Circuits involve active electronics and a dummy coil.

[Amit]

Yup just a follower is obviously the best way if you use matching pickup and dummy.
In my case I'm trying to tame a Tele, so bridge pickup and neck pickup are way different.

As a middle ground between the pickups for the dummy I'll use a Strat single, hence why I look to add a bit of boost, to match the bridge noise level. neck obviously will need just passive pot adjustment.
I thought about using local feedback inverting amp with a single jfet like in tubes:
Designing Single-Stage Inverting Feedback Amplifiers
But I can't find schematics of such an amp using jfets on the web... jfets are not able to do that?


Thanks for the replay after all those years

[Mike Sulzer]

Sure, you can do that with FETs. But remember what we are trying to do. The idea is to put the voltage from the dummy in series with the pickup coil without the dummy's inductance adding to that of the pickup coil. Therefore we measure the dummy's voltage: a very high impedance is used for this so that you do not load the dummy and thus alter the relative levels of the different hum harmonics. The follower lowers the impedance while "following" the voltage so you can insert it in series with the "ground" lead of the pickup with minimal effect on the sound of the pickup from the adjustment pot..

Yup just a follower is obviously the best way if you use matching pickup and dummy.
In my case I'm trying to tame a Tele, so bridge pickup and neck pickup are way different.

As a middle ground between the pickups for the dummy I'll use a Strat single, hence why I look to add a bit of boost, to match the bridge noise level. neck obviously will need just passive pot adjustment.
I thought about using local feedback inverting amp with a single jfet like in tubes:
Designing Single-Stage Inverting Feedback Amplifiers
But I can't find schematics of such an amp using jfets on the web... jfets are not able to do that?


Thanks for the replay after all those years

[AlDiMeowla]

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

[Mike Sulzer]

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.

[AlDiMeowla]

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

[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!

[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.)

[Mike Sulzer]

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

bufferedDummy.pdf

[harry]

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

[ATTACH]43692[/ATTACH]

Thank you very much, Mike.

[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]

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!

[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]

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.

[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.

[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.