bernid wrote: > Hi, > I would like to return to the FCC audio connector topic. I keep thinking > about using of an external DAC with two independent clock 22.xx and > 24.xx. > Im considering designing the muxer/switch and use SPI interface to > drive DAC filter. > > 1. Can I use one of the schematics from 'this' > (http://www.eetimes.com/document.asp?doc_id=1202359) website. Which one > will be better -1' Simple Implementation of a clock switch'- or -3 ' > Glitch protection for unrelated clock sources'- ? > > 2. What chip(s) to use to make this muxer? 7400 series? (SN74LVC1G04, > SN74LVC74, HC7408 and 74LVC1G02) > > 3. Where on the Carrier board is a FCC audio connector? If possible , > please attach the part of the photo where this connector is located and > where is pin 1. > > 4. As a DAC I'm going to use DF1706 and 2xPCM1704 . Do the SPI signals > from pins :15 MC, 16 MOSI, 17 MISO would be able control DF1706 filter? > In particular, whether it will be possible to control the oversampling > ratio? For example, for streams with sampling rate upto 48kHz set > oversampling 8x and for files above 48kHz set to 4x?. > > Thanks, > Bern
1) There is no need to use any of those fancy clock schemes, a simple mux is all that is needed. 2) I use a 74LVC1G97 hooked up as a mux. 3) It is J17 on the left side of the board. I'll see If I can get a placement picture posted. I have a PDF, I'll see if I can post that. Pin 1 is on the right in this orientation. The cable comes out of the upper side of the connector. 4) the DF1706 doesn't sound nearly as good as the upsampling we are doing in software. I have done exactly what you are talking about with a very good discrete IV stage for the 1704s and what we are doing in CSP sounds better. But of course you are free to try anything you want, but it is going to have a hard time sounding as good. You might want to forget about the 1706 and feed the 1704s direct from the I2S (with a splitter of course) and let the software do the upsampling. Not only will it sound better but you don't have to program the DF1706. I think you are misunderstanding the SPI interface on this connector. The SPI pins of J17 are connected to the SPI pins of the DAC chips, NOT the processor. They are there to allow someone to program the DSP block in the DAC chips from an external system. If you want to get at an SPI port from the processor, that is on connector J11 which contains all the display interfaces. It is important to understand that J11 and J17 are on different power domains. J11 is on the "digital domain" which includes the processor and digital interfaces such as Ethernet and USB. J17 is on the "audio domain" which includes the DAC chips, low jitter clocks etc. Any interface between the two should be done with GMR isolators. Thus if you want to control the DF1706 from the processor you will need to get the SPI signals from J11 and run them through isolators to your DAC board. This also means you will need two power supplies so you can keep the domains separate. I hope this is clear, I'm a little out of it today. John S. +-------------------------------------------------------------------+ |Filename: CSP1_place.pdf | |Download: http://forums.slimdevices.com/attachment.php?attachmentid=15532| +-------------------------------------------------------------------+ ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=97881
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