ASKAMPMA N
Boogie Tricks & A Fuse Fix
Hey Amp Man,
I have a Mesa Boogie Studio . 22 that I
gig with regularly. It is loud enough with
the mic setup I made for it, but I never
use the lead channel because there’s not
enough volume – there is no separate
gain knob for this channel. The tone
of the lead channel is awesome, but it
doesn’t cut over the band, so I use a
pedal over the clean for leads. Obviously
I would rather use the Boogie tone – is
there a viable mod available that will
bring the second channel up a few dB for
live use?
Rick, The Fishin’ Musician
South Lake Tahoe, CA
Hi Rick,
I saw more than a few Mesa Studio Caliber
Series amps come through my shop back
in the day. I also remember them lacking
a “Lead Master” control and thought it
might be a nice feature. I guess a few other
players thought the same thing, because
shortly thereafter I saw the Caliber “+”
series, which incorporated a Lead Master
control. Not remembering much more than
that, I pulled out the schematics to check
out the circuit differences. After hours of
careful scrutiny – okay, five minutes – I can
tell you that I believe there is a solution to
your dilemma. I’ve come up with a modification that can be executed in one of two
ways: One being a fixed level adjustment
and the other an actual “Drive Level” control. This will not replicate the exact circuit
changes between the Studio and Studio
+ series amps, as those changes are a bit
more complex, but it should yield an equally useable result. As always, if you are not
familiar with servicing a tube amp, please
have someone qualified perform this
modification. It might also be beneficial to
have the Studio . 22 schematic to reference.
Locate R241 (47k) on the circuit board. It
should be in the area of LDR4 and is associated with the Master Volume control.
This resistor is placed in the circuit when
LDR4 is energized and is used to attenuate
the signal when the amp is placed in the
“Lead” mode. Unfortunately it’s attenuating the signal a bit too much for your
needs so we will need to remedy that.
The first method is to select a value that
will attenuate the signal less, which is a
trial and error process. Start by replacing
the 47k resistor with a 68k or 82k resistor.
Play the amp at your typical settings and
see if the balance between the rhythm and
lead channels suits your needs. If the lead
is still a bit too attenuated, move up in
value to a 100k or possibly a 150k – there
is really no correct value here, it’s simply
whatever works best for you.
The alternate method is to install a Lead
Master control. This will need to be mounted on the chassis, probably on the rear
panel. As a suggestion, you might want to
try leaving enough wire length on the pot
so that you can drape the pot outside the
chassis, temporarily remount the chassis
in the enclosure and play the amp while
adjusting the pot to see if this modification
will work for you prior to drilling the chassis and mounting the pot.
Lift the side of the 47k resistor (R241) that
is connected to ground. If this is not visually verifiable, then it can easily be checked
using a multimeter or continuity checker.
Look for continuity or zero resistance
between the chassis and the ground side
of the resistor. Using a tightly twisted pair
of wires, connect one to the pad on the
circuit board and the other to the disconnected side of the resistor. Connect the
other ends of the wires to a pot. Connect
the ground wire to the CCW (
counterclockwise) terminal on the pot and the other
wire to the wiper (center terminal). A good
starting value for the pot should be a 100k
linear. If this does not yield enough of an
increase when the pot is set to its maximum position then I would try a 250k. Like
before, there is no correct value – let your
ears be your guide.
There you have it – your own customized
Studio . 22 +. Now you can get back to
pickin’ and fishin’.
Jeff,
I am playing on a 2x12 Soldano combo.
I had a 5-amp fuse blow on me several
months ago. I assumed it was an outlet
thing, so I just didn’t plug in that wall
again. Well, recently it has blown the
fuse three times with two outlets that
haven’t given me a problem until now. Of
course I replaced the fuses and it seems
to be okay. I’m just curious what would
set the fuse off – is it the outlet or the
amp? If it is simply replacing the fuse, it’s
no problem, but I just want to make sure
there aren’t any hidden issues beyond
what I know. Thanks.
Brian S. Rosen
Hi Brian,
This is an issue I’m sure I’ve covered
before, but to briefly sum up for any new
readers, this symptom is typically indicative of an intermittently shorting output
tube. You need to have the output tubes
replaced and re-biased. True, a few 20-cent
fuses are far less expensive than a new set
of output tubes, but there will be a point
when the fuse remedy will no longer work.
By waiting, you also stand an increased
chance of damage to internal components.
Hidden issue solved.
Jeff Bober
Co-Founder and Senior Design Engineer
Budda Amplification
jeffb@budda.com or www.budda.com
©2007 Jeff Bober
