Bass Gear Review
Transcription
Bass Gear Review
by m To wlus Bo 56 bass gear Gasoline/electric hybrid automobiles are all the rage nowadays, and mentioning the word “hybrid” to most folks conjures up images of eco-friendly, high-mileage vehicles. For us bass players, we may also think of the typical hybrid bass head, which employs a tube preamp section paired up with a solid-state output section. A few non-conformists Markbass Classic 300 CL 810 ! T S TE bass gear might even think of some of the atypical hybrid heads, like the old Music Man HD150, which featured a solid-state preamp driving a tube output section. But this is the first time I have seen a hybrid which combined a tube bass head with a computer! But that appears to be exactly what Marco De Virgiliis has dreamed up with the Classic 300. This 300-watt head has a tube preamp, a tube output section, an LCD status display screen on the front, and a serial port on the back. Seriously! Always one to push the envelope and break new ground, Marco has really pulled out all the stops with this impressive new take on a hybrid bass head. Perhaps no less imaginative is the CL108 8x10 enclosure. If you start talking about sealed 8x10’s, certain ‘fridge-sized cabs (with weight to match) come to mind. But lightweight neodymium drivers are often associated with small, seemingly lighter-than-air bass cabs. The CL108 is not a small enclosure, and at 90 lbs, you aren’t going to lift it with your pinky finger. But considering that is almost four feet tall, handles 1,200 watts, and is basically two stacked 4x10’s in one convenient package, the weight is quite reasonable. If these specs don’t convince you, then moving a traditional 8x10 fridge will! Markbass has wowed the bass world with lightweight, compact heads like the F1 and LMII and equally portable cabs like the Traveler 102P and New York 604. 58 bass gear These products have rightfully earned respect for Markbass as a company that offers solutions for the player seeking featherweight rigs that don’t compromise on tone or output. With the Classic series, Marco proves that “lightweight” and “compact” are relative terms. ENGINEERING MASH-UP There is so much technology – both old school and modern – crammed into the Classic 300, I’ll leave the bulk of this discussion to our technical review. Rather, I’ll pretend like I don’t care what’s under the hood and focus on the more obvious features. The front panel offers a single ¼” input (no active/passive option), input Gain control, four-band EQ (+/- 12 dB at 80 Hz, 400 Hz, 800 Hz, and 3 kHz), DI level control, and a Master volume control. The footswitch input is also located on the front panel, which is a bit unusual, but nothing compared to what comes next. Standby controls and bias adjustments are nothing new to tube bass heads, but implementing these controls via microprocessor is certainly novel. The Standby control works just as you would expect, but the Bias control, which lets you select between “High Fidelity” and “Long Life” bias settings is just the tip of the technological iceberg. To the right of these controls is a 2x16 LCD display screen. This little screen is the most obvious clue that this is not your typical tube head. It manages to convey a good deal of useful information. When you first turn on the amp, it tells you that the tubes are warming up. Next, it runs through a bias check for both modes. Once it is ready to go, it lets you know. During operation, the display switches to an input signal meter (which, ironically enough, is reminiscent of a “magic eye” signal meter tube). The back panel features the AC connector, balanced XLR line out (with ground lift and pre/post EQ switch), effects send and return, unbalanced line/tuner out, and two Neutrik Speakon combo speaker output jacks – one for 4/8ohm loads and one for 2-ohm loads. The two more unusual features are the display function switch and RS-232 PC serial port. The switch toggles between three modes for the front-panel LCD screen: Normal (which shows the digital VU meter), Test 1 (which shows the bias of the power tubes), and Test 2 (which shows the tube voltages). The serial port is there to allow for service and maintenance functions by authorized Markbass technicians. Power is provided courtesy of six JJbrand KT-88’s, which I have used in numerous tube heads with great success. Output is rated as 175 watts into 8 ohms, and 300 watts into both 4-ohm and 2ohm loads. Our tests largely confirm these published figures. While the preamp features four more preamp tubes (also JJ’s), the signal also passes through a significant amount of solid-state circuitry. The CL 108 cab can be operated either as two 4x10’s, or as a single 8x10. There is a (lockable) switch on the back to select which configuration is active. The tweeter is defeatable, but not adjustable. The enclosure is covered in the same tolex as the head, and