One of the downsides (forgive my cynicism here) about such a design is the almost-inevitable reviewer comments about the preamp sounding "cold and clinical" 
Somewhere I saw someone say, about such things, that "Now don't think you're going to cool the cartridge!"
But actually you do. Oliver discusses this as well (about energy being pulled out of the higher temp component) and gives a rate for a perfectly matched conjugate load from d.c. to beyond light. The rate of cooling is, to say the least, not something that will lead to the need to de-ice your phono setup
Somewhere I saw someone say, about such things, that "Now don't think you're going to cool the cartridge!"
But actually you do. Oliver discusses this as well (about energy being pulled out of the higher temp component) and gives a rate for a perfectly matched conjugate load from d.c. to beyond light. The rate of cooling is, to say the least, not something that will lead to the need to de-ice your phono setup
Has anyone ever tried a Norton preamp - the one with the transformer feedback around a common gate/base amp? Ought to work with MC, although not so good for MM. The input impedance is set by the load impedance, so no explicit resistance to generate thermal noise at the input. Noise figures of 1-2dB easily achieved at RF. Flicker noise might kill it for audio, though.
Yes, but any lowering of overall noise must be a win win unless there are other errors offsetting the advantage...
If memory serves, the Bravura was made that way. And for MM, specifically the Shure V-15.
@Brad
Fair enough, but what one man does as his best may not be considered even special, let alone High End, by others.
Methinks High End is, at least today, relegated to the price tag only. There was a time when the High End actually defined the current state of the art. It pushed limits, and pushed hard.
Today, I feel like the High End has turned into a couch potato, simply recycling what we've seen many times. Most of it, I mean, there always were and there always will be some who will push the limits.
As for your "yet another phono stage", may I suggest this:
This appeared in 1990 in a German magazine. The author is one Holger Hermann, who works for Burr-Brown Germany, hence the BB op amps. It's simple, it's clean and it works like a charm even as is.
Add current boosting transistors to the op amp outputs,and it works even better, in fact, so well that it will give a run for their money to expensive units costing 20 times its price.
Add a shunt PSU and you are in orbit.
Fair enough, but what one man does as his best may not be considered even special, let alone High End, by others.
Methinks High End is, at least today, relegated to the price tag only. There was a time when the High End actually defined the current state of the art. It pushed limits, and pushed hard.
Today, I feel like the High End has turned into a couch potato, simply recycling what we've seen many times. Most of it, I mean, there always were and there always will be some who will push the limits.
As for your "yet another phono stage", may I suggest this:
This appeared in 1990 in a German magazine. The author is one Holger Hermann, who works for Burr-Brown Germany, hence the BB op amps. It's simple, it's clean and it works like a charm even as is.
Add current boosting transistors to the op amp outputs,and it works even better, in fact, so well that it will give a run for their money to expensive units costing 20 times its price.
Add a shunt PSU and you are in orbit.
@Brad
Fair enough, but what one man does as his best may not be considered even special, let alone High End, by others.
Methinks High End is, at least today, relegated to the price tag only. There was a time when the High End actually defined the current state of the art. It pushed limits, and pushed hard.
Today, I feel like the High End has turned into a couch potato, simply recycling what we've seen many times. Most of it, I mean, there always were and there always will be some who will push the limits.
As for your "yet another phono stage", may I suggest this:
This appeared in 1990 in a German magazine. The author is one Holger Hermann, who works for Burr-Brown Germany, hence the BB op amps. It's simple, it's clean and it works like a charm even as is.
Add current boosting transistors to the op amp outputs,and it works even better, in fact, so well that it will give a run for their money to expensive units costing 20 times its price.
Add a shunt PSU and you are in orbit.
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Oops hit the wrong key!
So if I charge more I can assure it will be considered sufficiently "high-end" lol?
The preamp looks ok, but (having just read the Marsh preamp piece in TAA 3/1980), the one immediate drawback is the ease with which it can be overloaded at high frequencies. Now one can argue that there's not properly much energy up there. Yet I saw (was it Popa in LA? Gerhard?) state that phono overloads should be as much as 36 dB! That's one of the reasons that what I envision is going to be costly, and as well I think require a very good clipper to avoid blasting downline components.
And there's the sneaky road to high OL of merely lowering the gain. I think that's cheating.
Brad
So if I charge more I can assure it will be considered sufficiently "high-end" lol?
The preamp looks ok, but (having just read the Marsh preamp piece in TAA 3/1980), the one immediate drawback is the ease with which it can be overloaded at high frequencies. Now one can argue that there's not properly much energy up there. Yet I saw (was it Popa in LA? Gerhard?) state that phono overloads should be as much as 36 dB! That's one of the reasons that what I envision is going to be costly, and as well I think require a very good clipper to avoid blasting downline components.
And there's the sneaky road to high OL of merely lowering the gain. I think that's cheating.
Brad
The Marsh preamp (advertized as a "Passively Equalized Phono Preamp" on the cover of that 3/1980 TAA issue) is very similar, except for using discrete opamps and +/- 24V rails. However, the load resistors for the input JFETs from what I could deduce take away about 12V of the available peak signal swing (they feed to a second differential stage, and then there's a little burden from the output emitter followers, so 12V is probably optimistic). With the gain set by the feedback to about times 22.5, or 27.0dB, and if one takes the cartridge canonical output voltage at 20kHz to be 50mV rms, hence 70.7mV peak, the overload margin for 20kHz at onset of clipping will be about 17.6dB, which is probably fine for most cases but nothing that JA would marvel at. But if that first stage gain is reduced, one begins to get into noise issues after the substantial attentuation of the passive RIAA network. Fortunately the second gain stage is like the first and will have decently low noise, probably about 7nV/rt Hz with roughly equal contributions from the 5564 JFETs and the 1.47k feedback divider resistor. And this is just voltage noise; his 46.4k termination resistor's current noise will begin to be significant at high frequencies with the nominal 700mH moving-iron cartridge inductance as a source. At least other parallel noise will be small.
But I suspect it sounded pretty good
Brad
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...
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.
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?
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 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.
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
.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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