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Old 27th February 2012, 10:44 PM   #2871
bcarso is offline bcarso  United States
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Quote:
Originally Posted by a.wayne View Post
Yes, but any lowering of overall noise must be a win win unless there are other errors offsetting the advantage...
I don't see any disadvantages as yet other than cost and ~complexity. And maybe a shock hazard, given how high the unrestricted output voltages may be . Maybe it will ship with the clipper enabled, and the customer instructed to defeat it, a bit like the internal anti-digital-domain record switch inside some early R-DAT machines. However, those who shun canine tail-chasing will not be pleased, as feedback will be used extensively, including inner loops. I can't see any way around it, as yet.

I worked on another phono pre with mostly sand-assisted hollow-state for my friend Don. Part of the "bargain" was that global feedback would be avoided, but I was allowed the use of current sources for plate and cathode loading. The MC portion was JFET/bipolar in lieu of transformers, as Don thought better good sand than poor magnetics (this was to be an "affordable" preamp). I did get as far as a prototype but things kept changing in the tube part. I did use the MC "pre-pre" for a while ahead of what some would consider to be other electronics that are beneath contempt, and I did enjoy it. One day I tried to move some of it and something shorted out, and I haven't had sufficient interest in determining what happened yet. One moves on...
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Old 27th February 2012, 10:47 PM   #2872
DF96 is offline DF96  England
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For the Norton amp see here and here. Bear in mind that for many purposes in RF work it is noise and third-order distortion which count; second-order is often much less important so may be ignored.
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Old 27th February 2012, 10:59 PM   #2873
bcarso is offline bcarso  United States
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Originally Posted by DF96 View Post
For the Norton amp see here and here. Bear in mind that for many purposes in RF work it is noise and third-order distortion which count; second-order is often much less important so may be ignored.
Thanks much! I know some of those transistors (particularly the 5109) and it's nice to see them again.

Reminds me of the RF engineer who wrote a piece in Electronics World about how screwed-up audio engineers were for paying attention to THD and not IMD. Anthony New I believe was the name, and he was absurdly ill-informed, evidently never having seen 19/20 kHz IMD spectral plots and the ilk. In fact he was typical of this peculiar tendency for people outside of a given field to believe that their very lack of knowledge is an enormous virtue, enabling them to cut through cant and jargon and limited thought as they bring to bear their superior intellect. Oh puhleeaze.

I fired off a testy letter that I probably should have slept on for a few nights. It was printed in its entirety (!) with no editing that I could detect (!!!). Doug Self also rose to the bait, and his letter was truncated, around the point where he suggested that perhaps he should start writing articles in RF magazines

AudioXpress reprinted the New article, as part of an exchange program with EW. I decided one nasty letter was enough.
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Old 27th February 2012, 11:26 PM   #2874
bcarso is offline bcarso  United States
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Originally Posted by DF96 View Post
For the Norton amp see here and here. Bear in mind that for many purposes in RF work it is noise and third-order distortion which count; second-order is often much less important so may be ignored.
From one of the refs: "This particular amplifier circuit is a variation on David Norton's "noiseless feedback" topology from the early 1970s. Norton's work may serve as a case study in which the US patent system worked to keep a high-performance, cost-effective, and rather trivial innovation out of the public's hands for close to twenty years. (A rant for another time.)"

Amen to that!

Yes, I remember now some of this from an old magazine article by Rohde, who was opening his blouse a bit to show us how good receivers were done (in a nutshell, don't worry as much about ultimately low noise as low IMD). It provoked me to buy his book.

And yes. When I stumbled recently across the Larson/Baxandall stage (inside Tektronix according to Addis, they and Larson called it the super-alpha, others the Baxandall super-pair) in a book on communication systems, predating the aforementioned authors/inventors by several years, the article in the book early on dismissed second-order as something easy to cure by balanced design, thus didn't much bother with it after that.

I wonder how many strictly-audio folk know what cross-modulation means?
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Old 27th February 2012, 11:44 PM   #2875
bcarso is offline bcarso  United States
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Applying this Nortonesque stage to phono stages is maybe not such a bad idea. As the gain stage one could use a current conveyor made of JFETs along the lines of EUVL's recent thread and Linear Audio article, with possibly some enhancements. Clearly the key trick would be to conjure a good-enough transformer, with an even more impressive span of <20Hz to >20kHz (the article mentions getting 100kHz to >30MHz). SY, do you have a ref for the preamp you mentioned as being used with V-15's?
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Old 28th February 2012, 12:17 AM   #2876
godfrey is offline godfrey  South Africa
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Originally Posted by bcarso View Post
I wonder how many strictly-audio folk know what cross-modulation means?
I guess those that do would care how their circuits behaved above 20KHz. Waitaminit, aren't those the kind of designers whose products get good subjective reviews despite the standard measurement results being nothing special. Then again, the standard measurements don't include injecting a bit of modulated RF into every available orifice of a piece of audio equipment.

Oops, suddenly this thread's back on topic.
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Old 28th February 2012, 12:29 AM   #2877
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Quote:
Originally Posted by bcarso View Post
Applying this Nortonesque stage to phono stages is maybe not such a bad idea. As the gain stage one could use a current conveyor made of JFETs along the lines of EUVL's recent thread and Linear Audio article, with possibly some enhancements. Clearly the key trick would be to conjure a good-enough transformer, with an even more impressive span of <20Hz to >20kHz (the article mentions getting 100kHz to >30MHz). SY, do you have a ref for the preamp you mentioned as being used with V-15's?
I can't find it for free, 65pV/rt-Hz but interacts with source R in a funny way. Upside is that it uses ordinary pot cores and DIY winding.

Low‐noise preamplifier with input and feedback transformers for low source resistance sensors
J. Lepaisant, M. Lam Chok Sing, and D. Bloyet
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Old 28th February 2012, 12:32 AM   #2878
bcarso is offline bcarso  United States
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Originally Posted by scott wurcer View Post
I can't find it for free, 65pV/rt-Hz but interacts with source R in a funny way. Upside is that it uses ordinary pot cores and DIY winding.

Low‐noise preamplifier with input and feedback transformers for low source resistance sensors
J. Lepaisant, M. Lam Chok Sing, and D. Bloyet
How low is low Scott? (that is, source resistance)
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Old 28th February 2012, 12:35 AM   #2879
bcarso is offline bcarso  United States
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Originally Posted by godfrey View Post
Oops, suddenly this thread's back on topic.
Not for long muahahaaahaaa
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Old 28th February 2012, 12:54 AM   #2880
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Originally Posted by bcarso View Post
How low is low Scott? (that is, source resistance)

.5 Ohm @ 77K (SQUID), but the information is there and you should be able to tweak it for a range of MC carts. They offer no data on distortion so this might be a dead end and require Jensen quality transformers anyway.
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