while it does look nice, it does mark fairly easily. There is a tilt-back handle on the back of the cab, near the top, and decent casters (though no kick plate). This makes moving the CL108 on a flat surface a breeze. But there are no other handles, which makes loading it into a car, or lugging it up steps more difficult than it needs to be. Side handles would really help, as the weight is not bad, but there is no place to grab it. Likewise, the wheels aren’t quite big enough to negotiate steps easily. Thankfully, the cab is light enough to make it moveable, despite the poor ergonomics involved in negotiation steps and loading into and out of vehicles. MARCO REVEALS HIS LOVE OF THE CLASSICS In our last issue, Vic Serbe presented a nice little back-story to Marco and Markbass, and many players are now familiar with the more light and compact products in the Markbass lineup. But I was curious as to the driving factors behind Markbass’ entry into both the tube power arena and the big, sealed 8x10 market. The modern trends are all towards smaller, lighter gear and Marco certainly has an aptitude for helping to define the trend, as opposed to following it. With the Classic line of products, Marco turned his vision backward, and spent some time considering the truly “classic” designs in bass amplification. You don’t have to look to far, or too long, before an Ampeg SVT stack comes into focus. Some variation of an SVT rig has been dominating stages and studios for decades, and the impact of the SVT head and cab upon the bass amplification scene cannot be denied. Marco saw much to appreciate and admire with regard to the warm, gritty tube powerhouse and the punchy, focused midrange attack of a sealed (closed) 8x10. But, he also saw room for improvement, especially considering modern technological advances. For instance, output tubes require proper biasing, and they will sound different with different bias settings. The decision of whether or not to allow the end user to control the bias of their power tubes – and if so, how best to design for it – has been a conundrum for every tube head manufacturer. Until now. The onboard Amp Management System (AMS) can monitor and adjust the bias to each tube, individually. This not only means less hassle, but also more consistency, tone-wise. Markbass claims that you can replace just one tube at a time (or multiple, un-matched tubes), and the AMS can adjust the bias properly. Another improvement Marco wanted to make involved (no surprise) weight and portability. Even though the Classic 300 (which employs a heavy, analog output transformer) is the heaviest of all the Markbass heads, it is still about half the weight of a classic SVT. How many 300watt tube heads do you know of that you can carry in one hand? I think that is a pretty impressive feat, if you ask me. With regard to the CL 108, Marco readily admits that those classic cabs owe much of their character to the fact that they are a sealed (or “closed”), versus vented, design. But, a big enclosure with eight drivers can be pretty darned heavy! Thankfully, the more drivers you have, the greater the benefit of lightweight neodymium magnets. In addition to the neo drivers, the use of lightweight Italian poplar helps get the weight of the CL108 down to about half that of a classic Ampeg (notice a trend, here?). You can turn the tweeter off for a more classic tone, or leave it on for extended high-range adventures. Each product, the Classic 300 and CL 108, were designed with the goal of recapturing and honoring some of the great, classic tones that backed up so many great shows and recordings. But they were also designed to do so while taking advantage of modern technology and weight-saving practices. That sounds great. Let’s see how these hybrids work in the real world! bass gear 59 PRESSED INTO DUTY The Classic 300 and CL 108 went out to their first gig about a day after I received them. I brought along a backup rig, in case things didn’t go well, or if I had too hard of a time dialing in proper tone. I needn’t have bothered. Right out of the box (literally), the Markbass Classic Monster took control and never let me down. The tone is appreciably full and rich, with a certain warmth that I have come to associate with a tube output section. But it was also quite clear and controlled, with good high-end extension. I did find myself boosting the low-mids just a tad, but other than that, I left it set fairly flat (with the bias set to High Fidelity). At this and subsequent gigs, I managed to try a number of different basses through this rig. While they all sounded good, the “instant classic” combination was with my Roscoe Beck V. That bass was just made for this rig (and, interestingly, is a bit of a hybrid blend of classic and modern designs in its own right). The Classic 300 does not do an over-the-top overdrive, but you can dial in some extra