps. I use my stable of Android tablets for 99% of my computing these days and DropBox is indispensable for sharing files between my various mobile devices and my PC (you'll want to install DropBox on a host computer which mirrors the contents in the cloud.)

Steve A. "Super Moderator" (I mention that only because I have moderator powers for all of the forums here and do not want to step on the toes of the actual moderator of each forum.)

*** There is free bonus space available. My Samsung Tab 4 7.0 tablet came with a one-time bonus of an additional 48GB space there but that expired after 2 years. Or you can pay $9.99/mo for 1TB space (ouch!) Here's a link explaining how to earn more space for free:

https://www.dropbox.com/help/space/get-more-space

Getting family, friends or co-workers to join DropBox gives you a 500MB bonus apiece (up to 16GB.)

[harry]

Maybe PM me, or upload and link to an external imagehosting site?

Ah! I am also interested in this. Funny how I find myself here 3 days after your request.
If you would be so kind, Mike Sulzer, I would really appreciate that!