CS4397 eval board - diyAudio
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Old 24th November 2003, 01:51 PM   #1
macaque is offline macaque  Canada
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Join Date: Nov 2003
Location: Canada
Default CS4397 eval board

Hello all, I'm new here.

I am considering order a CS4397 eval board to see what I can do with it. My first plan is to use my selead lead calcium battery supply I currently use with my Audio Alchemy DAC for the +-12 VDC required, and maybe some D cells for the +5 on the digital side. The board already seems to have regulators available. I will probably eventally replace enitre the output stage as well.

The interesting thing about this board (and chip) for me is that it uses a single Vref for both channels, and it expects the Vref to be from an external source. Looking at the eval board data sheet it seems a voltage regulator is used to produce +5VDC (the typical value for Vref listed in the 4397 data sheet) with a couple of resistors on the regulator determining the voltage.

It seems to me that if the chip works well over a range of Vref values, this would be ideal for implementing a volume control with a single pot at the regulator. The pot does not need stereo tracking capability, and the chip data sheet claims the channels are matched to within 0.1 dB. Also, the output impedance of the entire DAC would rest soley on what you use for an output stage.

I currently use a passive pre, and I would be hard pressed to to active, but this solutions gives you the benefit of no pre, no variation in output impedance based on volume, no stereo tracking issues, and no resolution tradeoff even with 24 bit or DSD source material for volume control (as with digital volume control). Keeping the digital and analog side on separate battery supplies is a cheap and easy way of eliminating all the AC hassles too.

Am I nuts? I can't see from the data sheets that adjusting VRef downward will affect performance although I guess I won't know till I try. This DAC seems fairly unique in its ability to use a single external Vref for both channels, and from the white paper it seems a lot of work was done on the chip side to be able to allow an external Vref instead of using an internal precision source.
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Old 24th November 2003, 03:17 PM   #2
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Join Date: Jul 2001
Location: The Netherlands
I can't comment on the Vref questions, but I do have the eval board of the CS4397 and like it very much. It was more expensive than I thought it would be. The board is very usefull as a DAC, receiver, preamp. You could stay passive with this board. It has a particalarry good bass timbre, very low noise etc etc.

I realized that the eval board is about as expensive as a NAD CD-player... hmmmmm .. makes me wonder if I made the right chooise..


Goodluck,
Thijs
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Old 24th November 2003, 03:20 PM   #3
tiroth is offline tiroth  United States
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Join Date: Dec 2001
Location: Pittsburgh, PA, USA
Generally performance will degrade as Vref is lowered, how much so is dependent on the topology. AD1853 is spec'd for up to 50dB of attenuation by reducing Iref, but Vref must be held constant. Implementation dependent--I suggest you contact their engineers before proceeding.

I would also imagine that the digital side may well be the biggest current draw, so I wouldn't recommend D cells ($$$). I have a Crystal ADC board that ends up drawing many hundreds of mA, mostly on the +5 supply.
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Old 24th November 2003, 04:23 PM   #4
macaque is offline macaque  Canada
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Join Date: Nov 2003
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Thanks for the info guys... regarding the price, I was quoted $150US here in Canada, not bad at all especially since the Canadian dollar quite high these days.

As far as Vref goes, this chip doesn't have a IRef so it is a voltage output rather than current output dac. It makes me curious as to how well it will perform at lower VRef, I imagine a voltage dac is less sensitive to Vref than a current DAC would be to IRef, altough I'm just speculating.
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Old 28th November 2003, 06:37 PM   #5
macaque is offline macaque  Canada
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Join Date: Nov 2003
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As I anxiously await delivery of my eval board I'd like any suggestions about improving what is shipped.

I already plan on using batteries for the power supply. It seems that the +5V for digital on this board is derived from the +12, as is the +5V for analog. I think I would like to try to keep the digital stuff on a separate battery. Also, the CS8414 tranceiver data sheet says the Vanalog should be as quiet as possible as it will directly affect jitter performance. The schematic for the eval board seems to show this pin is fed fro the +5V digital supply!

Also, the LT1028s on output - any views? I see them mostly mentioned in terms on phono preamps. Any one tried any subtitutes? Maybe I'll eventually try tubes, but that complicated the battery supply.

Thanks for any suggestions....
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