grit/growl, and certainly a good deal of added harmonic content. My preferred setting was with the pre-gain run pretty hot, which adds some excitement, but is not what you would call distorted or overdriven. The EQ controls are not overly powerful, with useful function over most of their range. The Low, MidLow, and Mid-Hi sounded better to my ears as a cut than as a boost (though slight boosts worked very well on all three). The High control worked very well and sounded musical with both more extreme boost and cut. The boost added high-end sparkle without getting harsh, and the cut mimicked a passive tone roll-off nicely. The mix of fullness, punch, and articulation definitely reminded me of another – yet far smaller – Markbass head: 60 bass gear the LMII. When you compare them backto-back, you can definitely tell that they come from the same family, and they do share some strong sonic characteristics. The Classic 300 is more focused in the mids, and definitely has a greater sense of “sonic texture.” The LMII, conversely, is a tad stronger in the low end and a little darker through the mids. While the highs are brighter on the LMII, they sing a bit more coming from the Classic 300, and are very rich. The LMII is known for its killer midrange punch, especially in the low-midrange. But the Classic 300 actually has greater note-to-note articulation in the meat of the midrange. The LMII may technically be the more clear of the two, but the impact and distinction (in the mids) offered up by the Classic 300 is just amazing. With the pregain set a bit higher on the 300, the articulation though the mids got even better (surpassing the LMII). The slap tone of the Classic 300 was very intriguing, and featured a ton of harmonic content (which might actually be a bit hard to control). But this amp is probably going to appeal more to heavyand fingerstyle handed pick-wielding players. If Marco’s goal was to capture the sonic impact of a classic SVT, but offer more modern tone-shaping controls, features, and safety /maintenance improvements, he succeeded. definitely has Compared to an SVT-VR, the Classic 300 captures a lot of the same midrange focus, and sounds much more like an SVT than does the more traditionally designed alltube Reeves Custom 225 (also reviewed in this issue). By contrast, the Reeves is bigger and deeper in the lows, and more clear and open in the midrange. Actually, the same can be said for the Mesa/Boogie Bass 400 (equipped with KT-88’s), and the Sadowsky SA200, which are more similar to the Reeves than to the Classic 300. The Classic 300 seems to fall somewhere between the Fat and Clean settings on the Sadowsky, with more midrange focus and a more aggressive attack than the SA200. Conversely, the Sadowsky is more smooth, full, and even, and can cop a wider range of tones. On a whim, I also compared the Classic 300 to the GK Fusion 550. Each has a similar low end, and similar harmonic content, though the Fusion ends up sounding more quick and clear. THE MINI FRIDGE As I mentioned above, the lack of side handles can make this cab a bit tricky for one person to handle, where a lot of lifting is involved. But if you have a buddy to help, or deal mostly with flat terrain, it is remarkably easy to move for an 8x10. The CL 108 presents an interesting mix of vintage fatness and more modern tones. It has that midrange punch that you only seem to get from a big, sealed cab with a bunch of 10’s, but with more control and refinement. The tweeter does add some nice high-end sheen (and further enhances this sense of refinement), but even with the tweeter turned off, the CL 108 has a good deal of high frequency information. This cab pairs up extremely well with the Classic 300. Each seems to provide the other with a greater range of options than you get when paired up with anything else. The CL 108 performed well with a variety of other heads (both solid state and tube), but the high end really smooths out when you drive it with the Classic 300. Compared to another compact, sealed “mini-fridge” – the Bergantino NV610 – the NV610 was more punchy and stronger in the low-mids, while the CL 108 had more presence in the upper midrange and highs. It turns out that the NV215 was actually a bit more similar to the CL108 throughout the midrange. However, the CL 108 had a more brilliant high end (which it should, pitting its tweeter against the NV215’s 6” midrange driver), and the NV215 had a more deep, full low end. Again, Ampeg proved to be perhaps the most direct comparison (at least with the CL 108’s tweeter turned off ), but again, this sense of added control and refinement was present with the Markbass. The CL 108 proved to be a pretty versatile performer, and could cover a good deal of ground from vintage to more modern tones. THE BOTTOM LINE I have to admit, I was really surprised when I first saw the Classic 300 and matching line of