Circuits involve active electronics and a dummy coil.

[Alan0354]

So are the two design mentioned the only ones on the market or patented?

[Joe Gwinn]

No, Ethan, I did that. It should come up in a search. I will try to remember to do that later, although it should not be hard for anyone to find. The idea is that the pickup remains passive; just the dummy has a buffer. A single FET can be used, running on a few volts and well under 1 ma.

Yes. I don't recall having published a circuit, although I may have commented on some of them.

[Alan0354]

Anyone know of any other active noise cancelling design other than the two mentioned?

I read from a few comments that the EB did not really work out very well. I listened to the demo of the Suhr, not only it does not cancel very well, it change the sound a little also. For that kind of money, Suhr can keep it.

[Kindly Killer]

I tried Mike Sulzer's circuit but I think something is missing from the schemo that I'm too ignorant to catch. I have it in my pile of stuff to come back and try but I don't know when I will ever get to it.

It would be super-fantastic-wonderful if Mike would draw this up as a complete OS project. (unsubtle begging)

I also tried the Illitch [/Suhr] type low impedance dummy coil in series approach - I just followed the recipe in the patent verbatim. It worked great on a disembodied pickguard, but when I stuffed it into a guitar it didn't reduce enough hum that I thought it would be worthwhile. I'm very distantly considering buying one of Suhr's for one of my strats and try to clone it for my other one, but realistically I probably already spent all the time on this that I'm going to.

Part of my approach to all of this is that the problem of hum kinda takes care of itself. Seems like the big productions I play in never have hum problems - it's only at the rowdy places where people drink a lot of beer (where they have a lot of neon signs). I almost feel like a noisy guitar amp humming between songs - or during soft parts - is part of the ambiance of those places. It's like an idling motorcycle motor or something - and they can't wait for me to peg the tach LOL

Oh yeah - the reason I'm replying: I built what I described in my first post - output of 5-way switch into preamp, plus output of dummy coil into preamp, combined after the pre. I used the Tillman pre instead of opamp. Tone controls and volume are 25k pots, switched separately on a 4-pole switch. Works perfectly as far as canceling hum, but it sounds and feels WAY different. I considered it for about 1.5 seconds and ripped it out.

[Mike Sulzer]

I tried Mike Sulzer's circuit but I think something is missing from the schemo that I'm too ignorant to catch. I have it in my pile of stuff to come back and try but I don't know when I will ever get to it.

Did you measure the dc voltage at the top of the 27K resistor (at the connection to the FET)?

[Kindly Killer]

I did. I don't remember the exact number, but it was reasonable...

[Mike Sulzer]

I did. I don't remember the exact number, but it was reasonable...

OK, good. If you connect the dummy coil directly to the amp and listen for the hum, and then connect it to the circuit, jumpering across the pickup, do you get a similar level of him, but maybe more higher frequency buzzing?

[Alan0354]

I did not know about the Ernie Ball design/patent. From the patent it is clear that he has an unnecessary complication in the design, adjustable loading on the dummy to get the frequency response right. From the explanation above, it should be clear that infinite load is correct and no adjustment is necessary as long as the dummy is very much like the pickup.

In my design, I use op-amp, I invert the signal for the middle pup so even when you are in position 2 and 4 when both circuit are combined, the effect cancel out.

What do you mean by adjusting the load on the dummy coil to get the frequency response? I did put a 250K volume pot as a variable resistor across the dummy coil and adjust the load and I cannot get rid of the noise at all!!! I tried using a lag lead network ( a cap or different value in series with the 250K pot) and cannot get rid of all the noise. Mainly the buzzing where you see like a spike and a few rings of about 10KHz riding on the 120Hz at the same point. Getting rid of the 60 and 120 is very easy, the buzzing is the kicker. The Suhr don't work very well in the demo either.

[Mike Sulzer]

In my design, I use op-amp, I invert the signal for the middle pup so even when you are in position 2 and 4 when both circuit are combined, the effect cancel out.

What do you mean by adjusting the load on the dummy coil to get the frequency response? I did put a 250K volume pot as a variable resistor across the dummy coil and adjust the load and I cannot get rid of the noise at all!!! I tried using a lag lead network ( a cap or different value in series with the 250K pot) and cannot get rid of all the noise. Mainly the buzzing where you see like a spike and a few rings of about 10KHz riding on the 120Hz at the same point. Getting rid of the 60 and 120 is very easy, the buzzing is the kicker. The Suhr don't work very well in the demo either.

