February 2006Grommes 360 Mono Amplifiers
by Tim Aucremann
Have you heard of Grommes? Before the opportunity to review the Grommes 360 amplifiers presented itself, Id never heard of the brand. However, a quick Google search found Grommes components a regular topic of conversation on the online vintage-equipment forums. People uncover a Grommes 102 tuner at a thrift shop or get a Model 221 amplifier from Grandpa and want to restore it to hear how it sounds. This is gear from the 1950s and 60s -- the days when names like Scott, Fisher, Harman, and Stanton populated the American hi-fi scene.
It was 1946 when William Grommes (pronounced like "grommet" but with an "s" at the end instead of a "t") founded Grommes-Precision Electronics, Inc. to make signal-trace equipment. Today, the Precision Electronics division makes commercial audio products. In the 50s, under the direction of chief engineer Al Hart, the Grommes division built high-end amplifiers, preamps, stereo amplifiers, and tuners. The Little Jewel amplifier kit gained recognition as both a good value and a fun way to learn about electronics, and today its popularity still holds with vintage geeks (and younger geeks, too).
By 1955, Life magazine declared Grommes one of the best buys in high fidelity. In 1959, Grommes released the Al Hart-designed 60-watt 260A mono amplifier. The 260A gained a loyal following, and Hirsch-Houck Labs deemed it "one of the finest power amplifiers made, by virtue of its rugged, conservative construction, and remarkably low distortion." Yes, this is the same Julian Hirsch famous for noting that even a non-engineer may "sometimes observe subtle differences in sound among very high-quality amplifiers."
In the 1970s, when more and more home stereo equipment shipped from overseas, Bill Grommes did not do what many high-fidelity manufacturers did -- he didnt sell his companys name to foreign competition. Nonetheless, as brands like Onkyo, Sansui and Technics came to dominate, Grommes business shifted primarily to commercial applications.
Now, Grommes is back. In 2002, the company re-entered the high-end market under the technical leadership of designer Alan Kimmel and remains an American company based in the Chicago area. Kimmel, who is no stranger to vintage gear, had the opportunity to work with Al Hart in the early 1980s. He has also designed mods for the famous Dynaco ST-70 amplifier, and more recently collaborated on the design of the ModWright SWL 9.0SE line-stage preamp.
The 360 amplifier ($4000 USD per pair) descends directly back to the original 260A. One look at the Grommes 360 monoblocks and you sense their heritage is grounded in value -- no exotic curves or birdcage-like tube holders here. The amps' classic form-follows-function layout does not stray far from that of the original 260A.
Specs for the Grommes 360 state it delivers 60 watts of continuous RMS power into 6 ohms. Power and output transformers dominate the top of the amps black metal chassis, which, along with its array of tubes, measures 16"W x 11 1/2"D x 8 1/2"H, and weighs in at roughly 36 pounds. The trannies are custom made for Grommes by an American company. Alan Kimmel identifies the wideband output transformer as one reason the 360 can provide 60 watts from 20Hz to well over 60kHz. True to Grommes' "make em like they used to" policy, all components are hand-wired point to point; there are no printed circuit boards in the 360.
The 360 is a push-pull design using an EH 12AX7 tube to amplify its input signal. That triode couples to a GE 6U8A phase splitter, which also serves as a buffer to the 12AX7. An EH 12BH7 triode acts as a buffer between the phase splitter and the output tubes. In contrast to the Grommes 260A, the 360 uses no global feedback from the output stage back into the input. Instead, Kimmel designed a mu stage that provides the only voltage gain in the driver circuitry and is linear enough that it needs no input feedback. As he explained to me, "The mu stage design cleans up the voltage gain stage by avoiding distortion as opposed to using feedback to cancel it."
The output stage features a pair of JJ 5AR4 tube rectifiers and a pair of JJ KT88 power tubes. A Sovtek 6L6GB regulator tube powers the KT88 screen grids in both pentode and ultralinear modes. Via a switch on the backside of the chassis, the user may select either mode of operation. Kimmel notes that a regulated supply to the ultralinear screen grids is unique.
Power tubes in the Grommes 360 are individually biased by hand. This means that you dont need to replace tubes in matched pairs (though Grommes still recommends it), and there is no auto-bias circuitry. Using the meter built into the 360s front panel, I found the bias procedure simple. A switch selects the tube to bias, mutes the output, and lights up the meter. Each tube has a slotted potentiometer located on the chassis top; turn one with a screwdriver to set the tubes idle current to the proper value on the meter. Once I set it, the bias held steady throughout my use of the amplifiers.
