Max Mini! A Roundup of Ultra-Lightweight Class D Mini Amps

At the turn of the 21st century, lightweight, high-powered amps became the rage when switch-mode power supplies and Class D amp topology were adapted to the demands of the musical-instrument world.
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At the turn of the 21st century, lightweight, high-powered amps became the rage when switch-mode power supplies and Class D amp topology were adapted to the demands of the musical-instrument world. Suddenly, bottom dwellers could tuck a concert-capable rig into the pocket of their gig bag. This re-purposed technology from the hi-fi world was not initially designed for bass amplification, and many first-generation mini amps were accused of lacking punch, not delivering the true wattage claimed by the manufacturer, or sounding sterile. But the platform’s convenience was undeniable, and suddenly it seemed every company had a mini amp in their lineup. The technology has consistently improved over the past 16 years, and designers have learned to implement it more effectively, making this the best time ever to jump on the Class D platform, or upgrade to the newest generation of diminutive dynamos.

A high-powered mini amp paired with a lightweight neodymium-loaded cab is a potent solution for the working bassist, and I’ve been a convert for many years. This roundup is a sampling of what’s on the market, not a ranking. I’ll provide an objective perspective of my experience with each amp, and point out distinguishing features. As my exposure to most of these amps was limited to a few weeks, I cannot speak to their reliability over time. My benchmarks were a Fender Road Worn Jazz Bass strung with DR Strings flats for the old-school side, and a ’74 Jazz loaded with a first-generation J-Retro preamp and spankin’ fresh Dunlop Marcus Miller strings to represent the modern thing.

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Mesa/Boogie Subway D-800 Head

Street $700 

Power Output 800 watts @ 4Ω or 2Ω 

Bottom Line The latest in an emerging trend of no-compromise lightweight heads, the Subway D-800 offers tons of headroom, volume, and flexibility, with grit for rockers and clean punch for the rest.

As is almost universally the case with Mesa/Boogie amps, the Subway D-800 is handsome, with a no-nonsense exterior and elegant front-panel graphics and layout. The controls are self-explanatory. Input governs gain at the J-FET-based first stage and couples with the o/d indicator to precisely monitor overdrive. The voicing filter is a complex, variable-frequency response curve that is essentially flat when it’s fully counter-clockwise and progressively more “smiley-face” as it’s rolled up, with boosted bass and treble and a progressively attenuated midrange at higher settings. The 4-band EQ is standard fare, with shelving bass and treble filters accompanying two bands of peaking midrange. Finally, master operates as expected, controlling the input signal’s gain as it enters the power amp. There’s also a deep switch, which slightly boosts low frequencies and lowers the cutoff of a highpass filter (more on that below).

Like virtually every other lightweight Class D/SMPS head on the market, the Subway D-800 utilizes a 3rd-party power amplifier and power-supply module, in this case the ICEpower 700ASC/X. The know-how and R&D resources required to design a high-performing Class D amplifier and robust switchmode power supply are simply out of the scope of most bass amplifier manufacturers, especially given the extraordinary performance of modules from ICEpower and other manufacturers selling amp/power supply modules as original equipment. Rather, the unique stamp of each amp builder is better seen in the preamp tone and overall design integration of a given head. A well-engineered amp/PS module ought to just make the preamp sound louder. The 700ASC/X is an exceptionally high-performing unit that’s more than up to the task, and unlike some other Class D/SMPS modules, it’s perfectly happy cruising along at a nominal 2Ù impedance. To further ensure stability, the Subway includes an internal, always-on highpass filter with a cutoff around 30Hz (this lowers a bit when the deep switch is engaged). It limits wasting power reproducing low frequencies that are below almost every bass cabinet’s low-end rolloff. 

ACOUSTIC B1000HD

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Street $600
Power output 1,000W @ 4Ω
Weight 8.2 lbs
Bottom Line A powerful mini that comes close to capturing the classic Acoustic 360 tone, but can dish up modern hi-fi, as well.

