LCR phono stages we know about

I have to apologize. The two phono stagas I mentioned, the BMC MCCI, and the 47 labs, are both current driven phono stages, which is an entirely different subject, but I do have interest in that mode of operation for low output moving coil cartridges. However I don’t think either of those is LCR type.
So I guessed correctly, that the 6F12P is in fact a Russian tube designation with Cyrillic converted into English.

Thanks for your inputs, Jarrett, engine, and Indie.  Sometime after my last post in 2016, I bought a Manley Steelhead.  It suits my particular needs for (1) multiple phono inputs, (2) MM and MC gain capability, and (3) LCR.  It's LCR through the MM gain stage and uses autoformers to add gain for the MC inputs, so far as I can tell.  Manley are fairly secretive about this circuit, but I got some info from an interview that Evanna Manley gave to 6 Moons Audio, where she described the output stage.  From her description, I was able to tweak the output a bit which has made a positive improvement.  Thomas Mayer seems to make some great stuff, and I envy you, Jarrett.  Indie, what the heck is a 6F12P tube? Is that a Russian designation where maybe some of the letters are moved over from that cyrillic alphabet?
I still have curiosity for the BMC MCCI and for the 47 Labs 4712, which has the lowest input impedance of any I know about, nearly zero.  I'd have to have one in my own system, at this point.  Talk only goes so far.

As I age, I tend to think, "less tinkering, more listening". I've got around 2200 LPs that need listening to. That's why I am much more likely to purchase an LCR phono stage than to build one of my own, although I have a friend who would walk me through that process.

Mordante et al, I apologize for not defining the acronym. I thought most analog aficionados would know about LCR RIAA circuits. But here goes a definition:
In analog history, nearly every commercial phono stage has been based on using RC filters to achieve RIAA equalization. An RC filter is one that uses resistors and capacitors to achieve each of the three 6db per octave "shelves" in the frequency response that constitute an RIAA correction. Most such RC-based RIAA networks require the use of a fairly high value resistor in series with the phono signal coming out of the first gain stage. And some require the use of at least one capacitor in series with the signal, as well. The advantage of an LCR network, used to achieve the exact same RIAA correction, is that it places only an inductor in series with the system, which has very low DC resistance compared to the resistor mandated in RC type RIAA networks. Capacitors and resistors are used as well, but all of these are in parallel with the signal, connected to ground. Theoretically that does less "damage" to the signal, where "damage" can mean different things to different audiophiles. Proponents of LCR type RIAA correction circuits believe that they sound better, pure and simple. However, implementing such a network presents a lot of problems to the designer. Thus = expensive.

Yes, JFrech, I knew that Allnic (in the H3000 and H1500) make LCR type phono stages, and I knew about Zanden. Did not know about Ypsilon being LCR type. All of these are VERY expensive. (Well, the Allnic H1500 is not too far off the charts.) Have you heard any of these 3? In fact, I would love to hear from anyone who went from a very fine RC type phono stage to a top of the line LCR type. I would also like to hear from anyone who has actually listened to any LCR type phono and who has an opinion about the advantages based on real world experience.

That's not quite correct or at least possibly confusing as written, Sqlsavior.
LCR vs RC has nothing to do with active vs passive RIAA. Either technique can be implemented in a passive RIAA filter. It's just a matter of how the filter is created, with inductors in series with the signal vs with Rs and Cs in series/parallel.

Addendum. After composing that long treatise, I did some surfing to find out more about the Slagle LCR phono stage owned by my neighbor. It turns out that the phono stage is called "Emia" and is marketed by Dave and Jeffrey Jackson, in collaboration.
Here

Further, the "Kahn" Experience phono stage is also a product of this same collaboration, only it's more expensive than the Emia.

So these two would be important players in the LCR game, albeit hardly mass-market.

John, I am very familiar with your association to K&K. I agree they make very fine products. However, what has any of that got to do with the price of eggs or the topic of this thread? I guess I can be faulted for not having catalogued every possible way of designing an RC RIAA network. For example, you did not mention that it's also possible to use a capacitor as the first element in an RC RIAA, tapped in series off the plate of the input voltage amplifier, instead of a resistor. Nor did I wish to turn this thread into a debate about the relative merits of each type of RIAA filter. I just want to know more about LCR type phono stages that are already out there as commercial products, and how they sound in comparison to other good phono stages.

