otomatsu BDR-HPA01E User manual

Thank you very much for purchasing the Otomatsu amplifier kit.
Please read this manual carefully prior to commencing assembling
the amplifier kit. Ensure to pay attention in preventing any
accidental electrical shock.
Table of Contents
1. Introduction and Circuit overview
2. Assembling Headphone amplifier module. 2 sets
3. Assembling the Balance drive module
4. Assembling the Power supply module
5. Case set
6. Assembling the case and cover modules
7. Assembling the back panel
8. Attaching together modules to the case
9. Wiring the power supply
10. Wiring signal path -1, -2
11. Checking all wiring
12. Checking the voltage level of key areas
13. Modification of Headphone cable
14. Improvement options
How to Assemble the Balanced Headphone Amplifier Kit BDR-HPA01E
(Estimated assembly time: 10 hours)
otomatsu
If you have any technical question, please contact: [e-mail]
Input Stereo RCA un-balance line signal
Output Stereo XLR Balance x1. or Un-balance 1/4inch phone x2
Or capable to drive XLR input Power Amplifiers
Frequency Response 5Hz -80kHz
Total Harmonic Distortion + Noise 0.0046％@40Ω load 1kHz
Output power 1600mW x2 max. @40Ω load
Headphone impedance matching 16Ω -300Ω
Power supply AC100V –120V 50-60Hz
Size W230mm x D180mm x H50mm
o t o m a t s u
Both of XLR and 1/4inch Phone jack are supported by the Combo
jack. In the case of 1/4inch phone jack, the AMP drive has a
single-end, and supports two headphones.
1
Rev.1.0 E All Copy Right Reserved by otomatsu

1. Introduction and Circuit Overview
AC100V –
120V
+ / 16V
Regulators
Transformer
System Block Diagram
L-CH XLR output
R-CH XLR Output
RCA Input
L
R
Volume＋
Balance
rive
circuit
1 ¼`` Jack
HOT
COLD
HOT
COLD
Left-CH
Right-CH
Total System configuration
- Headphone Amplifier Module x2
- Volume + Balance conversion module x1
- Power Supply Module + Transformer x1
- XLR Combo jack, Screw, Knob, Petet, Wire, AC inlet…etc set x1
- Case set x1
Transformer Regulators module Case set
Headphone Amplifier Modules ｘ2
Volume + Balance drive Module
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E
2
Rev.1.0E All Copy Right Reserved by otomatsu
The assembling of 2 sets of headphone amplifier module and adding a volume +
balance conversion circuit comprises a balance drive model headphone amplifier. For
a power supply circuit, we use a stabilization power supply kit to compliment an
exclusive compact, stylish case kit.
The line level signal that goes to the RCA jack enters the volume control of the
conductive plastic model which is made by TOKYO KO-ON DENPA Co. Ltd. Because
this volume control has fewer ganging errors, it balances the right and left volume
more efficiently.
The signal then enters an unbalanced-balanced conversion circuit that makes 2
distinct high and low contradistinction signals of +HOT and -COLD. This part uses an
OPAMP NE5532. It has 2 circuits and conducts precise, low noise and low distortion
rate signal conversion. In addition it has a DC amplifier setup so that the frequency
characteristic is flat from DC to 100 kHz
The signal then enters the headphone drive amplifier which amplifies the electric
power that drives the headphone. This part uses an OPAMP LME49710 with 1 circuit.
We triple this amplification in order to be able to supply enough electrical current to
the headphone impedance load between 16Ωand 300Ωin output buffer IC and
LME49600. By using WIMA’s film capacitor for the input, we cut the DC component
from the first part. Also for the output, it connects to the headphone jack through the
audio grade bipolar electrolysis capacitor of the low direct current equivalent
resistance and low leak current level not appearing on the DC component to the
headphone.
For the power supply circuit, we make the AC20V of 2 systems from 110V by using a
toroidal transformer and making the DC stabilize with low noise Schottky Barrier
diode and regulator IC LM317. It is a 2- system with a complete independent
stabilized rectification that keeps the ground level stabilized.
The headphone jack that is NEUTRIK brand supports both of XLR and standard stereo
phone jack. For the balanced headphone wiring, insert L to the left, R to the right. It
becomes perfectly balanced and is superior to LR channel separation. You can enjoy
full drive SN too. In addition, you can insert it into a regular stereo phone jack. When
you use a regular stereo phone jack, the same signals are made for both the right and
left jacks so you can operate 2 headphones simultaneously. More over, by using a XLR
balanced cable, you can operate a BLT power amplifier and use it as a balanced model
preamplifier.
In addition, it will be possible in the future to enhance the performance by replacing
OPAMP.