The solid-state Acoustic 360/361 was a cornerstone of high-volume music from the late ’60s into the ’70s, and fans of Jaco Pastorius and Larry Graham know the amp was an integral part of their tone. The brand was resurrected in 2007, and the B1000HD is Acoustic’s new entrant into the Class D world, along with 300-watt and 600-watt models. My inner skeptic didn’t expect this amp to remind me of the legendary 360, but upon plugging in my passive Jazz Bass, I heard it—the crystal-clear top end, the almost strident midrange, and taut bottom jumped right out—with the amp set flat. Diehard 360 fans will no doubt argue the point, but to my ear, it was close enough. One of the coolest things about the old 360 was the built-in fuzz circuit, and the footswitchable overdrive on the B1000HD sounds great, whether set for a light browning or full-throttle thrash—I annoyed my neighbors for hours.

Plugging in an active Jazz Bass, I was equally surprised by how well the amp conveyed more modern sounds. The input pad was useful, as the onboard preamp proved too hot, but the B1000HD spat back my attempts at Marcus-style funk with clarity and depth. The features you need are there, along with a backlit 8-band graphic EQ, compressor, super-lo and super-hi boosts, and link in and out jacks to daisy-chain to another amp. The variable notch filter sweeps from 50Hz to 1kHz, but it did not prove very useful in my testing. Oddly, the cooling fan is mounted in the middle of the top panel, and it is noisy—but you won’t hear it over the roar this amp produces. The amp produces more self-noise than others in this roundup, but its unique tone, versatility, cool fuzz, and pure watts-per-dollar value make it one to check out.

AGUILAR TONE HAMMER 500

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Street $700
Power output 250W @ 8Ω, 500W @ 4Ω
Weight 4 lbs
Bottom Line The sought-after Aguilar tone in a small, light package, with enough oomph to take care of business.

Aguilar rocked the amp scene in the early 2000s with its legendary DB 750 head, a tube/solid-state hybrid monster that became the rig of choice for the most discerning. The mighty DB 750’s DNA lives on through its cousin, the DB 751, and the Tone Hammer series of mini amps. Aguilar has successfully captured the essence of its signature sound in a Class D format, saving the player both pounds and dollars. Separate gain and drive controls work together to give you clean, modern response or varying shades of vintage. The 3-band boost/cut EQ has the lows set at 40Hz and highs at 4kHz—frequencies used as corners in several other Aguilar products—and a midrange that sweeps from 180Hz to 1kHz. All the expected conveniences are there: effect loop, a full-featured DI, Speakon connectors, tuner output, – 10 dB pad for active basses, and switchable voltage for worldwide travelers. The Tone Hammer feels muscular, even without help from the ample EQ, and gives you enough guts to drive a 4Ω load on a big stage. It’s easy to see why it has become one of the standard bearers in the mini-amp kingdom.

ASHDOWN ROOTMASTER RM 500 EVO

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Street $600
Power 500W @ 4Ω
Weight 8.3 lbs (as tested)
Bottom Line The RM 500-EVO is a solid performer with the grit that makes Ashdown a worldwide favorite.

With its mirror-like faceplate and glowing VU meter, the RM 500 EVO is a sturdy piece that exudes class and it delivers a wide range of tone choices. The Ashdown signature tone could be described as aggressive, but refined—stout, but not tubby, and perhaps clean, but not squeaky. The RM 500 EVO is all that and more. The 5-band EQ is tuned for bass at 100Hz, with a dedicated control set for 240Hz; middle is tuned to 660Hz, with another dedicated control at 1.5kHz; and treble is set for 7kHz. The shape button gives you the Ashdown version of the mid-scoop contour control that beefs up the lows and extends the highs. These tone tools make the RM 500 EVO flexible enough to point any type of instrument toward your sonic goal, but there is always that characteristic gristle that sets the brand apart. However, with the handy EQ bypass, the amp gives you a clean slate that allows more modern-sounding instruments to retain their clarity, and you can still access the SHAPE control.

