Wednesday, May 4, 2011

Why are digital tuners quieter (well, mostly) than older analogs?

[After listening tests on Sunday and Monday, I posted this to the FMTuners group on Yahoo, one of my favorite haunts.]

Recently I've been using a number of great digital tuners, Kenwood KT-6040 (my
latest fave), Sony XDR-F1HD with modified output stage, Sony 730ES, Yamaha
TX-1000. Just from memory, I'd rate noise (with 60dB signal strength, slightly
suboptimal) from quietest to noisiest (with the last 3 being very close):

XDR-F1HD virtually silent, except for some clicking (impulse noises?)
Yamaha TX-1000
Kenwood KT-6040
Sony 730ES

I most recently acquired the KT-6040, it is a very sweet sounding tuner. At
first really blew me away as more musical sound than XDR-F1HD (but that's true
of the 730ES also). I don't think Yamaha sounds quite as sweet, but it was
quieter when tested last. The XDR-F1HD analog output modification (including
corrected EQ) really improves sound, but it's still overprocessed sounding, not
necessarily the best for serious listening.

All of the above, however, exhibit a periodic "clicking" sound. I'm not sure
what causes this, possibly digital communications of some sort. It happens a
few times every minute.

ALL of the above have less background hiss than the analog tuners I've tested.
But just a few days ago I brought back the Kenwood 600T, which is one of my
quietest analogs, and I noticed in contrast to all of the above...the clicking
sound is simply gone. Very nice! I could get used to that!

Well, that might go along with the more bulletproof front end. The downsides
are a non-ignorable level of background hiss and the sound quality. I mainly
keep the Kenwood for it's wonderful signal strength meter, I don't really much
like the sound of it anymore. In contrast to other tuners, and especially other
Kenwoods (including KT-8300) I have, it sounds warm and slightly diffuse. The
usual Kenwood sound seems to be very clear and open (possibly with excess highs
or even stridency or thinness), which I've noticed in past Kenwoods (KT-917 and
KT-7500) as well and from what other people tell me. But the more open and
musical sounding KT-8300 is simply too noisy for me to enjoy on my 60dB strength

That got me to the question above. It seems like the older tuners, if anything,
had better front ends and IF's. Are the digital tuners quieter because of
detector or MPX? The newer MPX chips (like LM3410) do use some sort of
walsh-function-like or harmonic canceling scheme which older MPX's lacked, and
some digitals go even farther with analog multiplier (such as TX-1000).

If the noise difference is entirely in the MPX, one could just add outboard MPX
to get same effect. But that wouldn't explain differences in mono specs anyway
(though I haven't done much mono listening to tuners...perhaps the mono specs
aren't really that significant under my conditions).

Could difference be in detectors? Newer tuners typically use PLL or quadrature
detectors, don't they? Are those detectors fundamentally quieter than the older
ratio and foster seeley detectors?

Could the difference is in the transistors or chips used in the detectors
getting quieter?

If the quieting were only in the front end, one would think the KT-6040 would be
the ultimate with very few competitors, since it has GaAsFET front end. But it
does not particularly seem quieter than other digitals I have, and may be
surpassed by some. I don't think front end is the biggest factor in background
hiss level, anyway, except for extremely weak stations.

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