Jazdom, Hi. Can you say more about the Kahn phono stage. I presume the name refers to our mutual friend in Silver Spring. But maybe not.
John, I own a Silvaweld phono stage, designed and produced by the same Mr. Park who later went on to produce the Allnic products. He evidently had a huge change of heart after Silvaweld went under. Silvaweld phono stages are all RC types, use a capacitor as the first element in the filter, thus avoiding high value resistors at that point in the signal path (or any resistor, for that matter). However, using a capacitor has it's own theoretical issues, since capacitors are also imperfect devices; one might say they are more imperfect than resistors in fact. So the Silvaweld circuit is a far cry from the LCR used in the Allnic H3000 (or H1500). The Silvaweld also uses a JFET input to add gain for MC cartridges, followed by an all-tube RIAA correction network that by itself develops sufficient gain for any MM. In contrast, Allnic phonos use built-in SUTs for this purpose. I use my SWH550 only for MM cartridges, so I bypassed the JFET permanently, and then I rather drastically modified the tube circuit downstream, with some help and advice from a more knowledgeable DIYer. (Kept the capacitor-led RIAA as is.) The result is shockingly good. I have a neighbor up the street who just got hold of a LCR MM made by Dave Slagle and his business partner. I do not know the commercial name. I heard that the other day and am VERY impressed. I am familiar with my neighbor's system and had heard it previously with two other very good phono stages, Coincident and Dolshi. By comparison, the Slagle unit sounded very open, airy, effortless. He's made some other changes in his system along the way, so one cannot attribute all of the improvement to the new phono stage, and I would not say that the new phono "kills" the previous two, but.... it's very beguiling.

So, here's a list of some of the LCR phonos mentioned above:
Allnic H3000, H5000 (not a real-world possibility for me), H1500
Lounge
"Kahn" Experience Music
Ypsilon
Zanden (did not previously know that was an LCR type)

I know there are others in between the extremes of cost ($32K for the H5000 vs $250 for the Lounge [maybe the Ypsilon is even more costly than the H5000]), but my mind has gone blank. The Dave Slagle design costs ca $5000, plus the cost of any added SUT for MC. There's another one available via eBay from the orient that has received favorable mention. I am really curious about the H3000 and am on the look-out for a used one.

For the really far out theoreticians, I have read about LR-based RIAA filters, which use no capacitors at all. Apparently that's very tricky to execute because the values of the inductors must be very precise in order to achieve good RIAA compliance.

Dave, I looked it up. Not much info regarding the innards. Seems to be solid state. Does not seem to have adjustment for load R and C. However, it does have a mono switch. (I don't know how you can build a phono stage with high end pretensions and not include a mono switch.) As you know, I'm partial to tubes, but I'd like to hear this one. Do you have direct knowledge?

Yes, that's one problem with designing a tube-based LCR; the needed 600-ohm impedance on the input side is hard to achieve with tubes. There are many interesting threads on that subject. One such claimed that you only need 600 ohms on one side of the LCR, not on both input and output side; I am not sure about that. Some use a transformer to achieve the needed impedances. But another approach is to build an LCR that can be driven by a higher impedance, 10K ohms being another more recent standard. A very smart DIY guy I know in Australia has built a high-gain LCR RIAA using ~20K ohm LCR, built from parts supplied by Dave Slagle. I have the schematic. I actually have no idea how or why 600 ohms was ever adopted as a standard or why it is anathema (to some) to deviate from that value. It could merely be that the original LCR modules, made by Silk and/or Tango, in Asia, were set at 600 ohms, and everyone jumped on that bandwagon when those were the only LCR modules available. I welcome input from others who may know more about this.

Good point. That's where Dave Slagle jumped in, to design and build chokes that will work well in "high-impedance" LCR designs. Dave can create very precise modules.

