TUBE DRIVE CHANNEL
- This channel and it's associated TUBE TEXTURE section contains one of
the most musical preamps and comprehensive overdrive control circuits ever included on a guitar
amplifier in this price range. Using a real 12AX7 dual triode preamp tube and direct-driving the con-
trol grid using "servo-feedback" control technology (aerospace and rocket science influence here
from our resident rocket control engineer), we can make this tube do things previously considered
impossible. The TUBE GAIN control uses “loop feedback” to control the drive level to the tube over a
very wide range. This allows for many subtle settings that are completely responsive to your indivi d-
ual playing style. Set for clean or overdrive, this preamp is warm, rich and full of natural harmonics.
The TUBE VOLUME control sets the overall volume of this channel. The noise floor of this tube cir-
cuit is exceptionally low, even at super-high gain settings.
TUBE TEXTURE SECTION
- This unique control section (including 4 front panel Switches and 4 but-
ton foot switch) affects only the TUBE DRIVE channel, and allows tailoring and customizing of sev-
eral circuit parameters important in defining your individual tone. The following discussion of these
features will help you understand this powerful section and will enable you to create your own custom
tones quickly and easily. Once you see how versatile this preamp is, you won't want to play anything
else!
FET/TUBE SWITCH
- Switches between the CLEAN and TUBE channels. This function uses noise-
less dual FET switches for studio quality operation. Pushing the switch “in” lights the LED indicator
and switches the preamp from the CLEAN channel to the TUBE channel.
MIX SWITCH
- Mixes the CLEAN and TUBE channels together. When the amplifier channel switch is
set in the FET position, engaging the MIXSWITCH adds the TUBE channel to the CLEAN channel
and lights the corresponding LED. When the amplifier channel switch is set in the TUBE position, en-
gaging the MIX SWITCH adds the CLEAN channel to the TUBE channel. As you can see, these two
function switches work together to layer the different gain stages in different ways for different effects.
Adding clean signal to an overdrive signal will generally improve definition and add a bit of sparkle to
the sound. Adding the overdrive signal to the clean signal will generally fatten up the sound and give
it a more aggressive texture. Of course, this will depend on gain and tube overdrive function switch
settings.
BOOST SWITCH
- When engaged, this function adds as much as 26 dB of additional drive, depend-
ing on the TUBE GAIN control setting. The BOOST curve tracks the TUBE GAIN control setting,
therefore the maximum boost is at the fully clockwise position of this control. This tracking function
maintains the overall “feel” of the tube channel and makes the amp more responsive to varied playing
styles.
USE CAUTION WHEN ENGAGING THE BOOST SWITCH WHILE USING HEADPHONES.
ATTACK SWITCH and ATTACK CONTROL
- This unique function could also be called a “harmonic
multiplier", and serves to increase the bite or attack of the sound. Turning the ATTACK control clock-
wise increases the ratio of the harmonic content (and overdrive components) in the waveform. This is
one way to increase aggressiveness and sustain without muddying the sound, which is a useful tool
when working with heavy overdrive and full chords. Changes will be more distinct and “in your face”
without mush or slop. This function is switched with the ATTACK switch and corresponding LED indi-
cator.
BODY and PRESENCE CONTROLS
- These two controls act as a form of shelving equalizer with
carefully chosen break points to enhance TUBE channel sound. The BODY control is especially use-
ful in creating the thick and heavy chunk (about 125 Hz) found in modem rock and alternative guitar
styles, and is also useful in thinning out a bottom heavy, muddy instrument. The PRESENCE control
will add snap and spank to the tone (about 3 kHz), al- lowing it to stand out in the mix. It will also mel-
low an over-edgy or harsh guitar. These controls have a gain range of approximately 18 dB.
SWITCH FUNCTION OPERATION
- The switches on the amplifier affect only the tube channel
(other than the obvious channel switching and mixing), allowing layering of the functions as “pre-sets"
or additional gain stages. Pushing the switch in engages the function, and the corresponding LED will
illuminate. Also provided is a 4-button footswitch. The switching logic has been designed so that the
function can be selected by either the amplifier switch or the footswitch. When either the amplifier or
footswitch button is pressed, the function will be engaged. Therefore, the same switch must be used
to de-select that function, so be sure all four of the amplifier switches are in the "out" position to en-
able the footswitch to function property. The amplifier indicator LED's and the footswitch indicator
LED's follow the actual amplifier switching function, allowing easy confirmation of the mode selected.
Summary of Contents for IVAC65-112
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