Infineon MERUS MA12070 User manual

User Manual Please read the Important Notice and Warnings at the end of this document V 1.0
www.infineon.com/demo-bassamp-60w-ma12070 page 1 of 13 2020-05-28
UM_2005_PL88_2005_092929
User manual for MERUS™ MA12070 musical
instrument bass amplifier
DEMO_BASSAMP_60W_MA12070
About this document
Scope and purpose
This document describes the functional setup and user guide for the MA12070 musical instrument bass
amplifier. It includes a description of features, performance specification, schematics, PCB layout and bill of
materials (BOM) of the amplifier.
Intended audience
This user manual is for audio amplifier design engineers, audio system engineers, audio software engineers and
musicians interested in technology.
Table of contents
About this document....................................................................................................................... 1
Table of contents............................................................................................................................ 1
1Board overview...................................................................................................................... 2
1.1 Features and performance......................................................................................................................3
2User interface ........................................................................................................................ 4
2.1 User controls ...........................................................................................................................................4
2.2 Setting up the amplifier for use ..............................................................................................................6
3Hardware documentation ....................................................................................................... 7
3.1 Schematic................................................................................................................................................7
3.2 PCB...........................................................................................................................................................8
4BOM.....................................................................................................................................10
5Revision history ....................................................................................................................12

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Board overview
1Board overview
The MA12070 musical instrument bass amplifier is a wall-adapter or battery-powered, 60 W, professionally
featured and ultraefficient pocket-sized bass instrument amplifier. It is modeled after classic vacuum-tube bass
amplifier topology. It utilizes the exceptional audio quality and best-in-class efficiency of Infineon’s MERUSTM
amplifier technology (Infineon class D audio amplifier solutions) to amplify every nuance of a real vacuum-
tube pre-amplifier.
It incorporates a 12AU7/ECC82 vacuum tube for real-tube class-A amplification, which is run at low plate-
voltage, excluding high-voltage generation circuitry, and the ultrahigh fidelity MA12070 multilevel switching
audio power amplifier.
The design is made for direct use as a self-contained amplifier head or as a combo including a speaker. It only
requires an external +24 V regulated power supply.
Figure 1 MA12070 musical instrument bass amplifier
Figure 2 Block diagram
Please see the Infineon application note MA12070 musical instrument bass amplifier for further details.

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Board overview
1.1 Features and performance
The key features and performance of the MA12070 musical instrument bass amplifier are as follows:
One “classic tube sound” bass instrument channel
1 x 60 W at 4 Ωspeaker output.
Powered by off-the-shelf regulated wall adapter (+24 V DC/3 A)
Unparalleled power efficiency –with very low power losses and cool operation
No external heatsink (full volume, bass instrument playing)
Dual 12AU7 triode class A pre-amp run directly on adapter voltage for genuine tube sound
Passive instrument input jack with -12 dB input pad switch for active instruments
Gain and volume controls for tube overdrive
Bright switch for “slap-bass” sound
Dynamic “breathe and feel” when fully dimmed
Classic three-band passive Baxandall tone control: treble, middle, bass
Stereo 3.5 mm AUX input for practicing/street accompaniment
XLR DI: frequency-compensated, true balanced output for live PA/mixing desk (phantom power safe)
XLR DI ground switch
Protection: power supply reverse polarity and hot-plug, thermal, DC and speaker short-circuit
Speaker jack output with low-cost LC-filter
DC barrel input jack
Low idle power consumption even with vacuum tube
Small dimensions: 185 mm x 60 mm x 30 mm
Table 1 Electrical specifications
Power input
+18 V to +24 V, 3 A regulated, positive tip 2.1 mm, DC barrel
Idle power consumption
2.7 W at 24 V input
Power input at 10 Wrms output
15.3 W at 24 V input
Output power
60 Wrms at 5 percent THD, 4 Ω24 V input
Output load impedance
4 Ωto 16 Ω, 6.35 mm jack
Instrument input sensitivity/impedance
25 mV/1 MΩ, 90 mV/65 kΩ, 6.35 mm mono
AUX input sensitivity/impedance
400 mVrms/200 mVrms, mono/stereo, 4.7 kΩ, 3.5 mm jack
Bass control range
±12 dB at 40 Hz
Treble control range
±14 dB at 4 kHz
Middle control range
11 dB at 380 Hz
DI output level
True balanced: -6 dBm, true ground lift
DI output frequency response (-3 dB)
55 Hz to 8 kHz, 6 dB/oct

