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Quest for an Acoustic Bass Amp

Shifting gear for the right fit

Think YOU had a hard time finding the perfect amp rig? Imagine being an upright bass player. I was looking for a rig that produced decent tone for an upright with a pickup or an electric upright bass – a rig that actually sounds acoustic. Making the challenge even more difficult – I wanted a rig that could double nicely for electric bass for small gigs.

Most of the music I’ve been playing for the last decade or so has mixed contemporary blues with old school blues from the ‘50s and ‘60s. Playing that song list requires doubling on electric bass and an upright bass.

It also requires finding the gear that makes it all work.

Making the Switcheroo

For doubling, the first challenge is finding a way to switch between the two instruments. My simplest solution has been to simply unplug one, tweak the volume and EQ on the amp, and plug in the other one – not a very satisfying arrangement, because it requires remembering the different settings and taking a bit of downtime to swap plugs.

A better choice is to use an A/B switch. I’ve tried a few, from Craig Anderton’s do-it-yourself box (but that cut highs and volume) to a Morley A/B/Y (which turned out to be almost the same passive circuit) to my current Boss AB-2 pedal (around $35) that switches actively and barely messes with the tone. More elaborate solutions include boxes like the high quality Lehle pedal (over $200) or the ToneBone BassBone (look for a review in a future Premier Guitar web exclusive) that provide less intrusion into your sound or even offer different tone shaping for each instrument.

An A/B box solves one part of the situation, but there’s another twist – piezo pickups require a higher input impedance than magnetic pickups. Usually 1 megohm is the minimum. Go lower than that and you’ll get a scratchy, brittle sound from the piezo. One longstanding solution is to use an outboard buffer preamp, like ones made by Fishman, K&K, L.R. Baggs and others. Another solution is to use an amp with a 1 meg input – most do these days, but they are still voiced more for electric bass (usually a push of the highs and lows). I’ve just started working with an expensive preamp box, too. More on that in a moment...

Pass the Highs, Please!

Three features beyond impedance matching help out tremendously for amplifying upright bass. One is a highpass filter (HPF). The deal here is that piezo pickups – even with their fairly natural sound – produce infrasonic frequencies along with the instrument’s actual notes. These infrasonics are below our hearing range, but the amp and the speaker can “hear” them nonetheless. Amps require additional power to produce infrasonics; speakers fly around wildly from them. A highpass filter essentially cuts out low frequencies below a certain point, using a steep rolloff curve. A common cut point is around 40 hz – the lowest note on a 4-string bass. Raising the rolloff point of the HPF can also help get rid of some of the mud in a boomy room. Where do you find these filters? The Fishman Pro-EQ Platinum Bass Preamp offers such a thing. It’s also part of the Acoustic Image amps. Most recently, a little inexpensive box made by Francis Deck combines both phase reverse and HPF, too.

The second useful feature is a phase reverse switch. Basically, an acoustic instrument’s top responds not to only the sound it makes but to the sound it hears from the room and the amp. Each note has its own wavelength and these lengths can synch up with the instrument’s distance from the amp. When that happens, you’ll get feedback every time you play that note. With a phase switch, the soundwave is reversed so that it is out of synch with the instrument’s note. It’s not anything you’ll hear, but when you flip a phase switch each way, one way will feed back (and sound more bassy) and one way won’t (and will have a more natural bottom end). Some outboard preamps offer this feature, as do a very few amps.

The third feature is the notch filter. In some rooms, with some instruments, you’ll get some ringing feedback on the notes more in the midrange. A notch filter has a very deep cut in a very narrow band that can be tuned to cut that resonance out. You’ll find this feature on the L.R. Baggs Para D.I. and, again, on the Acoustic Image amps.

Bringing in the Amp Factor

Upright bass players these days are shifting to tiny, light, high-powered amps. Sure, the classic Gallien-Krueger MB150 combos are still getting plenty of use. But amps by MarkBass, Acoustic Image, and Euphonic Audio are gaining in popularity (as is a legendary, almost mythical head from Walter Woods, something that can’t be bought in stores and is made by one guy living out in the California desert).

