Many undersaddle pickups have some sort of battery-powered preamp/buffer, which has an output that is compatible with a mini-mic signal.
Many have solder pads to attach a mic to the ring channel. Some provide power for the mic from the battery and others require phantom power
for the mic. The Mixpro will work with either type and can provide power for the mic (and pickup) if necessary.
The following chart shows some common combinations and requirements:
* when used with 3ft stereo cord
** requires Strapjack Plus 4-pin stereo jack. See enclosed RTS supplement
*** you may find that an acceptable level of crosstalk is achievable with a high-output ceramic piezo pickup
4.2 Crosstalk: Crosstalk is interference or "bleed" between two signals within a common shield, such as a stereo guitar cable. This common
problem is often encountered when a high-impedance piezo pickup is mixed with a low-impedance active source, such as a mini-mic. The bleed
signal from the mic mixes in the cord with the pickup signal and appears in the pickup channel. The higher the amount of amplification (gain)
required for the pickup (and longer the cable), the more of the mic signal will be present in the pickup channel. It is common to encounter 25% to
50% mic bleed into a clean pickup channel.
Often the best relative phase for a particular pickup and a mic will require that the actual mic channel be out of phase with the phase of the bleed.
This causes frequency response problems with the mic and leads to a confusion of the phase relationship between pickup and mic. This causes
unpredictable frequency cancellation.
Worse, it is often impossible to get the mic bleed in the pickup channel low enough to allow it to be turned up without the mic starting to feed
back! The only adequately clean way to send a high-impedance piezo pickup and a mic signal side by side down one cord is to have some sort of
active buffer for the piezo on the guitar itself.
4.3 Buffer Jack: The Buffer Jack preamp is phantom-powerable by the Mixpro and provides an input for the mic on the ring and an all-discrete
class A preamp/buffer for the piezo on the tip. The Buffer Jack eliminates crosstalk, preserves the integrity of both signals and gets the batteries off
of the guitar. It is available from L.R. Baggs.
4.4 Setting the Gain: Gain is not volume. Gain is the amount of amplification
that is applied to an input signal to boost it to a useful level. To accommodate a
wide range of pickups, active devices and such, the Mixpro has adjustable gain.
The idea is to adjust the gain to find a window between hiss and distortion.
For instance, if you are using a low output passive pickup such as the Ribbon
Transducer, and you fail to turn the gain way up, you will need to turn the PA up
so high to hear the pickup that there will be a lot of hiss. Conversely, if you plug
in a high output active pickup and do not turn the gain way down, there will be
massive distortion. The Mixpro is so quiet that the gain window is pretty wide.
But there is a smaller sweet spot within that window.
With everything plugged in and turned on, play your instrument very hard. Turn
the gain trim up (clockwise) slowly while playing until you begin to hear some
distortion, then back the gain off (counter-clockwise) until the distortion just
disappears. This setting will be the richest sounding and the most quiet. Once
you have determined your preferred setting, we recommend that you leave the
gain control alone. Do not use the gain control as a volume control. Using it in
this manner will vary the character of your sound as you adjust it up and down.
Pickup
Mic + Ribbon
Transducer
Mic + LB6
Mic + Hex Pickups
Mic + Matrix
Mic + B-Band
Mic + Magnetic Pickup
Contact P
Ribbon Transducer
Onboard Buffer Required?*
Yes -- use Buffer Jack or RTS
preamp**
No -- but best with Buffer
Jack***
No
Yes -- use Matrix preamp or
Buffer Jack
Yes -- use B-Band preamp
only
No
No
Pickup
Ground
Hot
Mic
Ground
Hot
3rd wire
