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Expandable
Modular Audio Mixer
for any channels
P1
P21

P12

P13

R15 R16

R18 R9 R8

R19
R10
R14

1

2

Printed Circuit Boards for instrument and hi-fi preamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Top and bottom PCBs and overlay of stereo jFET preamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Top and bottom PCBs and overlay of simple dual OpAmp preamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Top and bottom PCBs and overlay of INA217 microphone preamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Two single OpAmp - stereo universal preamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Two single OpAmp - stereo low noise universal preamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Top and bottom PCBs and overlay of power filters (ver.3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Top and bottom PCBs and overlay of power filters (ver.2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Top and bottom PCBs and overlay of power filters (ver.1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Top and bottom PCBs and overlay of power filters (ver.4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Top and bottom PCBs and overlay of power filters (ver.5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Switch module for preamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
The PCB of power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Variable line output board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Simple headphone amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Balanced headphone amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Images and Picasa galleries about the prototype of this project . . . . . . . . . . . . . . . . . . . . . . 38
Modelling the PCBs of this project before manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Examples how to setup the 3 stages of mainboards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
The selectable prototype of jFEt and OpAmp projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Audio mixer with jFET and OpAmp preamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Microphone preamp with INA217 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

5

6

-15V
1
2
3
4
5
6

A

GND

7
8
9
10
11
12

A

+15V

GND

Header 6X2A

+15V a1

R9

1
8
P1
1.6kA

6.8K

3
2

C12
47uF 60V

C13
47uF 60V

R13
2.2K

GND

REF

R4
1K

GND
R7

RG_1
RG_2

INA217 AIP

V_OUT

R10
1M

GND

C11 10uF

J1

R11
100K

7

C
6

P2
47kB

U3
OPA137
2

4

3

-15V a2

GND

GND

+15V a2

10uF
47uF 60V

R12
470
C14
100nF

GND

2
C10
3

6

V_IN-

R14
2.2K

U2
OPA137

470

6

V_IN+

R5
1K

C5

C15

Input Jack 6.3

1
2
3
4
5
6

B

7
8
9
10
11
12

GND

GND

R15
100K

10uF

Output

C

Bal In 1 GND

GND

+48V

P4

Header 6X2A

Header 6X2A

12
11
10
9
8
7

6.8K

U1

R1
47K

6
5
4
3
2
1

8
R8

5

7

D2
1N4148

4

R6

B

D4
1N4148

0
1
2
3
4
5

D1
1N4148

4

-15V a1

D3
1N4148

P3

Bal In 2

GND

P6

D

1
2
3
4
5
6

GND

7
8
9
10
11
12

Title

GND

Header 6X2A

Mic and instrument preamp with
assimatrical/simmetrical inputs

Size

D

Number

Revision

A3

http://custompcb.blogspot.com/
http://diyguitarpa.blogspot.com/

Date:
File:

1

2

3

11/6/2011
Sheet of
D:\!Works\..\INA217-MicPreamp-MOD.SchDoc
Drawn By:

4

5

6

The Picasa album about prototype testing

Bill of Materials
Comment

OPA137
Res2
Res2
Res2
Res2
Res2
Res2
Res2
Res2
Cap Pol1
INA217AIP
1N4148
Cap Pol1
Header 6X2A
Input Jack 6.3
Pot Mono
Pot Mono
Cap

Mainboards for any channels expandable modular audio mixer . . . . . . . . . . . . . . . . . . . . . 31

Schematic, BOM and PCB for any channel mixer mainboard stage1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Schematic, BOM and PCB for any channel mixer mainboard stage2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Schematic, BOM and PCB for any channel mixer mainboard stage3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4

P5

Schematics and BOM for expandable mixer project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Schematic and BOM of cheap microphone preamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Stereo jFET guitar (instrument, effect) preamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Stereo dual OpAmp instrument or audio preamplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Stereo circuit with 2 single OpAmp, instrument and audio preamplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Stereo low noise 2 single OpAmp instrument or hi-fi preamplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Schematic and BOM of power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Schematic and BOM of power filter module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Schematic and BOM of variable line output module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Schematic and BOM of simple headphone output module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Schematic and BOM of balanced headphone output module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3

V-

English blog and PCB order: http://custompcb.blogspot.com/
Hungarian blog and PCB order: http://diyguitarpa.blogspot.com/
The Youtube Channel • Picasa gallery • Email: gitarfogas@gmail.com

Schematics and Bill of materials for modular mixer
Schematic and BOM of cheap microphone preamp

7

This project is similar than my “Modular audio mixer”, but the another is made for 4 or 8 channel mixers only, this
mixer is expandable to any inputs and any outputs. The input preamplifiers of this project is same than in the
simple modular mixer, but I have new line output and headphone amplifier modules. With this mixer, have 3 stages
of mainboards. The first is the required only, this is 4 channel inputs and power supply connectors. But the first board
can be continued with 2nd and 3rd stages. The 2nd stage made for 2 channel inputs, the 3rd for line or headphone
outputs.