2.1. Assembling Headphone amplifier module. 2 sets
IN/OUT Jack x2
We don’t use those parts, so they
are not included in this AMP KIT.
330uF x2
Power GND
Power –Vcc
Power +Vcc
Signal In HOT
Signal Ground
Signal In COLD
Signal Out HOT
Signal Ground
Signal Out COLD
R11,R12 no t use
Top View
L-CH only
LED Power supply
R3,R4 Gain Adjust
Part # Parts Value Qty
IC1 IC2 OPAMP LME49710 2
IC1 IC2 IC Socket 8pin 2
R1 R2 Metal Film Register 1k 1/4W 2
R3 R4 Metal Film Register 2k 1/4W 2
R5 R6 Metal Film Register 100k 1/4W 2
R7 R8 Oxide Metal Film Register 9.1Ω 1W 2
R9 R10 Metal Film Register 4.7k 1/4W 2
R11 R12 R13 not use
Gain adjust Metal Film Register
1k 1/4W 2
Gain adjust Metal Film Register 4.7k 1/4W 2
C1 C2
Film Capacitor
No polarity Red
3.3uF 2
C3 C4 C5 C6 C7
C8 C9 C10
Ceramic Capacitor
No polarity Blue 0.1uF 8
C11 C12
Bipolar Electrolytic
Capacitor
No Polarity Green
470uF 16V 2
C13 C14 Electrolytic Capacitor 100uF 25V 2
PCB with LME49600 1
R1,R2 1k x2 BrBlBlBR Br
R3, R4 2kΩx2 ReBlBlBr Br
R5, R6 100kΩx2 BrBlBlOr Br
R7, R8 9Ω1W x2 WhBrGoGo
R9,R10 4.7k x2 YePuBlBr Br
G. Adjust 4.7k x2 YePuBlBr Br
G.Adjust 1k x2 BrBlBlBR Br
Color code of Registers No Polarity
+-
nichicon MUSE
Polarity 3
R13 no t use
Rev.1.0E All Copy Right Reserved by otomatsu
Procedures for assembling the 2 sets are the same.
1. Take out each signal wire and power supply wire directly
from the main circuit board.
2. Wire 2 jumper wires to the Volume.
3. Wire 2 jumper wires to the power supply SW.
4. When you make R3 and R4 into 2k, AMP gain
(amplification rate) will triple. This is the default value.
If it’s 1k, the AMP gain will only double. If it’s 4.7k, it will
increase 5.7times. We added 1k, 2k and 4.7k, so you can
choose the one that matches your headphone.
Please refer to [14. Improvement options] for details
calculation formula.
Wire jumper wires
here. Please use a
lead wire of cut
out resister.
Wire jumper wires
here. Please use a
lead wire of cut
out resister.
No Polarity
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E

C11 and C12 (Green) are in a
condition of slightly above the
circuit board because of the
wide pin pitch.
Please solder as close as
possible to the circuit board.
Those C11,C12 are Bipolar
type electrolytic Capacitor
They have no polarity.
AMP module completed
PCB
IC3,IC4 Output Buffer IC
LME49600 x2 are pre-
mounted.
1PIN is not connected
Please keep open.
R3, R4 are gain adjust registers
Please refer to “ 14. Future Development”
Left CH only
C3 0.1u
C11 470uF 16V BP
C14 100u 25V
-
+
IC1 LME49710
3
2 6
74
R5 100k
C6 0.1u
C2 3.3uF
R2 1k
R8 9.1 1W
C10 0.1u
R9 4.7k
R7 9.1 1W
R10 4.7k
C8 0.1u
-
+
IC2 LME49710
3
2 6
74
R1 1k
C7 0.1u
R3 2k
IC4 LME49600
2
1 4
53
C12 470uF 16V BP
R6 100k
C9 0.1u
C13 100u 25V
R4 2k
IC3 LME49600
2
1 4
53
C1 3.3u
C5 0.1u
C4 0.1u
Vcc+
GND
Vcc-
IN +
GND
IN -
OUT HOT
GND
OUT COLD
4
Rev.1.0E All Copy Right Reserved by otomatsu
2.2. Assembling Headphone amplifier module. 2 sets
The Portable headphone amplifier kit has a virtual +/- 2 way power supply,
but in this kit, we changed to a real +/- power supply. There is no basic
circuit change except this.
By supplying +16V,-16V with this change, it can give the full performance
that OPAM has that are THD, SNR, Slew Rate, Frequency Response, ….all
of specification.
Moreover, capability of output buffer IC LME49600 also increases as you
can reserve sufficient drive force for the load fluctuation of the
headphones.
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E

