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becomes greater than .7V P/P, then the diodes D1 and D2 begin to turn on.
This brings R14 into the gain equation as well. Now you have an Rf = R14 in
parallel with R16. This brings the overall gain down to less than .1, now the
amplifier is working as an attenuator. The best part of the diodes is that they
don't just "snap" on, they have some variance before they are on fully, so this
creates what is called "soft clipping". This soft clipping is a close relative of
distortion, but much more tolerable. This soft clipping circuit prevents a person
from overloading amplifiers or speakers by preventing high volume levels from
exiting the mixer.
The output from the microphone amplifier is then mixed in with the line level
audio as well. Before exiting the MX-5 though, the output of U1:A and U1:B is
controlled by the master level control, R6.
The power supply for the MX-5 is simple enough, it consists of a 9-18VDC
input or battery, and a voltage divider to provide for a split supply. The spilt
supply is necessary to operate op-amps as we have done. C9 is used to filter
out most of the noises that may be present in your power supply since they
can infiltrate the audio.
MX-5 Page 6
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