The Grommes 360 should prove to be a tube-rollers delight. You can easily change the sonic signature of this amplifier by using different output tubes. The manual identifies the correct current values to set the bias for a variety of power tubes. Among those supported are the 6550, KT90, KT100, 6L6GC, 7581A, EL34 and others. Adding to this flexibility, the 360s top deck includes small ports for using your own meter to monitor real-time voltage at the cathode of each output tube.
The angled front panel includes inputs for balanced and single-ended interconnects. A small toggle switch selects the input type. Grommes specifies 10k ohms impedance for single-ended inputs and 14k ohms for balanced. Power is applied by another toggle switch, and a red lamp glows when the unit is on. A volume-control knob allows use of the amp without a preamp.
The back panel sports an AC fuse holder and a standard IEC receptacle. A small toggle switch offers ground lift; choose its position for lowest hum. A larger toggle switch changes the operating mode between pentode and ultralinear. As you might expect, ultralinear mode yields less power than pentode -- the docs say about 40% less. There are no strict guidelines on selecting a mode. The type of music played, the sensitivity of your speakers and, most important, your ears are the best arbiters. Speaker cables attach to plastic-capped binding posts that I wish were sturdier. There are no labels on the back-panel switches; however, an attached plaque diagrams the layout of all items on the amp.
When sitting in front of my stereo, I listen to LPs most of the time and use CDs more for background music. My vinyl-playing front-end consists of a Shelter 901 cartridge mounted on an SME V tonearm attached to a cocobolo Teres 255 turntable. The phono cable is an FMS Blue II. A Pass Labs Xono phono stage connects to a Conrad-Johnson ACT2 line-stage preamp via FMS Zero interconnects. My CD player is a belt-driven Parasound 2000 that connects to the ACT2 with Shunyata Aries interconnects and sits on Symposium Rollerblocks. All other electronics rest on Walker or Mapleshade brass cones and normally plug into an original six-outlet, Corian-clad Shunyata Hydra. A Conrad-Johnson Premier 140 amplifier connects to the ACT2 through an eight-foot run of FMS Zero interconnects. Speakers are Audio Physic Avanti Centuries connected with Shunyata Lyra speaker cables. For this review, I plugged both the C-J Premier 140 and Grommes 360s into a wall outlet.
As I've noted, the 360s are feature-packed: volume control, bias adjustment, ground lift, pentode/ultralinear switching, meter jacks, and balanced and single-ended inputs. I tried all but the balanced inputs. During the 360s first outing in my system, I could not help noticing a high-frequency buzz through both speakers. For the first time in my years of being an audio hound, Id encountered a ground loop. A ground loop can occur in a stereo rig when some of its components do not connect to the same ground as others. Flipping the 360s ground-lift switches didnt make a difference. Other simple resolutions failed, and I ended up using cheater plugs on the amps power cords, and these stopped the buzzing. This is a system issue, not something inherent to the Grommes amps. If they were to take up permanent residence, Id solve the problem rather than bypass it. A wee bit of mechanical hum came from the amps' hefty power transformers, but this did not intrude on my listening.
It was fun to play with the pentode/ultralinear switch, but after weeks of experimenting, I did not come to a conclusive preference for one mode versus the other. In either mode, the fundamental character of the 360s came through. I learned to turn the amps off and wait a few moments before changing modes, however; otherwise, I got a nasty click through the speakers.
My normal practice is to let tube gear warm up for at least a half hour before critical listening. The Grommes 360s definitely sounded best in my system with a minimum 60 minutes of warm-up time, preferably a little more. Thats something to keep in mind if you audition them in a dealers showroom.
I initially listened to the 360s in pentode mode. I put on an HDCD of José Serebrier conducting the London Philharmonic Orchestra in Rimsky-Korsakovs Easter Overture [Reference Recordings 89CD] and wandered down the hall to think Kevorkian thoughts over my wifes ancient 386 computer as it gasped and wheedled through another day. My inner ear broke the mood: "Hey buddy, that sounds good." From the listening room came a sound clear and dynamic. The music drew me back.
As I sat down in position prime, it was obvious the Grommes amps had a good handle on dynamics, here evidenced by the horns. On the Rimsky-Korsakov piece, listen to the trombone solo a voce piena -- in full voice -- as it crests and falls across the measures. Accompanying cellos and double bass were tight, resonant and decidedly clear. The crisp, punchy attack from the trumpets surprised me. I not only heard but also felt their entrance. And those trumpets came from a different vertical plane than the rest of the orchestra, their notes floating high and back to the right. The amps delivered nicely separated orchestral voices from each section and a deep soundstage. They say you dont get a second chance at first impressions, and the Grommes amps did well. I wanted to hear more.
