Frequency Central More VCAs Build Documentation

A compact pair of arp influenced vcas

Frequency central

Key to PCB screen print:

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

The PCB shows the correct orientation for BC557. Other transistor types can be used (eg

2N3906), but please observe the correct pinout. Please observe the correct polarity of the

electrolytic capacitors.

470R x 4

1K x 2

4K7 x 2

12K x 2

22K x 2

27K x 2

100K x 2

1M x 2

All resistors ¼ watt

metal film.

Build documentation for:

More vca

A compact pair of ARP influenced VCAs.

Bill of Materials

0uF x 4

47uF x 2

LM13700 x 1

BC557 x 2

16 pin IC socket

Alpha 9mm B100K

100K trimmer x 2

Box header x 1

Male header x 1

Female header x 1

3.5mm socket x 6

Table of Contents

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Page 1 Frequency central Build documentation for: More vca A compact pair of ARP influenced VCAs. Key to PCB screen print: p: This signifies PNP BC557 transistors. Note the correct pinout as shown by the half circles. The PCB shows the correct orientation for BC557. Other transistor types can be used (eg 2N3906), but please observe the correct pinout.
Page 2 Main PCB assembly 1. Solder all resistors 2. Solder the IC socket 3. Solder both transistors – watch the polarity! 4. Solder the box power header. Make sure the notch lines up with the screenprint legend. If in doubt, have a look at a power cable, and make sure when inserted into the header the red stripe lines up with the -12V screenprint.
Page 3 Calibration • Bias: Adjust Bias trimmer to sweet spot, ie a nice clean undistorted VCA output with no DC 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.