Features like an aux in jack, effect loop, and DI are expected, but the RM 500 also gives you a nice one-knob compressor, a snarly drive circuit, and a sub-octave generator, the latter two footswitch-operable. The drive has a warm, organic feel, and a nice, useful range before you hit the wall. Even at full blast, the sub-octave generator is subtle, and so it should be considered a thickener rather than a pronounced effect. It’s an interesting feature, although it can be a little glitchy. Although the 500 is beefy, an 800-watt big brother is available for just $100 more, so you might want to drop an extra C-note for more power, particularly if you mostly drive an 8Ω load.

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CARVIN AUDIO BX700

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Factory direct $449
Power output 300W @ 8Ω, 550W @ 4Ω, 700W @ 2Ω
Weight 5.9 lbs
Bottom Line Factory-direct pricing makes the BX700 an aggressive competitor against loftier models, and a standout in its own price category.

Carvin Audio’s BX700 head is a feature-rich mini with punch and detail. The preamp allows you to run through or bypass the single 12AX7 tube—an inventive option. Another unique trait is its ability to drive a 2Ω speaker load, just in case you like carrying more boxes. The red panel lighting makes it easy to see the many controls for onstage adjustments, and it looks cool. The EQ section offers bass and treble shelving controls (cornered at 50Hz and 10kHz), two bands of semi-parametric midrange, and a smartly tuned 9-band graphic EQ that can be bypassed. Having this much EQ shaping on tap can work against you if you’re inexperienced or heavy-handed. I found it best to first explore the tonal range available using the drive control and tube, and then apply EQ as needed. But for challenging source material like slap upright bass, the extra tone control is a real plus. Standard utility features are present, including a headphone/tuner output, DI with ground lift, and effect loop. The BX700 is slightly wider than its contemporaries, but its slim profile and ultra-light weight make it a mini that can hang with the big boys.

DEMETER AMPLIFICATION BASS 400

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Street $1,000
Power 250W @ 8Ω, 400W @ 4Ω
Weight 8 lbs
Bottom Line Classic Demeter tube tone in a lightweight package.

When your company name is virtually synonymous with clear, rich tube tone, it’s a challenge to make a mini amp that lives up to the lineage. The Demeter VTBP-M-800D amp mated Demeter’s tube preamp with a Class D power amp, and the results were stunning. The new Bass 400 is a stripped-down version that manages to stay true to the legacy, and costs about a grand—a relative bargain for a U.S.-made, hand-built piece of this quality. The VTBP-201 preamp is the heart of the Bass 400, with a hand-picked 12AX7 tube feeding the passive EQ section. The mode switch gives the amp three subtle characters: dark, normal, and bright, pointing the amp in the right direction based on your preference. The tone controls are not necessarily intuitive, but they work together to sculpt your sound. The flat setting has the bass and treble at 12:00, the mids up full, bass frequency switch set to 120Hz, and the presence knob at 0. Starting there with plenty of gain, I was able to get any tone I desired, but unlike some amps, the Demeter won’t “cover” for a bad-sounding bass—garbage in, garbage out. However, playing a great-sounding bass (passive or active) through the Bass 400 is one of life’s treasures. The Demeter massages the tone with studio-grade sweetness that can be best appreciated with a good full-range cab.

Although rated at 250 watts into my 8Ω cab, the Bass 400 was surprisingly loud and clean. I turned the single volume control up to 3:00, and even with the attenuated active input, it handled the peaks and transients of funk slap with ease, and shook the walls. The Bass 400 is taller than most, but at eight pounds, with a sturdy handle, carrying it is a breeze (there is also a cagemounted version for desktop use). The DI is pre/post EQ, and can be upgraded to a Jensen transformer for an additional $200, a nice option for studio cats. The preamp out and power amp in jack can be used as an effect loop, or to daisy chain the amp to another power amp. While not as feature-laden as some in this roundup, the Demeter Bass 400 has tone and impact that ends that conversation quickly.

GALLIEN-KRUEGER MB FUSION 800

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Street $900
Power 560W @ 8Ω, 800W @ 4Ω
Weight 5.5 lbs
Bottom Line All the GK sound you could want, and more.

