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Unfiltered NOS DACs sound

I Have been experimenting with some NOS DAC chips and redbook material.
I very much like the NOS sound, and frankly think in terms of transparency it trumps any of the modern DS DACs Ive heard. The biggest drawback is THD and noise levels, on paper the modern chips out perform the older NOS chips and I think thats easy to hear but its superior ability to preserve of timing and spatial information in the music makes that problem relatively insignificant.

I have experimented with high quality software based upsampling, the conclusion is that any form of oversampling loses the ’’special’’ NOS sound.

Steep analogue filters did not affect transparency as much as software digital filtering, but the sound became dull and lacking vibrancy. I would choose the ’’processed’’ digitally filtered sound over this dull analogue filtered sound any day, but still NOS remains sounding the best.
I tried gentler (simpler circuit) analogue filters and more extended (filtering higher into the ultrasonic range), and the gains from the filters were never worth the filters influence on audible frequencies.

So as it stands the best sound I can achieve with these NOS chips is with a raw unfiltered PCM output.
The artifacts within unfiltered 44.1kHz PCM are very significant but ultrasonic, so it seems that the audible influence of this ultrasonic noise has on the system is not as siginificant as the means of removing it.... but this is probably not true in all systems.

What amazes me the most is that this is with redbook material... DS DACs and upsampling are supposed to be the more advanced methods of dealing with the limitations of 16 bit 44.1kHz data.
Unfiltered NOS naturally seems the most transparent and accurate way of experiencing Hi Res DXD and 192kHz material.

I know that unfiltered NOS has a sort of cult following, are there any other fans of it here?

suix6
audioman58's avatar
audioman58
3,882 posts
 
There are a lot of factors , for example my Belcanto dac has
2 Femto clocks -that is Trillions, older dacs are in picoseconds. ,  much much better accuracy 
reading the digital signal , power supplies also Very critical 
seperate very low noise for analog as well as digital signals very 
important , and many other things . My New 2.7 dac sounds very much like the older types, smooth very musical and still very accurate. It is all about the implementation. Many companies 
do digital but not all are musically involving.
abraxalito
93 posts
 
I also use a DIY TDA1387 DAC but my findings are rather different from yours @suix6. I've found analog filters improve the sound - best if the filter comes prior to the I/V stage. Could be I'm using different filters - LC (passive) ones.The improvement passive filtering brings is in the focus - somehow the instruments are rather ill-defined in the soundstage without a filter, they become more clearly delineated when the filter's included. Overall dynamics improves a fair amount too.
I'm still experimenting with I/V stages as these are perhaps the most critical part of a NOS DAC as regards subjective performance.
suix6 OP
10 posts
 
Hello @abraxalito,  you are also a member of diyaudio? thank you for work with these DAC chips!

I have used RC and LC filters. For IV resistors and LM4562 Op amps. What you describe sounds like part of the filterless sound. The sound could be described as more wild and hazy compared to filtered. The calmer sound of filters would be the gains described above. 
Digital upsampling was the preferred choice for getting a more accurate detail and presentation.
abraxalito
93 posts
 
Yes, I hang out on DIYA a lot. You're welcome, happy to share interesting results from these amazingly good value chips!

'Wild' sound could be it yeah, more 'refined' with the filter in place. I've tried running NOS and 2X OS, could barely hear the difference when the upsampling's run on my PC. Could be a nearby digital filter chip generates noise, we'll have to see. I plan to use a very low power CPU to do local upsampling.

As regards opamps, I tend to give them a pass nowadays. They need too much care and feeding on the supplies.
devilboy
1,172 posts
 
On my fith Metrum DAC and loving it.
Metrum Onyx. 
I use it for both my loudspeaker and headphone systems. 
Amazing.
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