3.1 Assembling the Balance Drive Module
Please check and confirm that all parts are included before commencing soldering each of the parts onto the PCB.
Volume control (VR1) is the last part to be soldered onto the board. The volume control is made of a plastic conductive material, so be careful not
to overheat the part and the surrounding area when soldering.
1k x8 BrBlBlBr Br
120Ω x4 BrReBlBl Br
47Ω x4 YePuBlGo Br
100kΩ x2 BrBlBlOr Br
All parts
Completed
Registers color code
NE5532P x2 IC socket x2
Metal Film
Registers
PCB Terminal Volume
Film Capacitors 0.1uF x4 electrolytic capacitors
100uF 50V
+-
Electrolytic Capacitor C5,C6 100uF 50V
has pin polarity +/-
Long lead is plus +
Short lead is minus -
Other components have no polarity
OPAMP pin orientation
Top View
Parts List
Parts number parts parameter peaces
VR1 Volume Control 50k A 1
R1 R2 Metal film register 100k 1/4W 2
R3 R4 R5 R6 R9 R10 R17 R18 Metal film register 1k 1/4W 8
R7 R8 R11 R12 Metal film register 120 1/4W 4
R13 R14 R15 R16 Metal film register 47 1/4W 4
C1 C2 C3 C4 Film Capacitor 0.1uF 63V 4
C5 C6 Electrolytic
Capacitor 100uF 50V 2
CON1 CON2 CON3 CON4 Terminal 3P 4
IC socket IC socket 8pin 2
IC1 IC2 OPAMP NE5532 2
PCB Print circuit board 1
Caution: The
Conductive Plastic
Type material
Volume control is
very sensitive to
overheating when
soldering with a
soldering iron.
5
Rev.1.0E All Copy Right Reserved by otomatsu
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E

3.2 Balance drive module schematics
Volume + Balance drive
R4 1k C4
0.1u
R14 47
GND
L+
C1
0.1u C3
0.1u
R-
R8 120
R10 1k R+
+
C6
100uF 50V
Vcc-
-
+
IC1 NE5532P
2
3
4 8
1
R11 120
R15 47
L
Vcc+
+
-
5
6 7
R7 120
GND
GND
R9 1k CON2
R
CON4
R12 120
R1
100k
R2
100k
+
-
5
6 7
Vcc-
R3 1k
CON1
L-
Vol1 50k A
R16 47
-
+
IC2 NE5532P
2
3
4 8
1
+
C5
100uF 50V
C2
0.1u
CON3
R13 47
Vcc+
R5 1k
R6 1k
R18
1k
R17 1k
GND
6
Rev.1.0E All Copy Right Reserved by otomatsu
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E

Top View
4.1 Assembling the Power supply module
This is the jumper wire for
making +/- two voltage.
Please make use by cutting
out the lead of the registers.
Please refer to the manual of Regulator kit as there is no change.
1. Soldering the jumper wire on the regulator PCB for making +/-2 two voltage supply.
2. Soldering four jumper wires between Transformer and Regulator PCB.
3. Mounting four terminals onto the regulator PCB. (Two are in the regulator set and the additional two are in the case set)
4. Set the output voltage +16 and -16V by adjusting trimmer pot screw. Trimmer pot, Blue small cube
Set the output voltage by adjusting
the screw.
+16V
+16V
GND
GND
GND
GND
-16V
-16V Additional terminal x2 are
bundled in the case kit parts.
Please mount the four
terminals as shown in the
below picture.
Actual parts are little bit different from this picture 7
Rev.1.0E All Copy Right Reserved by otomatsu
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E

