PCM1798 - looking for advice on cheap and simple I/U

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Alexium

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Joined 2010
#1
I'm building my first DAC based on PCM1798. I'm new to this, and I'm not very good with electronics (though I'm trying to learn). That's why I ask for your help.
I am about to assemble the I/U and adder according to datasheet using NE5532. Are there possible improvements to be made in this schematics, or is it good enough as it is? Advices or references to other good outputs for 1798 would be much appreciated.
Thanks in advance.

PCM1798 datasheet. Subject schematics is on page 19.
 
#4
I know 5532/34 are not much appreciated, but some other people say they can sound good enough when applyed correctly. They are so cheap that I want to experiment with them.
And I have a problem with price/availability of some opamps in my region. LM4562 are avaliable, but they are more expensive than AD811/826 etc., OPA2132, OPA627 and such. It's $7, to be specific, which is not cheap here.
I can get very cheap LM2904; OPA1632 and OPA2134 are also available for a reasonable price.
And I still hve to resolve the problem of obtaining the "right" schematics - most suitable for the particular opamp, I mean. They say datasheet schematic has its issues, and I'm not good enough to understand it...

There's a problem with the picture above, and I can't edit messages, so this is the right one:
An externally hosted image should be here but it was not working when we last tested it.


P.S. Sorry for my English, I'm doing my best to be clear, but sometimes I fail...
 
#7
Alexium said:
I know 5532/34 are not much appreciated, but some other people say they can sound good enough when applyed correctly. They are so cheap that I want to experiment with them.
Click to expand...

My sentiments entirely - the 5534 is amazing bang for the buck, so experiment away and let us know how it goes. In my experience (I'll get around to putting it on my blog soon) layout and power supplies (noise control in general) are more than 90% of the sound of a DAC. Changing opamps once the layout is exemplary seems to make almost no difference.

And I still hve to resolve the problem of obtaining the "right" schematics - most suitable for the particular opamp, I mean. They say datasheet schematic has its issues, and I'm not good enough to understand it...
Click to expand...

I don't consider the datasheet recommended schematic that you posted up to be ideal. My guess is this one that gives the best numbers for the datasheet but it doesn't give me the best sound. The 2700pF feedback cap is way too big, I've experimented with less than a tenth of this value and such a reduction seems to open up the sound considerably. I'd also take issue with the first stage passive filtering - the 220R/27nF is too low a load, even for a 5534. I'd scale up the resistors to at least 680R here, with a proportional reduction in the capacitor size. Be very careful in regards to the grounding of the decoupling capacitors if you want the highest transparency. Beyond that, see what sounds good.
 
#10
Sure, if the PS is so bad that will induce noise in the outputs, the PS is the point of improvement. I see here people that complain about hum, ground loops and such. Yes, OpAmps won't make a difference there.

But if we are talking about TDH+N below -60dB, the cheap, "bargain" OpAmps are the weak point. In all my mods that involved swaping OpAmps in existing DAC's, the results where noticeable - from 'wow' to just a slight change.
 
#11
SoNic_real_one said:
Sure, if the PS is so bad that will induce noise in the outputs, the PS is the point of improvement. I see here people that complain about hum, ground loops and such. Yes, OpAmps won't make a difference there.
Click to expand...

Well I've moved a little way beyond having hum as a problem in my DAC designs😉

But if we are talking about TDH+N below -60dB, the cheap, "bargain" OpAmps are the weak point. In all my mods that involved swaping OpAmps in existing DAC's, the results where noticeable - from 'wow' to just a slight change.
Click to expand...

Not having bought or built myself a THD analyser, I couldn't be sure that that's the change I'm seeing. I have had rather strange audible effects with NE5532s in my current DAC exploration though, to be mentioned in my blog in due course. Never had a 'wow' change from swapping an opamp in an I/V conversion job, but they're the most sensitive ones IME.
 
#12
I recommend you consider a TI differential amplifier like the THS4131 which sounds amazingly good with both the PCM1798 and the PCM1794A. This is what I used in my dac, and then a line to line (600:600) transformer to convert the differential output to unbalanced. This is the best sounding combination I have yet heard.

Operational Amplifier (Op Amp) - Fully Differential Amplifier - THS4131 - TI.com
 
#20
Nazar_lv said:
But simple put 4131 as I\U converter for DS DAC is really not good, dac glitch and HF noise terribly reduces sound quality)
Click to expand...

What do you mean?
What measures are needed to filter glitch similar to those used in Picardian Chord?

Or that the application THS4131 in conjunction with the DS DACs, in particular the PCM1794, does not sound good at all?
 
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