Modular audio mixer for any channel inputs

V+

Schematics and BOM for
expandable mixer project

3 -

Footprint

006E
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
Cap, Tantal, 1mil
DIP-8
DO-35
Elco 12 mm, 2 mil pins
HDR2X6_CEN
Jack input 6.3
Pot Mono MetalCase
Pot Mono MetalCase
RAD-0.3

Value

OPA137
100K
1K
1M
2.2K
470
47K
6.8K
8
10uF
INA217 AIP
1N4148
47uF 60V
1.6kA
47kB
100nF

Preamp-INA217
Module.PrjPcb
Quantity

2
2
2
1
2
2
1
2
1
3
1
4
3
4
1
1
1
1

34

Description
FET-Input Operational Amplifiers
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Polarized Capacitor (Radial)
Instrument Amp
High Conductance Fast Diode
Polarized Capacitor (Radial)
Header, 6-Pin, Dual row
Resistor
Resistor
Capacitor

11/10/2011
Model:Footprint
DIP; 8 Leads; Row Spacing 7.62 mm; Pitch 2.54 mm
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing
Resistor; 2 Leads
Resistor; 2 Leads
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing
Resistor; 2 Leads
Resistor; 2 Leads
Resistor; 2 Leads
DIP, 8-Pin, Row Spacing 7.62 mm, Pitch 2.54 mm
Diode, Axial; Body 3.8 x 1.9 mm (LxDia. max), Lead Dia. 0.53 mm (max)

Connector; Header; 6x2 Position
3 pin mono metal case pot, 2 mil
3 pin mono metal case pot, 2 mil
Capacitor; 2 Leads

16:31:13
Pins

Designator
#Column Name Error:Price
#Column Name Error:PriceH
Total
Total H
U3, U4
$0.00
0 Ft
2 R11, R15
$0.00
0 Ft
2 R4, R5
$0.00
0 Ft
2 R10
$0.00
0 Ft
2 R13, R14
$0.00
0 Ft
2 R7, R12
$0.00
0 Ft
2 R1
$0.00
0 Ft
2 R6, R9
$0.00
0 Ft
2 R8
$0.00
0 Ft
2 C10, C11, C15
$0.00
0 Ft
8 U1
$0.00
0 Ft
2 D1, D2, D3, D4
$0.00
0 Ft
2 C5, C12, C13
$0.00
0 Ft
12 P3, P4, P5, P6
$0.00
0 Ft
6 J1
$0.00
0 Ft
3 P1
$0.00
0 Ft
3 P2
$0.00
0 Ft
2 C14
$0.00
0 Ft
8

SUM: $0.00

Notes

This circuit made for mono microphone inputs only. The input is mono, 6.3 mm jack inserted directly
to the board with unbalanced/balanced converter, and 3 inputs header for symmetrical phones with
XLR output. Switch module required to select between two inputs (unbalanced jack or balanced XLR).
The main amplifier of this circuit is INA217. This instrument amp is very cheap, and noiseless. Volume
and gain potentiometers included. This circuit must be soldered to the first stage of mainboard of audio
mixer via 2x6 pin male “L” header.
Document last modified and saved: 11 November 2011 5:40 PM

0 Ft

Modular audio mixer for any channel inputs - 4

5 -

Schematics and Bill of materials for modular mixer
Stereo jFET guitar (instrument, effect) preamp

Schematics and Bill of materials for modular mixer
Stereo dual OpAmp instrument or audio preamplifier
1

1

2

3

4

5

2

6
5
4
3
2
1

1
2
3
4
5
6

R1
5.1K

J1

B

0
1
2
3
4
5

C3

A

10uF

R2
10M

R3
51K

R5
220

GND

10uF

GND

R4
51K

GND

B

GND

P1

GND

Header 2

GND

2
1

Q1B
2N3958

7

R7
22K

R8
10M

C6
10uF
D

100nF

BC548C
Q2
R10

12K

47nF
C8

+15V Input

8

B

1

Pot stereo
5kA

R7
1M

C

-15V Clean
C

Title

3

Bill of Materials
29-04
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
Cap, Tantal, 1mil
Elco 6mm, 1 mil pins
HDR1X2
HDR2X6_CEN
Jack input 6.3
Pots Plastic Stereo
Pots Plastic Stereo
RAD-0.3
RAD-0.3
TO-71

+15V

C

-15V

1
2
3
4
5
6

Stereo Dual jFET preamp

Size

GND

Number

Revision

7
8
9
10
11
12

GND

Header 6X2A

D

A

2

Footprint

GND

P6

11/6/2011
Sheet of
D:\!Works\..\jFet-Preamp-Stereo-MOD.SchDoc
Drawn By:
4

5

Value

10M
12K
220
22K
5.1K
51K
10uF
47uF 60V

47kB
5kA
100nF
47nF

Preamp-jFET
Module.PrjPcb
Quantity

1
2
1
2
1
2
2
5
1
1
1
1
1
1
1
1
1

25

Description
Amplifier Transistor NPN Silicon
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Polarized Capacitor (Radial)
Polarized Capacitor (Radial)
Header, 2-Pin
Header, 6-Pin, Dual row
Resistor
Resistor
Capacitor
Capacitor
N-Channel Dual JFET (General Purpose)

Title

D

6

http://custompcb.blogspot.com/
http://diyguitarpa.blogspot.com/

1

11/10/2011
TO, Flat Index; 3 In-Line, Axial Leads; Body Dia. 4.8mm; Leads 0.48 x 0.5 mm (max)

Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing
Resistor; 2 Leads
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing

Connector; Header; 2 Position
Connector; Header; 6x2 Position

Capacitor; 2 Leads
Capacitor; 2 Leads
Can; 7 Leads (1 Absent); Pin Circle Dia. 2.54 mm; Lead Dia. 0.48 mm (max)

