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Modulus Quantum 5 Special Fretless – Bartolini Electronics Update

Jack Marshall sent us in this article of his bass modifications. Thanks, Jack! If you’d like to contribute your own tips-and-tricks or informational or modification article, send it on over to editor@bestbassgear.com. You can send over your article as a Word DOC/DOCX, LibreOffice ODT (free!) document, OpenOffice ODT (free!) document or exported document saved from Google Docs (free!) or Microsoft Word Online (free!) Please scan your document with VirusTotal (free!) before sending to us, thanks!

 

Way back in 1988 I finally got a real job and decided it was time for a really nice bass. I loved playing fretless and the idea of a five string instrument was intriguing. I had made friends with Geoff Gould, the mastermind and founder of Modulus Graphite in San Francisco and he started feeding me ideas about a through-body five string fretless bass. He was designing a bass for Bakithi Kumalo (the great South African bassist with Paul Simon’s Graceland band) and convinced me that it would be a great bass for me too. I agreed pretty quickly and a few months later I drove up to San Francisco to pick up this gorgeous bass.

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The body is mahogany with a book matched American black walnut top and the graphite composite neck extends through the body. The pickups are Bartolini Washburn style with a coil selector switch for the neck pickup. The electronics were originally configured for volume, pickup blend and passive treble cut controls with a simple Bartolini preamp with no active tone circuit. Somewhere along the line I swapped in a Bartolini NTBT preamp to add active bass and treble controls. The bass is light and well balanced and has always sounded great. But even 25 years later, I just had the feeling the full blooming fretless potential of this instrument had yet to be realized. Then I noticed a new Bartolini preamp on BestBassGear.com. The NTMB+ FL preamp has active bass, treble and midrange controls and the EQ is voiced especially for fretless basses. I know Bill Bartolini knows his stuff, so I decided to give it a try.

There were a couple of design choices to be made. First, I wanted a switch to adjust the midrange center frequency. Fortunately, Bartolini offers an easy way to do this. I used an on-on-on mini toggle switch and two capacitors to allow selection of midrange center frequencies as suggested on the Bartolini website. Without this modification the center frequency is 250 Hz, but with the toggle switch and caps the frequency is selectable from 250, 500 or 840 Hz.

The second choice was whether or not to keep the neck pickup coil selector switch. In 25 years of playing this bass, I’ve mostly favored the bridge pickup with varying levels of the neck pickup mixed in, and the nicest sounds from the neck pickup have always been in the series hum canceling configuration. I didn’t want a second toggle switch cluttering the control layout, so I eliminated the coil selector switch and wired the neck pickup to provide series hum canceling.

Last, I didn’t feel there was enough space for an additional tone control pot, so I opted for stacked bass and treble pots.

So, now to work. The first thing was to pull out the old electronics. While I was at it, I felt that additional shielding wouldn’t be a bad idea, so I lined the control cavity with adhesive copper foil. I tack soldered the various pieces together and I formed a copper tab at each of the screw holes to make contact with foil on the inside of the cover. Here’s how the cavity looked at that stage.

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Next, time to build up the electronics. It’s tough to solder stuff together inside the control cavity, so I made a jig from a scrap of 1/8” plywood. It has holes in the right sizes and positions for each of the controls as they would appear from inside the cavity. This allows building up a complete wiring harness away from the bass itself before installation. The plywood is also a great place to write notes to keep everything organized. Here’s the plywood ready to accept the four pots and the toggle switch.

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All built up it looked like this.

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Then the wiring harness is easily removed from the plywood and installed in the control cavity of the bass. Here’s the nice neat result.

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After applying copper foil to the inside of the cover and snapping in a fresh nine volt battery the whole thing gets buttoned up.

Here’s a view of the new control layout.

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From top to bottom, the controls are volume, pickup balance, midrange and stacked treble (small knob) and bass (ring). The three position midrange selector switch lives in the middle.

So, I plugged into my favorite amp and… nothing. It was dead quiet. I unplugged and opened up the control cavity. Pretty quickly it was clear that the three lugs on the volume pot were very close to the new copper shielding. I took out the pot and trimmed out the copper in just the small area where the lugs might touch it. I also added two layers of black vinyl tape as extra insulation. I checked out the connections on the other pots and added insulation for those as well. Then I buttoned it all up and tried again. Ahhh… much better. There was that nice Modulus fretless sound back again.

So, how does it sound? I have to say Bill Bartolini absolutely nailed it. Even with the controls set flat the sound is fuller and richer. But, add in some bass boost and mid boost at the original 250 Hz center frequency and the full, singing sound of the middle and upper ranges just pops out of the instrument. This is what the bass has needed for 25 years. The bass is still the great Modulus bass Geoff Gould built for me in 1988, but it sounds bigger and better than ever. The additional midrange settings may or may not turn out to be useful – time will tell on that one. Overall I am really pleased.

Thanks to BestBassGear.com for providing one stop shopping for great bass projects.

5 thoughts on “Modulus Quantum 5 Special Fretless – Bartolini Electronics Update”

  1. It’s just like the 4.7 A/P except that the preamp module is the NTMB+FL instead of the standard NTMB. A prewired circuit isn’t available for the +FL so I purchased individual components and wired it myself.

    Reply

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