Simple PCM2707 bus powered I2S source, is this circuit good or bad? - diyAudio
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Old 1st December 2008, 05:13 AM   #1
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Default Simple PCM2707 bus powered I2S source, is this circuit good or bad?

Hello, this is my first post in this forum. My english is not perfect, sorry about that. :-)

I want to make myself a I2S source for my modded California Audio Labs Tempest II cd-player. The cd-drive unit is bad, but the digital board and analog board is working fine.

I have built two boards with the PCM2707.

I ordered two PCM2707 from ebay, one was destroyed when desoldering, while the other one worked a whole evening before i got "Unknown USB device" from windows.

The fault with board #1 was my usb cable.(Changed the PCM2707 before checking the cable; man,do I feel stupid ) I took a cable from a UPS, which had a usb connector in one end, and a RJ45 in the other end. When i was trying to find the fault, i found that the D+ and D- in the cable was not twisted pair, as the usb standard demands. I changed the cable, and the new PCM2707 worked, for 3 hours. I suspect that since I had gone with external power supply, I have done something wrong in connecting / powering the chip. Datasheet for the 2707 says that the usb MUST be active before applying external power to the chip.

Board #2 power the PCM2707 from the USB VBUS +5V. The PCM2707 has got an internal 3.3 Voltage regulator built in for the circuits that require 3.3 Volts. Just have to hardwire the pins on the outside. When i desoldered the once working chip from board #1, and soldered it onto board #2, windows came up with the same error message. The chip is destroyed. I have ordered a new chip, but i am not soldering it on to the board before I am sure that my circuit is correct. I have used application examples from the datasheet as a loose reference of what to do and not to do.

I have got many years of experience in automation / electrical engineering / programming microchips (PIC16), but the price of the PCM and the extended wait for parts to arrive from asia (I live in norway), makes me think twice now before testing this layout once again.

Would it be a good idea to put, say 22ohm, resistors on the I2S lines?

What do you people think of this design?
Is there something missing?
Do anyone know any better ways to do this?

The circuit is shown in the attached picture.

Best regards
Jogeir Emil Gjersdal
Norway
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Old 1st December 2008, 07:03 AM   #2
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Sorry I don't have any advice for you, but if you need more IC's I have a decent quantity of PCM2706 I could give you a very fair deal on.
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Old 1st December 2008, 02:29 PM   #3
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Default fair deal on pcm's

theAnonymous1: what would you consider a fair deal to be? I am interrested in just a couple of PCM's to start with. If I get this design to work, me and my friend is thinking of a tubed dac later on. This might grow to a kit, but for now it is just prototyping.
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Old 2nd December 2008, 01:14 PM   #4
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Hi Jogeir,

I noticed in your schematic that you have left the suspend pin floating; this should be pulled high. I'm not sure if that has anything to do with your problem or not.

Did you receive my email?
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Old 2nd December 2008, 03:00 PM   #5
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Hi, I checked my mailbox just now, and I must say that it is a fair deal. ebay-stores charge $19.90 for the same chip. Before I posted this thread I ordered a pcm from ebay. :-(

Today I talked to TI here in Norway and they told me to get a sample from TI's homepage, so I have ordered a sample from TI.

I thank you for the offer, but it looks like I dont need more pcm's in a little while.

The suspend pin is an output from what I can tell. It is used to suspend external circuits like filters and so on. It is low when the pcm is suspended. happens after 5ms without activity.

dddac schematics indicate the same thing; SSPND is left floating in the schematic.

-Jogeir Emil
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Old 2nd December 2008, 03:10 PM   #6
kuroguy is offline kuroguy  Germany
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I requested samples at the TI web site and they mailed me 5 each of pcm2707, pcm2706, pcm2902, pcm2906 for FREE. No questions asked, and they arrived in 3 days. Price doesn't get better than that.
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Old 2nd December 2008, 03:12 PM   #7
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No problem, glad you can get some samples.

The only reason I mentioned suspend is because I have seen it tied to Vccp in another schematic.

http://www.ecp.cc/NOS-USB-DAC.html

EDIT: Oops, I guess that was just a mistake in the sch.

http://www.diyaudio.com/forums/showt...10#post1041910
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