XR-Spectra: Passive Mode

First, a big and special thank you to all early adopters who preordered on the first batch. Thank you for your trust and support! You are the confirmation that I need to assure me that this project is all worth it. Most of all, thank you all for sharing this passion with me on full-range pickups. Much appreciated!

Passive Configuration

So… About the passive mode. The XR-Spectra pickup can be configured as passive (no electronics, no batteries) by replacing the Preamp board (installed by default underneath the pickup), with the Passive board (also included):

There are six pins (three pins each) for both the Main I/O and External Coil (see legend in the passive board image above): hot, cold and ground, plus four more for the configuration pins, for a total of 10 pins (3+3+4). The configuration pins are provided for wiring two or more passive XR-Spectra pickups as single, dual series or dual parallel, for maximum flexibility (image right). These pins can be configured using header shunts (included), or toggle switches (user provided). The Main I/O is fully balanced, with connections to hot (OUT+), cold (OUT-) and ground (GND).

Passive Connectivity

XLR

The passive output can connect to a balanced XLR connector for superior noise rejection and ultra low-noise performance, direct to the mixing board, audio interface, or external gear with XLR inputs. Alternatively, the balanced output can connect to a balanced ¼ TRS jack, assuming again that your endpoint supports it (many mixing boards and audio interfaces do).

Wampler Pedals dB+ buffer/boost pedal

The original plan was to have the passive signal level hot enough to drive standard instrument amplifiers. That was the main reason for using medium impedance coils with the original rails design. The motivation was to raise the signal output to a level comparable to an underwound single coil. Yet, as discussed in my previous post, after our 2-week optimization bout, it turned out that the steel rails were eating up some high frequencies (above 15kHz) causing a slight droop in the frequency response.

The rails had to go. But the downside is that the raw passive signal became weaker. One easy solution is to use a low-noise, clean boost buffer pedal such as the Wampler dB+ (image right). Here’s a link to a list of the “17 Best Boost Pedals in 2021” to choose from. I’m pretty sure there are more out there. Just keep in mind that we are placing the pedal at the input stage, before subsequent potentially high gain stages. You’ll need a boost pedal with sufficiently low-noise performance.

Below, I will try to offer another solution.

Possibilities

For extended versatility, the Preamp board and Tone Block can be placed outside the guitar, ideally in a stomp-box/pedal (or the Nexus). It occurred to me the other day after discussing with Ryan Van Wagoner, one of the early adopters, that it is possible to place the Preamp board and Tone Blocks in small, separate, pedals for a very versatile setup. A single Preamp pedal plus one or more Tone Block pedals, in series, and with bypass foot switches allows for vast tonal capabilities. I am seriously considering providing such an option in the future. The electronics is already there. Example:

Here, the preamp is always ON, with an external 9-18v power supply. It should be!  Compared to typical Hi-Z passive pickups, the XR-Spectra’s passive output is rather weak. The preamp is there to boost the signal to instrument-level. The input to the preamp can either be balanced or unbalanced via ¼ TS or TRS jack. The XR-Spectra pickup supports both balanced or unbalanced inputs. Each Tone Block with different settings can yield tonal variations from dark-and-heavy to pristine-crystal-clear, switchable via the foot switches. The Tone Block is passive. It requires no power. Other pedals can be inserted before each Tone Block. The only requirement is that the pedal’s output stage is buffered (this is typical of pedals anyway).

One More Thing

OK, so there you go… But before I go, a quick update on the recent idea of having LED lights on the rails. For now, I decided not to pursue the idea. Instead, I will use surgical grade, austenitic stainless-steel (essentially non-magnetic) for the top rails. These are mostly for aesthetics. They have more or less the same magnetic (relative) permeability as the Neodymium magnets (1.003 – 1.05) and does not affect the resonant frequency of the pickups, which should be well above the human hearing range for full frequency response. Let’s keep it simple. In the future, perhaps I will revisit the LED illumination idea, but not as standard, instead as an option for those who want it.

The XR-Spectra will be the most versatile monophonic pickup ever. Promise!

 

 

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