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User interface
2User interface
2.1 User controls
Figure 3 User controls overview
Table 2 User controls description
Front of PCB (left to right):
1. INPUT: Instrument input jack
Connect a shielded ¼ in. mono jack cable from the instrument
to this jack. 1 MΩ/65 kΩinput impedance.
2. PAD: -12 dB input pad switch
When using active instruments or instruments with a high
output level, use this switch for matching the input sensitivity
of the amplifier for a clean sound. 65 kΩinput impedance
when engaged.
3. GAIN: Gain control
Adjusts the signal amplitude from the first tube gain stage into
the second tube gain stage. Combined with the master volume
control (8) it is possible to overdrive the tube for genuine tube
distortion.
4. BRIGHT: Bright switch
Boosts the higher treble harmonics of the instrument when
engaged. Works in conjunction with the gain control (3). Most
effective when the gain control is at its lower settings.
5. TREBLE: Treble tone control
Adjusts the treble frequencies of the instrument. Passive
Baxandall type with the capability of both boosting and
cutting treble frequencies of approximately ±15 dB at 4 kHz.
Set to middle position yields a flat treble response.
2
3
4
5
6
10
8
9
12
11
13
7
14
1

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User interface
6. MID: Middle tone control
Adjusts the insertion level of the Baxandall tone control.
Perceived as boosting or cutting mid-range frequencies
compared to treble and bass frequencies. Set to middle
position yields ±14 dB of range of the treble control, and ±12
dB range for the bass control.
7. BASS: Bass tone control
Adjusts the lower frequencies of the instrument. Passive
Baxandall type with the capability of both boosting and
cutting bass frequencies with ±12 dB at 40 Hz. Set to middle
position yields a flat bass response.
8. VOLUME: Master volume control
Adjusts the overall output volume of the amplifier. Combined
with the gain control (3), one can overdrive the tube for
genuine tube distortion while still controlling the output
volume of the amplifier.
9. AUX IN: Auxiliary input
3.5 mm stereo input jack for connecting a phone, MP3 player
or other sources for accompaniment or practicing along. Post
master volume input.
10. POWER ON/OFF: Power on/off switch
and LED
Switches the amplifier on and off, with the red LED indicating
on when lit.
Back of PCB (left to right):
11. SPEAKER: Speaker output jack
Connect this to a speaker cabinet (4 Ωmin.) via a ¼ in. mono
jack cable. Do not connect to ground.
12. POWER INPUT: DC power input barrel
Connect +24 V DC/3 A wall adapter with positive tip into this
socket.
13. DIOUT: Balanced XLR speaker
simulated DI output
In a live situation, connect this frequency-compensated
output to the front-of-house (FOH) mixing desk. In a recording
situation, use this output for direct recording. Post master
volume, and phantom power safe. The output cuts the
extreme highs and lows for more realistic sound when going
into live or recording full range systems.
14. GROUND LIFT: Ground lift switch
If experiencing ground-loop hum or noise in a live or recording
situation, press this switch to disconnect Pin 1 in the XLR from
the amplifier ground. This will in many cases remove hum or
noise. Be aware that the amplifier ground is now floating from
the rest of the system.

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User interface
2.2 Setting up the amplifier for use
1. Put the on/off switch (10) in the depressed position (off).
2. Set all the controls at 12’o clock. Set the volume control (8) to minimum.
3. Put the pad switch (2) in the depressed position (high sensitivity input).
4. Put the bright switch (4) in the depressed position (not bright).
5. Connect a speaker (4 Ωminimum) to the speaker output jack (11) via a 6.35 mm mono jack cable. Make sure
the jack cable is a speaker-grade cable.
6. Connect a +24 V DC/3 A regulated power supply to the DC power input barrel (12). Make sure it has a
positive-tip scheme (inner tip is positive, outer ring is negative).
7. Connect a bass instrument via a shielded 6.53 mm mono jack cable to the input jack (1).
8. Turn-on the amplifier by pressing the on/off switch (10). The red LED (10) should light up.
9. Turn up the volume control (8) to the desired level.
10. Turn the controls until the desired response and sound is achieved (see Table 2 for a detailed explanation of
functions).
11. Connect a mono or stereo AUX signal (e.g., from the telephone headphone output) via the AUX IN 3.5 mm
stereo jack (9) for playing along with or for rehearsing song material (this input is placed after the volume
control (8) so the AUX signal volume can be controlled from the AUX source).
12. In a live or direct recording situation, connect a three-pin shielded XLR cable from the DI OUT XLR connector
(13) to a mixing desk or sound card. This injects the amplifier’s pre-amp signal with frequency
compensation. Press the ground lift switch (14) if ground-loop/noise problems occur.
13. Play!

