MIMF

A couple of weeks ago, I had a couple days with some sparetime. I thought it would be fun to make a simple stick (double) bass.
Although the instrument is rather simple, the sound is great. I've used two pieces of birch plywood which I glued together after routing a trussrod slot and installing a martin-style trussrod (although the trussrod is not needed, but that is hindsight).
The taper I saw with an electric scrollsaw and cleaned it up with the router and a fence.

The stringlength is 800mm (little less then 32"), and I choose this stringlength to match the strings I had lying around (0.145 - 0.090 - 0.055 - 0.032).
The bass is tuned in fifths starting with a low C. The pickup is made of a piece of electric wire connected to a 1:500 current transformer and some ceramic magnets, this yields a signal which is comparable with a microphone signal. With a mic to line adapter it can be connected to a regular bassamp. I just feed it straight into my usb soundcard. It has a flat fingerboard, because I don't intend to bow it (I used roundwound bass strings) and for the sake of simplicity.

I've stained the wood with strong coffee and finished it with a hard floor finish from Glitsa.

I've used an old cymbalstand to mount the bass.

Cool...! Explain the pickup further?

The pickup is a so called low impedance single loop pick up.
It works pretty much the same as a regular pickup: When the strings are plucked, a voltage is generated in the coil around the magnets.
Where a regular pickup will have a coil with a couple of thousands of windings, this pickup has a coil of only one winding (the electric wire).
The voltage that is generated is really smal (that's the reason why a regular pickup has more windings, to get a higher voltage), but this can be transformed to a higher voltage with a transformer.

The alumitone pickups from Lace are based on this design.

There are two things I really like about this design:
- It picks up low and high frequenties evenly, so it can be used for instruments with an extended range
- A pickup is very easy to make. A prototype can be assembled in 15 min.

I've used this type of pickup for a studiorecording and it worked out fine.

Downside is that the signal is at microphone level, so you either need a microphone preamp or a mic to line level adapter (about 25 dollars).
I generally connect my instruments to a usb soundcard with a micpreamp and use my laptop as a effectprocessor and this works works great, but I've plugged them in a regular guitar amp as well and this worked fine although I had to adjust the eq a little bit.

Hope this explains it a little bit.

There is a thread on the MEF explaining this design: http://music-electronics-forum.com/t5447-4/#post315021

Simple and cool.

The thick C string surprises me - although i understand that the thickness ratios of the strings follow immediately from the tuning. But my 5 string fretless with also 32" scale will sound better if the B string is taken a bit thinner, say .125.

The voltage that is generated is really small (that's the reason why a regular pickup has more windings, to get a higher voltage), but this can be transformed to a higher voltage with a transformer.

But like with any other low impedance pickup design You will lose the bandwidth advantage if You use a transformer, don't You?

BTW: i am going do use that pickup concept in the archtop i just converted to 5 string quintic tuning as well. 5 small neodymium magnets tightly surrounded by a loop of wire and one or two current transformers.

Beate Ritzert wrote: The thick C string surprises me - although i understand that the thickness ratios of the strings follow immediately from the tuning. But my 5 string fretless with also 32" scale will sound better if the B string is taken a bit thinner, say .125.

In theory, if you shorten the string you have to thicken your string to maintain the same tension. And my experience is that the Low C has a tendency to sound floppy when the string is too thin.
But in practise: if it works, it works...

When preparing, I do noticed that a double bass string has a higher tension then a bass string. Whereas a bass string has a tension around 20 kg, a double bass string has a tension of about 30 kg, so that's why I used these heavy gauged strings. I think it helps to get that percussive "plop"-sound which is typical for a plugged double bass.

But like with any other low impedance pickup design You will lose the bandwidth advantage if You use a transformer, don't You?

You are right, but you still have a lot less windings then a conventional pickup. I haven't made a frequency response curve (and don't know how to do so), but that would give some good data to evaluate the pickup.

BTW: i am going do use that pickup concept in the archtop i just converted to 5 string quintic tuning as well. 5 small neodymium magnets tightly surrounded by a loop of wire and one or two current transformers.

I would really love to hear and see more of this!
What tuning are you planning to use? A dropped C to a regular e?
I've found that when you take the gauge of your highest string as a reference you can calculate the next string with the golden ratio (1.618), this resulted in a heavy bottomed string set but strangly enough it feels balanced, more then when I used the 3/2 ratio which matches the fifths tuning.

Hans Bezemer wrote: What tuning are you planning to use? A dropped C to a regular e?

Yes, i do.

I've found that when you take the gauge of your highest string as a reference you can calculate the next string with the golden ratio (1.618), this resulted in a heavy bottomed string set but strangly enough it feels balanced, more then when I used the 3/2 ratio which matches the fifths tuning.

This is also my impression, and interestingly this also correspondents to the string gauges proposed for tenor guitars in quintic tuning. Actually i have used the 3/2 from E to A (.10/.15), and the A sounds a bit thin and floppy with respect to the other strings. I'll need a bit of experimenting, maybe try a heavy top and a lighter bottom (mostly because of the weakness of the guitar).

It'll probably take some time before i actually start with a prototype, but i'll report - at least in music-electronic-forum, especially the experimenting phase i expect, but if there is general interest in actual results also here.