Full Text Searchable PDF User Manual
56
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Tom
Bowlu
s
Markbass
Classic 300
CL 810
bass
gear
TEST
!
TEST
!
G
asoline/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
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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 4/8-
ohm 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 JJ-
brand 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 2-
ohm loads. Our tests largely confirm these
published figures. While the preamp
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.
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 300-
watt 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!
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the LMII. When you compare them back-
to-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 pre-
gain 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 heavy-
handed
fingerstyle
and
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
has
definitely
succeeded.
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 all-
tube 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.
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, Mid-
Low, 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:
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!
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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
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MARKBASS
2008
CLASSIC 300
Bass
Head
:
G E N E R A L
Company
Parsek Srl Via Po, 52
66020 San Giovanni Teatino
Chieti Italy www.markbass.it
Country of Origin
Italy
Warranty
3 Year
Listed Price
$2,599.00
Street Price
$2,599.00
Test Unit Options
None
Accessories
None
Price as Tested
$2,599.00
Available colors
Black
Available options
Footswitch to control mute
inhand
onbench
TEST SUMMARY
1-5 (unacceptable to impeccable)
Features
4
Tonal Flexibility
3.5
Ease of Use
4
Aesthetics
3.5
Ergonomics
4
Tone
4
Value
4
SONIC PROFILE
Lows – taut, controlled, warm; not
overly big
Mids – focused, punchy; aggressive;
nice complexity and texture
Highs – average brightness, but
cranking the pre-gain adds high-
end excitement
Chassis
4
Vents and cooling
3
Knobs / Lights
4
Finish / Handles
4
Jacks / Sockets
4
Pots / Switches
3.5
Chassis Layout
3
Components Resistor/Cap 3
PCB / Power Transformer 3.5
Solder / Dress
4
Internal / Overall Build 3
Output Power Rating 4.5
Portability
3
Roadworthiness
4
Ease of Repair
3
Warranty
3
Quality per price
4
C O N D I T I O N S
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.
The Classic 300 delivers vintage
midrange punch, and a hint of
grit, with more control and
wider range of tones than
vintage counterparts
TONE-O-METER
In-Hand Score
3.9
average
On-Bench Score
3.5
average
E N C L O S U R E
Material
Wooden head cabinet
Getting inside
4 bolts, 9 screws, 7 cable connectors
Time to assemble
5 minute
Time to disassemble
5 minute
Dimensions
19 5/8” w x 12 3/8” d x 11 9/16”h
Weight
50.8 lbs
Rackable
No
P R E A M P
Inputs
1/4” jack
Mode
Tube preamp, solid state EQ
Tubes
2 Ecc083, 2 Ecc099
Input Impedance
340 kOhm
EQ Type / Features
4-band
/
Bandpass EQ
Compressor/Limiter
Non-user adjustable limiter
Potentiometers
PC mount
DI Output
Switchable pre/post EQ, level
control on front panel, ground lift
Effects Loop
Pre-EQ send
Additional Features
Footswitchable mute
P O W E R A M P
Mode
Tube
Tubes
6 KT-88
Power Supply
Toroidal transformer
Outputs
1 Speakon for 8/- ohm, 1 for 2-ohm
Impedance Options
8/4, 2-ohms
Pre/Power PCBs
4 printed circuit boards
Power Transformer
Toroidal
Output Transformer
Taps for 2-ohm and a 4/8-ohm tap
Cooling System
Fan
Line Voltage Options
120VAC
Line Voltage Setting
User-variable
M E A S U R E M E N T S
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
-74 dB
120 Hz
-87 dB
180 Hz
-78 dB
EQ Controls Flat, Idle Noise 200 Hz - 1 KHz
-74 dB
1.1 KHz - 20 KHz
-87 dB
EQ Controls Up, Idle Hum
60 Hz
-94 dB
120 Hz
-81 dB
180 Hz
-75 dB
EQ Controls Up, Idle Noise
200 Hz - 1 KHz
-89 dB
1.1 KHz - 20 KHz
-97 dB
H A L F P O W E R S T R E S S
1/2 Manufacturer Spec - Tested at 150 W into 4 ohms
TEMPERATURE
0
F
Idle
5min
15min
30min
Front Power Switch
75
80
90
96
Front Input Jack
74
80
86
93
Rear Power Jack
74
81
90
104
Rear Speaker Jack
77
83
96
98
Power Transformer
77
95
105
116
Output Transformer
76
88
94
119
Middle KT88 Retainer
95
117
155
144
Fan noise
Ambient
52 dB SPL
Fan Low
57 dB SPL
Fan High
64 dB SPL
Signal interrupt (sec)
0
0
0
0
Thermal shutdown (sec)
0
0
0
0
POWER
TESTS
bass
gear
POWER
CERTIFIED
8 ohms 1kHz
199 watts
MARKBASS
CLASSIC 300
F U L L P O W E R O U T P U T
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
199 Watts
295 Watts
266 Watts
Input Signal
1.0 Volts
1.0 Volts
1.0 Volts
Voltage drop
0.7 Volts
0.6 Volts
1.0 Volts
G STRING @ 98Hz
Power
199 Watts
288 Watts
263 Watts
Input Signal
0.6 Volts
1.0 Volts
1.0 Volts
Voltage drop
0.7 Volts
0.9 Volts
1.0 Volts
D STRING @ 73Hz
Power
195 Watts
286 Watts
263 Watts
Input Signal
0.6 Volts
1.0 Volts
1.0 Volts
Voltage drop
0.6 Volts
0.8 Volts
0.7 Volts
A STRING @ 55Hz
Power
193 Watts
288 Watts
251 Watts
Input Signal
0.6 Volts
0.9 Volts
0.6 Volts
Voltage drop
1.0 Volts
0.4 Volts
0.9 Volts
E STRING @ 41Hz
Power
196 Watts
272 Watts
251 Watts
Input Signal
0.7 Volts
0.8 Volts
0.4 Volts
Voltage drop
0.4 Volts
0.4 Volts
1.1 Volts
B STRING @ 31Hz
Power
193 Watts
278 Watts
244 Watts
Input Signal
0.6 Volts
0.8 Volts
0.4 Volts
Voltage drop
0.6 Volts
0.5 Volts
0.2 Volts
Manufacturer ratings: 300 / 300 / 300 watts at 8 / 4 / 2 ohms.