Imagine an amp that weighs between 5 and 7 pounds, yet puts out between 300 and 500 watts. How? These amps use a combination of switching power supplies and Class D power amps that rely on solid-state circuitry. Yes, despite the clamor for tube amps in the guitar world, the best bass amps are almost always solid state. For bass, high levels of clean power takes priority over the magic of valves.

What stands out in these three lightweight heads is their voicing – for the most part, there is no voicing. These rigs have preamps that provide natural sound, with their EQ helping to match the amp to the room as much as anything. The bright highs of bass guitar amps are toned down; the big bottom end is likewise more natural. Both these tonal characteristics help an upright bass sound like itself, but bass guitars might need some additional EQ – or a pedal in front like the SansAmp Bass Driver DI – to shape the tone and frequencies more to what we’ve become accustomed to with contemporary amps.

Call Me a Cab, Please!

The last element of putting together a rig for upright bass (and doubling) is the cab. This choice depends on both the size of the gigs you play and whether you’re doubling with electric bass. In general, cabs with 15” speakers don’t cut it for upright (too boomy, not enough punch), and fortunately, the electric world has moved away from them, too. Cabs with 10” or 12” speakers are the best choice because of their focused bottom and punch. For big gigs, a 4x10 or 2x12 cab will do well and should be excellent for doubling (it seems like almost everyone is using a single 4x10 cab these days). For small gigs, a cab with a single 12” speaker works very well, although some players swear by a single 10” for a cab with a pair of 8” speakers. One very hot new choice is the Euphonic Audio Wizzy 10, that puts out a lot of sound in a small, light package (under 20 lbs!).

For these smaller cabs, top choices seem to be from Bergantino and Euphonic Audio, but there are lots of other excellent choices from companies like Eden, Gallien-Kreuger, Schroeder Cabinets, Acme Sound and others. These cabs tend to be fairly expensive, but are nicely designed with top quality components.

My Own Solutions

So where do I land in all this? For my doubling gigs, I’ll take a G&L L-2500 electric bass (a 5 string) and an Azola BugBass electric upright (see top photo). Mine is a solid body model, one of the company’s earlier designs. The BugBass approximates the upright sound, but takes up little stage space, is easy to play – and never feeds back! With its volume knob, I can set up similar output levels from both axes and then switch between them with the Boss AB-2 pedal.

I plug into a somewhat vintage (1988) SWR SM-400 amp that offers lots of tone-shaping options between a 4-band graphic EQ and bass/treble shelving knobs. It puts out 400 watts (bridged) at either 4 or 8 ohms into my Gallien-Krueger 410SBX, a bit unusual because it’s a sealed cab, unlike the common shelf-ported cabs. This cab has a nice, smooth top end that works well with the electric upright, but also does nicely with the G&L bass guitar.

For smaller gigs, I go with the Acoustic Image Clarus top (400 watts into 4 ohms at about 5 lbs.!) into an Euphonic Audio Wizzy 12. At a recent outdoor restaurant gig on electric bass, I kept getting comments from the band that I needed something smaller because this little 29 lb. cab was so loud – a nice doubling setup. The secret to the Wizzy cab is its transmission line porting that gets more low end out of a small box, along with a wizzer cone (like the old car speakers) that projects the high end from a single speaker.

The Clarus/Wizzy setup also works well for electric upright or acoustic upright gigs, because it has options for adjustable highpass/notch/phase reverse settings.

Getting to this point in my own rig required two things. First, is building a knowledge base. I’ve been reading about gear trends at online discussion boards for several years. If you trot down to your local music store, whether big or small, most of the generalists there won’t have heard of these brands or the problems that they’re designed to solve. They’re not in most catalogs, either.

A second requirement is shifting around all the gear that you use. For several years, my standard rig was an SWR Bass 350 head or a GK 700RB head into a pair of Eden cabs (a 210 and a 115). But none of this gear had the right sound or the right features to do the job. Larger gigs required hauling two cabs, while small gigs ended up with a 210 cab that took more space than we could sometimes spare. I had also tried an SWR Workingman’s combo, which sounded nice for small gigs on electric bass, but just had the wrong voicing for upright.

Ending an Arduous Journey

To get to the gear I’m now using required patiently selling off each part – either online or locally – over the course of a few months. And then I had to save up gig money to make the whole thing happen. Happily, this recent gear swap has provided a pair of rigs I should be able to use in quite a variety of settings.