ejaouen said:
It should work provided the power amp has enough gain. You have not said if it is a single ended or balanced amplifier. The output impedance is basically that of the I/V resistors.
Cheers!
Russ
scottj said:
I have high hopes for the WM8741. And I would not say its a problem per se.
The PCM1794 is one of the best. Its just the way it is. Just run at 96khz and you will be happy. 🙂
Russ White said:
The power amplifiers have balanced input (INA134 at the input) and the sensitivity is 1,2 V for full power (70W) : it is about 28 db gain.
I will try it direct from COD module output (using the resistors and capacitors
) for my mids and highs amplifiers.
If this does not work loud enough (and if there is too much noise floor) I will wait untill the discrete balanced I/V module for COD is ready !
Voltage out DAC? Hmm, must be switched capacitor filter *checks datasheet* yep. I cannot honestly consider this "hi-fi" in any sense of the word.Russ White said:
AD1955 sounds better. TI's device beats it in a few of the numbers, but overall and actual sound, ADI wins. I'm also still waiting for a linearity graph from TI.
I am not sure how abzug is attracted to this thread. But I am glad he has found his favorite part! 😀
abzug said:
Ahhh, well then you must have noticed that this is MY current output DAC. Not just any current output DAC. I hope you enjoy yours, please post it in its own thread. Perhaps I will post there! And I will even stay on topic! 🙂
Russ White said:
Russ please see my reply above.
Also I could try double mono mode with 2 COD modules per stereo power amplifier this way I double current and have a bit more voltage at the ouput.
You said with the passive resistor I/V the sound is "warm" colored, I will probably like that for my mids and highs.
Also Russ the pcm1794 pleases me PERFECTLY : it is said a bit less chirurgical sounding than AD1955. The PCM1794 has even better dynamic and noise figures ! Long life to to the COD module with PCM1794 !
thank you
Thanks Ejaouen. 🙂
I think your setup will be just fine. I would start with something like 221R for the I/V resistors and if you need to adjust upward or downward. It should sound very good.
Cheers!
Russ
I think your setup will be just fine. I would start with something like 221R for the I/V resistors and if you need to adjust upward or downward. It should sound very good.
Cheers!
Russ
Hi Russ,
I've ordered two of the COD pcbs, an IVY pcb, and an assembled tested SPDIF module. It would be great if you offered the standoffs and connectors as well as the bare boards as separate items. I'd be happy to add a few $ in order to have this option.
I'm looking forward to receiving the boards and assembling a new dac using them.
Very OT, but do you have any thoughts to interfacing a PMD100 HDCD decoder to the 1794/1798 dac. Is it possible? I'll be using a couple of 1798 samples I have on hand when I build up my COD pcb, and they'll be configured as mono dacs with the IVY for I/V conversion. I plan to switch the PMD100 into the path only when HDCD is detected.. Will I have to think about a way to disable the 1798 internal filters?
I've ordered two of the COD pcbs, an IVY pcb, and an assembled tested SPDIF module. It would be great if you offered the standoffs and connectors as well as the bare boards as separate items. I'd be happy to add a few $ in order to have this option.
I'm looking forward to receiving the boards and assembling a new dac using them.
Very OT, but do you have any thoughts to interfacing a PMD100 HDCD decoder to the 1794/1798 dac. Is it possible? I'll be using a couple of 1798 samples I have on hand when I build up my COD pcb, and they'll be configured as mono dacs with the IVY for I/V conversion. I plan to switch the PMD100 into the path only when HDCD is detected.. Will I have to think about a way to disable the 1798 internal filters?
kevinkr said:
Sounds like a fun project. I am not sure that the 1794/1798 allow bypassing the on-board filters like the WM8740/8741 does. So I am not sure using the PMD100 is possible.
I will look a little deeper, but my initial impression is that it is not possible (without a lot of work) to interface that chip with the COD. I will let you know if I see anything that shows me otherwise.
Cheers!
Russ
Page 22 of the PCM1794A datasheet shows an application bypassing the internal digital filter, but the odd thing is it only shows one data in line.... usually there is one for left data and right data.
Ok the more I look at it the more I think it will work, I would just send DOR to one DAC, and DOL to the other.
I don't have a PMD100 to play with so I can't tell you for certain.
Yes since you are doing mono you should be in good shape. There is no harm in trying it. 🙂
I don't have a PMD100 to play with so I can't tell you for certain.
Yes since you are doing mono you should be in good shape. There is no harm in trying it. 🙂
Russ White said:
Well I'm up for a challenge.. 😀
I think first I'll get the basic dac working, then devise some electronic switching and a buffer with enough fanout to handle the pmd100, a metronome at some point, and the two dacs. (Dacs normally connected to the spdif receiver.)
One note when using the IVY with mono PCM1794. You may need to recalculate the feedback resistors to get the desired output level. The resistors in the kit are for 2VRM from the 7.8mapp swing. In mono mode the output will be double, so if you still want 2VRMS from 2 mono DACs into the IVY you will want to halve the value of the feedback Rs (R1-R4).
There is no harm leaving the Rs as supplied, it just the output will be 4VRMs.
If you will just be using the SE output you could get that output to 2VRMS just by changing R9,R10,R13,R14 to double their supplied value, and leave R1-R4 alone. this will actually lower THD slightly. 🙂
You could also use one IVY per channel (much like the datasheet application) in mono mode, and take the SE outputs as balanced outputs. This would yield the absolute best THD.
Cheers!
Russ
There is no harm leaving the Rs as supplied, it just the output will be 4VRMs.
If you will just be using the SE output you could get that output to 2VRMS just by changing R9,R10,R13,R14 to double their supplied value, and leave R1-R4 alone. this will actually lower THD slightly. 🙂
You could also use one IVY per channel (much like the datasheet application) in mono mode, and take the SE outputs as balanced outputs. This would yield the absolute best THD.
Cheers!
Russ
Interestingly enough the PCM1798 has half the output current of the 1794 so I should be able to use the original resistor values, but as I bought the bare board version this won't in any case be a problem.
kevinkr said:
I would very definitely suggest using one IVY per mono chanel, that will yield MONO balanced outputs at the outputs labeled SE on the IVY.
If you still need single ended output you could then use a third IVY PCB and just populate the BAL/SE opamp and its resistors and caps, not the THS section. You would then wire the balanced signal into the terminal blocks market for balanced output.
This will get you the best DNR and THD.
I will draw up a document soon on these different options.
Cheers!
Russ
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