also will be a proper impedance match and allow the maximum power and headroom.
One 4 Ohm cabinet (such as a 2x12 using 8 Ohm speakers wired in parallel) should be connected to one of
the two 4 OHM SPEAKER Outputs.
A 2x12 with 8 Ohm speakers wired in series – presenting a 16 Ohm Load – should be connected to the 8 OHM
SPEAKER Output. The maximum power will not be possible in this scenario, but it will be a mismatch in the
safe direction.
We use predominantly 16 Ohm speakers wired in series for our 2x12 cabinet production so that players can
combine two 8 Ohm 2x12 cabinets – one in each of the 4 OHM SPEAKER Outputs – as a way of getting 4x12
performance and coverage in an easier-to-carry weight (and bulk) range and still get the same full-rated power
from the amplifier.
Some prefer the sound and feel of the 8 Ohm speakers themselves, citing more bold punch in the midrange
and top end that remains more attached and cohesive. In a 2x12 scenario (two 8 Ohm Speakers wired in parallel
at 4 Ohms total Load), and with a single such cabinet, use the 4 OHM SPEAKER Output even though the full
rated power will not be available. Most players find it is more than enough headroom and power and accept the
trade-o in power for the dierence in voicing compared with its 16 Ohm-loaded 8 Ohm 2x12 counterpart. They
are both great-sounding cabinets, it’s just what you need and want in regard to overall voicing and power. The
standard 16 Ohm-loaded/8 Ohm version will be more scooped in the midrange and harmonic laden, excelling
at rock and metal sounds, while the Custom Order 4 Ohm version will be more filled-in regarding midrange,
sound rich and balanced, and excel in most other musical genres with a bit more punch and cohesive, attached
top end.
NOTE: If you decide to order a 2x12 with 8 Ohm speakers wired in parallel – for a 4 Ohm total impedance –
remember that you will not be able to combine that with another cabinet as the amplifier is not designed to
accommodate impedance loads below 4 Ohms.
MESA 4x12 cabinets can be treated just like the 1x12 Extension Cabinets, as they also present a total impedance
load of 8 Ohms (each pair wired in series then the pairs combined in parallel to achieve 8 Ohms total). Remember,
it is not the number of speakers, but rather the total impedance that is important for your amplifier’s output
transformer.
For more information and a recap of speaker impedance, wiring styles, and total loads, see the Speaker Wiring
section in the rear of this manual.
SIMUL-CLASS/CLASS A (OUTPUT POWER)
This switch determines the output power and its wiring style created in the power amp section of your amplifier.
Selecting SIMUL-CLASS (upper position) brings on-line all four of the output tubes and the full 75 watts of power.
SIMUL-CLASS utilizes two of the four octal tube sockets wired in Class AB to produce optimum power and
headroom with the most punch and authority possible, while the other two octal sockets are wired Class A,
producing a lower threshold where clip begins, a smoother transition into clip and a warmer, less forward
character. Combining these two types of wiring and operating classes creates a superbly musical and harmonically
rich character that filters out the harsher artifacts associated with Class AB, while the more pleasing elements
are accentuated and showcased from the Class A-wired tubes.
The SIMUL-CLASS mode will provide the greatest headroom for clean work, the tightest tracking low end and
articulation for heavy gain work, and overall, a round, robust, and rich, three-dimensional sound. We consider
this the “normal” operating mode, as it delivers the best tonal attributes and musical balance from this innovative
way of wiring a 4-tube “100-watt” output section. The SIMUL-CLASS setting will round out, optimize, and propel
your preamp sounds in the most accurate and authoritative way possible, and the result is a huge, wide,
harmonically complex, and captivating sound.
PAGE 27
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