Pins

Designator
#Column Name Error:Price
#Column Name Error:PriceH
Total
Total H
3 Q2
$0.00
0 Ft
2 R2, R8
$0.00
0 Ft
2 R10
$0.00
0 Ft
2 R5, R9
$0.00
0 Ft
2 R7
$0.00
0 Ft
2 R1, R6
$0.00
0 Ft
2 R3, R4
$0.00
0 Ft
2 C1, C2, C3, C4, C6
$0.00
0 Ft
2 C7
$0.00
0 Ft
2 P3
$0.00
0 Ft
12 P4
$0.00
0 Ft
6 J1
$0.00
0 Ft
6 P1
$0.00
0 Ft
6 P2
$0.00
0 Ft
2 C5
$0.00
0 Ft
2 C8
$0.00
0 Ft
6 Q1
$0.00
0 Ft

SUM: $0.00

Notes
This very simple, small, cheap and noiseless preamp made for musical instruments with stereo (or mono) input.
The main part of this circuit is 2N3958 dual jFET. Ideal for stereo or mono guitar effects, keyboards, or to
connect another devices with stereo outputs like audio mixers. Stereo jack, gain and volume adjustable resistors
are inserted to the PCB. Very cheap and very good quality for guitars. The possible gain is not too high of this
circuit, but enough for guitars and guitar effects with very warm sound.

0 Ft

2

3

Number

D
Revision

A
Date:
File:

11/6/2011
Sheet of
D:\!Works\..\OPAMP-Preamp-Stereo-MOD.SchDoc
Drawn By:
4

5

6

The Picasa album about OpAmp amplifier

16:46:17
Model:Footprint

Dual stereo OpAmp w. power filter

Size

The Picasa album about jFET amplifier
Comment

+15V Clean

GND

GND

GND

7
8
9
10
11
12

Header 6X2A

47uF 60V
C7

P5
1
2
3
4
5
6

P3
Pot stereo
100kA

7

TL072ACN

GND

Date:
File:

BC548C
Res2
Res2
Res2
Res2
Res2
Res2
Cap Pol1
Cap Pol1
Header 2
Header 6X2A
Input Jack 6.3
Pot stereo
Pot stereo
Cap
Cap
2N3958

U1B

6

R6
4.7k

R9
220

+15V Stage

C5

10uF

R5
4.7k

4

6

GND

GND

GND

100k

C4

5

Header 2

10uF

68p
R4

5

C

B

C6

C5

R3
22K

GND

1

GND

P2

R6
5.1K

P2
Pot stereo
47kB

TL072ACN

R2
1M

C4 10uF

2
1

A

3

Input Jack 6.3
B

U1A

2

Input Jack 6.3
P3

10uF

68p
R1

C3
10uF

0
1
2
3
4
5

Pot stereo
47kB

1

3

6

100k

J1

Q1A
2N3958

5

C2

C1

P1

C1 10uF

GND

C2

7
8
9
10
11
12

Header 6X2A

2

Header 6X2A

A

A

Out 1

Out 2

4

P4

P4

12
11
10
9
8
7

3

6
http://custompcb.blogspot.com/
http://diyguitarpa.blogspot.com/

A

Modular audio mixer for any channel inputs

Bill of Materials
Comment

Res2
Res2
Res2
Res2
Cap Pol1
TL072ACN
Header 2
Header 6X2A
Input Jack 6.3
Pot stereo
Pot stereo
Cap

Footprint
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
Cap, Tantal, 1mil
dip-8
HDR1X2
HDR2X6_CEN
Jack input 6.3
Pots Plastic Stereo
Pots Plastic Stereo
RAD-0.3

Value

100k
1M
22K
4.7k
10uF

100kA
47kB
68p

Preamp-dual OpAmp
Module.PrjPcb
11/10/2011
Quantity

2
2
1
2
4
1
1
3
1
1
1
2

Description

Model:Footprint
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing

Resistor
Resistor
Resistor
Resistor
Polarized Capacitor (Radial)
Low-Noise J-FET Dual Operational Amplifier DIP; 8 Leads; Row Spacing 7.62 mm; Pitch 2.54 mm
Header, 2-Pin
Connector; Header; 2 Position
Header, 6-Pin, Dual row
Connector; Header; 6x2 Position
Resistor
Resistor
Capacitor

Capacitor; 2 Leads

17:02:26
Pins

Designator
#Column Name Error
R1, R4
$0
2 R2, R7
$0
2 R3
$0
2 R5, R6
$0
2 C2, C3, C4, C6
$0
8 U1
$0
2 P1
$0
12 P4, P5, P6
$0
6 J1
$0
6 P3
$0
6 P2
$0
2 C1, C5
$0
2

21

SUM: $

Notes

This is another really simple, good quality and cheap preamplifier with stereo jack input for guitar
effects or keyboards. The possible gain is much higher than jFET circuit, and the sound is better for
keyboards or mixers than the guitars or guitar effects. The dual OpAmp must be compatible with TL072.
Gain and volume pots has inserted to the PCB board.
Document last modified and saved: 11 November 2011 5:40 PM

Modular audio mixer for any channel inputs - 6

7 -

Schematics and Bill of materials for modular mixer
Stereo circuit with 2 single OpAmp, instrument and audio preamplifier
3

