Forum DAC tweaking thread

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gbyleveldt

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I'm starting this thread for the tweakers out there for the DAC GB found at http://www.avforums.co.za/index.php/topic,1548.0.html This seems like a better place to do it.

To keep the costs down, I'd be using NE5534 for all the opamps on the project. The first step would be to change the differential opamps for higher spec types and keep the 5534 as IV. It is also possible to change the IV as a second step. My next mod will be using THS4131 opamps in the IV. This requires little daughterboards to be made, I'll be doing this a little later as I'm doing the next batch of home-brew pcbs for the multi channel preamps. There are truly a multitude of options to use here and it would be impossible to cater for all tastes. These are in DIP8 packages that's easy enough to swop for other chips. I can supply fancier ones on request, though. Also, I catered for pulse transformers on the SPDif line, but this seems unnessecary with a single ended medium. I'd be sending the PCB's without these, but it can be fitted if desired for R30 each. Laastly, the unit has inputs for 4 SPDif lines but are configure for only 1. More can be added by populating the missing parts.

Also, there is a lot of tweaking possible on the output filter network. You can go for the brickwall MFB filter as suggested in the application sheets, or go for the minimalist approach. I'll be posting some component values for the various upsampling rates should it be required. To my ears, I found the minimal filter route to be the best, probably because of the minimal phase shift introduced at higher frequencies...

In any case, any input or suggestions are welcome. I've tried to leave as much flexibility as possible on the PCB, so let's see where this goes.
 
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