So once upon a time I was a proud and happy owner of a mexican made Fender Jazz Bass. It had that classic sunburst look with a tortoise pickguard. Unfortunately I had to sell it for economic reasons, but ever since that I've had this itch to make a Jazz copy of my own, with that classic sunburst finish.

As always, I started building two builds at the same time, this "The Classic" and "Red Red Wine". One of my best sounding basses I've ever built had a body made of aspen. To keep it on the classic side I chose maple for the neck and wenge for the fretboard.

Of course this bass needed jazz bass style pickups, and I remember seeing some cheap and chearful ones with alnico 5 magnets on a domestic webshop, from which I had previously bought a lot of parts for my build.

The bass builds I've done over the years had always been 34 or 32inch scale lengths, so I had been wondering (for a while) what a 33" bass would feel, sound and play like?

Time to lay down some specs;

Construction: 4-string (bolt-on)
Scale Length: 840mm (33")
Strings: Dunlop 45-105
Number of frets: 24
Tuners: Gotoh GB707 (Chrome)
Bridge: Gotoh style (Chrome)
Frets: Sintoms Medium Jumbo

Neck wood: Maple, Merbau (5-piece)
Body wood: Aspen, figured birch top.
Fretboard wood: Wenge
Neck pickup: OL JB
Bridge pickup: OL JB

On a previous bass build I made a sunburst finish with ordinary rattle spray cans. That didn't really turn out as I would have hoped, so this time I thought I'd try a different method. No spray cans with solid colors, only dyes. Tried to get a faded orange tint, lighter in the middle of the body and darker out towards the edges. And finally a black dye around the edges.

Not so easy to get it looking nice and even, especially with this figured birch top. But as always, I tend to learn by doing.

Since this was supposed to be a "classic" bass build, I wanted no active elctronics in it. However, I wanted to test out the now-so-familiar-to-me active preamp circuit, the Tillman preamp/buffer. Just as on "Red Red Wine" I wanted to make these passive pickups basically active by buffering each one of them with this simple preamp/buffer. By connecting both pickups to its own dedicated preamp circuit, you isolate the neck and bridge pickup from each other, which will eliminate the problem of the two pickups interacting with each other when the balance (blend) pot is set to middle (both pickups full on). Another advantage is you can get a little gain boost, you dont have to, but in this case each preamp circuit is boosting the signal about +9dB.

Surfing the net looking for info on what type of potentiometers (pots) to use for a passive bass I stumbled across this very interesting article at Seymour Duncan's. Bass Tone Caps: From the top.

The value of the capacitor used will have an effect on how much treble is cut. The standard tone capacitor value is .05u (~47nF) for a bass. So, what will switching this out do? Simply put, capacitors with lower values will cut less highs when the tone pot is turned counter-clockwise, and higher value capacitors will cut more highs. 

The plan from the begining was to have one tone pot for each pickup. So I got this idea, that what would it sound like, if you would increase the value of the neck pickups cap a lot? So much that the treble and mids would be cut of when the tone pot is turned counter-clockwise. That way you would be able to use the fat, round and warm sound of the neck pickup and blend it together with the punchy mid-rangy bridge pickup.

So for the bridge pickups tone pot cap I chose a 22nF (0,022uF) cap and for the neck pickups tone pot cap a 220nF (0,22uF), almost 5 times bigger than a standard 47nF cap.

This is how the neck pickup sounds without the tone pot engaged:

And this is how the neck pickup sounds with the tone pot engaged:

Add the sound of the bridge pickup and this is what you get:

And for reference, this is both pickups, no tone pots engaged.

Which sound you prefer is a matter of taste, I guess. It is what it is...

Here's a sound sample. The bass plugged directly into my Focusrite soundcard. Both pickups (blend pot in the middle), both tone pots fully open.


UPDATE, Jan 2018:

As the tone controls didn't turn out as useful as I thought they would, I decided to remove the passive tone pots and install a onboard active preamp/EQ instead.

Working on "The Seven Seas" I had made some research and testing on my DIY preamps. However, the previous preamps used a op-amp with a fairly normal power consumption of 8-10mA's. This much power drain in a onboard preamp powered by a singel 9V battery would drain the battery fairly quickly. The average capasity of a 9V battery is about 500mAh, and with a circuit power drain of 8mA's, you get about 40 hours of power. Sounds like a lot, but it really isn't.

So I measured some of my factory made onboard preamps that I have, and it turned out the power consumption on those is only about 0,4mA's. That's 95% less than 8mA's!

So I had to do some research to find a dual op-amp with very little power consumption, which fortunately turn out to be quite easy. The OPA2137 is a dual FET input op-amp with a very low quiescent current of 0,22mA per amplifier. So I soldered the complete circuit together and measured 0,87mA's. That's more like it, now the battery capasity was increased to about 400 hours.

Click on picture for a bigger version (opens in new tab)

Since there really wasn't any space for a additional mid pot, I got the idea to replace the mid pot with a switch instead which would be placed in between the bass and treble pot. All that was needed was a SPST on-on-on switch and two 50k resistors. So the switch now worked as a mid-cut/flat/mid-boost switch.

And while I was at it modifying the electronics I also decided to add a low battery warning LED circuit, just as I did on "The Seven Seas". So this is the layout I ended up with.

So there it is, now the bass is a much more versatile instrument.

Happy days...