The Luna is an interesting product that I have not seen before. It must be a new model, because I had been intrigued by their earlier phono circuit which used a pentode as phono input tube, and RIAA correction was accomplished by a circuit located between the plate of the pentode and B+. This is a very novel idea. Now it seems that the designer seeks to cash in on the popularity of LCR phono correction, which is fine and can sound great too. I am not so crazy about all those transformers in the signal path, but hearing is believing. Note too that using a step-up transformer for MC sets an upper limit on the load resistance seen by the cartridge, as in this case it's 100R and down from there. I don't usually blow the horn for stuff I personally own, but for a full-function preamplifier, you might also consider the Atma-sphere MP1, which has enough inherent phono gain such that you don't need a SUT. The only thing I would criticize it for is relative lack of flexibility and the fact that it actually has too much gain for MM or MI cartridges, some of which I like a lot. That said, the MP1 blows away every other phono stage I have used for MC cartridges, in my main system. I just bought a Steelhead for my "other" system. It's too soon to say which is better between those two, but my money is on the MP1. The Steelhead is MUCH more flexible as regards phono; the MP1 is MUCH more of a true full-function preamplifier, however, in that it offers multiple hi-level inputs, phase reversal, etc, etc.
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Dear Lewm, like you I too fail to understand why transformers (which involve Kms of wires) would be useful in the signal path however some of the best preamps and power amps I have heard are transformer coupled so I am ready accept that I don't know much. For instance the Wavac PR-Z1 is my reference for tube preamps and it is transformer coupled input to output. Similarly for solid state amplification the First Watt F6 is one of my reference and it too is transformer coupled input to output. I also like the top Audio Note preamps which are again transformer coupled. So I seem to have ample evidence that transformers has a case for itself when done right.
I think you might have answered your own question somewhat. Besides all the number guys and their theory's you listen to interstage transformers and guess what it sounds like real music. Lcr same thing. I did not realize that someone had a interstage phono. I built my own with with interstage and LCR 3 tubes per channel. Best thing I ever did.
I have built so many tube phono stages I can not remember. I have played with almost all variables. But the latest is by far the best.
I do not know how many stages or which tubes or power supply etc. But it looks like they have the LCR / interstage going for them.
And if nothing else you know you got some expensive iron under the hood not just some caps and resistors.
Enjoy the ride
Pani, I think I was misunderstood. I did not mean for my comments to imply that transformer-coupling cannot work well and sound great. My point was that using a SUT between a LOMC cartridge and a phono stage per se limits the impedance with which you can load the cartridge. This is only because the turns ratio of the SUT determines the impedance "seen" by the cartridge looking in to the phono input. Case in point, the Luna starts at 100R and goes down from there. Most LOMCs will work fine into a 100R load, but lately it has been my observation that many LOMCs can sound even better with less of a load. I spent the last two nights, in fact, listening to two different LOMC cartridges with load 47K ohms. I found that I slightly preferred that to 100R or even 1000R. (Load is selectable on my MP1.)
In the case of the Luna, and without having seen the schematic, I wager that the interstage transformer was necessary for the sole purpose of reducing the output impedance of the stage driving the LCR correction circuit; the impedance has to match that of the LCR module, and most require 600R, although in recent years LCRs that need to see higher impedances have been devised, when the needed inductors can be precisely wound. This is not necessarily a bad thing; it just is what it is.
Pani, Also, prepare yourself for the onslaught of the Herron-lovers. There are many of them here, so many that I don’t doubt its excellence. Keep in mind that the Herron uses an "old fashioned" CR type of RIAA correction and no transformers in the signal path. There are many paths to Nirvana.
(I still want to hear the older Trafomatic phono that places the RIAA correction in the plate circuit of the input tube.)
Tom, Have you posted the schematic of your "interstage LCR" phono design? I certainly remain interested in LCR and even LR phono correction.
I do not schematic software. But a quick over view. It is a 3 stage with the Riaa correction between the 1st and 2nd tube. The 3rd tube can be 2a3 1 to 1 out and still have low output impedance. Or your use a higher gain tube 2 to 1 step down to get a lower impedance. On the first 2 tubes I am using diode bias and the 3rd is fixed. Each tube has its own choke tube power supply. And separate filament power supply for each tube.
I am using Dave Slagle 7k chokes for riaa so opens up many tube options. In regards to sut loading I have a separate box with 4 pair of different suts and replaceable resistors to load before after or both. So I can go from 0 to anything.
The reason I posted here is it sounds like Pani is looking for something that has body and soul. If hi fi was his thing the options are endless. I realize pretty much no one wants to be over the top like what I built but I think the interstage/lcr is going get you pretty close to a home run!!!
Enjoy the ride
And I think it's a mistake to think that any particular topology is per se going to sound great regardless of who designed it and regardless of parts quality. In your case, you got chokes made by Dave Slagle, i.e., the highest quality I can imagine. Do we know that the Trafomatic sourced their chokes from an equally prestigious source? Plus, you describe your phono stage that is off the charts for more reasons than just the quality of your chokes, or the 7K value of your LCR that permits a much more simpatico tube circuit than does the typical 600R LCR module. In a commercial product, and given Pani's lack of DIY expertise, I would almost say that simpler (CR correction) is likely to be better, on a dollar for dollar basis, but of course there are exceptions to any rule. For sure, the Trafo deserves an audition. By the way too, not everyone is crazy about interstage transformers, even those who like transformers and tubes. I'm just saying. I personally have no opinion on that score (use of interstage transformers per se), because I do not feel qualified to have one.