4

5

6

Notes
1

1
2
3
4
5
6

7
8
9
10
11
12

Header 6X2A
GND

C1
C2

68p

B

C3

0
1
2
3
4
5

C4

10uF
R2
1M

10uF

Input Jack 6.3

GND

P1
2
1
C

Header 2

1

GND

GND

6
5
LF356D

C6
P6

10uF

68p
R4
100k
7

+15V Clean

U4

2

8

GND
P3
Pot stereo
100kA

7
8
9
10
11
12

C

GND

Header 6X2A

GND

GND

-15V Clean

Title

http://custompcb.blogspot.com/
http://diyguitarpa.blogspot.com/

3

D

Stereo single OpAmp preamp w. power filter

Size

2

1
2
3
4
5
6

Number

Revision

A
Date:
File:

11/6/2011
Sheet of
D:\!Works\..\LF356-Preamp-Stereo-MOD.SchDoc
Drawn By:

4

5

6

1
2
3
4
5
6

Bill of Materials
Comment

Res2
Res2
Res2
Res2
Cap Pol1
LF356D
Header 2
Header 6X2A
Input Jack 6.3
Pot stereo
Pot stereo
Cap

Footprint
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
Cap, Tantal, 1mil
dip-8
HDR1X2
HDR2X6_CEN
Jack input 6.3
Pots Plastic Stereo
Pots Plastic Stereo
RAD-0.3

Value

100k
1M
22K
4.7k
10uF

100kA
47kB
68p

Quantity

2
2
1
2
4
2
1
3
1
1
1
2

22

Description
Resistor
Resistor
Resistor
Resistor
Polarized Capacitor (Radial)
Wide-Bandwidth Single J-FET Operational Amplifier

Header, 2-Pin
Header, 6-Pin, Dual row
Resistor
Resistor
Capacitor

Model:Footprint
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing
DIP; 8 Leads; Row Spacing 7.62 mm; Pitch 2.54 mm
Connector; Header; 2 Position
Connector; Header; 6x2 Position

Capacitor; 2 Leads

Notes
A

Header 6X2A
GND

C2

68p
R1

10uF

100k

J1

Input Jack 6.3
P1

Header 2

8

GND

2
1
GND

GND

6

3
R2
1M

C4
10uF

1
LT1028CN8

8

R7
1M

R5
4.7k

-15V

+15V

R6
4.7k

C

P3
Pot stereo
100kA

6
1

-15V Clean 1

P7

GND

1
2
3
4
5
6

LT1028CN8

GND

GND

7
8
9
10
11
12

GND

Header 6X2A

http://custompcb.blogspot.com/
http://diyguitarpa.blogspot.com/

D

Title

D

Stereo preamp w. 2 single OpAmp and 2 power filters

Size

Number

Revision

A
Date:
File:
1

2

3

11/6/2011
Sheet of
D:\!Works\..\LT1115-Preamp-Stereo-MOD.SchDoc
Drawn By:

4

This is the last version of
OpAmp preamplifiers. This
have best quality. This is
the reason why two single
OpAmp included instead
of one dual. LT1115 or
LT1028 recommended for
best result, maybe one of
LF or NE serial OpAmps.

GND

+15V Clean 1

U2
5

3

7
8
9
10
11
12

Header 6X2A

100k

2

1
2
3
4
5
6

GND

10uF

68p
R4

C

P6

-15V Clean

C6

C5

R3
22K

B

GND

5

2

C3
10uF

0
1
2
3
4
5

U1

7
8
9
10
11
12

Header 6X2A

+15V Clean

B

P5
1
2
3
4
5
6

P2
Pot stereo
47kB

C1

This solution is really cheap,
against the noise one powerfilter circuit included (for
both OpAmps). Stereo
jack input, stereo/mono
and bypass switch, gain
and volume potentiometers
inserted to the board.

11/10/2011

6

7
8
9
10
11
12

5

6

The difference between
this and the previous version of board, here we
have two power filter,
one filter for one OpAmp
for the best result of really
low noise and distortion.
The circuit recommended
for home hi-fi and instruments, included instrument effects.
Gain and volume potentiometers, bypass and
stereo/mono switches included to the board with
stereo jack input.

Because the circuit noise,
distortion (and the gain)
depending on the included
single OpAmp, the solution
recommended for all nonguitar instrument, and audio amplifiers for home hi-fi
solutions.
Preamp-single
OpAmp
Module.PrjPcb

5

P4

A

LF356D

D

1

R6
4.7k

5
4

1

R7
1M

R5
4.7k

6

3

+15V

-15V

C5

R3
22K

B

GND

U3 8

3
4

J1

2

7
8
9
10
11
12

Header 6X2A

10uF

100k

7

R1

P4
1
2
3
4
5
6

P2
Pot stereo
47kB

This circuit looks like the
previous version of TL072
compatible dual OpAmp
preamplifier, but for this,
two single OpAmp device required, instead of
one dual. The reason of this
solution is the better quality,
if you want to use really
noiseless single LF or LT
serial integrated circuits
instead of relative noisy
one dual TL072.