2 ohms 1kHz
266 watts
4 ohms 1kHz
295 watts
K E Y T O T E S T S
Half Power Stress:
How well does this head handle the heat?
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.
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MARKBASS
2008
CL 108
Bass
Cabinet
:
G E N E R A L
Company
Parsek Srl Via Po, 52
66020 San Giovanni Teatino
Chieti Italy www.markbass.it
Country of Origin
Italy
Warranty
3 Year
Listed Price
$1,399.99
Street Price
$1,399.99
Test Unit Options
None
Accessories
None
Price as Tested
$1,399.99
Available colors
Black
Available options
None
inhand
onbench
TEST SUMMARY
1-5 (unacceptable to impeccable)
Features
3.5
Tonal Flexibility
3
Ease of Use
4
Aesthetics
4
Ergonomics
3
Tone
3.5
Value
3.5
SONIC PROFILE
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
Power Handling
4.5
Portability
2.5
Road Worthiness
3
Components
3
Hardware
3.5
Wiring
4
Covering / Finish
3.5
Frequency Response 4.5
Low End Response
4
Sensitivity
4.5
C O N D I T I O N S
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.
The Markbass CL108 8x10 has
immediate warmth, with great
control. There are aggressive
upper-mids and multiple high-
end personalities.
TONE-O-METER
In-Hand Score
3.5
average
On-Bench Score
3.7
average
E N C L O S U R E
Configuration
8x10 mono, 4x10 dual
Impedance
4-ohm mono, 8-ohm dual
Rated power handling
1,200 watts mono, 600 watts dual
Inputs/Outputs
2x Speakon
Dimensions
45.25” h x 22.625” w x 18.5”d
Weight
90 lbs
Ports
None, sealed box; made as 2x 4x10
Covering
Black Tolex, yellow piping
Baffle Board
Multi-ply Poplar
Cabinet
Multi-ply Poplar
Grill
Cloth
Handles
1x bar across back
Feet
2x rubber in front
Casters
2x non-swivel in back
Corners
Metal, painted black
Speaker Mounting
8x hex screws
D R I V E R S / C R O S S O V E R
Woofers
B&C 10”
Material
Glass fiber
Magnets
Neodymium
Tweeter
1” Compression Driver with Horn
Adjustment
Tweeter On/Off
Protection
NA
Speaker Connections
Faston
Crossover
Fixed
Impedance Options
4-ohm or dual 8-ohm
M E A S U R E M E N T S
Frequency Resp, +/-10 dB
35Hz - 20KHz Tweeter ON
Frequency Resp, +/-10 dB
35Hz - 3.8KHz Tweeter OFF
Impedance
4.48 Ohms
Low End Frequency Resp SPL
A weight C weight
98 Hz
104.50
84.56
104.16
73 Hz
101.25
77.04
100.55
55 Hz
96.64
69.50
95.65
4 1Hz
81.30
49.03
79.76
31 Hz
80.50
46.49
77.62
Average
92.84
65.32
91.55
Sensitivity
SPL
A weight C weight
1 KHz
102.19
102.19
102.20
200-900 Hz
97.01
91.89
97.00
Low End Response
92.84
65.32
91.55
CABINET
TESTS
bass
gear
Cab Test
CERTIFIED
MARKBASS
CL 108
Sensitivity
92.84 dB
Low End -10dB
35 Hz
Chart 1 showing SPL with Tweeter On
Red - 1 watt Gray - 10 watts
Green - 25 watts Yellow - 50 watts
Chart 2 showing SPL with Tweeter Off
Light Blue - 1 watt Purple - 10 watts
Blue - 25 watts Orange - 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
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
2008 Markbass
Classic 300
Bass Head
AMP
LAB
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
ECC083
Preamp Tube
Sextet of KT88
Output tubes
ECC083
Phase Inverter
ECC099 Post PI
Buffer/Driver
ECC099 Post PI
Buffer/Driver
Fig. A - Chassis showing tube location
Fig. B - Gut shot
Fig. C – A view of the surface mount
circuitry that comprises the
equalization section
Fig. D – The
microprocessor
controller
Tom Lees’
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.
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. 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
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
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 in-
phase. 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. L – Optimally Flat at Speaker Output (red) compared to the
Effects Send (green) and Effects Return (blue)
Fig. K– Low Frequency Sweep – High Fidelity Setting
Fig. J – Mid Low Frequency Sweep – High Fidelity Setting
Fig. I – Mid High Frequency Sweep – High Fidelity Setting
Fig. M – Flow diagram
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 well-
implemented – as it appears to be in the
Classic 300. However, the labeling on the
amp chassis, touting the amp as an “all-
tube 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.
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 “pre-
emphasis,” 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
b
g
:
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
Fig. N - Frequency set flat. Green trace-long life setting
Red trace-high fidelity setting