NOS PCM56 with NL17SZ04 ? - diyAudio
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Old 25th July 2011, 07:09 AM   #1
regal is offline regal  United States
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Default NOS PCM56 with NL17SZ04 ?

There is a common NOS PCM56 scheme where Fsynk in is inverted for the right channel PCM56 with an 74HC04. The problem is this introduces a prop delay on the right channel vs the left. There have been many schemes suggested with the only real solution being a programmed fpga which is out of reach for most DIYer's.

What about substituting the 74HC04 with a NL17SZ04 ? Would this faster part make the prop delay inconsequential?
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Old 25th July 2011, 07:15 AM   #2
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Quote:
Originally Posted by regal View Post
There is a common NOS PCM56 scheme where Fsynk in is inverted for the right channel PCM56 with an 74HC04. The problem is this introduces a prop delay on the right channel vs the left. There have been many schemes suggested with the only real solution being a programmed fpga which is out of reach for most DIYer's.

What about substituting the 74HC04 with a NL17SZ04 ? Would this faster part make the prop delay inconsequential?
The so called stopped clock scheme has no delay. But with the AD1865 I found the method using an inverter for the latch sounded slightly better....
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Old 25th July 2011, 10:15 AM   #3
regal is offline regal  United States
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Originally Posted by QSerraTico_Tico View Post
The so called stopped clock scheme has no delay. But with the AD1865 I found the method using an inverter for the latch sounded slightly better....
Yes familiar with the stopped clock method, developed a schematic and looked at all the CMOS devices and couldn't help but think this is bad for a sqare wave audio signal (digital). Seemed crazy when a programmed fpga could do the same thing (although those have issues also.).

Anyway it is intersting you find the simple approach sounded better, and now there is a faster single part simple solution that I am thinking it may be worth a try for an NOS DAC using a chip you can still buy from Mouser.

Always been a PMD100 DAC person looking to try somehing different.

Here is some advice I saved from one of the NOS disciples (I am guessing the TDA1541 specs are for double crown):

DAC THD&N SNR
AD1865 - 88dB -110dB
AD1862 - 98dB -119dB
PCM56 - 94dB -110dB
PCM63 - 92dB -120dB
PCM1704 - 92dB -120dB
TDA1541A -100dB -110dB
TDA1543 - 75dB - 96dB
TDA1545A - 88dB -101dB


Seeing this table shows the TDA1541A as actually having the lowest THD & N at full scale. The AD1862 and PCM56 are second and third respectively, followed by the newer BB PCM Chips and with the AD1865 and TDA1545 bringing up the rear with the almost poorest performance, but that honour actually goes to the TDA1543.

So, my first suggestion, if one is desirous of a high quality NON-OS DAC is to select one that uses DAC's that have a low THD & N, which seems to limit us to TDA1541A, PCM56 and AD1862. It would also seem that it is best to avoid the TDA1543, and probably too the TDA1545A and the AD1865.
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Old 25th July 2011, 10:40 AM   #4
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Unhappy Most standard specs are meaningless

Most standard specs are meaningless, especially for DACs

Let me elaborate:
TDA1543 a little harsh
TDA1545 very un-involving
AD1955 no depth, no bass slam
PCM56 does have bass slam, but AD1851 has better highs
AD1865 often shows irritating glare...but has bass.
etc. etc.
On top of that the used IV-converter can make or break the sound.

Square wave is always perfect NON-OS no matter what method to get left-right separation
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Old 25th July 2011, 11:33 AM   #5
regal is offline regal  United States
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Thanks for sharing your impressions. My experience is mainly all PMD100 OS'd: PCM63K, AD1862J, and PCM1704K. I too have found that the analog stage is very influential, but I have also never found an off the shelf digital filter I like besides the PMD100. My only experience with NOS was a poorly designed TDA1543 which literally stopped at 12khz, every tone above this was pitched down to 12khz.

But recent attempts with different Hirez digital filters all failing to satisfy as the PMD100 has me thinking of revisiting the NOS design. I mean trying these different filters, some different revised FPGA firmware on the same DAC has me thinking maybe no filter is best. Or I may try serial programming a WM8741 to hear its 6 different OS algorithms. Too bad we DIYers can't buy the expensive Blackfin type filters used in new DAC's like the Berkley Alpha, Meridians, Cambridge, etc.
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Old 26th July 2011, 01:00 AM   #6
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You don't need to go to Blackfin to do digital filtering - I'm running a clone of an SAA7220 on an LPC1114 at the moment. So maybe that part is an answer to your prayers - its cheap (under $2) and the tools are in the main free.
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