4

7

A

P5

3

7

A

2

4

2

Schematics and Bill of materials for modular mixer
Stereo low noise 2 single OpAmp instrument or hi-fi preamplifier

4

1

Modular audio mixer for any channel inputs

Bill of Materials

17:06:34

Comment
Pins
Designator
#Column Name Error:Price
#Column Name
Total
Total H
Res2 Error:PriceH
2 R1, R4
$0.00
0 Ft
Res2
2 R2, R7
$0.00
0 Ft
Res2
2 R3
$0.00
0 Ft
Res2
2 R5, R6
$0.00
Cap Pol10 Ft
2 C2, C3, C4, C6
$0.00
0 Ft
LT1028CN8
8 U3, U4
$0.00
Header 20 Ft
2 P1
$0.00
0 Ft
Header 6X2A
12 P4, P5, P6
$0.00
Ft
Input Jack0 6.3
6 J1
$0.00
Pot stereo0 Ft
6 P3
$0.00
Pot stereo0 Ft
6 P2
$0.00
0 Ft
Cap
2 C1, C5
$0.00
0 Ft

SUM: $0.00

0 Ft

Footprint
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
Cap, Tantal, 1mil
dip-8
HDR1X2
HDR2X6_CEN
Jack input 6.3
Pots Plastic Stereo
Pots Plastic Stereo
RAD-0.3

Value

100k
1M
22K
4.7k
10uF

100kA
47kB
68p

Preamp-single HQ
OpAmp
Module.PrjPcb
Quantity

2
2
1
2
4
2
1
4
1
1
1
2

Description
Resistor
Resistor
Resistor
Resistor
Polarized Capacitor (Radial)

11/10/2011
Model:Footprint
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing
Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing

Header, 2-Pin
Header, 6-Pin, Dual row

DIP; 8 Leads; Row Spacing 7.62 mm; Pitch 2.54 mm
Connector; Header; 2 Position
Connector; Header; 6x2 Position

Resistor
Resistor
Capacitor

Capacitor; 2 Leads

Ultra Low Noise Precision High-Speed Operational Amplifier

17:12:23
Pins

Designator
#Column Name Error:
R1, R4
$0.
2 R2, R7
$0.
2 R3
$0.
2 R5, R6
$0.
2 C2, C3, C4, C6
$0.
8 U1, U2
$0.
2 P1
$0.
12 P4, P5, P6, P7
$0.
6 J1
$0.
6 P3
$0.
6 P2
$0.
2 C1, C5
$0.
2

23

SUM: $0

Document last modified and saved: 11 November 2011 5:40 PM

Modular audio mixer for any channel inputs - 8

9 -

Schematics and Bill of materials for modular mixer
Schematic and BOM of power supply
1

2

3

4

A

3

5

15V AC - 1

KBL04

C6
47n

3

B

D1

+15V In
C2
10 1W
2200u

C1
2200u

6

OUT
ADJ

C4
100n

2

D2
16V Zener

C3
47u

H1

B

C10
2200u

R2

D3
16V Zener

100n
C13

-15V In

C

2

IN

ADJ
OUT

D
http://custompcb.blogspot.com/
http://diyguitarpa.blogspot.com/

C12
47u

1

2

C

3

D

BC550C
BC560C
Res2
Cap Pol1
Cap
Cap
Cap Pol1
Header 6X2A

Sheet of
Drawn By:

5

6

LM317BT
LM337BT
Res2
KBL04
16V Zener
Cap Pol1
Cap Pol1
Connector
Cap
Cap

Footprint

221A-04
221A-04
AXIAL-0.4
Bridge hor.
DIODE-0.7
Elco 12 mm, 2 mil pins
ELCO 22 MM 4 MIL
panel connector 3 input big
RAD-0.3
RAD-0.3

Value

10 1W
47u
2200u
100n
47n

PowerSupply.PrjPcb 11/10/2011
Quantity

1
1
2
1
2
2
4
2
4
4

23

Description

Pins

3-Terminal Adjustable Positive Voltage Regulator TO, Thru-Hole, Vertical, Heatsink Mounted; 3 In-Line Leads; Pitch 2.54 mm

3

3-Terminal Adjustable Negative Voltage Regulator TO, Thru-Hole, Vertical, Heatsink Mounted; 3 In-Line Leads; Pitch 2.54 mm

3

Resistor
Full Wave Diode Bridge
Zener Diode
Polarized Capacitor (Radial)
Polarized Capacitor (Radial)

2

Capacitor
Capacitor

Axial Device, Thru-Hole; 2 Leads; 0.4 in Pin Spacing

4

Diode, Thru-Hole; 2 Leads; 0.7 in Pin Spacing

2
2
2

3 pin, 3 mil connector
Radial Cap, Thru-Hole; 2 Leads; 0.3 in Pin Spacing
Radial Cap, Thru-Hole; 2 Leads; 0.3 in Pin Spacing

3
2
2

12K

C6
47nF

47uF 60V
C7

B

GND

2

Footprint

29-04
29-04
AXIAL-0.4
Cap, Tantal, 1mil
CAP, WIMA, 2MIL
CAP, WIMA, 2MIL
Elco 6mm, 1 mil pins
HDR2X6_CEN

Number

Date:
File:

10/11/2011
D:\!Works\..\PowerFilter.SchDoc

3

Value

BC550C
BC560C
12K
10uF
100nF
47nF
47uF 60V

4

Power Filter.PrjPcb
Quantity

1
1
2
2
2
2
2
1

Revision

A

Description
Transistor NPN Silicon
Transistor PNP Silicon
Resistor
Polarized Capacitor (Radial)
Capacitor
Capacitor
Polarized Capacitor (Radial)
Header, 6-Pin, Dual row

Sheet of
Drawn By:

D

5

6

11/10/2011

17:20:43
Model:Footprint

TO, Flat Index; 3 In-Line, Axial Leads; Body Dia. 4.8mm; Leads 0.48 x 0.5 mm (max)
TO, Flat Index; 3 In-Line, Axial Leads; Body Dia. 4.8mm; Leads 0.48 x 0.5 mm (max)

Resistor; 2 Leads

Connector; Header; 6x2 Position

Pins
3

Q2
3 Q1
2 R1, R2
2 C4, C5
2 C2, C3
2 C6, C8
2 C1, C7
12 P1

Designator
#Column Name Error:
$0.
$0.
$0.
$0.
$0.
$0.
$0.
$0.