I switched to ultralinear mode, and the 360s again offered excellent soundfield depth, this time on a live performance of Mahlers Symphony No.1 "Titan" performed by the Bavarian Radio Symphony under the baton of Rafael Kubelik [Audite 80467] -- an elegant, lyrical interpretation nicely packaged one movement per side. Not only was the orchestra laid out in panorama, but so was a portion of the audience, which I heard coughing and rustling about. Instruments were steadfastly located in space, and their outlines were not too sharply drawn. This may be more believable to those who do not perceive precise imaging during live music. The amps offered a believable sense of air and location that took me into the presence of both listeners and musicians.
If you are looking for a lush, sweet tube amp, the Grommes 360 may not be your cup of tea. From the middle of the midrange through the midbass and into the low bass, they exhibit a convincing tonality closer to neutral than warm. Thats roughly the range from the top end of a soprano clarinet to the bottom of a bass clarinet. And, indeed, the character of the woodwind "cuckoos" in the opening movement of Mahlers First -- especially from the clarinets -- was wholly believable. The 360s' leading-edge transient response and clarity revealed the initial attack of tongue against reed with a nice follow-through into the bloom of a properly woody-sounding clarinet.
Later in the movement, timpani and woodwinds briefly duel in a quick trade of notes back and forth. This handful of bars is a challenge for any piece of gear. The 360s did a nice job individuating the instruments and contrasting the kettle-ish resonance of the timpani from the darting flutes and clarinets, all the while maintaining the air and spatial cues of the percussion from the back of the hall and the woodwinds closer to the audience. To wax Yoda-esque: "Quick little tube amps these 360s are."
From the lower midrange into the low bass, the Grommes 360s quickness, dynamic facility and tonal weight are remarkable. The ability to handle rapid midbass dynamic swings with clarity belies their 60 watts. Listen to the entrance of the bowed cellos at the beginning of "Titan's" second movement (they startled me), or to the reverberant thunder of the timpani as the third movement starts with a bang. Switching albums, the kick drum on Paul Simons "Crazy Love Vol. III" from Graceland [Warner Brothers 25447] was solid, not boomy. On "It Feels Like Rain," from Aaron Nevilles Warm Your Heart [Classic Records/A&M RTH5354] the Grommes amps discovered a previously unnoticed rich bass voice tucked among the backup singers. The amps may have a petite midbass bump -- Im not certain -- but the lower registers are well controlled. Here, attack takes precedence over decay. If youre of a mind that a smaller tube amp cant do bass well, the Grommes 360s could change that.
The 360s clarity and quickness extend into the upper octaves. They never sounded bright or nasally, though occasionally triangles and trumpets might come a little forward with a faint edge. When an orchestra is going full bore and the volume turned up high, I perceived the tonal character of massed strings more toward the yang than the yin -- slightly dry and with the barest hint of a whitish coloration. I refer mostly to the top two octaves from violins and the top octave for trumpets. To hear an example, consider the strings in Liszts Roumanian Rhapsody from the Rhapsodies album [Classic Records/RCA LSC-2471], specifically when Stokowski pushes the dynamics to double forte. I heard a slight discontinuity in tonality from the highs versus the lower midrange. Nevertheless, the violins were well articulated, and the amps held onto their rhythmic control. On less complex music, string tone is richer as the Grommes amps discriminate details and deliver refined microdynamic contrast. The 360s beautifully captured the virtuosity in the fade-away pizzicato from Oleg Kagaans violin as he follows Sviatoslav Richters piano towards the end of Mozarts Sonata in G major for Piano and Violin [EMI SLS-5020].
I also connected the Grommes 360s directly to the solid-state Pass Labs Xono phono stage; this meant adjusting volume and balance by each amps output control. Until then Id never heard the Xono without an intervening line stage, so comments here are better taken in terms of the synergy between these components. Listening in ultralinear mode to "She Moves On" from Paul Simons Rhythm of the Saints [Warner Brothers 26098], my notes describe the detail, drive, and clarity from the assorted rattlers and scratchers, bongos, congas, and gourds -- all going at once. The 360s neatly parsed the diverse percussion across the soundstage as the musicians played at a good clip. I felt my pant legs ripple from the solid whack delivered to the congas during "Born at the Right Time." The brass and sax on "Cool Cool River" had punch and pulse. Simons voice was forthright but not quite as harmonically full as when the ACT2 drove the 360s.