cabs at the winter NAMM Show in 2007. Having just come from ogling the mini-wonder F1, the Classic line seemed like a totally different direction; which of course it is. The impressive thing is that Markbass has been able to switch-hit and still knock one (or two, as the case may be) out of the park. With the Classic 300 and CL 108, Marco successfully evokes the glorious power of tubes driving big, sealed enclosures. But he has also managed to add a host of modern features and amenities, without spoiling the vintage appeal. The amount of technology that has gone into the Classic 300 and CL 108 is amazing. What is more impressive, though, is how well it works in practice. It has really been a pleasure to watch the rise of Markbass in the bass amplification world. Beginning with the Ernie Ball Music Man Audiophile head and cabs, Marco De Virgiliis has been thinking outside of the box, and has showed undeniable vision and style. I can’t wait to see what he comes up with next! bg : bass gear 61 test MARKBASS 2008 : bass gear CLASSIC 300 Bass Head ENCLOSURE Material Getting inside Time to assemble Time to disassemble Dimensions Weight Rackable Wooden head cabinet 4 bolts, 9 screws, 7 cable connectors 5 minute 5 minute 19 5/8” w x 12 3/8” d x 11 9/16”h 50.8 lbs No PREAMP Inputs Mode Tubes Input Impedance EQ Type / Features Compressor/Limiter Potentiometers DI Output Effects Loop Additional Features 1/4” jack Tube preamp, solid state EQ 2 Ecc083, 2 Ecc099 340 kOhm 4-band / Bandpass EQ Non-user adjustable limiter PC mount Switchable pre/post EQ, level control on front panel, ground lift Pre-EQ send Footswitchable mute POWER AMP Mode Tubes Power Supply Outputs Impedance Options Pre/Power PCBs Power Transformer Output Transformer Cooling System Line Voltage Options Line Voltage Setting Tube 6 KT-88 Toroidal transformer 1 Speakon for 8/- ohm, 1 for 2-ohm 8/4, 2-ohms 4 printed circuit boards Toroidal Taps for 2-ohm and a 4/8-ohm tap Fan 120VAC User-variable MEASUREMENTS Freq Resp - Preamp from DI post EQ 20 Hz - 20 KHz +/- 9.9 Freq Resp - Preamp & Power Amp 20 Hz - 20 KHz +/- 11.8 EQ Controls Down, Idle Hum 60 Hz -71 dB 120 Hz -80 dB 180 Hz -84 dB EQ Controls Down, Idle Noise 200 Hz - 1 KHz -99 dB 1.1 KHz - 20 KHz -100 dB EQ Controls Flat, Idle Hum 60 Hz 120 Hz 180 Hz EQ Controls Flat, Idle Noise 200 Hz - 1 KHz 1.1 KHz - 20 KHz -74 dB -87 dB -78 dB -74 dB -87 dB EQ Controls Up, Idle Hum -94 dB -81 dB -75 dB -89 dB -97 dB 60 Hz 120 Hz 180 Hz EQ Controls Up, Idle Noise 200 Hz - 1 KHz 1.1 KHz - 20 KHz GENERAL Company Country of Origin Warranty Listed Price Street Price Test Unit Options Accessories Price as Tested Available colors Available options Parsek Srl Via Po, 52 66020 San Giovanni Teatino Chieti Italy www.markbass.it Italy 3 Year $2,599.00 $2,599.00 None None $2,599.00 Black Footswitch to control mute CONDITIONS Acquired from Markbass Dates August through November, 2008 Locales Ohio Test gear Nordy vJ5, Celinder VP4, LeCompte CBSC-4, Fender Roscoe Beck V, Dingwall Z3, Dingwall SJ4, Markbass CL108, Bergantino NV610 & NV215, Sadowsky SA410, Ampeg SVT-VR, Mesa/Boogie Bass 400, Sadowsky SA200, Reeves Custom 225, Elixir & Planet Waves cables. TEST SUMMARY 1-5 (unacceptable to impeccable) inhand onbench Chassis Vents and cooling Knobs / Lights Finish / Handles Jacks / Sockets Pots / Switches Chassis Layout Components Resistor/Cap PCB / Power Transformer Solder / Dress SONIC PROFILE Lows – taut, controlled, warm; not Internal / Overall Build Output Power Rating overly big Mids – focused, punchy; aggressive; Portability Roadworthiness nice complexity and texture Ease of Repair Highs – average brightness, but cranking the pre-gain adds high- Warranty Quality per price end excitement Features Tonal Flexibility Ease of Use Aesthetics Ergonomics Tone Value 4 3.5 4 3.5 4 4 4 In-Hand Score 3.9 average On-Bench Score 3.5 average TONE-O-METER The Classic 300 delivers vintage midrange punch, and a hint of grit, with more control and wider range of tones than vintage counterparts 4 3 4 4 4 3.5 3 3 3.5 4 3 4.5 3 4 3 3 4 HALF POWER STRESS 1/2 Manufacturer Spec - Tested at 150 W into 4 ohms TEMPERATURE 0F Front Power Switch Front Input Jack Rear Power Jack Rear Speaker Jack Power Transformer Output Transformer Middle KT88 Retainer Fan noise Ambient 52 dB SPL Idle 75 74 74 77 77 76 95 5min 80 80 81 83 95 88 117 15min 90 86 90 96 105 94 155 30min 96 93 104 98 116 119 144 POWER TESTS MARKBASS CLASSIC 300 KEY TO TESTS Fan Low 57 dB SPL Signal interrupt (sec) Thermal shutdown (sec) 0 0 0 0 Fan High 64 dB SPL Half Power Stress: How well does this head handle the heat? 0 0 Full Power Output: These numbers are largely self-explanatory, but please note that the Input Signal tells you what input voltage was required to hit our mark, with the EQ set to “optimally flat” and the gain stages set for best THD performance using a 1 kHz signal. Voltage Drop shows how much the AC line voltage sagged during our testing. 