A Short Guide to Ultra–Portable Bass Heads

Though it’s impossible to bottle the mojo of backbreakers like Ampeg’s B–15N or SVT, modern engineers are closer than ever. Today’s bassists have more and more reasons to make the switch to portable amplifiers and save themselves thousands on that SVT–induced hernia surgery.

Class D power amps have long been hallmarks of the portable audio market. Offering unrivaled efficiency, Class D amplifiers have powered everything from hearing aids to mobile phones for years.

Recently, amplifier manufacturers have taken this technology to new heights, using the increased efficiency and decreased heat loss to produce quality, lightweight amplification at competitive price points.

Without question, this technology has become a fixture of the modern bass amp market. With more powerful, lightweight options to suit any gig than ever, Class D amplifiers are becoming an essential part of modern amp history.

Let’s take a quick look at the engineering behind these efficient, shrinking amps.

The Technical Side of Class D Amplifiers

Class D amplifiers, also called switching amplifiers, amplify analog audio signals by converting them into high–frequency square waves.

By sending both a triangle wave and an analog audio signal into a comparator, a Class D circuit generates a pulse–width modulated square wave that maps the amplitude and frequency of the incoming triangle wave and analog signals. The resulting square waveform adds a ton of information around 250–300kHz — far above the range of human hearing — compounded with the original analog input signal.

Next, the compounded signal is amplified. After the signal is amplified, it’s sent to a low–pass filter to de–gunk the high–frequency harmonic information. To take care of the remaining voltage bias, engineers then add a high–pass filter so that only AC can pass through to the circuit’s output.

What we’re left with at the end of this chain is a louder version of our input signal and almost no heat loss, which allows builders to create the more compact circuits we’re seeing today.

If any of that sounded like gibberish, all you need to know is that Class D power amps have given builders the ability to deliver insane wattage in a tiny machine and that this technological advance makes well–powered amps with modern perks (like direct outs, aux in, and headphone outs) cheaper to build and easier to afford.

Let’s take a look at some of the best in class from around the industry. Here’s a rundown of seven compact bass amplifiers that won’t break the bank — or your back, for that matter.

TC Electronic BH250 — $250

TC Electronic’s wildly powerful Class D amplifier, the BH250, features TC Electronic’s patented TonePrint technology. It offers up a palette of six different effect types under a four–pound hood, in addition to a host of other player–conscious add–ons, like a built–in tuner that works for 4–, 5–, and even 6–string basses.

At first glance, the BH250’s 3–band EQ seems like your garden variety EQ section. But behind the simply labeled bass, mid, and treble knobs are carefully engineered cuts and boosts that make for more musical, expressive equalization.

The bass knob cuts at 80Hz and boosts at 100Hz; the mid knob cuts at 500Hz and boosts at 800Hz; the treble knob cuts at 1.8kHz and boosts at 3.15kHz. These chained resonances make for stellar EQ response, which makes the amp a pleasure to play.

By far the coolest feature of the BH250 is its built–in effects processor. Using TonePrint technology, players can change the effects algorithm with a computer or by sending pulses from your phone through your pickups into the amp.

Users can choose between six different effects types and dozens of different presets through TC Electronics TonePrint app. Once your desired effect is loaded, the TonePrint knob determines the amount of effected signal blended into your clean tone.

Overall, at just $250 and 4 pounds, the TC Electronic BH250 is a superb value. However, at 250W, it’s easy to see how the BH250 may not be enough rig for the gig. Luckily, the BH250 does have a Balanced Output feature for any venue applications.

Genzler Magellan 350 — $439

Jeff Genzler’s Class D designs have been widely touted as some of the most elegant, tiniest amplifiers. Genzler Amplification’s Magellan series amplifiers are an excellent continuation of Genzler’s legacy of lightweight titans.

Clocking in at just 3.5 pounds and featuring 350w at 4 ohms (175W at 8 ohms), a three–band active EQ circuit with a parametric mid control, a switchable two–mode contour response curve selector, and a balanced line out, the Magellan is a workhorse amplifier that can satisfy even the pickiest tweeter tweaker.