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Hardware documentation
3Hardware documentation
3.1 Schematic
Figure 4 Schematic

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Hardware documentation
3.2 PCB
Top side
Bottom side
Placement
Figure 5 Main PCB layout

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Hardware documentation
Top side Bottom side Placement
Figure 6 Tube PCB layout

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BOM
4BOM
Table 3 MA12070 musical instrument bass amplifier BOM
Designator
Description
Manufacturer
Part number
Qty
C10
Electrolytic capacitor, FK series, 100
µF, 35 V, 8 x 10 mm
Panasonic
EEEFK1V101P
1
C18
Electrolytic capacitor, FK series,
1000 µF, 35 V, 12.5 x 20 mm
Panasonic
EEUFR1V102B
1
C3,C9,C11,C19,C24,C25,C2
7,C28,C29,C30,C44,C49,C5
0,C51,C53,C54,C60
Ceramic capacitor, 10 µF, ± 10
percent, X5R, 25 V, 0805
Samsung
CL21A106KAYNNNE
17
C5,C6,C7,C12,C13,C14,C15,
C23,C31,C32,C33,C34,C35,
C36,C37,C38,C39,C40,C41,
C42,C43,C45,C46,C57,C58,
C59,C62,C63,C64,C65
Ceramic capacitor, 1 µF, ± 10
percent, X7R, 50 V, 0805
Samsung
CL21B105KBFNNNE
30
C1,C2,C8,C22,C26
Ceramic capacitor, 22 nF, ± 5
percent, NP0, 50 V, 0805
TDK
C2012C0G1H223J125AA
5
C17,C47,C48,C52
Ceramic capacitor, 47 nF, ± 10
percent, NP0, 50 V, 0805
Murata
GRM21BR71H473KA01L
4
C16
Ceramic capacitor, 4.7 nF, ± 5
percent, NP0, 200 V, 0805
Kemet
C0805C472J2GECTU
1
C4,C20
Ceramic capacitor, 2.2 nF, ± 5
percent, NP0, 100 V, 0805
Kemet
C0805C222J1GACTU
2
C55,C56,C66,C67
Ceramic capacitor, 220 pF, ± 5
percent, NP0, 50 V, 0805
Vishay
VJ0805A221JXACW1BC
4
R4,R6,R17,R19,R24,R35
Resistor, 1 MΩ, 125 mW, 1 percent,
0805
Vishay
CRCW08051M00FKEA
6
R1,R9,R12,R16,R21,R34
Resistor, 47 kΩ, 125 mW, 1 percent,
0805
Vishay
CRCW080547K0FKEA
6
R15,R18
Resistor, 33 kΩ, 125 mW, 1 percent,
0805
Vishay
CRCW080533K0FKEA
2
R2,R39
Resistor, 20 kΩ, 125 mW, 1 percent,
0805
Vishay
CRCW080520K0FKEA
2
R3,R7,R11,R13,R25,R26,R2
7
Resistor, 18 kΩ, 125 mW, 1 percent,
0805
Vishay
CRCW080518K0FKEA
7
R22,R23
Resistor, 4.7 kΩ, 125 mW, 1 percent,
0805
Vishay
CRCW08054K70FKEA
2
R29,R30,R40
Resistor, 2.2 kΩ, 125 mW, 1 percent,
0805
Vishay
CRCW08052K20FKEA
3
R5,R10
Resistor, 1.5 kΩ, 125 mW, 1 percent,
0805
Vishay
CRCW08051K50FKEA
2
R14,R20,R28,R31,R32
Resistor, 680 Ω, 125 mW, 1 percent,
0805
Vishay
CRCW0805680RFKEA
5
R37,R38
Resistor, 300 Ω, 500 mW, 5 percent,
1210
Panasonic
ERJT14J301U
2
R36
Resistor, 22 Ω, 125 mW, 1 percent,
0805
Vishay
CRCW080522R0FKEA
1
L1
Common-mode filter, 700 Ω, 4 A, 7 x
6 mm
TDK
ACM7060-701-2PL-TL01
1

