Friday, March 21, 2014

PCM converters

Dan Lavry sets the story straight regarding PCM AD converters.  First of all, non-sigma-delta converters are PCM (or that's the term he uses).  Sigma delta converters can be 1-bit or multibit.  All converters were at first PCM, then 1-bit sigma delta appeared.  1-bit sigma delta had problems, so it has been almost entirely replaced by multibit sigma delta converters.

The Pacific Microsonics Model One and Model Two were PCM converters.  NOT sigma delta.  The actual AD unit in these (?both?) were Analogic PCM units tweaked by them.  The DA they used was from Analog Solutions and designed by Dan Lavry.

Lavry's DA924 converter is PCM, as is the Lavry Gold.  They are not a straight forward architecture though.  They were an improvement on earlier designs he did for Pacific Microsonics, Levinson, Wadia, and others.

Lavry now (2007) thinks multibit sigma delta are OK.  PCM still has advantages, but it is very expensive to do correctly, with hand calibration and the like.

The output of a 1-bit modulator can be copied straight to DSD, or it can be decimated to PCM.  But 1-bit modulators were replaced by multi-bit modulators.  Multibit sigma delta modulators require either an downsampler (AD) or upsampler (DA) to complete the system.

The Analogic AD used by PM was similar to Lavry's ZAD-16 made by Analog Solutions.

Whenever one tries to criticize converters based on specific things, such as architecture, he gets very testy.  Reminds me of the late James Bongiorno, who got testy whenever I tried to ask him any questions.  But we cherish our great designers regardless of personality, and Lavry is the best.  Meanwhile it seems to me completely fair to say 1-bit anything is total crap, multibit sigma delta is better, and PCM done right is the best.

Sadly, the unique (PCM with auto calibration) DA924 converter is discontinued.  So perhaps that is probably why Dan Lavry got testy and refused to say unambiguously what I just said.  He may have already decided to move on to multibit sigma delta, believing it to be better.

But designers are not always the best judge of their own work.  WRT James Bongiorno, while he may have been a brilliant designer, emulated by others, I think many of his designs weren't that good in totality.  The Sumo Nine was one of his favorites, but it had a fatal flaw IMO, it used fans (as did the original Ampzilla).  Likewise nearly everyone who isn't a Bongiorno fanboy thinks The Charlie wasn't the best tuner at the time (I don't have one of his personally adjusted ones with rack handles, but I've heard lousy reports regarding those also).  With Dick Sequerra, his best tuner was likely not the one with his name, but the Marantz 20b, and FM has continued on far longer than he ever anticipated.  And so on.  How can I be the idiot that I am, and know these things that the genius designers didn't know?  I don't know.  All I do is listen and think.

I think designers of analog converters have been far too preoccupied with voltage accuracy.  The most important thing, most likely, is in preserving timing.  And as James Bongiorno told me point blank, the truth is not in the measurements.  It is in the math.  I now believe he was correct.  I was asking him what measurement I could do to find the weakness in a pulse count detector.

I think if I had the money, I would try to get the DA924.

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