SUM: $0

Notes

17:24:05
Model:Footprint

BC550C
Q2
R2

13

This is the power supply. Very simple and good quality low power circuit. Two adjustable regulators
can be fixed to the heatsink. The adjustable regulator with Zener diode have cleaner output than simple
7815 and 7915 regulators.

Comment

GND

C2
100nF

Power filter module

Size

This schematic is the partof preamps and EQ projects. This module filtering the symmatrical (+-) power for
circuits. PCB and another modules, mainboards are available.

Comment

Notes

Bill of Materials

C8
47nF

GND
GND

Bill of Materials

Revision
D

4

12K

C4
10uF C5
10uF

C3
100nF

C

1

A

3

BC560C
Q1

http://custompcb.blogspot.com/
http://diyguitarpa.blogspot.com/

-15V Out

10/17/2011
D:\!Works\..\Power supply.SchDoc

R1

Title

C14
100n

Number

Date:
File:

6

Header 6X2A

Power supply

Size

5

C

U2
LM337BT

Title

C1
47uF 60V

7
8
9
10
11
12

H2

1

10 1W

GND

3

GND
2200u
C11

1
2
3
4
5
6

B

C5
100n
1

C9
47n

4

A

P1

C7
47n

C8
47n

3

+15V Out

2
GND
15V AC - 2

2

A

2
1

1

1

R1

Schematics and Bill of materials for modular mixer
Schematic and BOM of power filter module
A

LM317BT
U1
IN

Modular audio mixer for any channel inputs

This module required for the preamplifier boards. This is the power filter circuit. I like to use this simple circuit to filter the problems of power. These circuits have to be connected to the 12 pins headers
on the preamp PCB. If you think this is not important, you can wire pin 8 to pin 11 and pin 7 to
pin 12 to ignore these circuits and boards.

Designator
#Column Name Error:Price
#Column Name Error:PriceH
Total
Total H
U1
$0.00
0 Ft
U2
$0.00
0 Ft
R1, R2
$0.00
0 Ft
D1
$0.00
0 Ft
D2, D3
$0.00
0 Ft
C3, C12
$0.00
0 Ft
C1, C2, C10, C11
$0.00
0 Ft
H1, H2
$0.00
0 Ft
C4, C5, C13, C14
$0.00
0 Ft
C6, C7, C8, C9
$0.00
0 Ft

SUM: $0.00

We have four versions of power filter PCB. No difference between schematics, only the PCB size
is the0 Ftdifference.

Document last modified and saved: 11 November 2011 5:40 PM

Modular audio mixer for any channel inputs - 10

11 -

Schematics and Bill of materials for modular mixer
Schematic and BOM of variable line output module

Schematics and Bill of materials for modular mixer
Schematic and BOM of simple headphone output module
1

1

2

3

4

5

Modular audio mixer for any channel inputs

2

3

4

5

6

6

R1
A

1k
R2

A

A
4

+15V clean
U1A
TL074J

2

R5

3

A

1

R1
100

U1B
TL074J

6

R6

B

5

GND

GND

1
2
3
4
5
6

GND

7
8
9
10
11
12

U1D
TL074J

13

R8

12

D

14

1k

R4
100

4

100k

GND

1
2
3
4
5
6

GND

R5

P2
Pot stereo
47k

Header 6X2A

P1

GND

Header 6X2A

21

GND
+15V

GND 3
18

-15V

1
20

+15V
J1

C

0
1
2
3

Pot stereo
47kB

-15V

Jack input 3.2

J2
GND

J4

0
1
2
3
4
5

Bill of Materials

Title

C2
100n

B

C1
100uF 25V

C3
100n

2

Size

Footprint
AXIAL-0.4
AXIAL-0.4
HDR2X6_CEN
J014
JACK INPUT 3.2
Jack input 6.3
Pots Plastic Stereo
Stereo RCA input

Value

100
100k

47k

Date:
outputsFile:

Mixer
Stage3.PrjPcb

Quantity

4
4
2
1
1
2
1
1

Number

D

C4
100uF 25V

11/11/2011
D:\!Works\..\Mixer outputs.SchDoc
4

Description
Resistor
Resistor
Header, 6-Pin, Dual row
Low-Noise JFET-Input Operational Amplifier

Resistor

11/10/2011

http://custompcb.blogspot.com/
http://diyguitarpa.blogspot.com/

Sheet of
Drawn By:

5

Model:Footprint
Resistor; 2 Leads
Resistor; 2 Leads
Connector; Header; 6x2 Position
DIP; 14 Leads; Row Spacing 7.62 mm; Pitch 2.54 mm

6
17:50:29

Headphone amp for modular Mixer mainboard stage 3

Size

Revision

1

Designator
#Column Name Error:Price
#Column Name Error:PriceH
Total
Total H
2 R1, R2, R3, R4
$0.00
0 Ft
2 R5, R6, R7, R8
$0.00
0 Ft
12 P1, P3
$0.00
0 Ft
14 U1
$0.00
0 Ft
Comment
5 J1
$0.00
0 Ft
Res2
6 J3, J4
$0.00
0 Ft
Res2
6 P2
$0.00
0 Ft
Cap
3 J2
$0.00
0 Ft

