Frequency Central System X Amplifier Build Documentation

Based on the roland system 100m vca

Build documentation for:

System X Amplifier

Based on the Roland System 100M VCA

Frequency central

Version 2 / April 2013

B100K

A100K

CV2

CV1

Initial

Input 1

Input 2

Gain

Key to PCB screen print:

n: This signifies NPN BC547 transistors. Note the correct pinout as shown by the half circles.

p: This signifies PNP BC557 transistors. Note the correct pinout as shown by the half circles.

f: This signifies 2N5485 FETs. Note the correct pinout as shown by the half circles.

Gnd: Ground

Please observe the correct polarity of the 6 electrolytic capacitors. The 4 x 22uF are

configured in sets of 2 back to back (negative to negative).

The PCB shows the correct orientation for BC547/BC557/2N5485. Other transistor types can

be used (eg 2N3904/2N3906/BF245), but please observe the correct pinout.

Table of Contents

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Page 1 Build documentation for: System X Amplifier Based on the Roland System 100M VCA Frequency central Version 2 / April 2013 B100K B100K B100K A100K A100K Initial Input 1 Input 2 Gain Key to PCB screen print: n: This signifies NPN BC547 transistors. Note the correct pinout as shown by the half circles.
Page 2 Trimmers Bias: Adjust Bias trimmer to sweet spot, ie a nice clean undistorted VCA output with no thunk when a snappy ADSR is applied to a CV input. I do this without any audio at the inputs. The chances are that that the sweet spot is around the mid position. Linear: I tend to turn this to around fully anticlockwise.