Genzler’s bass knob is a ±15dB boost/cut shelving curve with a corner frequency of 75Hz — slightly above the average frequency. The result is dastardly clear low–end response. The Magellan excels with its mid–frequency selector — a variable knob from 150Hz–3kHz — that’s depth controlled by the mid knob, which applies/cuts up to 15dB. The treble knob is a shelving curve with a corner frequency of 6kHz, providing players with glassy harmonics that don’t end up sounding sterile or tinny.

At $439, The Magellan 350 is a must–try portable amp head. Simply put, this three–and–a–half pound behemoth has tone for days without slouching on its power rating.

Ashdown Engineering RM MAG 220 Rootmaster — $230

Ashdown Engineering has always dedicated its amplifiers to “busy, hard–working bass players on a budget.” And for those busy and hardworking players, Ashdown has built the Rootmaster 220 — 220W of solid–state power packed into 16.5 pounds. And though this is our heaviest offering on this list, the few extra pounds are repaid in stellar tone.

With bass equalization coming in at 100Hz, low–mid at 220Hz, middle at 660Hz, high–mid at 1.6Hz, and treble at 7kHz, the RM–220 meets all expectations as a workhorse Ashdown amp head.

The amp succeeds in almost perfectly representing your bass’s acoustic tone before you even touch the EQ. If you want to dial in your bass response for more of a rounded rumbling, on the other hand, you can be assured that your note definition will still remain clear. And if you’re looking for glassier, scooped mids, check out the shape effect.

The RM–220 is additionally outfitted with transparent and natural–sounding compression, a pleasantly fuzzy drive knob, a sub feature that can add thickness or synthesis, and a blend feature that can tie everything together.

Being 16.5 pounds and with its unfussy and rugged construction, you can be assured that this head is not only a bang for your buck but can withstand any abuse it might encounter on the road.

Recently, Ashdown has also iterated on the Rootmaster series with the RM–500–EVO and the RM–800–EVO, which are great, higher–powered alternatives to the RM–220 if you're looking for some extra gigging wattage.

Ampeg Portaflex PF–350 — $299

Best known for its legendary tube amplifiers, Ampeg stepped into the Class D market in 2011 with its Portaflex series of amp heads and cabs.

The PF–350 is Ampeg’s no–frills take on Class D amplification, featuring a three–band EQ, 350W of solid–state power, an onboard limiter, a -15dB pad, 1/8” headphone out, and 1/8” audio in, the PF–350 provides classic solid–state Ampeg tone with updated modern practice tools at just $299.

Sonically, the PF–350’s EQ circuit is comparable to a (tubeless) Heritage B–15R, with its bass EQ centered at 40Hz, mid–range centered at 500Hz, and treble centered at 8kHz. To its credit, this small amplifier has a lot of Ampeg character to it. Yet, in my experience, the PF–350 is best used as a practice amp or for low–volume rehearsal situations. However, like all of the other Class D amps we’ve reviewed, it does have a balanced XLR line out.

If you’re looking for a catch–all gigging and practice amplifier, go for the PF–500. With just three extra pounds added to the total carriage, the PF–500 adds in a solid compression circuit, an ultra lo that boosts the low–end response and cuts some of the mid–range frequencies, an ultra hi switch that enhances high–frequency output by 9dB at 8kHz, and a five setting parametric mid–range frequency selector.

Aguilar Tone Hammer — $499

Aguilar’s hybrid bass amp heads have quickly become some of the most sought–after modern bass amps. Punch and beef are the two immediate tip–offs of an Aguilar tone.

The Tone Hammer 350 distills 350W (at 4 ohms) of Aguilar’s distinctive tone into just 3 pounds. The Tone Hammer’s three–band EQ also features a mid frequency knob that lets players adjust the frequency center of the mid knob, selectable from 180Hz–1kHz. With a bass band centered around 40Hz and a treble band set around 4kHz, Aguilar’s Tone Hammer preamp is perfectly capable.

Another key feature of the Tone Hammer 350 is its dedicated drive channel. Using Aguilar’s proprietary adaptive gain shaping circuit, the drive knob introduces a woollier, tube–esque texture to your bass tone. I like to dial in the drive knob to about 8 or 9 o’clock for a little bit of extra growl, almost like an SVT.

