Bass Player Readers' Choice Award for Best Preamp: Audere JZ3              Bass Player Editors' Award
Introducing Jazz Hum and Noise Cancelling Preamps - keep the Single Coil Tone and Touch Response - lose the Hum and Noise              BP Magazine Review
Zmode switch

CAD circuit board section

Impedance Control Matters

Impedance:
The electrical expression of capacitance, resistance and inductance in a circuit.
An electrical force that opposes the flow of alternating current.
Symbol: Z

As we mentioned on the Z-Mode page - all of the electronic components in the set-up of an Electric Guitar or Bass are sources of impedance (Z) variations. This includes the pickups, tone and volume pots, external cables, and the first amplifier, internal or external.  The difference with a Z-Mode preamp is it takes control of this impedance load that is placed on the pickups, isolating them from the changes that occur down stream.

For our purposes we can break the sound chain into 2 sections: the pickups with output impedance and the rest of the electronics which present the pickups with input impedance, which is often called a load.

How these two sum up is important to the sound; the combined load changes the fundamentals of your pickup's frequency response. The example below shows the change in the frequency response of the same bass pickup connected to three different input loads.

Vintage Early 70s Z-Modes
Vintage Fender Early 70 Bridge Pickup.

But the pickup loading also changes how the string's vibration is damped. Your guitars pickups are small electrical generators. They extract mechanical energy from the vibrating string and generate an electrical output. If you change the loading on the pickups this is reflected back into the string's vibrations. More info is available at Z-Mode string damping.

The Sound Clips show the different Z-Modes used with different playing styles; there is also a comparison of the Z-Mode sound based on pickup (bridge and/or neck) and external amplifier.

Since impedance is the opposition to electron flow, you might think you would always want a High or Low Z, but this is too simplistic. First, remember that the output impedance of your pickups and the input impedance of the load combine to create the frequency response, so it matters what pickups you have. Second, the different impedance loads change how the strings dampen. Third, and most important, the different Z loads don't necessarily sound good or bad, just different. And that can be used to your advantage.

The first graph shows the effect of the Z-Mode switch and the corresponding 3 pickup loads: the first two, High Z and Mid Z are pretty traditional Z loads available on different brands of preamps; the third, Low Z-Mode is a new, ultra clean low mode.

Adding Capacitance

The Z-Mode switch allows you to select the load in real time, while you are playing. In addition, when you do your initial set-up you can dial-in additional High Z-Mode capacitance and further change the frequency curve. The example below shows how adding capacitance moves the resonant peak frequency response for a pickup. Because pickups have differences in construction and installation, the response to a change in impedance is specific to that pickup.

Fender Squier Duncan Designs Pickup with Cap Kit

Our Z-Mode module offers control of the Z load on your pickups and it replaces your existing on-board hardware with sophisticated on-board electronics which capture the tone without inter-modulation noise (i.e. no mud) and it includes flexible selection of volume and tone controls; plus we will pre-wire it to your specific configuration for easy installation.

For those who enjoy the technical side, here are a few good reference books.