Hi All, the subject of phono-pres, specifically 'adapted' to MM came up in some related postings.
IF, and only if, MMs are much to ones liking --- why spend your buck on some 'halve backed' 60dB plus, MC gain requirement, stage? Why not consider put the $$$ into a TOP 40dB gain stage of either SS or tube?
Raul had more thoughs on the subject as he mentioned before, and might share, why he knows that a TOP MM compared to MC stage circuit requirement might NOT be -one suit fits all-.
There could even be a nice argument to fit a tube gain stage only into an otherwise SS only system!?
Again, the $buck saved on the 20dB plus circuitry could be translated into the BEST circuit for an MM. I realise, that most such stages were simply fitted inside some older TOP pre-amps, (e.g. Jadis...). I have not come across a **dedicated** , current 40dB stage neither in nor outside a pre-amp.
Raul, Do you mean to say that every time you change from an MC that likes to see, for example, ~100R to one that needs significantly higher R, you actually take the 3160 to the workbench and solder in the required higher R? Or do you use some plug-in system that obviates the need for a switch but still puts mechanical (i.e., unsoldered, pressure-based) contact points in the signal path? Or do you still have a switch for load resistance? (Your post suggests you eliminated switching between input jacks, rather than between load resistors. Even with a single pair of inputs it would be desirable to be able to switch load resistors.)
Kirkus, I just paid too much for a B&O MMC20CL off eBay. I hope I will be happy. The AD797 is one of the ICs I had in mind when I noted that the op amp-based schematic that was posted above might be upgraded with later, better chips. (The schematic used TL072, I think.)
I just paid too much for a B&O MMC20CL off eBay. I hope I will be happy.
I think that I was looking at that one too . . . glad you got it. If it's in good shape, then you didn't overpay. Stellar cartridge.
On the AD797 - this opamp is capable of extremely high performance, but it's definately NOT one to swap into an existing circuit without careful consideration, especially if it originally uses TL072s! The AD797 really shines with low source impedances (not MM cartridges), but on the other hand, it can be limited in its useable output current . . . so it doesn't necessarily do the best job of driving the low-impedance feedback network that suits its low eN characteristics. That's why I used the discrete JFETs as a buffer, and why I used it in the second stage, where it can be driven from the low source impedance of the first. The AD745 is FET-input, so it works great with an MM cartridge . . . but it's not stable at lower gains, so stability and phase margin have to be carefully considered in application. Then there's the fact that the TL072 is a dual, and AD797 and AD745 are singles.
Dear Lewm: That's right, if I need a different load impedance then I soldered a new resistor value, no switch. Normaly almost all the LOMC cartridges comes with a very low internal resistance where 100 Ohms can cope all them. The other subject is that due to the Ponolinepreamplifier characteristics you don't need to change the load impedance, only in extreme very extreme cases.
Lewm, one way or the other normaly a switch makes a degradation to the cartridge signal so you have to make a decision on trade-offs between quality or convenience, we choose for quality performance.
Kirkus, Would you care to comment in more detail on your earlier statement that a balanced input is per se not ideal for an MM cartridge? At least I think that is what you meant to say.
By the way, thanks largely to Kirkus' input I am beginning to learn some things about MM phono stages and phono stages in general that I did not know.
This thread has been informative and I'm better understanding some of the nuances of phono stage design, both MM and MC architecture.
And I'm beginning to see the value in having a dedicated MC phono preamplifier if LOMC cartridges are preferred. Why bother with 40 dB gain and 47K loading for MM cartridges. The design would, at most, have binding posts to change loading resistors. Being able to change the amplification (gain) would be handy but not necessary if the output voltages of the preferred cartridges were within a fairly close range.
Oops. Meant to include a thank you to Axel and Lewm for answering with understandable information. And Axel, I didn't intend to sidetrack the thread with my question about dedicated MC phono preamps. Just seemed like a similar question in that having phono stages designed specifically for the type of cartridge engine makes sense.
What I'm not sure about is whether you'd be able to hear the difference (as Lewm suggests) between a dedicated minimalist design vs a preamp with variable gain/loading options. I often read that it does make a difference, that having switches or plugs or jumpers degrades the signal, but as Lewm also suggests, if the problem is that noticeable, why do even high end manufacturers provide gain/loading flexibility in their phono preamps?
Hi Tom, you say: >>> Just seemed like a similar question in that having phono stages designed specifically for the type of cartridge engine makes sense. <<<
I have the idea that Raul will be the person to explain to you in his words why he has opted for two **dedicated** phono-pre option in his 3160 and NOT a one-serves-all (just with a jumper to switch from 40 to 60dB).
