Sunday, 3 January 2010

Make a Sound Card with PCM2704

This article relates to my previous article Make a sound card with PCM2702. In this time I used newer IC from Texas Instruments PCM2704. Thanks to this circuit with all necessary features inside 28pins SSOP package I was able to built quite small sound card. The result is sound card with size of gumstick.


This device is fully functional sound card for PC. The main advantage of using PCM2704 against PCM2702 is much easier construction. As you can see on the block diagram it has built-in 5V and 3.3 voltage regulator, HID interface (MUTE, VOL+, VOL-), S/PDIF output. The circuit can be powered directly from USB port. Next advantage is that the outup DAC is able to drive directly 32ohms headphones, but the ouput power is only 12mW. For all details please refer to the PCM2704 datasheet.

Block diagram

The schematic is very simple. It is almost copy of the datasheet circuit diagram. You can see the core IC PCM2704 (U1), crystal with supporting parts (X1, C1, C2, R1), connection to the USB (USB connector, R2, R3,R4, L1), a lot of blocking capacitors for all voltages (C3, C4, C5, C6, C7, C8), S/PDIF output header (J1), HID header (J2), output filter (R5, C11, R6, C12, R7, R8), coupling capacitors (C9, C10) and output 3.5mm Jack connector (J3).

Schematic of sound card with PCM2704

I designed my own PCB. The dimensions of the PCB are 55x18mm, including USB and Jack connector it is 73x18mm. To keep the size as small as possible 0805 size of capacitors and resistors were used. The L1 is ferrite bead which reduce high frequency hum. With good soldering iron and litle experience it is possible to assembly the PCB by hand.

Assembly diagram (top side)

Assembly diagram (bottom side)

PCB (top side)

PCB (bottom side)

Assembled PCB (top side)

Assembled PCB (bottom side)

I built two pieces of this sound card. I have tested the sound card under Windows XP and Windows Vista and it works without any problem. I wanted to use this device for my Internet radio receiver, which I'm building according to the project published on The receiver is based on Asus WiFi router WL-520GU with OpenWrt Linux distribution. The sound card works under the Linux as well, but it stop and start playing the sound periodically (the period varied from few minutes to one hour). I guess it is driver problem (if somebody has any idea how to fix it I will be very grateful).

You can ask me why to build this sound card when you can buy similar device for few bucks. I have also one sound card from China which cost around 5$ but the quality of the sound is very bad, so the main difference is sound quality.

PMC2704 (TI)
PCM2704 Evaluation Board (TI)


Richard said...

I have created a custom PCB board design with your schematic. However during prototyping on the breadboard, I was not able to get the device to be recognized when connected to the USB... I have the schematic and PCB design uploaded here:

Anonymous said...

Richard, does it work at all? Check you have +5V and +3.3V chip power and 12MHz crystal, then USB wiring.

Richard said...

I have it setup the way you have posted. It is powered by the bus and has both 5V and 3.3V from the bus. It sometimes try to install the device but will fail and at times it would say the USB device is drawing too much power.

Richard said...

It seems like the V+ and V- lines on the USB were mixed up :) Working fine now, but the output is very weak...

Jovan said...

I have used PCM2906 in my design, and had problems with recording too. Unfortunately, this is described in TI note SLAZ036A. Their solution was to make improved version of a chip: PCM2906B. When I changed to this chip, problems were still present, but occurred less frequently... So, expect "Pop noise at irregular timing, intermittent continuous noise, or L/R Channel Inverse during recording"...

tamingfire said...

inspiring post, well done!
Thanks for the detailed writeup and sharing, cheers from Texas.

Anthony said...

Hey, do you have any more information on how you made the pcb? I would like to build one of these and would like to use your pcb.

Miroslav Batěk said...

@Anthony: The PCB was fabricated profesionally in one of the Czech PCB manufacturer. I have enough spare PCBs from new batch. The PCB is gold plated with black solder mask. They are pretty nice. The price would be 6USD + shipping. You can contact me at diy4fun [at] gmail [dot] com.

www said...


Before use, Is it need to modify USB discriptors via External ROM?

ArupBasak said...

Hi, can you upload the PCB raw files? I want to try once to develop it at home.

Alvin Smith said...

Useful information shared..Iam very happy to read this article..thanks for giving us nice info.pcb manufacture

Anonymous said...

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Gabriel Rodriguez said...

Excuse me, can you please simplify, the step's and make that pcb board with only the lines of where to connect the pieces. And can you please show me picture's of those little pieces that are soppose to be attached to the board. And please make a youtube video on how to make this sound card, please a lot of people want to make this. But this isn't enough information to help those who think this is like some sort of rocket-science project. Thanks you, and please message me back at

Bean said...
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Bean said...
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