Category Archives: Uncategorized

XR Preamp Schematic

      Uncategorized

I am incrementally updating the XR Data Sheet. I’ll post updates here every once in a while. Here’s the schematic of the XR preamplifier. The circuit utilises the Toshiba 2SC3324 low noise NPN transistors with an exceptional noise figure of 0.2dB (typical). The preamp configuration is a common emitter amplifier with both emitter feedback and self-biasing collector feedback. The collector feedback ensures that the transistor is always biased in the active region regardless of variations in Beta. The second stage is a simple emitter follower providing current gain and low output impedance.

(Click to view PDF)

XR_Preamp_Schematic

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Neo Series Active Polyphonic Pickups

      Electronics, Nu Series, Pickups, Uncategorized

Small, Modular Active Polyphonic Pickups.

Update: October 18, 2015. The original Neo pickups are now called the Nu. They will be available soon. Check the Blog for updates. More specifically: Nu Update and Road Map and Nu Update: Modular Design.

The Neos are the culmination of the Six-pack project. These are active pickups with low impedance coils and individual balanced, low-power, low-noise preamplifier for each coil. The Neo Series Active Polyphonic Pickups are very small, Neodymium-core active pickups that can be used individually or in groups. These are hacker friendly, general purpose pickups that can be used in a variety of applications.

Here’s a short clip with a “classical” EQ capture with the Cycfi Neo6 polyphonic pickup mounted on a Fender Stratocaster bridge position. The strings are panned from right to left, with the low-E at the right and the high-E at the left. See Sculpting the Tone for details.

Sound Clips

For more sound samples: Check out this link: Sculpting the Tone.

Info

Data Sheet
Wiring Options
Neo Base Boards

The Neos

neo1-iso

Neo1 Single Active Pickup

Imagine being able to place active pickups just about anywhere! The Neos are very small, Neodymium-core active pickups that can be used individually or in groups. These are hacker friendly, general purpose pickups that can be used in a variety of applications.

The Neos are the culmination of the Six-pack project. These are active pickups with low impedance coils and individual balanced, low-power, low-noise preamplifier for each coil. Neo1 contains a single coil with a single differential preamp. Neo2 contains two coils and dual differential preamps. And Neo6 contains six coils and six differential preamps.

neo2-iso

Neo2 Dual Active Pickup

The pickups are designed for polyphonic effects processing —one for each string (distortion, EQ, compressor, delay, pan, pitch-shift, etc). Such extensive processing is now very possible due to advances in digital signal processing and multi-channel audio interfaces and multi-track audio software becoming commonplace.

Modular Design

Various Neo1s and Neo2s pickups can be combined to get all sorts of configurations. Examples:

PU-Placement1

The modular pickups are not just for guitars. Neos can also be utilized for other musical instruments such as the bass guitar, harps, pianos, xylophones, etc. The Neos are perfect for fanned-fret electric guitars with the pickup poles positioned at various angles.

Frequency Response

Low-impedance pickups have a wide frequency response (full range). Unlike traditional high-impedance passive pickups, there are no big peaks and dips in the response, which to many give the pickup it’s “character”. That should not be a problem since we can always shape the frequency response later on in the signal chain using various tone-shaping methods. The pickup is very rich in harmonics. It has a lot more harmonic content than even the bright, but very noisy Stratocaster pickup. Having a wide and flat frequency response gives you the freedom to sculpt the tone that you want using analog or digital filters. The idea of a low-impedance pickup which imparts very little coloration to the guitar sound is appealing. You get whatever tone you want using appropriate tone shaping EQ rather than a fixed, predetermined guitar tone.

freq-response

Actual Measured Frequency Response

Low Power, Low Noise

The Neos use the OPA2314 in a differential configuration. This Op Amp consumes 150μA (quiescent current) per Op Amp, with a respectable 14 nV/√Hz (measured at 1kHz) noise figure. The coils, are connected to the + and – inputs of the differential amplifier without any direct path to ground (floating differential mode). The Neos give you best of class signal to noise ratio.

Measured SNR
Gibson Les Paul 59.57 dB
Fender Stratocaster 47.52 dB
Neo 72.91 dB

Options

strat-style-cover

Stratocaster Style Pickup Enclosure

emg-style-cover

EMG-style Pickup Enclosure

top-mount-base

Top-mount Base

double-coil-mount-base

Double-coil mount base

Open Source

The Neo is entirely Open Source. The designs (schematics, PCB layout, software, bill of materials, CAD drawings and source code) are freely shared, 100% free, under the Creative Commons Attribution-NonCommercial 4.0 International License. That means you can use the designs in your own projects for non-commercial purposes.

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This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

Neck Dressing

      Uncategorized

Gorgeous Elegance!

Headstock with locking Grover tuners installed (click to zoom)

Head back (click to zoom)

It’s been a while. My last post was in November 3. Actually there’s one more unpublished post in December about “Sustain” Myth and Science but I need more time to do tests and analysis, so that will have to be posted later. The project is very active, thanks to help from some folks. I am having loads of fun testing the prototype. The guitar sings and weeps like no other. There are two more prototypes underway and the development is now focusing on production. We’ll have more on that later. Now, it’s about time to continue documentation.

The Bind

Stainless Steel Binding (click to zoom)

Binding the guitar using stainless steel proved to be very tricky. This is the first time I used stainless steel as binding material. Plastic is very easy to handle. Stainless steel is many times more difficult. No wonder no one is using this for binding. But the end result is gorgeous and it is all worth the extra effort (image at right).

The first issue was determining the gauge to use. Plastic binding generally ranges in width from 1.5 mm (~0.060″) to 2mm (~0.090″). At 1 mm, stainless steel is very difficult to bend into form. At 2mm, I’ll need a press to force the material into shape. One thing for sure is that I need to improve on metal working skills. For now, I settled for 0.5 mm stainless steel sheets.