Gallien-Krueger has been a major player for over 40 years, building amps highly regarded for intelligent engineering, useful features, reliability, and what has become known as the “GK sound.” There are two flavors in Gallien-Krueger’s MB line of heads: the solidstate MB 200 and 800 and the tube-driven MB Fusion 500 and 800. With three 12AX7s in the circuit, the basic tone is warmer than that of the solid-state MB models, and channel B is ready to go if you want overdrive—if you ever felt GK was “too clean,” the MB Fusion could change all that. Channel A is structured for cleaner tones, and the included footswitch (nice!) lets you toggle between two distinct gain settings. The use of “smart buttons” gives you easy access to a multitude of features with a simple push, and the backlit controls illuminate white or blue depending on the function, making this one of the easiest amps to adjust onstage.

The 4-band EQ section gives you a shelving control for bass cornered at 40Hz, while the lo-mid and hi-mid controls are peak filters set with a wide Q at 250Hz and 1kHz. A shelving control for treble is set at 7kHz, with an additional bright voicing filter (via push button) that brings in +4dB at 10kHz for more sparkle. A deep voicing filter is similarly accessible from the push-button bass control, giving you another 4dB at 30Hz. The contour circuit is a big part of the GK tone, and it also can be switched to give you a cut at 500Hz or 800Hz. The MB Fusion 800 has all the utility features you would expect from a pro amp, and while slightly deeper from front to back than other amps in this roundup, it’s tiny compared to the pro-level performance it delivers—whether you need it for modern slap or vintage thump.

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GENZLER MAGELLAN 800

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Street $760
Power output 400W @ 8Ω, 800W @ 4Ω, 800W @ 2.67Ω
Weight 6.2 lbs
Bottom Line Hefty performance and a flexible preamp make this an excellent choice for a wide range of gigs.

The Genz-Benz brand raised the bar with its excellent Shuttle, Shuttlemax, and Streamliner mini amps. Jeff Genzler has since regrouped as Genzler Amplification, which recently introduced its Magellan line of cabs, and a new 800-watt head: the MG-800. For former Benz fans, the MG-800 takes the immediacy of the Shuttle, combines it with the hi-fi sweetness of the Streamliner, has two channels like the Shuttlemax, beefs things up with a vastly improved power supply, and adds a dual-voiced preamp. The solid-state preamp has a 1MΩ input impedance, making it piezo-friendly. The 3-band EQ is tuned to 75Hz for bass, 6kHz for treble, and mids are sweepable from 150Hz to 3kHz. The clean channel has an uncolored tone, while the drive side is deliberately less hi-fi, with separate gain and volume controls that can create a wide spectrum of “brown sound.” Selecting Curve A on the contour control sweeps “classic to modern,” which is basically flat response to a pronounced mid scoop. Curve B is “thicker to vintage,” which provides a bump to the low-mids while rolling back on the highs. Between the two channels and dual-voice contour, the MG-800 gives you four distinct sonic starting points before ever touching the tone controls. It has impressive power, reacts fast, and doesn’t crap out when you lay into it. The MG-800’s full feature set includes a front-mounted mute switch, –8.5dB input pad, channel select button (footswitch operable), a DI with pre/post EQ, mic/line level switch, ground lift switches, an effect loop, tuner out, aux input, headphone out, and dual Speakon speaker outs.

HARTKE TX600

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Street $400
Power 600W @ 4Ω
Weight 7 lbs
Bottom Line A loud and punchy mini with a unique approach to EQ. Economical, too.

The new TX600 is Hartke’s first dedicated Class D head, and its Class A tube preamp circuit is similar to the company’s popular LH1000 design. The TX600 is built around a tone-stack-type EQ that operates differently than typical boost/cut circuits—the bass control feeds into the mids, which feeds into the treble. And there is no “flat” position; with all knobs at 12:00, the amp is preset to an EQ curve that Hartke chose as the starting point. The bass control is tuned at 80Hz, and treble at 6kHz, but the midrange is handled via the shape and frequency controls, which form a variable notch filter. The frequency knob selects which point between 200Hz and 800Hz will be cut, and shape determines the depth of the cut—the deeper the cut, the narrower it gets. It’s initially a little odd to hear the low mids get fuller as you roll the frequency knob up toward 800Hz—cutting the upper mids accentuates the lower mids. The bright switch is set at 10kHz, giving you different amounts of boost depending on the gain setting. The interactive nature of the EQ means you’ll have to experiment more to find the sweet spot between the controls, but true to their intent, having the knobs at 12:00 was pretty close to what I wanted anyway.

