Serge Modular Rebuild
Box 2

Box 2 consists of a 106B Precision VCO, 106B Precision VCO, R6 Gate (VCA), 215B Envelope Follower, R9 Negative Slew, R6 Gate (VCA), R12 VCF, and a R2 Dual Mixer.

 

 

 

106B NTO VCO

Details on Box 1 page.

 

R6 Gate (VCA)

Additional details on Box 1 page.

This scope image shows linear operation of the VCA with a 6V control signal.

 

This scope image shows log operation of the VCA with the same 6V control signal.

 

215B Envelope Follower

The 215b is a combination preamp and envelope follower.  This board has been built for only the envelope follower.

         

 

Here are two scope images of the envelope follower in operation.

 

 

The original to my knowledge had no slew adjustment but the panel did so I added a slew control.  The first waveform is slew control fully counterclockwise and the second waveform is the slew control fully clockwise.  Note with no signal the envelope follower does go about 0.7V negative.  There is no offset adjustment.

 

R9 Dual Negative Slew

Details on Box 1 page.

 

R12 Voltage Controlled Filter

This R12 VCF has been potted in epoxy to protect the intellectual property.  Even the legends on the ICs were coated in epoxy.  What a mess and it makes it quite difficult to repair.  This board had a few loose pads that I repaired after this photo was taken.  I drilled small holes through the pad and looped 30 awg wire through the PCB to solder the pads to hold them firmly to the PCB.

         

 

This scope image shows the low pass, band pass, and high pass outputs.

 

This scope image shows the low pass, band pass, and high pass outputs with no resonance.

 

This scope image shows the low pass, band pass, and high pass outputs with the same settings and resonance.

 

This scope image shows the near self-oscillation.  The filter requires just a bit of signal input to oscillate.

 

This image shows the filter in low frequency mode filtering an ~11 Hz square wave.

 

R2 Dual Mixer

This is just a simple 4 input mixer with two instances on the PCB.

         

 

 

Construction

Two bus bars mounted on rear brackets holds all the PCBs which hinge on the bottom.  The potentiometers have to be mounted diagonally for clearance.  Three of the jacks are 1/4".

 

The power is daisy chained between all the modules except for the VCOs which have a dedicated power cable.  The twists in the power wires is to allow slack for the PCB to be rotated up.  Note that the two Gate (VCA) PCBs were broken so I epoxied extensions for mounting.

 

This side image shows the hinged standoffs and the panel wiring.  The VCOs and Mixer have a number of resistors mounted to the front panel components

 

The box is quite clean with only 4 panel screws in the front.

 

The rear just has the Serge 4 pin connector for power.

 

 

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