4.2. Power Supply Module schematics
JUMPER LINE x4
D11 1N4007
F1 FUSE holder 0.5A
J1
C4
0.15u
P1 5k
3
1
2
D7 11EQS06
C2
0.15u
R4
240 C10
100u 25v
D3
D12 1N4007
10VA
115Vx
22V
x2
D5 1N4007
D8
D9
C6
4700u 50V
DC OUT
2.5-22V
D6 1N4007
D1 11EQS06
H1
J2
1
2
HS2 U2 LM317
3
1
2
VIN
ADJ
VOUT
P2 5k
3
1
2
H2
D2
H3
C8
10u 50V
C5
100u 25v
H4
C3
10u 50V
R1
240
J3
1
2
+
T1
Troidal Trans
6
3
4
5
11
12
13
14
3
R3 240
-
D10
R2
240
DC OUT
2.5-22V
C7
0.15u
C1
4700u50V
D4
JUMPER
for
+/-
J4 2 HEADER
AC100V
50-60Hz
C9
0.15u
HS1 U1 LM317
3
1
2
VIN
ADJ
VOUT
8
Rev.1.0E All Copy Right Reserved by otomatsu
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E

5. CASE set
Case
1
Volume Knob
1
AC inlet
1
Power SW
1
Spark Killer
1
LED register 7.5k
1
Terminal for Power supply
2
Bipolar Capacitors
470uF 16V BP
4
RCA jack
2
XLR Combo jack
2
Wire Red, Blue
1.5m
Wire Black
3m
Petet
16
3mm screw short
20
3mm Screw long
4
3mmナット
4
Black Tapping screw for
XLR Combo
4
Washer small
1
Washer large
1
Y-lag for Ground
1
Band
4
Thermal shrink tube
5cm
Isolation sleeve
4
Panel Sticker
1
Petet x16 LED register Washer large 3mm nutx4 3mm screw x4 3mm screw x20 Black tapping screw x4
GND Y-lag Washer small x1
RCA jack x2 XLR Combo jack x2
Band x4 Thermal shrink tube
470uF 16V BP x4 Volume Knob
Power SW
Spark Killer
AC inlet
Isolation sleeve
Terminal x2
Wire Red, Blue, Black
CASE
Top x1
Bottom with GND screw hole x1
Side x2
Back panel x1
Front Panel x1
Hex socket screw x8
Hex wrench x1
Rubber foot x4 There are spare screws in the box.
Color of each parts might differ.
This capacitor is in the AMP Module box
Rev.1.0E All Copy Right Reserved by otomatsu
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E

6. Assembling the case and putting each circuit board in it
Use hex wrench to assemble the case
Place Power module like this.
No Pettet for Volume +Balance PC
GND screw hole
10
Rev.1.0E All Copy Right Reserved by otomatsu
Temporarily assemble the chassis and glue on the power supply circuit board.
Place the power supply circuit board on the back edge left; otherwise it will touch
the other circuit board or RCA jack.
Put the adhesive spacer on the each
circuit board with the screws.
Caution:
The adhesive spacer’s double
sided-tape is very strong.
Once you applied, it won’t
come off.
Before you glue the circuit
board, carefully make sure its
positioned without peeling
the white paper, then
carefully peel the paper and
install it.
Make a cut into the power SW’s hole at the front panel
using a file or another appropriate tool.
Match this cut and SW’s projection.
Decide a position where
the INPUT RCA jack and
the terminal of the power
supply circuit board will
not touch.
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E

7. Assembling the back panel
Pre-soldering
11
Rev.1.0E All Copy Right Reserved by otomatsu
Put the AC inlet and RCA jack on the back panel.
Put the vinyl sleeve cover on the soldered part to
prevent electrical shock and shorting.
The ability of soldering neatly to RCA jack is by putting the spare solder on both
terminal of the lead and RCA jack beforehand.
By doing this, it will melt together neatly providing good soldering coverage. For the
HOT terminal, covering the thermal contraction tube will protect the electric short
with other signals.
Attach 2 lock washers as shown in the picture on the left. One is with lead of GND.
This prevents making too much space between the knob and front panel because the 2 lock
washers for the volume control sticks out from the front panel. The lock washers make the
electric connection secure between the Volume control body and chassis ground. The
chassis is made out of a black anodized plated aluminum.
Since the volume is made of a conductive plastic material it will cause a humming noise to
occur when you touch the knob, so certain connection between Volume control body and
chassis ground is required. This is one technique for good SNR.
Attach the RCA jack to the back panels by
sandwiching the plastic washer on the back and
front.
This is to prevent the jack from coming into
contact with the electrical panel.
Wiring of the GND will be dropped from a power
supply substrate on the chassis later.
This is one technique for good SNR.
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E

