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4 • SM-500 USER GUIDE
SM-500 FRONT PANEL FEATURES
INPUT JACKS
Both input jacks accept a standard 1/4" phone plug and both inputs can be used at the same time.
Since the two inputs are totally independent, no loss in volume or tone will occur if two instruments
are used simultaneously. Please keep in mind, however, that the Active/Passive input has five times
more gain than the Active input.
Passive/Active Input
A “passive” instrument has no built-in preamp and does not use a battery. On the other hand, an
“active” bass utilizes a battery operated preamp, either for gain, tone controls, or both. Although
labeled “passive,” the Passive input jack will work with all instruments having a maximum output of
less than 1 volt RMS. Generally speaking, try the Passive input jack first. If you hear a small amount
of distortion and the preamp clip LED is not activated, try using the Active input jack.
Note: If you want to overdrive the first TUBE stage, this can be accomplished by using an exter-
nal preamp between your instrument and the Passive input. To obtain optimum sound when try-
ing this, make sure the preamp clip LED is not activated. If this occurs, turn down your Gain
control. The first preamp tube stage is NOT monitored by the preamp clip circuit for this reason.
Active Input
The Active input jack should be used with instruments having a built-in (on board) preamp that will
produce signals over 1 volt RMS. Basses with really “hot” pickups may be more compatible with this
input. If you are using a KEYBOARD or BASS PEDAL, etc. with the SM-500, we have found the best
choice to be the Active input.
Note: Using the Active input with a passive instrument may result in a loss of high end tran-
sients. Players who roll off their high end frequencies starting at about 2kHz or who prefer a
“darker” sound may prefer to use this input.
If you hear some distortion with your active bass and are using the Active input jack, check your
instrument’s battery. Also, make sure that the preamp clip LED is not lit. Following these instructions
can save you and a service technician a lot of aggravation.
GAIN CONTROL
The Gain control adjusts the volume of the preamp section. After the tone controls, Variable Graphic
Equalizer, and Limiter are set to your liking, the Gain control should be set to where the Preamp Clip
LED barely flashes upon striking your loudest note. Then adjust the Master Volume to the desired vol-
ume level. Utilizing these controls in this manner assures the user of maximum signal-to-noise ratio
and prevents distortion caused by the preamp circuits clipping.
PREAMP CLIP LED
The Preamp Clip LED will light if any portion of the preamplifier reaches clipping or runs out of head-
room. This can be caused by the Gain control being set too high or any tone or equalizer control set
in a high boost position. To correct this condition, turn down one of the previously mentioned controls.
Note: The Preamp Clip LED indicates that at some point the preamplifier is clipping. No harm is
being done to your amplifier but, clipping of the power amplifier can cause damage to your
speakers and is not recommended.