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COD - Current Output DAC

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#81
Hi Russ,

Actually I'm planning to do the summation in the current domain since the dacs can be treated as well matched independent sources driving a transimpedance amplifier with 0 input impedance. There should be no interaction between the sources at all and the accuracy of current summation at each I/V converter should depend solely on the trim quality of the dacs.

Paralleling current source dacs by summing currents is a common practice - some even do it with resistor I/V conversion where you can expect some interaction between the dacs.

Should this not work well I plan to design a discrete based I/V converter to do the job.
 
#84
COD revisited. 🙂

Well well well, Long time since I revisited this thread. But I have been playing around with COD again since I had some new things to test(JT2 code).

I have a couple of observations which some of you may find useful.

First... I think I have found a very very good setup for COD.

COD --> IVY basic (I will explain later) ---> JT2

Now here is the thing. The output of the COD is pretty darned clean. It does not really need heavy filtering as long as you use the fast rolloff digital filter. So, what I have done is setup IVY with just 392R feedback(I/V) resistors and no filter caps in feedback. None.

Now when I tested this (with my humble gear) the DNR and THD were pretty darn close to Buffalo. And it does sound very very good.

So any of you with a COD and IVY should consider ditching the feedback (filter) caps. I think you will discover a nice change of pace. 🙂

To me it sounds like an entirely new DAC.

Cheers!
Russ
 
#89
Can someone please take a look at my wiring schema? I'm not too certain I got it right....

Are the modules connected ok and is the grounding ok?

Thanks!!!

Jeroen
 

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#94
BrianDonegan said:
I would join the two LCDPS GNDs at the supplies, then run a single ground to COD (they are both joined on the COD board). Also eliminate the I2S GND from Metronome.
Click to expand...


Hi Brian,

Thank you for taking a look at it.

Why is joining the grounds at the PS better than joining at the boards? Is it preventing from current flowing between the boards? I sort of concluded that was not possible as the boards do not share a common. Is there current flowing through the I2S lines?

Thanks,

Jeroen
 
#96
BrianDonegan said:
I would join the two LCDPS GNDs at the supplies, then run a single ground to COD (they are both joined on the COD board). Also eliminate the I2S GND from Metronome.
Click to expand...

I soldered the boards, tomorrow I'll test with just some passive IV before I install the RAKK IV. Below is the adjusted schema, I did not add the clock to the common so it is isolated from the rest.

Jeroen
 

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#100
JeroenR said:


I soldered the boards, tomorrow I'll test with just some passive IV before I install the RAKK IV. Below is the adjusted schema, I did not add the clock to the common so it is isolated from the rest.

Jeroen
Click to expand...


It works. 🙂

One weird thing though... The COD and Metronome are stacked. I thought it would be wise to add some shielding in between so I added a 1.5mm alu plate (see photo). This proved a bad idea: every time I touched the chassis the sound disappeared... :xeye:

Anyone knows what happened? The alu shielding/plate and chassis were in contact through the screws but there was no ground/common from the circuit connected to the chassis???
 

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