0 0 FULL POWER OUTPUT Unregulated Line Voltage, Amplitude Sweep 3 to 5% Total Harmonic Distortion (THD) Average initial AC line voltage 120.4 - 122.4 Nominal 8-ohm Nominal 4-ohm Nominal 2-ohm 1K SINE WAVE Power Input Signal Voltage drop 199 Watts 1.0 Volts 0.7 Volts 295 Watts 1.0 Volts 0.6 Volts 266 Watts 1.0 Volts 1.0 Volts G STRING @ 98Hz Power Input Signal Voltage drop 199 Watts 0.6 Volts 0.7 Volts 288 Watts 1.0 Volts 0.9 Volts 263 Watts 1.0 Volts 1.0 Volts D STRING @ 73Hz Power Input Signal Voltage drop 195 Watts 0.6 Volts 0.6 Volts 286 Watts 1.0 Volts 0.8 Volts 263 Watts 1.0 Volts 0.7 Volts A STRING @ 55Hz Power Input Signal Voltage drop 193 Watts 0.6 Volts 1.0 Volts 288 Watts 0.9 Volts 0.4 Volts 251 Watts 0.6 Volts 0.9 Volts E STRING @ 41Hz Power Input Signal Voltage drop 196 Watts 0.7 Volts 0.4 Volts 272 Watts 0.8 Volts 0.4 Volts 251 Watts 0.4 Volts 1.1 Volts B STRING @ 31Hz Power Input Signal Voltage drop 193 Watts 0.6 Volts 0.6 Volts 278 Watts 0.8 Volts 0.5 Volts 244 Watts 0.4 Volts 0.2 Volts bass gear CERTIFIED POWER 8 ohms 1kHz 4 ohms 1kHz 2 ohms 1kHz 199 watts 295 watts 266 watts Manufacturer ratings: 300 / 300 / 300 watts at 8 / 4 / 2 ohms. test MARKBASS 2008 : bass gear CL 108 Bass Cabinet ENCLOSURE Configuration Impedance Rated power handling Inputs/Outputs Dimensions Weight Ports Covering Baffle Board Cabinet Grill Handles Feet Casters Corners Speaker Mounting GENERAL 8x10 mono, 4x10 dual 4-ohm mono, 8-ohm dual 1,200 watts mono, 600 watts dual 2x Speakon 45.25” h x 22.625” w x 18.5”d 90 lbs None, sealed box; made as 2x 4x10 Black Tolex, yellow piping Multi-ply Poplar Multi-ply Poplar Cloth 1x bar across back 2x rubber in front 2x non-swivel in back Metal, painted black 8x hex screws DRIVERS/CROSSOVER Woofers Material Magnets Tweeter Adjustment Protection Speaker Connections Crossover Impedance Options B&C 10” Glass fiber Neodymium 1” Compression Driver with Horn Tweeter On/Off NA Faston Fixed 4-ohm or dual 8-ohm MEASUREMENTS Frequency Resp, +/-10 dB 35Hz - 20KHz Tweeter ON Frequency Resp, +/-10 dB 35Hz - 3.8KHz Tweeter OFF Impedance Company Country of Origin Warranty Listed Price Street Price Test Unit Options Accessories Price as Tested Available colors Available options Parsek Srl Via Po, 52 66020 San Giovanni Teatino Chieti Italy www.markbass.it Italy 3 Year $1,399.99 $1,399.99 None None $1,399.99 Black None CONDITIONS Acquired from Markbass Dates August through November, 2008 Locales Ohio Test gear Nordy vJ5, Celinder VP4, LeCompte CBSC-4, Fender Roscoe Beck V, Dingwall Z3, Dingwall SJ4, Markbass Classic 300, Bergantino NV610 & NV215, Sadowsky SA410, Ampeg SVT-VR, Mesa/Boogie Bass 400, Sadowsky SA200, Reeves Custom 225, Elixir & Planet Waves cables. TEST SUMMARY 1-5 (unacceptable to impeccable) inhand Features Tonal Flexibility Ease of Use Aesthetics Ergonomics Tone Value onbench 3.5 3 4 4 3 3.5 3.5 4.48 Ohms Low End Frequency Resp SPL 98 Hz 104.50 73 Hz 101.25 55 Hz 96.64 4 1Hz 81.30 31 Hz 80.50 Average 92.84 A weight 84.56 77.04 69.50 49.03 46.49 65.32 C weight 104.16 100.55 95.65 79.76 77.62 91.55 Sensitivity 1 KHz 200-900 Hz Low End Response A weight 102.19 91.89 65.32 C weight 102.20 97.00 91.55 SPL 102.19 97.01 92.84 SONIC PROFILE Power Handling Portability Road Worthiness Components Hardware Wiring Covering / Finish Frequency Response Low End Response Sensitivity 4.5 2.5 3 3 3.5 4 3.5 4.5 4 4.5 Lows – not overly big, plenty of control Mids – punchy, complex, warm yet refined; stronger in upper-mids Highs – good extension even with tweeter turned off; tweeter blends in nicely In-Hand Score 3.5 average On-Bench Score 3.7 average TONE-O-METER The Markbass CL108 8x10 has immediate warmth, with great control. There are aggressive upper-mids and multiple highend personalities. CABINET TESTS MARKBASS CL 108 Chart 1 showing SPL with Tweeter On Red - 1 watt Gray - 10 watts Green - 25 watts Yellow - 50 watts Markbass Classic 108 with grill on Markbass Classic 108 with grill off B&C 10” Neodymium woofer B&C Compression Driver Back panel control plate Crossover bass gear CERTIFIED Cab Test Chart 2 showing SPL with Tweeter Off Light Blue - 1 watt Purple - 10 watts Blue - 25 watts Orange - 50 watts Low End -10dB Sensitivity 35 Hz 92.84 dB Tom Lees’ AMP LAB 2008 Markbass Classic 300 Bass Head The Markbass Classic 300 amplifier is the first amplifier from Markbass featuring a tube output section. The head cabinet is covered in black tolex, and the face of the cabinet is accented by neatly-applied (surprise!) yellow piping. A yellow logo, suspended to a screened vent arranged within an oval port on the face of the cabinet, provides a cool 3-D feature. The chassis is also black, and prominently features yellow silk-screened control labeling and a display screen positioned adjacent to the power switch. Internal Construction The tube complement of the Classic 300 consists