The correct load on the dummy is infinity. See post 13 above. The idea is to think of the equivalent circuit of the dummy when it is in series with the pickup, and then make a circuit that puts the same voltage in series with the pickup, but with a low impedance. I do not think that it is perfect as you approach the self-resonance of the coils (maybe 15 KHz), but it should be pretty good even at that high a frequency.

[Alan0354]

The correct load on the dummy is infinity. See post 13 above. The idea is to think of the equivalent circuit of the dummy when it is in series with the pickup, and then make a circuit that puts the same voltage in series with the pickup, but with a low impedance. I do not think that it is perfect as you approach the self-resonance of the coils (maybe 15 KHz), but it should be pretty good even at that high a frequency.

I tried infinity also. No matter how you play with the loading, you can't get rid of the hum. As I said, getting rid of the 60 and 120 is easy, by the buzz is a different story. Yes you hear it lower, but not cancelling. Nothing like the true humbucking pup. You have to have very very similar coil for the dummy to get a better effect.

[Mike Sulzer]

I tried infinity also. No matter how you play with the loading, you can't get rid of the hum. As I said, getting rid of the 60 and 120 is easy, by the buzz is a different story. Yes you hear it lower, but not cancelling. Nothing like the true humbucking pup. You have to have very very similar coil for the dummy to get a better effect.

Yes, the coils have to be very much the same. In the circuit with the FET you need a bit more sensitivity on the dummy, and so you can never be perfect at the high frequencies. In my case, if you turned the gain up very high you could hear a sort of wispy sound, the effect of the highest harmonics not canceling. You have a bit more flexibility with the op amps, but maybe more amp noise as well.

Are you sure all your noise is magnetic and not some from electric fields, which do not cancel?

[Alan0354]

Yes, the coils have to be very much the same. In the circuit with the FET you need a bit more sensitivity on the dummy, and so you can never be perfect at the high frequencies. In my case, if you turned the gain up very high you could hear a sort of wispy sound, the effect of the highest harmonics not canceling. You have a bit more flexibility with the op amps, but maybe more amp noise as well.

Are you sure all your noise is magnetic and not some from electric fields, which do not cancel?

Yes I am very sure because I have shield cavity. It really not depend of the shielding.

You can find opamp that is very low noise. I use MC33178 or MC33179 that work with +/-2V, only draw about 1.6 or so mA supply. I yet to find a lower or equal voltage noise spec that draw less, in $1.50 range each and 3MHz BW. 4558 draw more than twice the current.

Good thing about opamp is I drive direct and the impedance is very low, that's the reason I use a 3MHz opamp so the output impedance is theoretically zero ohm at 20KHz. And I can adjust the gain of the dummy signal without effecting the impedance.

[Steve A.]

Digging up an old thread to add some irrelevant comments...

FWIW when using passive dummy coils in strats it was easiest for me to wire them up in series between the "tail" of the volume pot and ground. I thought that worked great until I was playing in one of those Bars from Hell which would be a real nightmare with single coil pickups. As I recall the dummy coil worked fine at full volume but as you turned the control down the hum would come back. (I haven't done much with dummy coils since then- I never got around to trying a Suhr-style circuit which uses two pots although I did wire up a low impedance coil with 32GA magnet wire.)

Steve Ahola

P.S. The Gibson Blueshawk has a very interesting circuit using two P-90's and a passive dummy coil. The two pickups are RWRP with respect to each other and the selector switch inverts the leads from the dummy coil so that there is hum-cancellation in all positions (no need for the dummy coil in the middle position).

[David Schwab]

FWIW when using passive dummy coils in strats it was easiest for me to wire them up in series between the "tail" of the volume pot and ground. I thought that worked great until I was playing in one of those Bars from Hell which would be a real nightmare with single coil pickups. As I recall the dummy coil worked fine at full volume but as you turned the control down the hum would come back.

Because now you were just hearing the dummy coil.

[Steve A.]

Because now you were just hearing the dummy coil.

In "normal" environments (i.e. at home) it seemed to work great. And it was only in the middle range of the pot that the noise came back; once you passed the midpoint the hum went away again. But that was definitely the wrong way to hook it up- I should have inserted between the pickup grounds and the guitar ground but I was doing series/parallel switching so that would have gotten complicated...

I need to get back into dummy coils for some of my steel guitars. Like the 10 string Alkire E Harp that I just got...




Steve Ahola