Number

D

Revision

A
Date:
File:

2

11/11/2011
D:\!Works\..\HF-TPA6120.SchDoc

3

Sheet of
Drawn By:

4

5

6

Pins

Notes
This is the PCB for line level mixer outputs with volume level stereo potentiometer. Have to be connected to the stage no.3 of
mixer mainboard. This stage of mixer have balance adjustment feature if required. With this board, you have two line outputs
with variations:
2 pcs 6.3mm jack
1 pcs 6.3mm jack and 1 pcs 3.2mm jack
1 pcs 6.3mm jack and 1 pcs stereo RCA
1 pcs 3.2mm jack and 1 pcs stereo RCA

D

A

GND

3

Title

Output module for Mixer mainboard stage 3

16






P2
Header 6X2A

http://custompcb.blogspot.com/
http://diyguitarpa.blogspot.com/

Input Jack 6.3

GND

Res2
Res2
Header 6X2A
TL074J
Jack input 3.2
Input Jack 6.3
Pot stereo
Stereo RCA

6
7
8
9
10
11
12
13
14
15

GND

0
1
2
3
4
5

Input Jack 6.3

Comment

LVCCRVCC-

19

C

1
2
3
4
5
6

GND

Stereo RCA

1

LVCC+
RVCC+

Input Jack 6.3

TPA6120

7
8
9
10
11
12

2

D

GND

10

1
0

J3

NC
NC
NC
NC
NC
NC
NC
NC
NC
NC

R4

2

J1

GND GND

C

C

5

ROUT

RIN-

1k

B

B

RIN+

16

10
LOUT

LIN-

17

R6
GND

LIN+

5

1k
7
8
9
10
11
12

5
4
3
2
1
0

R3
U1

P1

GND

P3

C

10

8

R3
100

100k

-15v clean

B

U1C
TL074J

9

R7

100k
11

100k

7

R2
100

A
GND

Bill of Materials

SUM: $0.00

Cap Pol1
0 Ft
Header 6X2A
Input Jack 6.3
Pot stereo
TPA6120

Footprint
AXIAL-0.4
AXIAL-0.4
CAP, 2 and 3 MIL
Elco 6mm, 1 mil pins
HDR2X6_CEN
Jack input 6.3
Pots Plastic Stereo
Powerpad 20

Value

10
1k
100n
100uF 25V
47kB

TPA6120 Simple
Mod.PrjPcb
Quantity

2
4
2
2
1
1
1
1

11/10/2011

Description
Resistor
Resistor
Capacitor
Polarized Capacitor (Radial)
Header, 6-Pin, Dual row
Resistor

17:52:41
Model:Footprint

Resistor; 2 Leads
Resistor; 2 Leads

Connector; Header; 6x2 Position

Pins

Designator
#Column Name Error:
R3, R4
$0.
2 R1, R2, R5, R6
$0.
2 C2, C3
$0.
2 C1, C4
$0.
12 P2
$0.
6 J1
$0.
6 P1
$0.
21 U1
$0.
2

14

SUM: $0

Notes
This is the circuit for headphone output for mixer with volume level stereo potentiometer. Have to be connected to the stage
no.3 of mixer mainboard. This stage of mixer have balance adjustment feature if required. This board contains SMD circuit.
TPA6120 is the one of the best class-D headphone amplifier with 120dB dynamics. This is the smallest, cheapest, and simplest
application of this module.
Document last modified and saved: 11 November 2011 5:40 PM

Modular audio mixer for any channel inputs - 12

13 -

Modular audio mixer for any channel inputs

Schematics and Bill of materials for modular mixer
Schematic and BOM of balanced headphone output module
4

6
2

5

C7
100p

4

R11
4.7k

22uF 25V
U2B
NE5532AP
7

10k

R9
100k

6
5

R12
4.7k

GND

5

U3B
NE5532AP

R1

22uF 25V

C8
100p

1k
R2

R10
100k

7

2

GND

U1

R17
150

B

C9

1k R13

GND

1

R19 22uF 25V
100k

2

C10

R20 22uF 25V
100k

GND

1

2

NE5532AP

P1
C11
100p

GND

GND 3
18

-15V

1
20

GND

LOUT

ROUT
NC
NC
NC
NC
NC
NC
NC
NC
NC
NC

GND
LVCC+
RVCC+
LVCCRVCC-

Pot stereo
47kB

2

19
6
7
8
9
10
11
12
13
14
15

R4
10

R3
10
GND

Header 6X2A

GND

GND

1
2
3
4
5
6

Printed Circuit

J1
Input Jack 6.3
C

P4
7
8
9
10
11
12

B

TPA6120

GND GND

7
8
9
10
11
12

Header 6X2A

7
8
9
10
11
12

1
2
3
4
5
6

C12
100p

+15V

P2
Header 6X2A

1
2
3
4
5
6

P3

RIN-

21

GND

C

RIN+

16

3
1

GND

LIN-

17

1k R16

U3A

R18
150

3

1

LIN+

5

1k R14
1k R15

U2A
NE5532AP

A

1k

4
GND

6

C6

R7
8

8

10k
A

3

0
1
2
3
4
5

2

C5

R5

4

1

C2
100n

C3
100n

C1
100uF 25V

C4
100uF 25V

GND

GND

Boards for

Title

Balanced headphone amp for modular Mixer mainboard stage 3
D

Size
http://custompcb.blogspot.com/
http://diyguitarpa.blogspot.com/

1

2

3

Bill of Materials
Comment

Res2
Res2
Res2
Res2
Res2
Res2
Cap
Cap
Cap Pol1
NE5532AP
Cap Pol1
Header 6X2A
Input Jack 6.3
Pot stereo
TPA6120