The TX600 has a full complement of features like an aux in jack, headphone out, mute, effect loop, one Speakon and one ¼" speaker out, a compressor, active and passive inputs (both 1MΩ), and a DI with ground lift. The sturdy case has a built-in side-mounted handle that gives you a firm grip on the amp, something missing from a surprising number of entrants.

PEAVEY MINIMEGA

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Street $600
Power 700W @ 8Ω, 1,000W @ 4Ω
Weight 9 lbs
Bottom Line Big power and a ton of features make the Mini-MEGA a versatile rig for folks who like lots of control.

The Peavey MiniMEGA is loud and proud, with a feature set that requires a little manual time to get the best results. The backlit front panel and controls are easy to read, as well as being decorative (with ten color choices and a “light show” mode). Considering that the control panel has eight knobs and eight buttons underneath, being well-lit is a real plus. Under the gain control is the crunch button, which adds drive and rounds off the treble while thickening the bottom. The optical compressor knob has an enable switch, and can range from a light flattening to full squash depending on the level and input gain. The low eq is set at 40Hz, with a punch button that adds 4dB at 100Hz. The 2-band semi-parametric mids use concentric knobs for frequency and boost/cut, and are split for 200Hz to 800Hz for the low mids and 800Hz to 3.2kHz for the upper mids. Each band has a button that gives you a wide or narrow Q for more precise control. The high knob controls the range between 3.2kHz and 20kHz, with a bright button that adds 10dB at 8kHz. With all of this EQ available, you can point the MiniMEGA in a lot of directions, but be careful—some of the boosts can prove too much when combined with higher levels of EQ.

Peavey added two effects to the MiniMEGA, controlled on a concentric knob with an enable button. KOSMOS A is a sub-octave generator, and KOSMOS C is a psycho-acoustic “loudness” control that beefs up the bottom when playing at low volume, or through small speaker cabs. It’s a neat effect, but it must be used cautiously, as it can create mud if used with punch and lots of low EQ. I found the sub-octave glitchy and not particularly present when playing up the G string. With all these switchable features, Peavey wisely made many of them accessible from a 5-button MIDI footswitch (not included). The DI gives you pre/post EQ, a pad, and ground lift, as well as an additional ¼" TRS balanced out. Dual Speakon outs, tuner out, aux in, and an effect loop round out the features. The MiniMEGA comes with a carrying bag.

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PHIL JONES BASS D-400
Street $800
Power 200W @ 8Ω, 350W @ 4Ω
Weight 2.9 lbs
Bottom Line The D-400 is surprisingly stout for a relatively low-powered amp, with a clean, hi-fi response and effective EQ.

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Phil Jones Bass was an early champion of the light-and-loud movement, and the company’s D-400 head packs a considerable amount of punch, considering it pumped only 200W into my 8Ω cabinet. The switchable input has 4MΩ impedance when set to low, making the PJB the most upright-friendly of the roundup. Plugging my Gage Realist Lifeline-equipped doghouse straight into the head produced a beautiful, full-range tone, and the EQ was well tuned to let me tailor the sound however I wanted. The PJB has five bands: lo-bass centered at 70Hz, hi-bass at 160Hz, lo-mid at 630Hz, hi-mid at 2.5kHz, and treble at 12kHz. The limiter has a minitoggle bypass, and is preset with a 3:1 compression ratio. I found that it kicked in hard even at low settings when playing aggressive slap with an active bass, but it smoothes the rough edges nicely with less brutal input levels. The D-400 is simple, elegant, and smaller than most of the others in this roundup. It doesn’t have lots of bells and whistles, although its full-featured DI, headphone out, effect loop, and preamp out (for connecting to a powered speaker) cover the essentials. In spite of its seemingly low power rating, the D-400 has enough kick for medium-volume gigs, and for upright—maybe all you need. PJB is bringing out a 1,000-watt model in the near future, so if you really need to move mountains, help is on the way.