It is fun to go through a mental process and or research. But when it is all said and done we have to listen to our decisions. The only reason I I posted was from Pani post it sounded like he could hear what interstages could do.
If you need to prove to your self that interstages are a waste of money without listening to them; besides the band width issues your can not hold the riaa adjustment as close as with a r/c circuit.
Maybe Dave Slagle non LCR phono stage. I am pretty sure he is using lower impedance tubes so he can reduce load resistor values. He thinks you can get pretty close to a LCR unit.
If you are interested on how build and or understand phono stages Morgan Jones second or third ed. Valve Amplifiers is a must have. He is very much a numbers guy but is very through.
Once you get a understanding of tube amps you will see there are not that many variations as the marketing department would lead you to believe. In fact in all the experiments I have done the simple circuit is the best. No ccs tube or transistor. No cathode followers.
No grid stop resistors. No cathode bias caps you get the idea. Been there done it more times than I like to remember.
So if Pani is interested if he can find out how many stages and who's chokes and transformers. Also tube types. Maybe it will help you with your concerns.
Enjoy the ride
Lewm, loading a phono cartridge is a phenomena that is primarily for active MC stages. All this HF ringing and damping comes into picture when an active circuitry is amplifying the MC signal. It is more or less a band-aid in that context. When it comes to SUT, the primary job of an SUT is not exactly loading the cartridge but to convert the low-voltage-high-current cartridge signal into high-voltage-low-current one and feed the following MM stage with sufficient voltage gain to work on. In this process there is some loading due to the turns ratio in the SUT. But this is a much more of a natural thing which is not a band-aid. SUT matching is critical form the point of view of providing the right amount of voltage gain, not so much the loading aspect. That is also the reason cartridges behave very differently when "loaded" via resistors vs an SUT. So your concern about experimentation with loading while using SUT may not be that significant a concern actually. It will most probably just fall into place if the SUT is chosen to match the cartridge output to the requirements of the MM stage.
Regarding the Herron phonostage, I have heard it. It is nice for its asking price of $3.5k but I would not pay much more than that for it. I would not go into the details of how it sounded etc, it will probably drift the thread into a different discussion.
For the record, I do not have any DIY exposure into building equipments so I per se do not know how an interstage transformer would sound but I have noted that the best tube equipments are either pure OTL or loaded with high quality Iron wherever suitable. Trafomatic Audio uses all their transformers and chokes made by the designer (Sasa Cokic) himself. He is actually known to be a transformer Guru in the Europe. Whether his transformers are better than Slagle or not I cannot comment but whenever I have heard his amps I have always felt I am listening to a very good product.
Loading a cartridge has to be done regardless of sut. Most people add one on a mm phono which normally has a 47k load. So the transformer is now loaded on the secondary. So now the load on the cart is affected by the turn ratio of the transformer.
So with out getting into the math or theory let's just say most carts sound different when you change the loading. If the phono stage does not have a adjustment for this I would find out what it is and see if the cartridges you use match up pretty close.
Enjoy the ride
@pani Have a look at the ModWright PH-150 reference tube phono stage. It’s a contender fairly close to your price range and definitely works superbly with my Dynavector LOMC cartridge. I chose this unit over the Herron and Manley.
As a low-tech guy, I appreciate the convenience of ModWright’s front-panel adjustment of loading parameters. It’s built to a high standard, looks fantastic, and sounds great.
Tom, I think I said this before, but judging from your follow-up post, you did not "receive" my message. I keep an open mind on transformers in audio. I don't necessarily think interstage transformers are "bad", but perhaps that is the audio transformer function of which I am most skeptical. In my response, I was merely pointing out that some who know more about the advantages and disadvantages of IS transformers than I do have written about the disadvantages, and I was influenced by what I have read. But this hasn't caused me to dismiss the idea. t would be eager to hear your phono stage any time.
Pani, I know what a SUT does. However, the SUT will affect the impedance seen by the cartridge according to the square of the turns ratio. So, if your SUT is providing a 1:10 voltage step-up, then the impedance seen by the cartridge running into a SUT in series with a typical MM phono stage will be 470R (47,000 ohms divided by 100). My point was that lately I have been finding that I like to run my LOMC cartridges into more like a 47K ohm load (i.e., unloaded). To achieve that with a 1:10 SUT, I would need a 4.7M resistor across the secondaries. Since that resistor also serves as the grid resistor of the input tube, problems with grid current might be created by using such a large value grid resistance. (It would probably work OK with certain tubes, but not all.) Also, I do not agree that using a SUT necessarily avoids problems related to "ringing" that might otherwise be encountered if using an active gain stage with an LOMC (unless that gain stage is intrinsically flawed in design). There's a nice white paper on using Zobel networks to tame the response with SUTs, on the Jensen website.
I was interested to read your thoughts on the Herron. I've never heard one, but as you know, there are many devoted users here.
Lynn Olson did a study of the harmonic spectrum of different coupling techniques. His results might be of interest to those curious about IT transformers.
The smooth fall-off of harmonics is especially noteworthy in the transformer-coupled circuit - the reason for the excitement about the naturalness and "directness" of transformer coupling is obvious when looking at the spectral data. This is the best distribution of harmonics I've seen — looking almost exactly like an RCA "textbook" distribution of spectral content.http://http//www.nutshellhifi.com/library/FindingCG.html
Disclaimer: My phono pre., line stage, and power amps are all transformer coupled - input and output.