©2017 y Matthias Herr a │ Do ot opy or distri ute y a y ea s │ For private use o ly │ www.FONITRONIK.de

26.09.2017

Thomas Henry Voltage Controlled Crossfader/VCA (Eurorack DIY)

IntroductionBack in 2012 Thomas Henry published this circuit as a kind of

apprentice piece. One might think that this is a rahter large

module for being just a crossfader, however, it gives you a

lot of control. A lot.

You can find a detailed description of this design at the

Thomas Henry sub-forum at electro-music.com, where he

publishes most of his newer designs.

FeaturesVoltage controlled crossfade (2-in-1),

DC/AC selector for each input,

All CV inputs with attenuator,

VCA with two VC inputs and gain control

SpecificationsThe frontpanel measures: 12HP (Eurorack)

Mounting depth behind frontpanel incl. power plug: 40mm

Power consumption: TBA

BTW this is not meant as a beginners project. I do not provide

step-by-step building instructions. I just assume that you

already build quite a few projects and know how to read the

BOM and schematics.

Page 1 of 4

©2017 y Matthias Herr a │ Do ot opy or distri ute y a y ea s │ For private use o ly │ www.FONITRONIK.de

26.09.2017

Layout/Design

General mounting instructionsThis project uses two PCBs, one board with

the actual circuitry and an additional adapter

PCB carrying the front panel components.

The adapter PCB is used to mount the PCBs

to the front panel.

The PCBs are connected using two 1x10 SIL

headers/receptables with 2,54mm pitch

(.1in). Additionally you can use stand-offs.

When these stand-offs are made from metal

they will provide an additional GND path

from main PCB to adapter PCB.

Look out for something like this:

Page 2 of 4

©2017 y Matthias Herr a │ Do ot opy or distri ute y a y ea s │ For private use o ly │ www.FONITRONIK.de

26.09.2017

BOM, Overlay for Reference & Manual Wiring Guide

Manual WiringRefer to the schematics (last page in this document) for

off-board components.

M1-1

M1-2

M1-3

M1-4

M1-5

M1-6

M1-7

M1-8

M1-9

M1-10

M2-1

M2-2

M2-3

M2-4

M2-5

M2-6

M2-7

M2-8

M2-9

M2-10

Qty Value Parts

Resistors

2 10R or ferrite F1, F2

4 220R R1 - R4

1 1k R5

1 4.7k R6

2 10k R7, R8

1 22k R11

12 100k R12 - R23

2 100k (trimmer) R24, R25

2 270k R32, R33

1 330k R34

Capacitors

3 10pF (C0G/NP0) C1 - C3

2 220n (film) C10, C11

2 10uF C12, C13

8 10n C4 - C9, DC3, DC4

2 100n DC1, DC2

Semi's

2 1N4004 PD1, PD2

2 2N3906 Q1, Q2

1 LM13700 IC1

3 TL072 IC2 - IC4

Adapter PCB & Misc

7 100k (9mm

potentiometer)

R26 - R29, R29+, R30, R31

1 Socket PJ-301B J1 - J6

2 SPDT sub-mini SW1, SW2

2 1x10 SIL header female

2 1x10 DIL header male

4 M3 Stand-off + Screws

Page 3 of 4

IC1IC2IC3IC4

(R16)

AC

DC

AC

DC

100n

100n

-12V

+12V

10R or ferrite

10R or ferrite

1N4004

1N4004

LM13700

LM13700

10n

10n

TL072

TL072

10n

10n

TL072

TL072

10n

10n

10pF

100k

100k

100k

220R

100k

+12V

-12V

100k

220R

10pF

100k

100k

220R

100k

+12V

-12V

100k

220R

100k

10pF

100k

1k

220n

220n

100k

270k 4.7k

2N3906

2N3906

TL072

TL072

10n

10n

22k

10k

10k270k

330k

100k

100k

+12V-12V

CROSSFADE

GAIN CV1

GAIN CV2

+12V

+12V

-12V

IN-A SPDT sub-mini

IN-B SPDT sub-mini

OUT

EURO-1

EURO-2EURO-3

EURO-4EURO-5

EURO-6

EURO-7EURO-8

EURO-9EURO-10

1

MTA-156

DC1

DC2

F1

F2

PD1

PD2

U$5U$6

U$7U$8

4

3

1

5IC1A

13

14

16

12IC1B

7 8

10 9

11

6

C4

C5

2

31IC2A

6

5

7IC2B

84

C6

C7

2

31IC3A

6

5

7IC3B

84

C8

C9

C1

R16

R17

R20

R1

AE

S

R24R21

R2

C2

R19

R22

R3

AE

S

R25R23

R4

R18

C3

R12

R5

C10

C11

R13

R32 R6

Q1

Q2

2

31

IC4A

6

57

IC4B

84

DC3

DC4

R11

R8

R7R33

R34

R15

R14

M1-1

M1-2

M1-3

M1-4

M1-5

M1-6

M1-7M1-8

M1-9

M1-10

M2-1

M2-2

M2-3

M2-4M2-5

M2-6

M2-7

M2-8

M2-9M2-10

R26100k

R28100k

R29100k

R29+100k

J1

J2

J3

R27100k

R30100k

J4 SW1

R31100k

J5 SW2

J6

Q2

Q2

Q1

Q1

THOMAS HENRY VC-Crossfader/VCARev June 24, 2009

Redrawn schematic by Matthias Herrmann 2017

1.0

++

GND

+15V

-15V

Page 4 of 4