Carr Rambler Amp Manuel d'utilisateur télécharger pdf (Page 5)

PRESENCE SHIFT – Only available on Mesa Boogie Mark IV’s with a “Pull Shift” on

the Presence knob (USA LEAD and USA RHYTHM). When engaged, it normalizes

the amount of high frequencies produced in the power section. PRESENCE

will be more eective and will act on a higher frequency range. Note that it

may result in volume reduction since the negative feedback is increased which

lowers the loop gain.

PRESENCE FREQ – Alters the center frequency of the amp’s PRESENCE control.

DEPTH FREQ – Alters the center frequency of the amp’s DEPTH control.

POWER TUBE TYPE – Selects a specic power tube type and sets DYNAMIC

DAMPING. This doesn’t change the sound in the same way actually

changing tubes would because it only changes the distortion curves,

not the transconductance. In real amps, an EL34 has more than twice the

transconductance of a 6L6. This means the plate current will be twice as great

for a given grid voltage. This makes EL34s sound “more midrangey” and 6L6s

sound “tighter’”or “fuller”.

DYNAMIC DAMPING – Adjusts the plate characteristics. Defaults to the

appropriate value when an amp model or power tube type is selected.

POWER TUBE BIAS – Sets the quiescent operating current of the virtual power

tubes. Increase it to reduce crossover distortion and vice-versa. Lower values

approach pure Class-B operation. Higher values approach pure Class-A.

NEGATIVE FEEDBACK – Controls the amount of negative feedback in the power

amp. The feedback decreases output impedance, causing the amp to react less

to the speakers (”damping”). Higher values give a brighter, tighter, punchier

sound but can be harsh at very high MASTER levels. Lower values give a

smoother, loose and gritty sound and feel.

TRIODE1/2 PLATE FREQ – Sets the cuto frequency of the plate impedance for

the next-to-last (triode 1) and last (triode 2) triode in the chain, which allows

you to control the buzziness that sometimes occurs with higher gain settings.

The capacitor across the triode’s plate resistor is used to smooth the response

and reduce noise. You can adjust the amount of capacitance, and the resulting

frequency. Lowering the frequencies dials out sharpness and “zz”, making the

tone smoother.

If you are right on the edge of breakup the triode hardness is very powerful

as it controls the harmonic series. Higher values will cause the overtone series

to have a less steep decay and will increase perceived “sparkle”. Together with

PREAMP BIAS you can control how chimey and “round” the tone is.

PWR AMP BIAS – Controls the amount of power tube mismatch by adjusting

the oset voltage of the virtual power amp. A value of zero produces nearly

symmetrical clipping which will produce very little even harmonics. Higher

values will produce increasingly asymmetrical clipping which increases the

amount of even harmonics. Small amounts of even harmonics can make the

power amp distortion sound “warmer” and more bell-like while higher amounts

will give a “fuzzier” tone.

PWR AMP HARDNESS – Controls the hardness of the virtual power tube grid

clipping.

MV LOCATION – Location of the Master Volume.

PRE-PI – Before the phaser inverter (most amps).

POST-PI – After the phase inverter (AC types). This causes the PI to clip

before the grids (if the MV is less than full). This creates a very aggressive and

open sound.

PRE-TRIODE – Amp types based on Hiwatt models.

Setting NEGATIVE FEEDBACK to 0 disables negative feedback and replaces

the PRESENCE control with HI CUT. DEPTH is also disabled since it only aects

negative feedback.

POST-PI MV turns a lot of mid-gain amps into ripping monsters. The only

caveat is that, like a real amp, the more you turn the MV down the less

eective Presence and Depth become (since the loop gain is reduced).

Increase POWER TUBE BIAS to thicken clean tones; reduce it to add aggres-

sion to high-gain sounds. A value of 0.5 or so will run the virtual tubes at

around 75% of full power and clean tones will sound warmer but you will

lose that sizzle on high-gain tones.

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Carr Rambler Amp Manuel d'utilisateur Page 5

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