Circuits involve active electronics and a dummy coil.

[Alan0354]

I did some research and so far I found one design used in the Fender Elite Strat and one in Ernie Ball Silent circuit where both use active electronics to isolate the dummy coil from the main pup. Is there any other design out there? If so, can anyone show me the link or schematic?

Thanks

Alan

[Kindly Killer]

I don't have any info but I'm very interested in this. I was just about to try a Suhr type passive dummy coil because my friend (a gifted luthier) is interested in noiseless stuff; however I hate the idea of routing a strat like.

The Fender Elite looks like a fantastic idea.





After seeing that, here's what I'm gonna try: simple TL072 buffer after dummy coil, same thing at the normal output point of guitar circuit, combine. Switch in an additional dummy coil in parallel with the first one in positions 2&4. Assumptions: swimming pool route, 4-pole switch, unity gain all around.

[Alan0354]

I tried something similar already, you have to add inverted circuit for the middle pup as it is opposite polarity. One thing that does not work, you cannot have the tone control in the normal way because when you turn the tone pot up, you cut off the high frequency noise of the main pup. But the dummy pup still sense the high frequency noise and go into the main signal as there are no opposite noise from the main pup to cancel them.

I am looking for something different from the two I mentioned. I wonder whether there are any other designs on the market.

[CRU JONES]

Try using a differential amplifier or an instrumentation amplifier. Dummy coil on one input, pickup on the other.

I have also seen a circuit that uses a buffer for the dummy coil and the output of the buffer is used as the "ground" for the single coil. I think One of the guys here designed it. Joe Gwinn maybe?

cheers
Ethan

[Mike Sulzer]

Try using a differential amplifier or an instrumentation amplifier. Dummy coil on one input, pickup on the other.

I have also seen a circuit that uses a buffer for the dummy coil and the output of the buffer is used as the "ground" for the single coil. I think One of the guys here designed it. Joe Gwinn maybe?

cheers
Ethan

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.

[Alan0354]

Try using a differential amplifier or an instrumentation amplifier. Dummy coil on one input, pickup on the other.

I have also seen a circuit that uses a buffer for the dummy coil and the output of the buffer is used as the "ground" for the single coil. I think One of the guys here designed it. Joe Gwinn maybe?

cheers
Ethan

That is the Ernie Ball design. I designed both on my own without knowing it. I only found out through the patent search. This one has no restriction on the tone pot.

[CRU JONES]

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.

Ah, Thanks Mike! A very simple and clever design! I was impressed when I saw it Do post the circuit again, if you don't mind.

Sorry about that,
Ethan

[CRU JONES]

That is the Ernie Ball design. I designed both on my own without knowing it. I only found out through the patent search. This one has no restriction on the tone pot.

Alan, So are you saying the diff amp/ instrumentation is protected?

I would argue that, that design is "obvious to people skilled in the art" (such as yourself).

Ethan

[Alan0354]

Alan, So are you saying the diff amp/ instrumentation is protected?

I would argue that, that design is "obvious to people skilled in the art" (such as yourself).

Ethan

The Ernie Ball design is not differential. It is driving the ground side of the pup with the anti noise, the drive is low impedance so even if you take out the battery, you still can keep playing but with no hum cancelling. I read the patent very carefully as I designed to same thing on my own. The Elite Strat design is no big deal, that was the first one I designed and failed because of the tone control.

It is the concept they patent, not the scale of electronics.

[Mike Sulzer]

Ah, Thanks Mike! A very simple and clever design! I was impressed when I saw it Do post the circuit again, if you don't mind.

Sorry about that,
Ethan

Thank you for bringing it up, Ethan. Here is the circuit. The dummy coil should be like the pickup, but some more turns since the adjustment works only in the attenuation direction.

[CRU JONES]

The Ernie Ball design is not differential. It is driving the ground side of the pup with the anti noise, the drive is low impedance so even if you take out the battery, you still can keep playing but with no hum cancelling. I read the patent very carefully as I designed to same thing on my own. The Elite Strat design is no big deal, that was the first one I designed and failed because of the tone control.

It is the concept they patent, not the scale of electronics.

The Ernie ball sounds like Mike Sulzers design

If I understand you correctly... The tone control fails because it is before the active circuitry, no? The elite circuitry is: Two boosters built around Q1 and Q5. Q1 boosts the pickup, Q5 boosts the Dummy. The boosted signals are summed in mixing resistors R5 and R24. The discrete op-amp is only for the mid-boost, we can ignore that. Why not put your tone control after the mixing resistors?

[Kindly Killer]

Holy crap that EB/Mike Sulzer circuit looks fantastic! Questions about that:

How does it perform IRL?Does it do a good job cancelling hum? Is the sound/feel pretty much the same with it as without?

I don't quite grok how the signal from the dummy coil buffer combines with the pickups. I've only ever seen audio circuits that combine signals on the other side... I guess being AC it doesn't matter? I'm missing a concept here... Help?

[Mike Sulzer]

Holy crap that EB/Mike Sulzer circuit looks fantastic! Questions about that:

How does it perform IRL?Does it do a good job cancelling hum? Is the sound/feel pretty much the same with it as without?

I don't quite grok how the signal from the dummy coil buffer combines with the pickups. I've only ever seen audio circuits that combine signals on the other side... I guess being AC it doesn't matter? I'm missing a concept here... Help?

To understand this circuit, let's start by thinking about putting a dummy coil and a pickup in series, with the dummy on the low side, that is one side connected to ground. That works, but the inductance goes up , and the resonant frequency goes down, and so the sound is changed. (One way around this is to use a coil with a large area (Suhr), to get good sensitivity, but few turns, to keep the inductance down. This is another approach.) Suppose we could replace the dummy with a circuit that had the same output voltage, but a much lower output impedance. Then the hum would still be canceled, but we would not have the increase in inductance. That is what the FET does when connected in this way with the dummy as input. It is a source follower, with a gain of just under unity. (This is why we want to make the dummy a bit more sensitive than the pickup. Also we want to leave a bit of room for adjustment.)

The circuit only has to put out a few mv, that is, the hum voltage, and it also has to sink the current from the pickup signal, which is very small since the impedance is very high. So the circuit can run on low voltage and current. It cancels hum as well as a dummy can. How does it affect the sound? OK, I used those 10K pots because I had them. I would have preferred 5K or 3K. But the circuit is set up so that you adjust maybe 10% of the way down from the top of the pot. So the impedance looking into the pot slider is a bit less than 1K in series with the output impedance of the source follower, which is probably a few hundred ohms. So the impedance is a bit over 1K. To get an idea of how that influences the tone, think about how the volume control affects it. If you turn it down a significant amount, the tone changes. But if you turn it down just a bit, there is no significant effect on the tone. That is how much this circuit affects the tone. (The volume control used in this way puts a similar value of resistance in series with the pickup.)

[Mike Sulzer]

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.

[David Schwab]

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.

Here it is.



I used to have a schematic for a G&L guitar that had the output from the dummy coil's op amp going to the ground side of a pickup. I can't find it anymore though.