ER-VCA2-01

Features

• Eurorack card
  • 3U tall
  • 6HP wide
  • 3 card set
• Dual Voltage Controlled Amplifier (VCA)
• LM13700 based
  • LM13700 Operational Transconductance Amplifier
• Pots adjust between input and Mod jacks
  • CW - output is fully controlled by MOD jack
  • CCW - output is not controlled by MOD jack
• +/- 12V Power, 10-pin power connector

Credits

• Based on HAGIWO's LM13700 Dual VCA - Modular Synth Made for 550 Yen

Connectors

J1 - Daughtercard Pots

• POT1 = RV1 = Modulation Adjust Channel 1
• POT2 = RV2 = Modulation Adjust Channel 2

J2 - Daughtercard Eurorack Power

J3 - Daughtercard Control Card Jacks

• Controls card J3 = OUT1 (bottom left jack)
• Controls card J4 = OUT2 (bottom right jack)
• Controls card J5 = MOD1 (middle left jack)
• Controls card J6 = MOD2 (middle right jack)
• Controls card J7 = IN1 (top left jack)
• Controls card J8 = IN2 (top right jack)

Reference

• Dual Log/Linear VCA - Article by Ray Wilson
  • Has adjustment procedure
• Design a Eurorack “Vintage VCA” with the LM13700 - Electric Druid

Checkout

Rev 2

• Updated Controls card
• Using Rev 1 Analog daughtercard
• Headers line up
• Tested as set
• View from rear side

• Output clipping below 0V, missing 510K resistors between LM13700 out and Transistors set
  • Add 510K on back side U2-12 to U2-13
  • Add 510K on back side U2-4 to U2-5
  • Works much better, no clipping
• Created rev 3 daughtercard that incorporates resistors

Rev 1

• Headers between cards do not line up
  • Fix on Controls card
    • Make Rev 2 Controls card
    • Move down bottom header J2 to match daughtercard
  • Cut off 0.1" of controls card using vice/hacksaw
  • Use female headers on bottom of daughtercard
  • Use right angle pin header pins to connect to pads (remove plastic)
• Not shipping this version on Tindie

Assembly Sheet

• Two revs of Daughtercard
  • Rev 1 shipping (ships on Tindie starting 2022-11)
  • Rev 2 future version which will incorporate resistor rework
• Two revs of Controls card
  • Rev 2 ships (Tindie)

Rev 2 Daughtercard, Rev 2 Controls Card

• Future version
• ER-VCA2-01 Rev 2 Controls Card Interactive BOM
• ER-VCA2-01 Rev 2 Daughtercard Interactive BOM
• ER-VCA2-01 Rev 2 Assembly Sheet - Includes rework to add resistors

Rev 1 Daughtercard, Rev 2 Controls Card

• Current version on Tindie
  • Requires 2 additional resistor on rear of daughtercard
• ER-VCA2-01 Rev 2 Controls Card Interactive BOM
• ER-VCA2-01 Rev 1 Daughtercard Interactive BOM - Requires rework to add resistors
• ER-VCA2-01 Rev 2 Assembly Sheet - Includes rework to add resistors

Rev 1 Daughtercard, Rev 1 Controls Card

• ER-VCA2-01 Rev 1 Assembly Sheet - Requires rework to add resistors
• ER-VCA2-01 Rev 1 Daughtercard Interactive BOM - Requires rework to add resistors