8. Attaching together modules to the case
Do not touch the
Headphone AMP PCB and
Combo jack together here.
12
Rev.1.0E All Copy Right Reserved by otomatsu
We would like to caution again that because the double sided-tape has a strong adhesive bond, once you install the petetto on
the circuit board it will not come off.
After you attach the adhesive spacer to the circuit board with the screws, do not peel the white paper and please ensure its
positioned as you line up the circuit boards. Once you are confident that the positions are correct, peel the paper and attach
them carefully.
Even though it may only touch slightly, it will hardly come off so do it slowly and carefully.
Please pay special attention to this procedure.
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E

上面図
9. Wiring the Power supply
GND DC- DC+
GND DC- DC+
- +
Vcc+
Vcc- GND
Jumper wire
Spark Killer
No Polarity
LED register 7.5k
Power SW
AC inlet
Center ground
pin is open, no
connection.
DC+（16V）Red
DC- (-16V) Blue
GND Black
AC wiring Red
Please use isolation sleeves to prevent from accidental electric shock.
Use sleeve
For easy wiring access, take out the side panel of the case. 13
Rev.1.0E All Copy Right Reserved by otomatsu
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E

10.Wiring signal path-1
Signal HOT Red
Signal COLD Blue
Signal GND Black
L/ GND/ R
R+ R- GND GND L- L+
Chassis Ground
Use small Washer to
Screw bottom
Input RCA jack
LEFT RIGHT
XLR Combo jack
XLR Combo jack pin assignment
is as the following pictures.
All pins are independent and
isolated, so is a very flexible
configuration.
1 2
3
G
Front view of XLR plug (male).
XLR Combo pin assignment
S Sleeve
RRing
TTip
1 GND
2 HOT
3 COLD
GCase GND
Compare to ¼`` male plug
上面図
14
Rev.1.0E All Copy Right Reserved by otomatsu
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E

10.Wiring Signal Path -2
Protect case by vinyl tape underneath
Good soldering hint:
Wire should be pre-soldered to the plating before soldering ,
as shown as the below picture.
15
Rev.1.0E All Copy Right Reserved by otomatsu
Chassis ground is fasten by 3mm screw and small washer, like this
picture.
High light XLR Combo wiring.
Good soldering hint : All wires should be pre-soldered by plating
before wiring to the XLR socket.
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E

11. Checking all wiring
All wiring is finished.
16
Rev.1.0E All Copy Right Reserved by otomatsu
Use thermal shrink tube
for LED register
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E

12. Check the voltage level of key areas
上面図
Connect the Black lead of multi tester to Chassis ground
+16V
+16V
-16V
-16V
0V
0V
1. Use DC voltage setting of multi meter
2. All OPAMPs should remove from the socket.
3. If, all voltage are working OK, then insert OPAMPs and check the same points again.
4. All voltage should be the same before/after OPAMs insertion.
0V
0V
4pin 0V
4pin 0V
7PIN
+16V
4PIN
-16V
7PIN
+16V
4PIN
-16V
0V
0V
0V
8PIN
+16V
4PIN
-16V 4PIN
-16V
8PIN
+16V
Volume should be turned off.
0V
4pin 0V
4pin 0V
7PIN
+16V
4PIN
-16V
7PIN
+16V
4PIN
-16V
It is OK around 5-10mV at all “ 0V” points
17
Rev.1.0E All Copy Right Reserved by otomatsu
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E

