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Old 09-30-2020, 05:47 PM
James May James May is offline
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Join Date: Dec 2015
Location: Nevada City, CA
Posts: 650

As promised, a description of my first experience with installing my Ultra Tonic pickup in a high quality, carved archtop. In this case, I bought an Eastman AR610. Itís 17Ē, spruce top with mahogany back and sides. This guitar is beautifully made and has a very rich, resonant sound. Like all archtops, it is more midrange focused than a flat top, but this one is quite well balanced and has a healthy amount of bass. It came with a Lollar floating humbucker with thumbwheel volume and tone controls under the pickguard.

Executive summary:
It was a success and Iím very pleased with the sounds available! Here is a very short audio clip with four segments: 100% Ultra Tonic, ~67/33 blend, ~33/67 blend, 100% humbucker, recorded direct into the sound card. Iím not much of a jazz player, but here are some Freddie Green chords to give you a sense.

For those not familiar with the Ultra Tonic, it has an integrated feedback cancellation sensor that clears up low end mud and at the same time increases feedback immunity by at least 10dB.

First things first: access and visibility
Having the right tools is critical. I searched around and luckily found the right bits to make this tool:
pickup placement tool.jpg

Then I found this nifty inspection camera which allows stills or video to be captured on your smart phone. Fortunately, it just fit into the f-holes of the Eastman. The f-holes are the biggest Iíve seen, and Iím sure this camera wonít fit into most f-holes. Iím looking for a smaller alternative for the next install.
Ullman inspection mirror.jpg


The installation was fairly easy with the above tools. I always use adhesive putty and neodymium magnets to both position and clamp the discs. You just hover until you find the strongest pull, then let it down and it does the clamping for you. Go do something else for 10 minutes while the gel superglue sets up.

The magnet that came with the flex arm was sufficiently strong to work as is. If it hadnít been, I would have simply positioned one of my 3/8Ē x 1Ē neodymium magnets in its place with another ball-end clamp.

I surrounded the bridge with artist tape, marked the locations of the posts (outer marks on the tape). I removed the strings and bridge. This guitar is X-braced. I determined how close the braces were to the post locations, which is the ideal place to put the two main sensor discs. Fortunately, sensor locations on a guitar like this (with no bridge plate underneath) are not super critical. Due to the locations of the braces, I decided to move the discs inward just a little so as to not have them right up against the braces. That would have worked, but would result in slightly less signal strength out of the Ultra Tonic.
treble disc top.jpg
inspection camera.jpg
camera view on phone.jpg
tool with disc.jpg
installing treble disc.jpg
interior disc 2 glued.jpg

After installing the two main sensors, I located the feedback cancellation sensor at a point further back. Its location is not critical at all. Typically, I put it on the bass side, but it doesnít have to be. Its role is to pick up the same resonances as the main sensors, but far less of the direct string vibrations. It has opposite polarity to the main sensors. When the right amount of it is mixed in with the main sensors, the good stuff remains and the bad stuff disappears. And yes, I have a patent on this seemingly simple idea.
installing feedback sensor.jpg
all 3 sensors inside.jpg

Setting the Ultra Tonic
The Ultra Tonic sensor assembly has a quick disconnect to the endpin jack with circuit board. This makes it easy get it in and out of the round or f-holes. I ran it out of the f-hole, plugged it into the endpin circuit, and plugged into a full range amp.

The 12 position switch functions as a stepped attenuator which determines how much of the feedback cancellation sensor is mixed into the main sensors. It is passive, and the mixing uses capacitor dividers since piezo sensors are in effect capacitors. There is no frequency dependence in the mixing circuit. The exact resonances that are dealt with are only dependent on the guitar.

Finding the right setting for the 12-position switch takes just 10 minutes if you know what to listen for. Alternately, I have an automated calibration system available which does this for you in a few seconds.

To wrap up the pickup installation, I drilled out the endpin hole to 15/32Ē with my StewMac reamer, and pulled it into place with this homemade jack puller made out of copper tubing. Itís stiff enough to hold its shape, but can be bent a little if necessary to get it up for access through an f-hole, as was necessary in this case.
jack puller.jpg

Before tightening the nut, I twisted the endpin jack to take up the internal cabling slack and keep it from touching the wood.
installed wiring.jpg

This StewMac tool was also very helpful for fishing wiring and the jack around. That hook on the end is sized to grab the endpin jack tightly enough to pull it, but will let go without too much force. Itís bendable and very handy.
stewmac tool.jpg

Passive Blending

The mag/piezo blending circuit required a good deal of design effort, as it is not trivial to successfully blend a passive magnetic pickup with a passive piezo-based transducer system. However, I am happy to report I was able to achieve the following design goals:
  • Uses the same mag volume and tone pots. I shielded them with copper tape, and scooted the tone control over to make room for the blend control.
  • An Ultra Tonic volume control was not necessary since the mag pickup is hotter. Therefore, I cannibalized the existing Ultra Tonic volume control and turned it into a blend control with a variable treble bleed circuit so as to not lose acoustic highs when blending with the mag. This very similar to the variable bleed circuit that my standard Ultra Tonic volume control uses.
  • Mag volume control has a new treble bleed circuit so that reduced mag gain does not destroy the characteristic frequency bump that mag pickups achieve working into typical cable capacitances.
  • Since the mag is hotter, it needs to be turned down some to put it on a par with the Ultra Tonic. Then, the blend functions very well with a smooth and usable transition from full mag to full Ultra Tonic.
shield on top.jpg
modified controls.jpg

Whatís next

I may decide to package the mag volume/ mag tone/ blend circuit as a single stick-on manufactured assembly, and make it available as a special Ultra Tonic Archtop model for those wishing to do what Iíve done here. The design work is done, and the installation method is worked out. Making a product out of it will depend on how much interest I get on this idea.
James May
Audio Sprockets
maker of ToneDexter
James May Engineering
maker of the Ultra Tonic Pickup
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