Acoustic music is probably not the first thing that pops into your mind when you hear the name Marshall, so when I got a chance to check out the Marshall AS100D Acoustic Soloist Combo I was intrigued. How would the folks behind that famous British power sound-the staple of rockers from Hendrix to Green Day-approach acoustic amp design?

When I plugged into the AS100D and strummed the first chord, I had my answer. Marshall has designed this amp with care and attention to detail, and it sounds big and present without sacrificing the natural sound you want from an acoustic instrument. Even the look of the AS100D, with its brown faux-leather handle and exterior, seems like a deliberate statement to set it apart from its more raucous rock 'n' roll cousins.

At a list price of $1,250, the AS100D is not for the thin of wallet, but it offers a lot to the serious gigging musician: 100W into two 8-inch Celestion speakers and two polymer dome tweeters, two separate instrument channels (linkable for stereo inputs), three sets of tone controls (with sweepable mids on channel 1), two mic inputs (one on a third dedicated mic channel), feedback squelching circuits, a stereo effects loop, onboard stereo digital effects, stereo line and XLR direct outs, even RCA inputs for CD or cassette-did I miss anything? You won't, either. This is one feature-packed amplifier.

In fact, I have to admit thinking at first that the AS100D had too many features for most folks, but trying them out made me change my mind. Let's take a closer look, starting with tone control.

Sweeping Tone The key to a convincing acoustic sound is midrange, so the sweepable midrange control on channel 1 is a welcome addition. With a range of 250 Hz to 2.5 kHz and a depth of -12 dB to +3.5 dB, you get control where it's most needed-for cutting out the bad stuff. For example, you can notch out the ringing of piezo pickups, allowing the sizzle of strings and the airiness of wood to come through.

Although channel 2 doesn't have the sweepable filter, it offers a serviceable Contour button to notch out preset mids, plus the conventional Bass and Treble controls found on all three channels. It's worth mentioning that the latter are flat in the straight-up position, and can cut their respective frequencies as well as boosting them.

And speaking of cutting out the bad stuff, the powerful feedback squelch controls cover channels 1 and 2. You get two sweepable frequency bands, one ranging from 50 Hz to 250 Hz, the other from 60 Hz to 650 Hz. You can dial in a frequency from each band, and notch it out with the press of a button. The notch filters have a Depth switch, increasing the amount of filtering. The feedback circuit is a godsend in those chambers of horrors we all must enter from time to time when playing live or rehearsing.

Finally, the AS100D had an unexpected but useful feature-phase switches on each of the three channels. One common problem with electrified acoustic instruments is resonance from phase interference between the amplifier and the instrument itself. The phase switches helped me eliminate this problem in a couple of troublesome live situations.

Stereo Effects Like most amps, the AS100D has an external effects loop, but this one is wired in parallel rather than series, and has stereo returns. The AS100D can make use of these because it has two 50W amps; the three (mono) input channels feed both, while external and internal effects feed the sides separately.

Built-in stereo digital effects are a bonus when you want to walk into a room, plug in, and play. The trouble is, with many amps you get effects of dubious quality. Not so with the AS100D, which has built-in effects so good you may never lug your rack gear to a show again. It offers ten Reverbs (three Halls, three Rooms, three Plates, and a Nonlinear), Chorus, Flange, Delay, Modulation, and two combinations: Chorus Room and Ch/Dly/Room. An Adjust knob sets delay time for the reverbs and delay, as well as speed for the various modulation effects. An Effects Level control adjusts the overall levels of each effect.

My favorite effects are the plates, which sound smooth and natural, and the Chorus algorithms, which have richness and depth without artifacts. Particularly striking is number 15, Ch/Dly/Room, which gives a larger-than-life quality for strumming. I only wish the AS100D offered a Chorus/Delay/Plate setting.

Two Mics, Too For those who don't want to rely on sketchy house P.A.s in smaller venues, the AS100D sports some fancy extras. It has two mic inputs: one on the second instrument channel, and another on a third independent mic channel. Marshall designed the mic circuits thoughtfully: not only does each have phantom power, a phase switch, and its own volume and tone controls (Mic 1 shares these with Instrument 2), but the second mic channel can also blend internal and external effects. That way you can have separate effects for guitar and voice.

