My electric cello rig uses a stack of two bridge-foot pickup systems–one in-phase between the feet, and one out of phase between the feet, for bass and bow respectively. They require a preamp in order to work effectively with standard bass and guitar amps. My preamp of choice is the Tech 21 Sansamp Para Driver DI. This swiss-army-knife box can do a little of everything, and do it well.
First, it’s an impedance matching preamp. It has 4.7 megaohm input impedance, so it can handle most piezo pickups just fine. Second, its tone controls with parametric mid allow powerful shaping of the sound, and control of gain over a wide range. Third, the “Blend” knob activates a tube mic and acoustic body simulator, to make piezo pickups sound more like a miced instrument body. Fourth, it serves as a direct box with parallel 1/4″ and XLR outputs.
I find this really indispensable when amping up a cello or an upright bass, whether traditional or electric stick-instrument. It does wonders to eliminate excess “scraping” sound when using the bow, and to produce a full rich low end. I prefer these to the Bass Driver DI by the same company on these instruments, and also often on bass guitar. It can help some with violas and violins as well.
You can use this in a pinch as an amp simulator by turning down the lows and highs, and cranking the mids; the midrange control is tied tightly to the tube mic simulator and you can overdrive it on purpose for a useful recording or live tone.
Use the parametric mid control to reduce feedback.
And if you already have it around for any of these purposes, go ahead and try using it as a plain direct box in a pinch.
This is a pricier DI, but it’s so useful that it’s worth having a few around.
If you can’t afford this, but want a similar tool in your toolbox, look into the Behriner ADI21. It has most of the same features for a very low price. But they are less durable, need to treat them carefully. At the price, you might just want to keep more spares around if you use those.
Affiliate linksTech 21 Sansamp Para Driver DI Behringer V-Tone Acoustic ADI21