USB based DAC project

bluetech

Member
2008-01-22 10:26 pm
Hello everyone,

I am new to electronic design and I have to build an audio circuit for a college project.

I have to design and build a USB based hi-quality audio DAC.

After having a mini research I found the PCM2205 IC from Texas Instruments that does the whole job and more. I wouldn't like to use this IC though because it will be very easy. I may do it at the end but i would like to try to buid some of the part myself and not use one chip for the whole project.

I would like to find an appropriate USB module and build the DAC on my own(ideally).

Is the UM232R USB module appropriate for my project?http://www.ftdichip.com/FTProducts.htm
Can you suggest me any other way of interfacing a DAC to USB

I would really appreciate any help either on the USB part or on the DAC part of the circuit (part numbers, circuits, links, ...)

Thank you
 
I can't find any information on the PCM2205 IC, it's not listed on Texas Instruments website. That said, what you are going to want to do is get something like a PCM270x chip. This will act as the USB receiver, and it will output the I2S signal that many modern DACs use. After that, you've got a large number of options. Some good ones include the PCM1794/6/8. That is a pretty good one to go with because it has the digital filter uilt into it. If you use an older DAC, like say the PCM63, you will have to have a separate digital filter. If you wanted to go the NOS route, you could use the TDA1541A. I even believe I've seen some NONOS designs using the AD1865 chip.

But picking out the chips that you want to use is the easy part. You also have to work out the power supplies and voltage regulation, and then finally you have to do the schematic and the layout.

bluetech said:
Hello everyone,

I am new to electronic design and I have to build an audio circuit for a college project.

I have to design and build a USB based hi-quality audio DAC.

After having a mini research I found the PCM2205 IC from Texas Instruments that does the whole job and more. I wouldn't like to use this IC though because it will be very easy. I may do it at the end but i would like to try to buid some of the part myself and not use one chip for the whole project.

I would like to find an appropriate USB module and build the DAC on my own(ideally).

Is the UM232R USB module appropriate for my project?http://www.ftdichip.com/FTProducts.htm
Can you suggest me any other way of interfacing a DAC to USB

I would really appreciate any help either on the USB part or on the DAC part of the circuit (part numbers, circuits, links, ...)

Thank you
 
It is unclear what you are trying to accomplish here. You can use one of the PCM270X family parts to get your USB->I2S interface easily, then hook almost any DAC up to the I2S side. If you are worried about how hard using a part not optimized for this application will be, use the PCM270X. You seem to be asking for a setup that is easy...but not too easy.
 
b-square said:
You can use one of the PCM270X family parts to get your USB->I2S interface

You can also use the DAC built into the PCM270x... an idea i would have poo-pooed until i heard quite a decent exection of it (in the KingRex T20U). This outperformed a DAC using 270x>IS2>1543 that cost more than the KingRex.

dave
 
planet10 said:


You can also use the DAC built into the PCM270x... an idea i would have poo-pooed until i heard quite a decent exection of it (in the KingRex T20U). This outperformed a DAC using 270x>IS2>1543 that cost more than the KingRex.

dave

Re-read OP. He specifically does not want to use an integrated solution as this is a school project to learn something (but not too much!).

bb
 

bluetech

Member
2008-01-22 10:26 pm
Hello everyone and thank you for your help.

Someone said earlier on this forum that it is not clear what i'm trying to accomplish. It is true as i'm am new to electronic design and especially to usb.I t is the begining of my project and i'm completey lost. I change my mind 3 times per day on what i want to do.
Thank you for suggesting me the PCM270x series even though i knew it before i joined this forum. I have bought one of those, the PCM2705, as i cannot find in UK neither the 2706 not 2707. Can someone knows how i can find any of those two in UK??

I will try to make a first approach to this project using the TI chip.

My project though officially starts on October 2008 and finishes on June 2009. I have plenty of time to try for something more sophisticated that a single IC solution (or the TI chip with external DAC).

At the moment i'm trying to find a solution on the USB interfacing.

Originally i thought to use a USB module like the UM232R (USB to UART).

A second thought is to use a USB microcontroller like the PIC18F2450 in order to send USB audio data from a PC to my circuit. The microcontroller solution is better because if the time permits, i would like to exted the project into an complete audio preamplifier so i will need some kind of control there.

Thank you.
 

error401

Member
2007-03-24 7:54 am
Originally posted by bluetech
A second thought is to use a USB microcontroller like the PIC18F2450 in order to send USB audio data from a PC to my circuit. The microcontroller solution is better because if the time permits, i would like to exted the project into an complete audio preamplifier so i will need some kind of control there.

Thank you.
I could be wrong, but I'm not sure that PIC is going to be fast enough. Strictly it probably is, but managing the USB transaction and properly putting the data on the output bus is going to eat up the measly 12MIPS pretty quickly. You probably want to step up to something more powerful like an AVR32 or a small ARM.

The other issue you're going to run into is buffering and clock generation. You need to generate an output clock based on the rate that USB packets arrive. Doing so is probably the most difficult part of the project. The other issue with that PIC is that it only has 768B of RAM. You need to be able to buffer at least 1ms of audio data. At CD audio rates, that's about 1.5KB.

I would really recommend sticking with the ASIC solutions for this project. You're talking about a fairly large firmware development and debugging project, plus the associated hardware. I don't think you have nearly enough time to finish such a project on your own, with no experience, in 4 months. You might have more luck with a slightly less integrated chip like the TAS1020.
 

Archwn

Member
2006-10-25 4:18 am
Hi bluetech, USB+uC is a doable thing. but that would be a very advanced project (at least for me) it would involve somekind of device driver understanding sort of thing. but if you already know what's going on there, i would be delighted to see how your project goes.

for pcm2707, i think digikey uk or farnell uk has it. but if you re really struggle to get it, my supply would arrive in a week or two and I could sell some for you. or if you want a quick try, i can sell it with board/ components as well. it would be a good quick choice if you just want to evaluate this path before you go for usb+uC. ;)
 

Jambo

Member
2008-01-27 1:25 am
bluetech said:
I have bought one of those, the PCM2705, as i cannot find in UK neither the 2706 not 2707. Can someone knows how i can find any of those two in UK??

TI have a great policy with free samples - I'm sure they'd send a few to you at your college - just go to the product page at TI's website and click the free samples link. Might as well grab a few opamps as well...