of one ECC083 (12ax7) preamp tube, one ECC083 phase inverter tube, two ECC099 driver tubes and a sextet of KT-88 output tubes, as shown in Fig. A. The test amp was received with all new production, JJ-brand tubes. I have to admit, working on the Markbass Classic 300 felt more like working on a personal computer than a bass amp. The Classic 300 chassis may be accessed by removing nine screws from the back panel and four hex head bolts from the bottom of the cabinet. To avoid weight and stress on the chassis, the transformers are bolted to the head cab and the wiring from the transformers connects to the circuitry within the chassis using heavy duty molex connectors. In all, there are seven molex connectors that connect the power transformer, output transformer and fan to the amp circuitry. All of the molex connectors are heavy duty with the exception of the fan connector. When removing the back panel, care must be exercised as the fan, which is secured to the back panel, plugs into the chassis using a thin wires and a small, plastic connector. There is very little slack in the wires to position the panel out of the way enough to easily unplug the fan. As the fan is an important part of this amp and is computer controlled, it would be nice if this wiring were more robust. Fortunately, the front panel bearing the Markbass logo is secured to the head cab using Velcro, so a user can access the tubes without the need to remove the back panel. With reference to Fig. B, the internals of the amp consist of a main circuit board that contains the tube circuitry as well as the microprocessor circuitry (discussed below). The amp also includes a circuit board for the preamp/tone control circuitry as well as a few smaller circuit boards for the display, tuner and effects loop jacks, etc. The tube sockets are soldered directly to the main circuit board, so use care to gently remove tubes when performing tube swaps. With reference to Fig. C, as noted above, one of the circuit board contains the circuitry for the tone controls. This board is a neatly arranged collection of surface-mount components, including resistors, capacitors and operational amplifiers (opamps). The potentiometers are soldered directly to the pc board and Sextet of KT88 Output tubes ECC099 Post PI Buffer/Driver ECC083 Phase Inverter ECC083 Preamp Tube Fig. A - Chassis showing tube location ECC099 Post PI Buffer/Driver Fig. B - Gut shot Fig. C – A view of the surface mount circuitry that comprises the equalization section Fig. D – The microprocessor controller are panel mounted to the chassis. Microprocessor Control System If someone told me that they wanted to build a microprocessor-controlled, tube bass amp that has the vibe of a tube amp without the stigma that digital technology carries with certain musicians, I would say that I was talking to a person slanting at windmills. So is Marco De Virgiliis the Don Quixote of bass amps? Let’s investigate. With reference to Fig. D, the Classic 300 includes a control system that regulates key aspects of the output section of the amp. The heart of the control system is a PIC that monitors the amp and performs several useful functions. For example, the PIC automatically biases the amp for operation in one of two modes – “high fidelity” and “long life” – as selected by the Bias control on the front panel. Based upon the measurements provided by the Service Mode features of the amp, the high fidelity mode biases the tubes at approximately 60% max dissipation and the long life mode biases the tubes at approximately 40% max dissipation. From general observations, the long life setting yields slightly more harmonic distortion in normal operating ranges. The long life setting also produces slightly less output compared to the high fidelity option, given the same amp settings. For example, the chart in Fig. N illustrates an exemplary frequency response plot in the high fidelity mode (red trace), compared to the long life mode (green trace) for the same amp settings. The PIC in our test unit was equipped with Amp Management software version 1.1. This version of the management software does more than simply regulate the bias settings of the output tubes. The control system monitors the temperature inside the amp and controls the fan at one of several fan speeds as necessary to keep the amp cool. This keeps the fan noise to a minimum, such as when the higher fan speed is not necessary. Additionally, the microprocessor monitors critical functions, such as power supply voltage, tube health and speaker load connections. There was not enough time to test all of the microprocessor control functions. However, during testing, a short was (inadvertently) placed across the speaker output terminals while conducting an output power sweep. As suggested in the instruction manual, the microprocessor did correctly asses the short and safely protected the