13. Modification of Headphone cable
otomatsu
2 1
3
LEFT RIGHT
Gray
Yellow Blue
Red
Red BlueYellow Gray
Yellow L HOT
Gray L COLD
Red R HOT
Blue R COLD
SENNHEISER HD-25-1 II
SENNHEISER HD-598
Before After 18
2 1
3
Rev.1.0E All Copy Right Reserved by otomatsu
Modifying the regular headphones to the balanced drive model.
You can modify the headphones if the L and R cable are separated.
In the case of a headphone which has one cable, until we cut the jack we won’t know if LR wiring is separated. If you cut and there are only 3 wires, you can’t
remodel to the balanced drive model.
In this case, you can only use regular headphones. Please back to new regular jack.
SENNHEISER HD-25-1 II is full independence of L and R wiring, and you can exchange the cable.
If you cut the mini jack and peel the wire, 4 lead wires appear as the bottom left picture.
The body of the SENNHEISER HD-598 has 4 polarities. You can
change the cable.
There is one LR cable, but there are 4 independent wires inside,
so as you can see from the picture you can remodel it to the
balanced drive model.
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E

14. Improvement Options
1. Amplification Gain adjustment
You can change the gain as you change R3 and R4.
Please try a gain appropriate to the optimization of your
other headphones.
Formula (R1 +R3) / R1 = GAIN
Default value 2k (1k + 2k) / 1k = 3x gain
In the case of 1k ( 1k + 1k ) / 1k = 2x gain
In the case of 4.7k (1k + 4.7k ) / 1k = 5.7x gain
Note:
Make R3 and R4 the same value.
When you change OPAMP, confirm that the minimum
gain magnification is shown on the data sheet.
There is an OPAM that oscillate
when it becomes
less than double-quadruple such as
NE5534A,LT1028,OPA637 etc.
C3 0.1u
C11 470uF 16V BP
C14 100u 25V
-
+
IC1 LME49710
3
2 6
74
R5 100k
C6 0.1u
C2 3.3uF
R2 1k
R8 9.1 1W
C10 0.1u
R9 4.7k
R7 9.1 1W
R10 4.7k
C8 0.1u
-
+
IC2 LME49710
3
2 6
74
R1 1k
C7 0.1u
R3 2k
IC4 LME49600
2
1 4
53
C12 470uF 16V BP
R6 100k
C9 0.1u
C13 100u 25V
R4 2k
IC3 LME49600
2
1 4
53
C1 3.3u
C5 0.1u
C4 0.1u
Vcc+
GND
Vcc-
IN +
GND
IN -
OUT HOT
GND
OUT COLD
3. Change the OPAMPs
By changing the OPAMP, you can improve further performance.
You can enjoy the change of the sound quality.
Balance drive module (Dual in one package type)
Original NE5532P
Candidate OPA2134, OPA2604, LME49860
NJM2114, TL072, RC4558
JRC MUSE series
OPA627 x2, LME49990 x2 Need conversion socket
Headphone AMP module (Single in one package)
Original LME49710
Candidate OPA627A, LT1115, LME49990, OPA604
AD797, OPA827, NE5534A
In the case of OPA627A, need Dip mica capacitor 10pF between
pin2 and pin6 in order to compensate the phase.
20p capacitor is placed under the PCB
4.Change operation mode of LME49600 for much higher
speed response
1pin of f LME49600 is open, but when you connect to the land
of the board with the parings of the lead of the resistance, you
can change into broadband mode.
100Mhz of LME49600’s high level property extends up to
180Mhz. However in this case, depending on the equivalent
OPAMP and set up of gain, there is a possibility of oscillation,
so please add some 10pF to the phase compensation
condenser of DIP MICA between 2PIN and 6PIN of OPAMP.
You can amplify the output electric current as you pile up and
stack LME49600 and connect with each pin of 2 LME49600. In
this case, the amount of heat generated increases, so attach
some adhesive to the top and bottom of LME49600..
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Rev.1.0E All Copy Right Reserved by otomatsu
2. Improvement of super low sound level
characteristics
Eliminating the output coupling condenser
by removing the BP electrolysis condenser
of C11, C12 470u and by short-circuiting,
you can improve the super low sound level
frequency property.
But in this case, the DC offset voltage will
emit some mV. There is a risk of damaging
the voice coil if the large number of the DC
leaks a stream of electric current to the
head phone by any accident, wrong wiring,
and or a solder bridge. Try this challenge
only if you are confident.
otomatsu
Balanced Headphone Amplifier kit , BDR-HPA1E