What is the Silent Circuit?

Among the many technological innovations that Ernie Ball Music Man has brought forth in our 30 plus years making instruments, one of the most important is the development of our patented silent circuit. Put simply, the silent circuit is the answer to the long-standing problem of 60-cycle hum created by single-coil pickups. In order to facilitate clearer tones for guitarists without unwanted noise coming through the amp due to single-coil hum, our master luthier and instrument electronics wizard Dudley Gimpel helped develop an idea to create a system that eliminated this hum altogether. 

In order to better explain the technical aspects and to tell the story of the development, we sat down and spoke with Dudley to discuss the silent circuit and its integral place in Ernie Ball Music Man instruments.

Once the seed of the idea had been planted, Dudley went on a nearly year-long process of R&D (research and development) refinement, initially mapping out the idea on an old-school electronics breadboard to figure out the circuitry.

How did the idea for the Silent Circuit come about?

We had this idea and finally tried it. We sort of did what we call in electronics a “breadboard” thing where we built up the circuit, as was done back in the old days on a board where you could plug in components just to see if it was really going to work. And it did work, so we went to Sterling [Ball] and said, ‘Hey, we’ve got this idea here that has some merit, and we’re not familiar with anything else that does this.‘

The problem of 60-cycle hum had been around ever since guitars had been released with single-coil pickups. The earliest answer to the problem was the development of humbucking pickups, aptly named because their purpose was to literally buck the humming sound out of a guitar. However, they just don’t deliver the same brightness or tone as single coils. Dudley let us know what some of the context was in the guitar world before he had started on the silent circuit.

Had anything like this been done before?

Back in the ’80s, Fender had a design for a system, as did Alembic, where they had a separate coil for picking up the hum that didn’t really pick up the signal from the strings, and then that was all gone through a preamp. But it was a totally active circuit. So we came up with this idea about a way to do it where the pickup would still function as essentially a passive pickup. There would be no preamp between the pickup and the amplifier because the electronic circuit that makes the silent circuit is in between the ground side of the pickup and where the pickup would normally connect to the ground.

One would think that a breakthrough development such as this would require a very intimate knowledge of guitar electronics, but when you boil it down to its simplest aspects, the silent circuit actually works on a fairly ingenious principle.

So what is the main principle behind the Silent Circuit?

Basically what we’re doing is generating a hum signal that’s out of phase with the hum signal that’s being picked up by the pickup itself, and then by injecting that into the pickup, it cancels it out.

Essentially, the silent circuit is creating and infusing opposite frequencies generated by the actual pickup to neutralize the sound of the hum. Without actually eliminating the hum of a single-coil, it is able to maintain the same construction as a regular single-coil pickup, yet is still able to stop unwanted noise coming out of the amp. Dudley has said that it is possible to drop the Silent Circuit into any guitar, provided it has the space for installation as well as a battery compartment.

The process of creating new electronics entails a fair amount of elbow grease, progress, setbacks, and flexibility. Luckily, Dudley helped walk us through the developmental process.

How much iteration was required?

As far as R&D on it, we built up a number of circuits and a number of different coils. The whole idea was to get the coil as small as possible so we could mount it in a lot of different instruments with a minimum of modification to an instrument. The smaller we made the coil, the more gain needed to be added to the circuit so the amount of hum generated by the small coil would equal the amount of hum that was being generated by the normal guitar pickup.

The Silhouette guitar was really where we launched it. We went through a couple of different iterations with this, one early one we did actually had a stacked single-coil, which DiMarzio made for us, and it had the same shape as a Strat single-coil bobbin attached to the back of the pickups, and then we ran those coils through a buffer circuit and it worked fairly well in some respects. But as far as canceling the hum it went pretty well. The issue with doing it that way as if the coil that senses the hum, or is intended to only sense the hum, is mounted underneath the normal pickup then it inevitably picks up a certain amount of the signal from the strings just because of its proximity. So the idea is that it would not only cancel the hum but it would also cancel some of the signals that were being generated from the string, and we didn’t love that. We wanted to keep it so that the only thing that was being cancelled was the hum.

Is it just that simple that we created a powered circuit that takes care of all the noise in a guitar? Well, in some ways, yes. However, the answer goes much deeper.

Is the silent circuit all that goes into making Ernie Ball Music Man guitars as quiet as possible?

The shielding of the control cavities of the guitar and using the foil on the back of the pickguards all help to eliminate noise from the pickup. However, the type of shielding is the main factor. There are two basic types of noise. One is electrostatic and the other is electromagnetic, which often is referred to as EMI [electromagnetic interference]. The electromagnetic is what we’re trying to cancel, so in order to shield against EMI you need to use something that is magnetic, and of course, you can’t put a steel cover on a pickup because that will completely affect the magnetic field of the pickup, so it won’t work the same anymore. That’s why pickup covers are made out of materials that help with the shielding but primarily they’re more effective with the electrostatic kind of noise than the electromagnetic. It’s exactly why most pickups covers are non-ferrous metals like nickel.

For over twenty years now, the silent circuit has been an invaluable asset to Ernie Ball Music Man and the roster of demanding artists that have come to depend on the innovation, dependability, and precision of our guitars. The Silent Circuit is now used in the following Ernie Ball Music Man instruments:

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For further information on Ernie Ball Music Man guitars and basses, visit our website.