One of our readers has done a little digging into the Emia phono stage. Apparently it is NOT an LCR type. Rather, it is a novel CR type wherein the high value resistor(s) in the signal path have been eliminated. In fact, my correspondent says he was told that there are NO R's or C's in the series signal path between the input stage and the output stage; All Rs and Cs are shunted to ground. (I am only the messenger here.) Thus the plate of the input tube is direct-coupled to the grid of the output tube, with all the filter components shunting to ground. I can only say it sounds great, no matter what the topology. But I really do not know how one can avoid having either an R or a C in the series signal path and still get to proper RIAA equalization. On the other hand, the two designers are smarter than I.

Thekong, Thanks for mentioning the Thomas Mayer LCR phono stages. I had been meaning to do so as well. He seems to sell an LCR phono in kit form, using Dave Slagle LCR modules (aka "Intactaudio"). Very tempting. As to this shoot-out, it is not very helpful, although it seems the participants were having great fun. For one thing, several different SUTs were used with the Mayer LCR; I think the SUT will a major effect on sonics, if not THE major effect. I am somewhat familiar with the Scott Frankland phono stage mentioned. IMO, it is good but not a contender among today's best options. But you've added Thomas Mayer to our list. I wonder what he charges for that kit version?

Hiho, The output impedance of the input voltage amplifier or gain stage has to be accounted for in the design of the RIAA. Therefore, as you may be suggesting, output impedance is a factor in determining the values of the reactive components needed to effect an RIAA equalization. But output impedance per se cannot substitute for Rs and Cs that make up the RIAA. Perhaps I don't get what you wish to say. Suffice to say that if you do anything to alter the output Z of the gain stage, you have then to change the values of Rs and maybe the Cs in the RIAA (or at least the value of the first R). This still does not suggest to me how the Emia RIAA topology is achieved. Maybe Dave Slagle will walk by this thread and stop to enlighten us.

I am very familiar with that circuit. I revised my own Atma-sphere MP1 phono input (already a dual-differential design, like the RTP, but with an all-tube cascode input stage, unlike the RTP) to some degree to mimic the RTP shown here. However, I did nothing to the standard MP1 RIAA network (except see below), so I had not noticed, as you correctly point out, that the RTP has it's RIAA in shunt topology. (I don't like the term "invisible resistor"; it's the output impedance of that hybrid cascode to which you refer, and that's a factor in any RIAA network. The cascode will have a high-ish output Z in fact. But I take your point. Thanks.) Note however that the RTP is rather unusual in that there is no second gain stage after the RIAA (It's not needed because that hybrid dual differential cascode at the input develops tremendous gain by itself); nor is there a cathode follower at the output of the phono section so as to reduce output impedance to drive the attenuator and the linestage section.

When I installed a similar hybrid cascode gain stage at the phono input of my MP1, all I had to do to maintain correct RIAA was to change the value of the first (series) resistor in the MP1 RIAA network, to correct for the change in the output impedance of the gain stage. I listened to it before changing that R value; there was virtually no bass response. When I re-adjusted the series resistor value to compensate for the altered output Z of the gain stage, the bass came back. (Just to make my point that the output impedance is a factor in any RIAA network.) Now you've got me thinking I could possibly adopt the RTP RIAA network to my own phono section. Cool.

Jazdoc, Now that we know the Emia is not an LCR type, do you know anything more about the topology of the RIAA that you could reveal without violating any confidentiality agreement with the two designers? I am still wondering how they effect direct coupling and whether the accuracy of the RIAA equalization would be affected as the gain stage tube ages, and its output Z drifts accordingly. I think Hiho said it first; the virtue of the high value resistor at the output of the gain stage in typical RC RIAA networks is that it ameliorates the negative effect of tube aging. No matter; the Emia sounds excellent in the home of my neighbor, and he is thrilled with it.

I thought more about the Allen Wright RTP. As Hiho mentioned, the RIAA equalization depends upon the constancy of the input impedance of that 50K attenuator seen in the schematic. But at the same time, the signal must pass through a 2.2uF capacitor between the plate of the gain stage and the input of the attenuator. Those are at least minor drawbacks. My MP1 has a second gain stage downstream from the dual-differential cascode input stage. THAT second gain stage then drives the attenuator, thus isolating RIAA equalization from the attenuator. However, there's no free lunch; you still need a largish coupling capacitor between the output of the second gain stage and the attenuator. I use a smaller value capacitor (0.68uF) and an attenuator with a higher input Z, 100K ohms, to achieve roughly the same low frequency cut-off.