Snappy transients from electronic synthesizers in "Telephone Call" on Kraftwerks Electric Café [EMI EMD 1001] were extraordinarily fast, clear, and immediate in pentode mode, though I wondered if their leading edges were a tad overly incisive. Because the Grommes 360s do many things well, I became greedy for more and swapped in a pair of 1970s GE6550A power tubes in each amp. The NOS valves took off the faint edge and notes gained a pinch of richness. Tonally fuller, the music was more relaxed, while timing and clarity did not suffer. The guitar on Warm Your Hearts "It Feels like Rain" gained in soul quotient, and backup vocals on "Thats the Way She Loves" became more dimensional. I cant say if this change lent itself to the Grommes amps or compensated for the Xono, but my ears were happier and I couldnt help wondering what a set of Tung Sol 6550s or EL34s might do.
"Shell be the one -- when the partys over"
Yes, this is the comparison section, and its title is a line from the Elvis Costello tune "Big Boys." My current reference amp is the Conrad-Johnson Premier 140 ($7500). Other tube amps Ive heard over the past months are closer to three times the price of the Grommes 360s -- among these the Thor Audio TPA-30 Mk II monoblocks ($10,990 per pair) and the Nightingale ATS-90 monoblocks ($12,595 per pair). In my reviews, I consistently observed these pricier amps each to have their own internal coherency where no single attribute stands out in isolation from the whole. Is it fair to compare the 360s to the Big Boys? I cant say, but Ill tell you this: observations in the preceding section were made without compensation for cost.
In contrast to the Grommes monoblocks, the Premier 140 exhibits longer-sustained decay and brings a fuller dimensionality to singers and instruments, though neither amp is as dimensional as the lit-from-within presence I heard from the Thor TPA-30 Mk IIs. In terms of tonal character, the Thor amps are at the other end of the spectrum from the 360s, the former delivering warm and sumptuous harmonics from their twin EL34 power tubes. With the C-J amp, trumpets and French horns offer a sonorous golden tone, whereas the Grommes amps tonality is faintly attenuated in the upper registers. Richer tonality may be the singular difference between the Grommes 360s and the Big Boys. I cash this out as not so much a "neutral versus warm versus cool" comparison, but as degrees of harmonic refinement.
In terms of perspective, the Grommes amps put me several rows closer to the stage than the Premier 140. With excellent soundfield depth and a lucid separation of instruments, the 360s offered an audible sense of the recording venue -- it was easy to perceive back- and side-wall reflections. At the conclusion of a live recording of Shirley Bassey singing "I Who Have Nothing" (Greatest Hits [United Artists UA-LA715-H2]) the Grommes amps let me hear how applause starts from the center of the audience then ripples outward, though it barely moves past the edges of the speakers. Depending on the recording, the Conrad-Johnson amplifier suggests soundstage width beyond the speaker boundaries. I did find width from the Grommes 360s opening up when I played them at higher volume.
The Grommes sound is clear and open, and, to their credit, the amps gave no hint of grain or veiling when directly compared to the Premier 140. On "Abandoned and Pursued" from E.T. The Extraterrestrial [MCA-6109], both Premier 140 and Grommes 360s revealed the harpists finger technique in each pluck of a string as the harp overlaid violins and violas. On "E.T. And Me," the twin oboes are nicely individuated. These fine-spun details conjoin fastidious timing and microdynamic shading to offer a convincing presence. Bass from each amp is snug and resonant. The 360s are slightly more acute on the attack, though the C-J amp demonstrates greater weight and authority on low-end fundamentals, not a surprise considering the power differences. If aural memory serves, midbass control from the Grommes amps is close to that of the Nightingale ATS-90s, which is the best Ive heard.
While the Grommes 360s did not match virtue for virtue with the Big Boys, their sound and feature set are impressive for their price.
The Grommes 360s deliver honest clarity and nice value. Their open support for alternative power tubes is welcome. If youre looking for a tube amplifier that exhibits an excellent soundfield, is rhythmically adept and dynamically coherent, reveals detail and nuance, has exceptionally solid and nimble bass, and shows quickness and dexterity across the frequency spectrum, then youll want to give em a listen. Thirty years from now it will be no surprise to see the Grommes amp of today handed down to a new generation of audiophiles.
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