TECAMP PUMA 900

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Street $1,000
Power 600W @ 8Ω, 900W @ 4Ω
Weight 3.3 lbs
Bottom Line The Puma 900 feels tight and punchy, the power is there, and dialing in a great tone is as simple as it gets.

One of the smallest and lightest in our roundup, the Puma 900 is also higher-priced than many, but don’t be swayed by the feathery heft, or basic layout—the TecAmp is a serious piece of gear. Without a lot of hoopla, the Puma gives you the features you need: pre-or post-EQ for the DI, tuner, line, and headphone outs, an effect loop, aux in jack, mute, and a single Speakon out. The 1MΩ input gives piezo players a good step in the right direction, and the gain control is linked to a clip LED that helps you dial in the right level. The 4-band, boost/cut EQ is set at 30Hz for the lo control, with lo mid at 250Hz, hi mid at 800Hz, and the hi control at 8kHz. I found the controls to be extremely sensitive, particularly the LO knob, but the overall responsiveness brings to mind comparisons with German cars—well-built, high performance, sleek design, and tasteful. Speaking of tasteful, the “golden” knob on the Puma is the taste control, which points the amp toward a brighter midrange boost below 12:00 (called “dry”), and smoother, darker tones (called “rich”) as you roll clockwise. Setting taste at 12:00 gives you a relatively neutral starting place.

I was impressed by the Puma’s simple perfection. The true test of an amp is how it sounds with the EQ set flat, and the TecAmp sounded just like whatever bass I played through it. With the convenience of the taste control, it’s a snap to drastically change the personality of the head, and of course, if you do use the tone controls, you’ll have a lot at your disposal. I appreciated its girth of tone and raw power—the Puma leaves no doubt as to whether it’s beast enough for high-volume playing.

TECH 21 VT BASS 500

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Street $500
Power output 300W @ 8Ω, 500W @ 4Ω
Weight 6.5 lbs
Bottom Line When you need “that” sound, the VT Bass 500 gets you there without the schlep.

Tech 21 built its brand on a product that simulated an amplifier, the SansAmp, but its analog modeling circuit became so popular that Tech 21 decided to mate it with a power amp for a line of bass heads. There are several versions of Tech 21’s VT circuit in pedal, rack, and amplifier form, all designed with the intent to emulate the legendary Ampeg sound. Tech 21 offers two full-rack amps in the VT line—the VT Bass 1000 and 1969 models—but the 500 is a powerful mini amp with a decidedly classic-vintage personality.

The VT circuit has been reviewed in several iterations, but a new feature on the 500 is the button that shifts the mid frequency from 500Hz to 1kHz. Like the VT Rack and VTDI models, the VT 500 has a blend control to mix the emulated and clean signals. Rolling blend completely down gives you access to only the 3-band EQ. The fun starts as you roll blend clockwise, bringing with it the full participation of the VT circuit. The drive control opens up the gain structure, but be warned: It is designed to break up in higher settings. The character control sweeps through SVT and B-15 territory, and more, eventually landing in face-melt-land by the end of the rotation. The bite control is a presence boost that accentuates note attack in high distortion settings, and although there is no mute switch, the effect loop, headphone jack, and DI are front panel-mounted for easy access.

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WARWICK LWA 500

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Street $500
Power 250W @ 8Ω, 500W @ 4Ω
Weight 2.8 lbs
Bottom Line A tiny amp that truly kicks. Well engineered, transparent, and competitively priced.

