MK-1 Preamp Anatomy (EQUALIZER STAGE)

EQUALIZER SECTION

When the toggle switch is on the ACTIVE position, the mixed (Bridge+Neck) signal, once  amplified by the input stage (IC1)  is routed to the equalizer section of the preamp.

The signal processing is based on a classic 2 ACTIVE cascade BAXANDALL filters .

This is done apaarently for minimize the interaction of hosting a three band filters on a single active unit. 

To sum up here is the serial sequence of the operations:

• 1st  Half of IC2 is decoupling the signal coming from the BALANCER potentiometer

then feeding the

• 2nd Half of IC2 , providing the ACTIVE BASS+TREBLE Equalization filter

feeding the

• 1st  Half of IC3 , providing the ACTIVE MID range Equalization filter

The 2nd Half of IC3 is doing....NOTHING.

:-)

At the end of the equalization process, the signal is sent back to the TOGGLE SWITCH and finally routed to the 500k linear Volume potentiometer.

Schematic of the BASS - TREBLE Equalization stage rev-engineered:

Schematic of the MID Equalization stage rev-engineered:

In the next post We will model all the Equalizer curves to see and prove how the pream behaves also in respect of  the specifications declared semi-officially by the Factory.
If We will have a match this will mean the reverse engineering is mostly correct and We have a solid base to start with for applying future enhancements !

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KKPRINCE
:-)