Passlabs D1 (PCM63) vs. Threshold DAC-2 (Ultra Analog D20400a) - who have heard both?

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#61
BRN said:
My high frequency hearing has gotten so bad I probably won’t hear it even if it were there.
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Free low pass filtering with no phase shifts 🙂

Its sobering to see how early (40 years young) and how low (6kHz) higher frequency hearing is lost:
1663242462963.png
 
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#68
kazap said:
Free low pass filtering with no phase shifts 🙂

Its sobering to see how early (40 years young) and how low (6kHz) higher frequency hearing is lost:
View attachment 1091014
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even if this curves are without Flecher loudness corection they seems way off what I have measured over diferent individuals trought years its normal for 40year old man hear 6khz -5db , 10khz -17db (referenced to 1khz). however noth much can be heard after 15khz ,unless 15-17khz @100db level.
 
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#74
Jon Lord said:
I didn't audition both DACs so far, but about the basic DAC designs I can tell the following:

- Measurements of the PCM63 chip seem to reveal a design flaw, which heavily compromises Differential Non Linearity (DNL, as a measure of resolution) and noise for positive codes (0.2%..100%FS), while codes near zero and below are much (about 10dB) better. This design flaw can only be addressed by using two or more matched PCM63 per channel differentially (not only parallel, which Pass fortunately did right), but nevertheless this chip is pretty fishy in that regard.

PCM1702/1704 (As a potential upgrade to the D1) could be better, but so far were not tested regarding DNL. Bad DNL in a DAC produces nasty ("digital" sounding) distortions. A good DNL is IMO necessary for a good sound, but nevertheless doesn't guarantee it (as many Ʃ/Δ-DACs show).

- The D1 got rave reviews (Still seeking that German review, where they compared it to a dCS converter) and is still highly regarded. I think this is mainly due to its Crystall PLL for 44.1 kHz (Being tolerant to mediocre, jittery sources) and the ingenious (at its time) I/V converter. Many other designers copied OPA2604 I/V stage from the BB reference designs and this is indeed a bad idea to implement a PCM63 right. Nowadays there are better I/V implementations possible, without using open loop circuits with high Cgd MOSFETs.

- The Pass I/V stage uses power MOSFETs, which generate lots of high frequency distortions, due to unnecessarily high, non linear Cgd (Miller) Capacitance. Change glitch distortion against Cgd distortion of the I/V ...

- The D20400A is voltage output by design and thus doesn't need an external I/V stage or the like.

- The D20400A contains a deglitcher circuit, which no other high resolution (Except the Lavry DA924) DAC ever provided. The code dependent glitches of R2R DAC designs provide huge data dependent distortion/jitter, which only can be eliminated by "reclocking" the raw DAC output with a sample- and hold circuit (deglitcher) in the analog domian. If you don't use a deglitcher after a R2R-DAC (PCM63 included), every crystal PLL in front of it is almost in vain.

- The Threshold DAC is a maximum Implementation of the UltraAnalog "Chipset" using two D20400A differentially, AES21 input receiver (also with secondary PLL), and also the ingenious PMD100-Filter, which hopefully is implemented right (analog gain switching for non HDCD).

- I auditioned the Classé DAC-1, which is a very similar design to the Threshold (both products most likely designed by UltraAnalog Inc. directly). This DAC is among the best DACs (probably the best) I ever heard. I doubt that even the best PCM63 implementation (Pass D1 ?) could match it regarding clarity and sound stage, even if you would try to use 16 hand picked PCM64P-K per channel to get rid of the DNL problem.
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DNL is explained here:
https://www.allaboutcircuits.com/te...onverter-differential-nonlinearity-dnl-error/
DNL measuring results of PCM63P (and its successors) in the important area I don't find in the associated datasheets of Burr/Brown (now TI).
Is it possible, that these important parameters were simply omitted in order to better present the DAC-ICs?

It is known that with analog Class AB amplifiers, the compression effect, which is caused by the not infinitely low internal resistance of the power supply, has hardly ever been published at different load impedance values down to 2 ohms (only the German test magazine "Production Partner" carried out this test on some studio power amplifiers), because even versions with oversized power supplies were only mediocre in terms of this parameter.

This is annoying because in the 1990s, no one generally assumed (not even as a professional employee of a manufacturer or test magazine) that the approach of the Ultra Analog D20400 DAC circuit was better in terms of audibly best results in playback than that of Burr-Brown regarding the PCM63P and its successors.
Concerning D20400 replacement check out the URL in post #45 under
https://www.diyaudio.com/community/threads/ultraanalog-d20400-data-i-have-it-all.254748/page-3

P.S.: Images of the test magazine for D1 and DCS Elgar you will find in the attachment
 

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#77
Thank you. PCM63 will be in front.

I let it cool down and noticed ~70mV DC on startup, wherefrom it starts dropping. Hopefully, the DAC chips won't mind this for a few min. I suppose it D1 wouldn't be here if this were an obstacle.
 
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