John, The input stages of the Allen Wright RTP (shown in the schemtic posted by Hiho) and of the Atma-sphere MP1 are both dual-differential cascodes , i.e., balanced topologies. Thus in both cases, a CCS is used optimally at the junction of the cathodes of the two "bottom" tubes in the cascodes and ground. (Take a look at the RTP schematic; I think AW used an LM317, which is definitely not my choice, but it's a CCS nevertheless.) Thus there is no place for more CCSs on the plate side. However, your point is relevant to a single-ended topology. But in a single-ended topology, the output Z would be the parallel sum of the impedances of the CCS and of the cascode stage below. The impedance of the CCS is ideally infinite (but is always finite in reality, albeit very high). However, would not the impedance of the cascode below be a very finite number, thus dominant in the calculation of output Z? And also subject to change as the tube(s) in the cascode age? Please correct me if I'm wrong; you probably know more about this stuff than I.

Now I re-read your post, you seem to be talking about a dual-differential cascode with CCSs between cathode and ground AND between plate and B+. AW discusses that possibility in his TPCB. Have you ever tried that?

Ddrive, That's very cool that you have the Wavac. As I recall, it's "big bucks". I forgot all about the Cole; I remember reading about its pro's and cons on Romy the Cat's blog; that was an early contender in the LCR game. I'd love to hear either. That's the only way I am going to gain a feel for these beasts.

"With the single ended version the cathode CCS is bypassed with a capacitor." This is a sidebar to the topic, really, but are you imagining a single-ended phono input with CCSs between both the cathode and ground AND between plate and B+? Using a bypass capacitor around the lower CCS does not fit in with my understanding of the need for a bypass capacitor, the value of which needs to be inversely proportional to that of the more typical cathode resistor, in order to pass audio frequencies of interest. In this case, the CCS impedance is so high that a bypass cap would seem to be superfluous. Never seen that done.

I am guilty of going off topic in a thread that I myself started up.
I found a nice thread on Wigwam, among some English guys, one of whom built a LCR phono for another member, using inductors built by Dave Slagle. The builder explains that for an LCR, it either has to be driven by a source with an output impedance equal to its input impedance (e.g., 600R), in which case it can be terminated by an impedance that is ideally 10X higher, or the other way around. In other words, when I wrote that there needs to be 600R on either side of 600R LCR network, I was wrong. But 600R impedance is still very difficult to attain with tubes, without resorting to transformers, etc. This guy used 7K inductors made by Slagle.

John, I think there is a misunderstanding between us that comes from trying to describe a circuit in words rather than by schematic. Can you reference a schematic that illustrates your point? For my part, I can only say that I've taken a particular interest in balanced differential input stages, and I have never ever seen a schematic wherein the CCS ideally used between ground and the cathodes of the two tube sections that constitute the balanced input is bypassed by a capacitor. Plus, my understanding of theory tells me that it's not necessary, would even be detrimental. However, I stand ready to be educated; if you can point to a schematic it would help.

Ddrive, Are you in the UK? Please send me a PM via the Audiogon auspices. I might be interested, obviously. Thx.

The revival of this (my) thread enables me to ask a question:  I was reading an old review of the Manley Steelhead, in maybe 6 Moons, maybe from 2004 or 2005.  In that review, Evanna Manley herself describes the Steelhead circuit from input to output, and in those paragraphs she drops the tidbit that the Steelhead contains an LCR RIAA filter.  I have been unable to corroborate that information anywhere else, including on the Manley website.  Does anyone know anything about the Steelhead?

Dear Ghetto,
Thanks for the information on the Steelhead.  I wonder what they do via the MC inputs that bypasses the LCR corrector.  I do know that the MC inputs feed autoformers, but I thought that was to alter input impedance only.  

There are a few LCR phono stages that meet your cost criterion.  Unfortunately, I cannot rattle off their names with confidence, but the "Cole" is certainly one of them, probably for less than a kilobuck.  Lounge Audio LCR is another, very interesting because it uses LCR in the context of op amp gain blocs.  It gets very favorable reviews.