Aguilar’s Tone Hammer 350 is not a sophisticated Class D amplifier, but for those of you who want a portable taste of Aguilar tone, you can’t go wrong with the Tone Hammer 350.

Darkglass Microtubes 900 — $1,000

Darkglass Electronics’ Microtubes 900 is an astoundingly outfitted amp head with a bevy of incredible tones.

Featuring a four–band equalizer (including two parametric mid–range frequency selectors), a native Microtubes distortion circuit with two distinct modes, a balanced XLR out with a pre/post preamp switch, a preamp out for connecting to different power amplifiers, a power amp in for connecting different preamps, and Darkglass’ Intelligent Footswitch to switch between the clean, mute, and drive circuits, the Darkglass Microtubes 900 offers up a ridiculously diverse palette of bass tones.

At just 6.2 pounds, the Microtubes 900 delivers 900W gut–rumbling lows at 4 ohms, or 500W at 8 ohms. With a slightly higher bass frequency band on its preamp centered around 80Hz, the Darkglass pushes out crispy, well–defined lows. Two parametric, mid–range bands let players choose both axes for low and high mid–range frequencies.

For low mids, players can choose from 250Hz, 500Hz, and 1kHz; for hi mids, the selectable centers are at 750Hz, 1.5kHz, and 3kHz. This type of mid–range equalization is unprecedented and highly useful for a lightweight bass amp.

Half of the frequency of the Nano Mark’s 10kHz treble center, yet sitting just above both the Aguilar Tone Hammer 350’s 4kHz and TC Electronic BH250’s 3.1kHz, the Microtubes 900 features a treble preamp band at 5kHz — a middle–of–the–road treble center that adds finger noise and definition to your bass attack without rattling the fillings in your teeth.

The Microtubes 900’s drive channel features Darkglass’ Microtubes Engine that adds natural compression, enhances harmonic response, and provides players with authentic tube–type saturation. The distortion channel showcases two different flavors of Darkglass’ distortion circuit. The Vintage Microtubes (VMT) overdrive is a middier, thicker sound with a more neutral character, whereas the B3K introduces a punchier, more percussive distortion.

The tone knob controls the Microtubes Engine’s high harmonic content through a variable low–pass filter. Turning the tone knob clockwise adds clarity and punch; turning the tone knob counterclockwise yields a warm, smooth overdrive. I like to use the VMT channel with both the tone and blend knobs around 9 o’clock to add in a slight tube–type distortion.

Although its price tag is steeper than the other Class D amps we reviewed, the Darkglass Electronics Microtubes 900 outclasses the competition with its diverse features packaged into a sleek 6.2–pound container.

Mesa Boogie Subway D800 — $700

Mesa Boogie stepped into the ring with its superb portable bass amp, the Subway D–800. Insanely enough, Mesa Boogie engineered 800W at 4 or 2 ohms (400 at 8 ohms) into just 5.5 pounds of hardware.

Supplying a 4–band fixed, rotary EQ, the D800’s preamp hosts a bass control from 30–80Hz, a low mid control centered at 200Hz, a high mid centered at 480Hz, and a treble control from 2.5kHz up.

But the real winner for me is the D800s overlapping mid controls, allowing bassists to tinker with their low mid “bloom” and high mid “bark” with two independent mid controls. Even more compelling, Mesa Boogie’s Class D offering features a mute switch, an active/passive switch tailored to the input headroom of your instrument, and a classic Fender–style deep switch. The voicing knob determines the amount of “disco scoop” (increased treble and bass, scooped mids) applied to the preamp.

Lastly, the back panel of the Subway D–800 includes a direct output, a line/mic level switch, a ground switch, a pre/post source switch, an aux input, and a 1/4” headphone jack output for use as a headphone amp.

At $700, Mesa’s D800 is a decent value for good hardware. In my experience, these amps are particularly great for sub–woofer genres like reggae and hip–hop that need more low–end thickness and less top–end attack and clarity.

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