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CS6A4689 Headphone amplifier project
CS6A4689 Headphone amplifier project
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Old 24th June 2017, 01:43 AM   #1
tedkok is offline tedkok  Hong Kong
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Default CS6A4689 Headphone amplifier project

I plan to disclose the complete circuitry and PCB layout information of the following CS6A4689 headphone amplifier evaluation board.

CSEVB6401R2 Product Brochure-15June2017-16

If you are interested to purchase a sample of it, do please drop me a message.

Last edited by tedkok; 25th June 2017 at 04:21 PM.
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Old 24th June 2017, 12:47 PM   #2
tedkok is offline tedkok  Hong Kong
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The core circuit is the CS6A4689 based hifi amplifier.

The feedback path will control the amplifier gain.
In this circuit, three different gains
1.3x 4x 9x
is obtained by the three way switch SW3G$1

Besides the amplifier gain, the input audio volume
is also controlled by a dual-band RK09, a 50Kohm
variable resistor.

The output of the amplifier is connected to a 3.5mm jack
through relay K1. The control circuit of the relay will
be provided in the next post.

You may noticed that there are a lot of DNP components
which are provided to make the PCB layout to be able to adapt
to different component sizes, and also provided to allow
user to adjust the amplifier through beta-feedback circuit,
which will include the gain bandwidth, and tonal, etc.
In it's most pain form, the feedback path will just be
a simple resistor based voltage divider as shown in the
attached schematic.

Enjoy!
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File Type: png cs6a4689-sch.png (102.5 KB, 555 views)
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Old 25th June 2017, 12:58 PM   #3
tedkok is offline tedkok  Hong Kong
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From a 3.7V Li-ion battery to +/-10V dual rail supply, we applied the CS7D651 DC-DC converter. A very low noise DC-DC converter with enough output current for the high performance CS6A4689 amplifier IC

Noted that a simple connection of the DC-DC output and the amplifier with do the job in raw.....but with power on pop....We shall show you how we resolve that problem in my next post
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File Type: png cs7d651-dc-dc.png (117.8 KB, 520 views)
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Old 26th June 2017, 01:20 PM   #4
tedkok is offline tedkok  Hong Kong
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The Li-ion battery charge is performed by CS7R3831,
which is capable of 800mA charging. Good enough to charge
the Li-ion battery and provide enough power to drive the
headphone amplifier at the same time.
Attached Images
File Type: png cs7r3831.png (35.4 KB, 484 views)
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Old 27th June 2017, 01:06 PM   #5
tedkok is offline tedkok  Hong Kong
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The start up pop sound is removed by two separate delay circuit

1. The power on delay circuit. After switching on, VSYS will increase
from zero to 3.7V (the Li-ion battery voltage). Which will charge up
C32 through R1. This charge up action will create a delay.
After the capacitor C32 is charged up to 0.7V, Q2 will conduct, which
in turn will turn on PMOS G1 and G2, and conduct the Li-ion battery power to VCC and power on the DC-DC converter, and all then the headphone amplifier IC.

2. The other delay circuit is the power on headphone isolation circuit.
At power on, the headphone is isolated from the amplifier through relay K1.
The relay K1 will keep turning on until the DC-DC power supply stable,
than it will be closed (K1 is a normal close relay) with the relay coil power being removed.

There are a few more tricks needed to create a high quality headphone amplifier which will be described in my next post.
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File Type: png power.png (70.4 KB, 475 views)
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Old 29th June 2017, 11:04 AM   #6
tedkok is offline tedkok  Hong Kong
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You might have noticed that the DC-DC converter, and all associated power circuitry use AGND,

While the power amplifier use GNDA

Ground isolation is one of the best technique to create a silent background...much higher signal to noise ratio can be achieved by this
simple circuit technique.

Knowing that the circuit cannot has two unrelated ground, they have to be connected, and this is achieved via ferrite bead. We shall use WE-CBF from Wurth Electronics, and two ferrite beads are added on the pcb, which has a physically separated ground plan for GNDA and AGND.

Attached is the last piece of schematic for this project.

My next post will be about the pcb layout.
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File Type: png bead.png (7.2 KB, 438 views)
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Old 30th June 2017, 02:34 PM   #7
tedkok is offline tedkok  Hong Kong
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when we put everything together this is the final PCBA....a very compact working headphone that can fit into a slim excursion AL case.

1. Please note that the front and back side AL covers are leave out to show the inside.

2. This is a hand soldered sample, which you can obvious observe the poor soldering quantity. So...be minded with the very very poor soldering
Attached Images
File Type: jpg pcb.jpg (107.6 KB, 181 views)
File Type: png case-top.png (412.3 KB, 169 views)
File Type: jpg case-front.jpg (65.4 KB, 71 views)
File Type: png case-back.png (785.8 KB, 70 views)
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Old 5th July 2017, 03:45 PM   #8
tedkok is offline tedkok  Hong Kong
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Tonite, we shall post the PCB layout, and shall discuss the layout arrangement by tomorrow nite.

Attached Images
File Type: png top.png (176.8 KB, 100 views)
File Type: png bottom.png (98.1 KB, 87 views)
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Old 5th July 2017, 04:32 PM   #9
HotIce is offline HotIce  United States
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Nice project!
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Old 7th July 2017, 05:37 AM   #10
ammel68 is offline ammel68  United States
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CS6A4689 Headphone amplifier project
Quote:
Originally Posted by HotIce View Post
Nice project!
Yeah, but it's going to be limited to the number of people that can solder all those microscopic SMDs onto the board.
No doubt those devices make for a nice compact board, but it limits the number of people who are able to build it...including myself.

If I can't purchase something like this already assembled, tested and ready-to-go, then I personally stay away from these "nightmare to assemble" SM designs.
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