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Which good discrete R2R multibit DAC & why NOS ?

In another thread concerning upsampling and upconversion in servers, mention was made by georgehifi :
¨Should just have a good listen to Redbook 16/44 PCM converted through a "good" discrete R2R Multibit nos dac.¨
Which would these be and why NOS ? Are there no R2R multibit DACs being made today ?
My Reimyo CDP777 although quite old has the K2 conversion and being one-box and top-loading made sense  to me at the time of purchase.
Most importantly, would adding an external R2R bring a noticible improvement or just be sidestepping ?

Thanks in advance

rost
rost OP
91 posts
 
Please enlighten:

@georgehifi 
"But I can’t find what the Reimyo uses for dac chips, my guess would be the R2R PCM1704K’s, I don’t think it’s discrete R2R"
What is the difference between a discrete R2R & non discete R2R DAC ?

@djones51
" it wasn’t NOS and made use of good filtering and up sampling which any decent R2R implementation needs to do."
Please explain further, I thought R2R implied NOS or upsampling.

Thanks


abraxalito
93 posts
 
What is the difference between a discrete R2R & non discete R2R DAC ?

A discrete R2R uses individual (discrete) close tolerance resistors in the R2R ladder. The non-discrete uses an IC with those resistors on the die of the IC where they're trimmed by laser after fabrication.
djones51
4,947 posts
 
@rost 
The R2R PCM1704 chip doesn't do the oversampling it's the K2 DSP and Nippon filters that pass the over/up sampled signal to them. R2R is the DAC architecture there is more going on in a good DAC or CD player. NOS is in some kind of nostalgia thing right now but as you can see with your Reimyo the best even 20 years ago didn't do NOS without proper filters, Why? It didn't sound very good.

While each of the corporations contributes to the overall sound of the Reimyo, it is the K2 processor that gives it its heart and soul. The K2 processor, operating with 24-bit resolution, takes the incoming digital signal and oversamples it to 176.4kHz. From there the digital signal is passed on to the digital filters, which upsamples the signal 4 times to 705.6kHz before being passed on to the twin PCM-1704 digital to analog converters. The DAC's are multi-bit in operation. As a result, every CD that is played through the CDP-777 is reproduced at an incredible 705.6kHz, which is among the fastest sampling rates available from any CD player on the market today.

http://www.enjoythemusic.com/superioraudio/equipment/0304/combakreimyocdp777.htm
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