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BOM
L2
Power inductor, 47 µH, 1.9 A, 8 x 8
mm
Murata
1267AY-470M=P3
1
L3,L4
Power inductor, 1.5 µH, 7.3 A, 8 x 8
mm
Murata
1267AY-1R5N=P3
2
D1
Schottky diode, BAS3010, 30 V, 1 A,
SOD-323
Infineon
BAS3010A03WE6327HT
SA1
1
D2
LED, red, 5 mm, TH, T1-3/4
Broadcom
HLMP-3301
1
Q1
BJT, NPN, BC847C, 45 V, 100 mA,
SOT-23
Infineon
BC847CE6327HTSA1
1
U1
Buck controller, adjustable, 45 V, 1.8
A, SOIC-8
Infineon
TLE8366EVXUMA1
1
U2
Dual audio op-amp, TL072A, ±18 V
ST
TL072ACDT
1
U4
Multilevel class D amplifier,
MA12070, 2 x 80 W
Infineon
MA12070XUMA1
1
U5
Dual P-channel MOSFET, IRF9358, -
30 V, -9.2 A
Infineon
IRF9358TRPBF
1
RV1,RV2,RV4,RV5
Rotary potentiometer, TH, 250 kΩ
logarithmic, 16 mm
TT Electronics
P160KN-0QC15A250K
4
RV3
Rotary potentiometer, TH, 25 kΩ
logarithmic, 16 mm
TT Electronics
P160KNP-0QC20A25K
1
SW1,SW2,SW3,SW4
Push-button switch, TH, DPDT, 30 V,
0.1 A
Alps Alpine
SPUN191600
4
J4
Phone jack, stereo, switched, TH, 3.5
mm
Cliff
FC68133
1
J1,J6
Phone jack, stereo, switched, TH,
6.35 mm
Neutrik
NMJ6HFD2
2
J5
XLR connector, three contacts,
male, TH
Neutrik
NC3MAAH
1
J2
DC power connector, jack, 5 A, TH,
2.5 mm
Multicomp
SPC21365
1
J3
Header, eight contacts, one row,
right angle, 2.54 mm
Würth
61300811021
1
N1
Tube socket, TH, PCB, ceramic,
NOVAL
Belton
VT9-PT
1
V1
Electron tube, dual triode,
12AU7/ECC82, NOVAL
Electro
Harmonix
12AU7 / ECC82
1

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Revision history
5Revision history
Document
version
Date of release
Description of changes
V 1.0
28-05-2020
First release

Trademarks
All referenced product or service names and trademarks are the property of their respective owners.
Edition 2020-05-28
UM_2005_PL88_2005_092929
Published by
Infineon Technologies AG
81726 Munich, Germany
© 2020 Infineon Technologies AG.
All Rights Reserved.
Do you have a question about this
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Document reference
IMPORTANT NOTICE
The information contained in this application note is
given as a hint for the implementation of the product
only and shall in no event be regarded as a
description or warranty of a certain functionality,
condition or quality of the product. Before
implementation of the product, the recipient of this
application note must verify any function and other
technical information given herein in the real
application. Infineon Technologies hereby disclaims
any and all warranties and liabilities of any kind
(including without limitation warranties of non-
infringement of intellectual property rights of any
third party) with respect to any and all information
given in this application note.
The data contained in this document is exclusively
intended for technically trained staff. It is the
responsibility of customer’s technical departments
to evaluate the suitability of the product for the
intended application and the completeness of the
product information given in this document with
respect to such application.
For further information on the product, technology,
delivery terms and conditions and prices please
contact your nearest Infineon Technologies office
(www.infineon.com).
WARNINGS
Due to technical requirements products may contain
dangerous substances. For information on the types
in question please contact your nearest Infineon
Technologies office.
Except as otherwise explicitly approved by Infineon
Technologies in a written document signed by
authorized representatives of Infineon
Technologies, Infineon Technologies’ products may
not be used in any applications where a failure of the
product or any consequences of the use thereof can
reasonably be expected to result in personal injury.