Footprint
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
AXIAL-0.4
CAP, 2 and 3 MIL
CAP, Ceramic, 1MIL
Cap, Tantal, 1mil
dip-8
Elco 6mm, 1 mil pins
HDR2X6_CEN
Jack input 6.3
Pots Plastic Stereo
Powerpad 20

Value

10
100k
10k
150
1k
4.7k
100n
100p
22uF 25V
100uF 25V
47kB

Date:
File:

Quantity

5

Resistor

D

6

11/10/2011

Description
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Capacitor
Capacitor
Polarized Capacitor (Radial)
Dual Low-Noise Operational Amplifier
Polarized Capacitor (Radial)
Header, 6-Pin, Dual row

Revision

11/11/2011
Sheet of
D:\!Works\..\HF-TPA6120 Balanced.SchDocDrawn By:

4

TPA6120 Balanced
Mod.PrjPcb
2
4
2
2
6
2
2
4
4
2
2
3
1
1
1

Number

A

17:54:20
Model:Footprint

Resistor; 2 Leads
Resistor; 2 Leads
Resistor; 2 Leads
Resistor; 2 Leads
Resistor; 2 Leads
Resistor; 2 Leads

DIP; 8 Leads; Row Spacing 7.62 mm; Pitch 2.54 mm
Connector; Header; 6x2 Position

Pins

Designator
#Column Name Error:Price
#Column Name Error:PriceH
Total
Total H
R3, R4
$0.00
0 Ft
2 R9, R10, R19, R20
$0.00
0 Ft
2 R5, R7
$0.00
0 Ft
2 R17, R18
$0.00
0 Ft
2 R1, R2, R13, R14, R15, R16
$0.00
0 Ft
2 R11, R12
$0.00
0 Ft
2 C2, C3
$0.00
0 Ft
2 C7, C8, C11, C12
$0.00
0 Ft
2 C5, C6, C9, C10
$0.00
0 Ft
8 U2, U3
$0.00
0 Ft
2 C1, C4
$0.00
0 Ft
12 P2, P3, P4
$0.00
0 Ft
6 J1
$0.00
0 Ft
6 P1
$0.00
0 Ft
21 U1
$0.00
0 Ft
2

38

SUM: $0.00

instrument and hi-fi
preamps

0 Ft

Notes
This is the circuit for headphone output for mixer with volume level stereo potentiometer. Have to be connected to the stage
no.3 of mixer mainboard. This stage of mixer have balance adjustment feature if required. This board contains SMD circuit.
TPA6120 is the one of the best class-D headphone amplifier with 120dB dynamics. This module contains unbalanced/balanced converter for better result. If this feature not required, use the previous version of this schematic.

Document last modified and saved: 11 November 2011 5:40 PM

Modular audio mixer for any channel inputs - 14

15 -

PCB for the modular audio mixer
Top and bottom PCBs and overlay of stereo jFET preamp

Modular audio mixer for any channel inputs

PCB for the modular audio mixer
Top and bottom PCBs and overlay of simple dual OpAmp preamp

BOTTOM LAYER

TOP LAYER

PCB TOP OVERLAY

TOP OVERLAY ON TOP LAYER

P1
Q1
R3

7

R1

3

P2

R8
R1

C3

C4

C1

C2

C8

P3

C2

R6 R7 C6

Q2

C5

R6 R7 C6
C2

C2

R10R2

C4

C4

J1

R4 R3

R4 R3

J1

J1

3
1

J1

P1

P1

12
6

P4

7
1

P3

7
1

12
6

P4

C1

C5

P3

R10R2

C4

C6

C6
Q2

C3

3
1

C7

C5
C8

C7

C5
R9

R7

R1 R5 C1

R9

R7

R6

P2

U1

P3

R6

12
6

R4

R1 R5 C1

U1

P5

7
1

R5

R2

R8

5

1

C3

12
6

R3

OVERLAY ON TOP LAYER

P2

3

P2

R4

PCB OVERLAY

P5

7
1

P1
Q1

R2

BOTTOM LAYER

5

1

R5

C3

7

TOP LAYER

Document last modified and saved: 11 November 2011 5:40 PM

Modular audio mixer for any channel inputs - 16

17 -

Modular audio mixer for any channel inputs

PCB for the modular audio mixer
Top and bottom PCBs and overlay of INA217 microphone preamp

R8

P1

R1

J1
C10

U1

R9

C5

C15

R13

R14

R12

R10
R11

C13

P2

C12

PCB TOP OVERLAY

7
1

TOP LAYER

P4

U2

C14

R7

R6

R5

D4

D3

R15

D2
D1

R4

U3

C11

R8

P1

R1

J1
C10

U1

R9

C5

C15

R13

R14

R12

C13

P2
R10
R11

7
1
12
6

P4

U2

C14

R7

R6

R5

D4

D3

R15

D2
D1

R4

C11

U3

TOP OVERLAY ON TOP LAYER

C12

12
6

BOTTOM LAYER

Document last modified and saved: 11 November 2011 5:40 PM


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