Warwick is so committed to the mini-amp milieu that the company took its previous model, the LWA 1000, and cut it in half. The LWA 500 is about as small as it gets for a full-featured amp, but it doesn’t skimp on performance. The layout is attractive and efficient, and the backlit panel greatly helps you see the miniaturized controls. The Class A preamp and Class D power amp section produce robust, fast response, with a sweet, transparent tone that hardly needs EQ. But the EQ is there: ±12dB for bass at 100Hz, low mid at 800Hz, high mid at 3kHz, and treble at 10kHz. I found the low mid control tuned a bit high for use as a boost, but it worked perfectly as a cut for a more vintage tone. The compression knob is activated via a mini-toggle switch, and it is one of the more usable built-ins I’ve tried. The compressor levels out the peaks but leaves the punch, and adds make-up gain to keep the overall levels close to uncompressed tone.

The LWA 500 has a ⅛" headphone out and aux in on the front panel, and around back, a ¼” line out can be switched to a tuner out. The parallel FX LOOP is accessed via a ¼" TRS stereo jack (Warwick includes the necessary Y-cable in the box). The LWA 500 is the only amp of the roundup to include a wet/dry mix control for the effect loop, and it offers a nifty Neutrik Combo speaker connector that works for ¼" or Speakon plugs. The LWA 500 has the performance of an expensive amp, yet it is priced in the lower range represented here.

CLASS D AMPS & SMPS

Mini amps predominantly make use of two key pieces of technology. First, the power amps generally operate in a Class D topology. Class D amps achieve much greater efficiency than conventional Class AB amplifiers, so less output power is wasted as heat, and more of the input power is converted directly into sound. The resulting amps require fewer output devices, less heat-sinking, and a physically smaller power supply. The industry tentatively approached the technology in the ’90s and early 2000s, but now almost every manufacturer (except for hardcore all-tube specialists) makes at least one bass head that utilizes a Class D power amp.

The other critical component of today’s ultra-lightweight amps is the switch-mode power supply (SMPS). All amplifiers require a section of the circuit dedicated to converting the line power (from the wall) to the appropriate voltage, current, and phase for the amp’s operation. Conventional linear power supplies are not particularly efficient, losing energy as heat and as a consequence of voltage regulation.

SMPS amps take a different route. First, an SMPS rectifies the AC line power into DC. Then, a “chopper circuit” or “switching regulator” converts the DC signal back into AC, but at a much higher frequency than its original 60Hz. This frequency is typically above the audible spectrum (i.e., higher than 20kHz) and can go as high as 100kHz in some SMPS amps. Finally, this high-frequency signal hits a transformer again to step the voltage down or up for appropriate use in the amp. The trick is that since the power is at such a high frequency, a much smaller power transformer is necessary than the bulky iron anchors used in linear power supplies. The reasons get deep into physics-class territory, but suffice it to say, an SMPS can nearly eliminate the weight that a transformer contributes to the overall heft of a bass head. Coupled with a lightweight and efficient Class D power amp, you get the insanely lightweight heads of today.

CLASS D MODULES

Underneath the hood of a Class D mini amp is a Class D module, sourced from a third-party manufacturer. To get some clarity on this subject, we spoke with Paul Meister, Sales Manager for ICEpower America, which builds the module found in several of the amps in this roundup. He is also a pretty swanky bass player in his own right.

What does a module do?

The module should simply take the input signal—in this case, the preamp’s output—and amplify it while adding as little coloration as possible. For a musical-instrument amp, the idea is that whatever work the designer puts into the preamp is outputted as accurately as possible. As we hope to deliver as pure of an output signal as the input we receive, the amp’s designer and manufacturer have to pull their weight as well.

In what way?

Among many things, the manufacturer needs to ensure that their preamp outputs a signal that is properly matched for the amplifier module’s input, and make sure the internal layout is done efficiently, so as not to introduce noise into the system.

How has the module been improved for bass amp use?

While we have some new products that specifically lend themselves to bass applications, the improvements are over a wide variety of features, and were a result of customer feedback—much of it bass-related—as well as our own R&D over the past 16 years. Some of the newer products have seen a nice increase in continuous power ability, and a huge reduction in distortion figures. They also have several internal feature improvements, such as automatic voltage-switching for those who tour worldwide.

Does a good module guarantee a good bass amp?

Well, if they don’t pick the right feature set, or design a useful, pleasant-sounding preamp, it doesn’t matter what module they use!

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