amp until the situation was resolved. While I encourage users not to try out the speaker loading protections, it is assuring to know that the protections are in place and worked well in the test amp. Fig. E – Optimally Flat Frequency Response (red) compared to All Controls at Noon (blue) measured At the Speaker Output Fig. F – EQ Settings For Optimally Flat Frequency Response Understanding The Signal Flow To get a sense for this amp, refer to the flow diagram of Fig. M, which can also be found on page 12 of the Classic 300 manual. Working from left to right, a first, fixed-gain tube stage feeds a second, variable-gain tube stage, both implemented by the single ECC083 preamp tube. The Gain knob on the front panel interacts with the variable-gain stage to provide user-adjustable gain staging to the input of the amplifier. As Fig. A shows, the preamp tube is positioned away from the remainder of the tubes and is located in the left hand corner of the chassis, near the input jack and Gain knob when looking at the front of the chassis. From this point on, the remainder of the preamp processing is implemented with analog circuitry, but no tubes. According to the flow Fig. G – Optimally Flat Frequency Response measured at Speaker Output (red) compared to DI Output Post Setting (blue) and DI Output Pre Setting (Green) Fig. H – High Frequency Sweep – High Fidelity Setting Fig. I – Mid High Frequency Sweep – High Fidelity Setting Fig. J – Mid Low Frequency Sweep – High Fidelity Setting Fig. K– Low Frequency Sweep – High Fidelity Setting Fig. L – Optimally Flat at Speaker Output (red) compared to the Effects Send (green) and Effects Return (blue) diagram in Fig. M, the output of the variable-gain tube stage drives analog buffered outputs, including an effects loop send output and a 20 dB padded tuner output. Actual measurements of our test amp shown the tuner output to be padded by 12 dB, compared to the effects send. The output of the variable-gain tube stage also feeds an analog stage that enables parallel mixing of the input signal with the effects return (if the effects loop is configured for parallel operation) or buffering of the effects return, if the effects loop is configured for series operation. The output of the buffer/ mixer drives the equalizer section. The equalizer section is set on a circuit board, seen in Fig. C. The output of the equalizer drives an additional analog gain stage controlled by the Master volume control on the front panel. The output from the Master control passes through a limiter before reaching the tube phase inverter. The EC083 tube phase inverter receives the signal from the limiter and creates two copies of the signal out of phase with each other. Each output of the phase inverter is buffered by a corresponding ECC099, which ensures that the signal has sufficient capability to drive its half of the KT-88 sextet. The Classic 300 also features a handy footswitch input on the front of the chassis for controlling a mute function. The mute affects the speaker outputs as well as the DI output. However, the tuner, effects send, and effects return are not affected by the mute function. The effects loop in the Classic 300 is implemented pre-tone stack and after the initial tube gain stage. Moreover, the effects loop on our test unit was configured for parallel operation. However, there is no effects loop bypass or control over the blending of the parallel loop. During testing of the effects loop, a wire jumper was installed between the send and return jacks, a sine wave was input into the amp, and the output of the amp was monitored at the speaker output. The signal level increased by about 6 dB with the wire jumper in the effects loop, compared to the output with no wire jumper in the effects loop. This is precisely what was expected as the wire jumper essentially mixes in parallel, two copies of the same signal, thus creating a voltage gain of 2. As with all parallel effects loops, the typical caveats apply. Users should pay attention to make sure that any utilized effect returns a signal inphase. Also, certain digital signal processors induce a delay into the signal path that may affect the quality of the effect when blended back in with the original signal. Fig. M – Flow diagram Frequency Response Referring to Fig. E, the amp was adjusted to obtain its flattest response at the speaker output, which is shown in the red trace. Fig. F shows a photo of the tone controls for that setting. The tone controls were all adjusted to noon, and that trace is shown in blue for sake of comparison. Referring to Fig. G, the speaker output frequency response for the optimally flat tone control settings shown in Fig. F (red trace) is compared to the output of the DI (blue trace) and the effects send (green trace). Each signal was normalized to 0 dB for sake of comparison. The DI output tracks the speaker output fairly