Building the VCA Tile

Notes:

  • Latest version of the PCB has all surface-mount components on one PCB, and a separate smaller PCB for the power components. Values have been corrected on the PCB. Build guide is here: http://syinsi.com/projects/building-new-vca-tile/
  • The following picture shows where values are changed from what’s printed on the PCB (in yellow).
  • The circuit is a mostly faithful copy of the Sims 13700 VCA as described in his paper.
  • Component values changed for a 0-5V CV range.

 


BOM:

QTY
VALUE
DEVICE
PACKAGE
NOTES
Source
Source
33.5mm JackTHONKICONN style
6100nCapacitorC603
110uCapacitorC805
1120pCapacitorC805
21uCapacitorC805
1330pCapacitorC805
1390pCapacitorC805
2M7DiodeDO214AC1n4001-1n4007
1TL072Opamp (Dual)SO08
1LM13700OTASO16
12n3906PNP TransistorSOT23
210kPotentiometer9MM SNAP-IN, no panel flangeTayda, Alpha, Panasonic
1100kResistorR0805
110kResistorR0805
11kResistorR0805
11MResistorR0805
220kResistorR0805
130rResistorR0805
233kResistorR0805
162kResistorR0805
110kTrimpotTC33X
11kTrimpotTC33X
22 pinFemale Pin Header
22 pinFemale Pin Header
1"Male"Tile power connector

Schematic:


Build Instructions:

If necessary, separate panels carefully by gently flexing and twisting back and forth, ensuring that they break cleanly at the “mouse bites”. File the leftover tabs down until flush with the edge of the panel or PCB.

Clean PCB with isopropyl alcohol to remove any manufacturing residues.


Begin by soldering the surface mount devices.

Ensure the diodes and ICs are in the proper orientation.

 


Add the male and female headers.

It doesn’t matter which PCB get the male or female headers, just that they’re on the right side. The sides with the surface-mount components face the same direction (downwards when module is installed), and the PCB with most of the components is on the “bottom”. Use this picture as a guide.

 


Trim the top header pins on both sides if they interfere or make contact with the pots (they shouldn’t).

Solder the pots and jacks to the PCB. It’s useful to use the front panel to ensure they’re soldered flush and aligned.

When attaching the panel, make sure they are oriented in the right direction. The power cable should be “up” towards the top rail, and the lettering on both sides should be in the same direction.


Testing and Configuration:

Check all connections for shorts, particularly solder-bridges between IC pins.

Before applying power, check for shorts on the tile power connector.

Set both trimmers to the middle position.

Apply power and check that none of the components are getting hot.

 

Connect an audio source and a CV source and check that these and the knobs work work.

Trimming:

The left trimmer adjusts the gain, and the right adjusts the CV bleed-through. Both set to the middle position is okay if you don’t have the ability to trim.

To adjust gain (left trimmer):

  • Patch audio signal into audio input.
  • Patch 5V into CV input.
  • Turn “In Level” and “CV Amount” to full.
  • Connect voltmeters or oscilloscope channels to the audio input and audio output.
  • Adjust the trimmer so that both levels are close to equal.

To adjust CV bleed-through:

  • Remove cables from input.
  • Patch a fast square-wave (>100Hz) into CV input.
  • Turn “In Level” and “CV Amount” to full.
  • Listen to the audio output. You will need to turn it up (and don’t forget to turn it down afterwards!)
  • Adjust the trimmer to reduce the tone induced by the CV. It won’t be removed completely.

Done!