DAC + bridged gainclone idea...

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UrSv said:
Could it be that the DAC plays at a fixed level meaning that you will play at maximum all the time without possibility of adjusting the volume?

Yup.... but thats why i said to forget about the fact it has no volume control ;)
Ill add a simple course resistive relay switched vol control between the I/V opamps and the LM3886, then use digital volume control before the DAC for the rest.
But that would have overcomplicated the schematic, so ive left it out for the moment.

I havnt built this yet... i would just like confirmation from some of the other brains here before i spend the time making the PCBs, building it, etc.
 
I like your idea. Actually, I've been thinking about the same kind of thing, only with a digital crossover filter. But before I get there I have to get my design to work properly as a DAC.

I have my own oversampler up and running in a Xilinx FPGA, and modifying the filter coefficients for xover use shouldn't be that hard. If you trust the oversampler of the PCM1794, it should be possible to receive a digital 16bit/44.1 mono signal, filter it and present a "stereo" 16bit/44.1 signal to the DAC with one channel for each speaker element. Personally, I oversample on my own, so I'll need one converter for each element (no-df mode or whatever they call it.)

But you will still need some kind of volume control. I haven't yet started looking at digital potentiometers and programmable-gain amplifiers yet. But tell me if you find some promising ones!

Greetings,

Børge
 
Well this will actaully be used with digital xovers.
But from a PC (Linux + BruteFIR).
So, ill be making 3 of these PCBs (stereo out each) for Sub, Tweeter L&R, Low L&R.

Ive now decided ill be using PCM1798's in mono mode for the outputs.
The I/V opamps will be OPA627/637s (eek, ill need 12 of them!).
 
Oh.

One thing ive just thought of is that there is a Vcc/2 (2.5V) offset on the DACs current ouput pins.
With other DACs there is a VCOM or similar that is used to cancel this at the IV converter opamps.

With the PCM1798 there isnt such an output pin... they assume that the -Ve and +Ve offsets will be canceled at the ouput opamp.

To you guys have any ideas of how i could cancel this out without using series caps?
 
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