well, having a frequency response that extends just a bit deeper and higher, compared to the speaker output. The effects send is discussed below. From an inspection of the frequency response sweeps shown in Figs. H-K, it appears that the equalizer section comprises four bandpass filters. These filters align pretty closely to the manufacturer-specified center frequencies of 80 Hz, 400 Hz, 800 Hz and 3 kHz, as published on page 11 of the Classic 300 manual. One nice feature of the Classic 300 implementation of active analog filtering is that the adjustments to each band are nicely distributed across the rotation of the associated control knob, providing a smooth transition as the control is adjusted. In the frequency response plots, the traces are as follows: red = set to an approximate flat response; grey = off; green = 9 o’clock; yellow = noon; orange = 3 o’clock; and blue = full on. Referring to Fig. L, frequency sweeps were conducted to compare the speaker output to the effects loop. The illustrated traces have each been normalized for sake of comparison. The red trace corresponds to the output measured across the speaker load. The green trace corresponds to the effects send at the same amp settings. The effects send signal includes a “preemphasis,” which slightly boosts the treble of this signal. The blue trace corresponds to the effects return at the same amp settings. The effects return includes a corresponding “de-emphasis” to cut the treble of the received signal by an amount that corresponds to the amount of boost added to the treble by the pre-emphasis network at the effects send. The overall response is, theoretically, a flat frequency response to a device in the effects loop. However, the pre-emphasis/de-emphasis has the advantage of potentially lowering noise that may be caused by the device in the loop. Output Power The Classic 300 performed well in power testing. During the half-power/half-hour test, the transformers remained cool as the PIC adjusted the fan speed periodically. During the output power tests, the test amp exceeded the manufacturer spec of 175 watts at 8 ohms, down to 31 Hz. At 4 ohms, our power tests measured 295 watts at 1 kHz, which is extremely close to the manufacturer rated power of 300 watts. The 2-ohm load testing yielded power measurements that were a bit lower than the 4-ohm tests, measuring 266 watts at 1 kHz. The Classic 300 has a built-in limiter, so tests were not extended up to the full 5% THD for every test frequency, as doing so did not have a material affect on the measured output power. Conclusions There is a great deal to really like about this amp. The engineers at Markbass are clearly not afraid to embrace and pioneer new and emerging technologies. The control system that Fig. N - Frequency set flat. Green trace-long life setting Red trace-high fidelity setting is used in this amp is well-implemented, and it appears that Markbass engineers were thoughtful in implementing features that add value to the overall amp from a performer’s perspective. With regard to the overall construction, I understand why Markbass chose to mount the toroidal power transformer and the large output transformer to the head cab and not the chassis. However, it appears that the transformers were bolted to the cabinet before the tolex was dry, as there is some wrinkling and bubbling around several transformer mounting bolt holes. The tolex inside the cab was also not trimmed and glued very well. The tolex lifted in several placed making inserting and removing the chassis more difficult than it needed to be. The printed circuit boards inside the amp chassis are clearly labeled and are securely mounted. However, I wish that the tube sockets were chassis-mount instead of soldered to the circuit boards. Flexure of the circuit boards due to inserting and removing tubes can cause stresses in the circuit traces on the boards. That said, no significant flexing of the circuit boards was noted on the test amp during this evaluation; just be gentle if performing tube-swapping. I am not biased either for or against commingling tube and active analog (e.g., opamp-based) circuitry that is wellimplemented – as it appears to be in the Classic 300. However, the labeling on the amp chassis, touting the amp as an “alltube amplifier” is arguably misleading. The Classic 300 does sport a preamp tube in the first gain setting section of the amp. The amp has a tube phase inverter/driver section and an all-tube output section. However, the equalizer, DI, effects loop, limiter, etc. are all analog circuitry, and from the flow diagram in Fig. M, it appears that there is no way to pass a signal from input to output that does not pass through some form of active analog circuitry. Semantics aside, however, the Classic 300 is an impressive melding of “old school” and modern technologies, and it was a strong performer in our tests. bg :