Marshall has taken this one-man band even further by providing a pair of RCA inputs for a CD or tape player. In an extreme case, if you can live with Instrument 2 and Mic 1 sharing a channel, you can plug two guitars, two mics, and a tape player into the AS100D and perform a full duo show with tape and no P.A.

School of Hard Rocks The AS100D is unquestionably loaded with features, but how does it hold up under real-world conditions? Before I answer, a few words are in order about the instruments I used.

The main axe was a Martin 000C-16 cutaway with built-in Fishman pickups and EQ. I also tried my old Gibson J-50 with a new Thin-Line piezo pickup installed under the bridge, a Guild Crossroads with piezo and humbucking pickups, and even my Eric Aceto custom electric violin.

For guitars like my Guild, the AS-100D has a special feature: a link between channels 1 and 2, allowing you to plug in a stereo cable from a guitar with both piezo and magnetic pickups and control the tip signal via channel 1 and the ring signal via channel 2. Unfortunately, I could only get a weak magnetic pickup sound on channel 1 using this configuration, but my guitar appeared to be the problem. That notwithstanding, the normal channel 1 sound was the best that I've ever heard out of my Crossroads.

I road-tested the AS100D in three common situations: a rehearsal space with a stale, dead sound and thrash bands bleeding through the walls; a gig in a medium-size bar with three musicians and no drums; and a full rock band crammed into a small, cavernous club with a wretched P.A.

How well did the AS100D perform? One indicator is how little I had to do each time to get it to sound good. Regardless of the environment, I got a punchy tone that stood up to louder instruments, like drums and electric guitar, but still sounded acoustic-not bad for a single amplifier.

Sound Product Every manufacturer prides itself on its trademark sound, but my love for the classic Marshall sound (I own two Marshall rigs) actually prejudiced me against the AS100D-in this case we were talking acoustic, after all. I wondered how much of that high-volume rip-the rip I know and love for electric guitars-I would hear messing with my acoustic tone. The answer is favorable: enough to make it stand up to the other instruments, but not enough to become obnoxious.

With its clear, punchy sound and loads of features, the AS100D is all of the acoustic amp most us will ever need. For those who find the price daunting and don't need the extra features, Marshall also offers the leaner AS50R, a 2-channel 50W mono combo with analog instead of digital effects. But if you can swing the bucks, the AS100D is in a class by itself. Try one out and see. The next time you hear the name "Marshall," you might catch yourself thinking about your acoustic guitar.

Peter McConnell is cofounding a dot-com in Berkeley, California, after ten years as a composer at LucasArts. His current music projects include two game sound tracks and violin and guitar work with singer-songwriter Liz Anah. He virtually lives at www.petermc.com.

Inputs (2) 11/44" instrument, (2) XLR microphone, (2) RCA stereo auxiliary, (2) 11/44" effects loop returns Outputs (2) stereo XLR DI, (2) 11/44" stereo line out, (1) 11/44" mono effects send Speakers (2) Celestion 8", (2) Audax polymer-cone tweeters Amplifiers (2) 50W (RMS into 4*) in a stereo configuration Dimensions 23.6" (W) x 21.25" (H) x 9.9" (D) Weight 46 lbs.

Marshall AS100D Acoustic Soloist Combo $1,250 Overall Rating (1 through 5): 4.5 PROS: Punchy sound that's convincingly acoustic. Two instrument and two mic inputs. Flexible EQ and notch filter. Ability to link two channels for stereo input. Good-sounding stereo internal effects. Routing options for internal and/or external effects. Foot pedal to turn effects on and off. Stereo XLR DI and 11/44-inch line outs. CONS: If you don't need the mic or RCA inputs, you're paying extra for features you won't be using. Contact: Marshall Amplification/Korg USA (distributor); tel. (516) 333-9100; fax (516) 333-9108; Web www.marshallamps.com