Cutting the stainless steel sheets into strips is another matter. Forget about manually cutting stainless steel sheet into 6mm (my desired binding height) strips. I tried, but can’t do it cleanly and quickly. In the end, I settled for either laser cutting or water jet cutting. Both have drawbacks. With water jet, the edges are somewhat serrated with micro cut marks that need to be filed smooth. Laser on the other hand, can’t cut long and thin strips without micro bridges at intervals to hold the sheet into place. Without the micro bridges, the heat from the laser tends to make the strips twist and curl. It is easy to cleanly file and sand the micro bridges.

Binding The Fretboard

The stainless steel strips are glued in using structural epoxy specially formulated for bonding metal and wood. Glue is applied to the back side of the strips and the fretboard, making sure that the surfaces are sanded well for good adhesion. The binding is then placed into the routed-out groove and secured with tape making sure there are no gaps.

Applying epoxy specially formulated for bonding metal and wood.

Securing the binding with tape and wiping off excess glue.

Yet more tape to fully secure the binding and ensuring that there are no gaps.

Final wrap with taut vinyl tape. Now the neck looks like a Mummy!

Binding the Headstock

Before gluing, the stainless steel binding strip is pre-formed for a perfect fit around the headstock’s profile. This is done manually for now. Next time I’ll definitely use a template (water-jet cut) for bending the binding into shape, both for the body and the neck and headstock. After applying glue, the same procedure used in binding the fretboard is applied.

Applying epoxy on the headstock binding groove.

Applying epoxy on the back side of the pre-formed binding strip.

Carefully positioning the binding strip.

Securing the binding with tape: A fully Mummified neck.

Installing Frets

The layered carbon fiber-bamboo-epoxy fretboard has characteristics totally different from hardwood when it comes to installing the frets. With hardwood, the fibers easily grab the barbs immediately after the fret is pressed or hammered in. With CF-bamboo, I had difficulties using the traditional approach to fret installation. First, unlike wood, bamboo end grain splinters easily. There’s barely enough fiber cohesion to make the bamboo end grain reliably grab the fretwire barbs. While I can successfully hammer in frets into bamboo, I am not sure how reliably it will hold the frets in the long run. The carbon fiber outer layer adds to the difficulty. When a fretwire is forced into a tight fret slot, the carbon fiber-epoxy does not seem to sufficiently grab hold of the barbs. The epoxy tends to chip at the edges when the barbs are hammered or pressed. Post analysis shows that the material does not “heal” around the barbs enough to hold the fret in place as wood does.

Searching around for solutions, I found this article in the web offering a different approach, cutting a wider fret slot and using epoxy to hold the fret. Even with hardwood, the author notes that the barbs often lose their grip, and the frets pop out of the slots, leading to buzzing while playing. Surely, I too had problems like this before. That is why I always glue the frets in to make sure they sit firmly in the slots. Doing so also improves the tone considerably. This StewMac article says why: Fret jobs are often too loose. Super gluing your frets improves fret-fretboard coupling resulting in superior tone.

The fretwire is pre-bent to the curvature of the fretboard using a simple fret-bender jig (below). The fretwire slides in at the right and rolls through the middle, then exits the left roller bending it into the right amount of curvature. The amount of curvature does not have to be exact because the frets will be clamped in later.

Fret Bender Jig

To accommodate the binding, the fret’s tang must be trimmed at the ends. I do not have a fret tang nipper yet, but a good end-cutter will do just fine. The end-cutter’s cutting face is ground and sanded to make it as flat as possible for a clean cut without requiring a lot of filing afterward.

Fret End Cutter

Notched Tang

The fretboard slot is cut using a miter saw with kerf that is is wide enough to have the fret tang plus the barbs slip into the slot without resistance. With this method, we will not have to hammer or press the frets in. Since epoxy will hold the frets, we do not need a very tight fit. Masking tape is applied such that only the fret slots are exposed to ensure that excess epoxy does not get into the fretboard. After test-fitting the frets to see if they all fit well into each slot, epoxy is injected into the slots. Finally, the frets are clamped using a clamping caul made from acrylic plastic with strips along the edges to press the fret ends firmly and rubber padding in the middle to evenly apply pressure.

Injecting epoxy into the fret slots

Frets ready for placement

Frets placed. There's no need to hammer or press the frets. The frets slide in easily.

Clamping the frets until the epoxy cures overnight.

Dressing the Frets

After the epoxy cures (I give it ample time, typically leaving it to cure overnight), it’s time to dress the frets. The fret ends are trimmed flush (again using the end-cutter) and beveled using a fret-end file block with an edge cut at a 30-degree angle where a flat file is held in place by screws (below):

Fret-end file block

Fret crowning tool

This method ensures that the frets are seated perfectly and very little effort is needed in leveling the frets. Using a perfectly flat sanding block with a 320 grit high quality sand paper, the frets are leveled starting from one end near the body, continuing towards the nut. After several gentle passes along the entire length of the fretboard, a narrow and shiny flat top should be noticeable on all frets indicating that the frets are leveled.

The fret edges are rounded off using a fret crowning and burnishing tool (above). Starting with 220 grit, proceeding to 400 grit then 600 grit sandpaper held over the tool’s groove, each fret is shaped and burnished until there are no more sharp edges and the frets feel perfectly smooth. The frets are finally polished with a polishing wheel using the dremel.

Further Reading

  1. Fretting
  2. Super glue your frets to improve your tone!
  3. Fret Dressing using “Essential tools” that don’t break the bank
  4. How to Install Bindings
  5. Fretting Simplified
  6. Installing the Frets in a Fretted Stringed Musical Instrument