Having read all my and Kirkus' comments should have made the point, but let's see if Raul can put it into a 'nut-shell' for us.
In my view, one of the hard to resist features of the 3160 (Raul's product) is the completely separate MM and MC phono stages, not to mention the fact that both are balanced circuits (or at least I know that the MC one is balanced).
Raul might respond to Tom's question about why "high-end" phono preamps have switchable load resistances by saying that there is a demand for it among end-users, for the sake of convenience, not optimal sound quality. Most end-users of such products want remotely switchable everything, so they don't have to get off the couch. Raul wants optimum performance as his end-all and be-all. What I meant to infer when I said that most of us would not know whether switches degrade the sound is that most of us have not done the experiment properly in order to make a judgment. Most of us have one phono stage which either does or does not have switches in the signal path. And no one (other than Raul) has come forward to say that removing switches from phono inputs has made an audible improvement in sound. Or that adding same caused a deterioration. For my part, I own an Atma-sphere MP1 in which I have made considerable mods to the phono stage. The MP1, like Raul's preamp, has no switches in the phono input, but one can change load resistance by installing resistors between two screw terminals on the outside rear of the chassis. Purist that I am, I have never used those screw terminals for loading or for anything; I solder my load resistors right at the grids of the input tube (or the gates of an MAT02 NPN transistor, in the case of my modified unit). Oops, I am off-topic.
One thing that comes out of this so far, thanks to Kirkus and Quiddity, is the concept that there truly IS a difference, primarily at the input voltage amplifier stage, between an ideal MM phono and an ideal MC phono. One topology does not ideally fit all. I'd still like to hear more from Kirkus on balanced mode with an MM cartridge. Anyway, I've decided that I do want a separate dedicated MM phono stage, which is kind of where I started but now I have more info to go on.
Hi, Lewm, nicely stated explanation. And after reading Raul's responses again I see what was implied, that convenience may override preamp performance. I can certainly understand the convenience factor.
But Axel, I'm confused a bit by your comment that the 3160 has a jumper to change from 40 dB to 60 dB of gain. Are jumpers considered to be acceptable, that is, they do not degrade signal path, at least in the amplification portion of the circuit? Or did I interpret your comment incorrectly?
Tom, >>> ... confused a bit by your comment that the 3160 has a jumper to change from 40 dB to 60 dB of gain.<<<
That is not what I said, neither implied, since the 3160 has dedicated (like two seperate units) MM & MC stage(s) inside the line-pre-amp.
Jumpers are just somewhere in the hierarchy of 'switches' and perhaps a bit preferable (but not for comfort). They are normally very closely placed to where things need to get 'switched', Raul will NOT have any of those either, I'm sure. A solder joint, or no joint at all, is still THE BEST (as long as it does not create a diode :-) A.
Dear Axel: Why in a MC commercial world any phono stage or any Phonolinepreamp manufacturer have to take care about the MM alternative? when the MM alternative almost does not " exist " by commercial business.
So in the last years almost everyone commercial manufacturer build phono stages for the MC market even the ones that are for MM because it does not have enough gain for MCs but that they recommended using with external SUTs.
Only a few of us ( like Kirkus. ) that understand and like the MM virtues start to care on the subject and that through a research find that the MM needs are way different that the needs for the MCs.
That's why our units has separate and dedicated MC and MM phono stages that cope totally the MC specific needs and the MM specific needs. These different topologies make a quality differences on the sound reproduction?, ABSOLUTELY YES.
Lew sum up correctly: " One topology does not ideally fit all. "
IMHO the MM alternative is so good an friendly that even if the phono stages are not designed on its specific needs the sound reproduction quality on these cartridges is just glorius.
Now, on the convenience to switch from one stage to other or to choose load impedance through switch/jmpers or the like Lew say " I'm purist " an even that my Atmasphere has those jumpers I solder the resistors directly. A switch/jumper or the like is always a compromise even if that compromise is at minimum even if you can't hear it. When we are talking of MC/MM we are talking of very delicate signal at very low output/gain where these low signal are easy to contaminate even if you " bread ". That's why I prefer ( between other things. ) integrated units ( Phonolinepreamplifiers. ) instead phono stage that has to be connected to a line stage through additional cable/connectors.
Btw Lew our uit is differential/balnaced too in the MM stage.
Hi Lewm . . . so for the subject of balanced inputs for phono preamps. First, its important to understand exactly what type of noise a balanced input is capable of rejecting. The overwhelming majority of cartridges and tonearm/turntable cartridge wiring treat the cartridge winding as a balanced source -- this alone is wholly sufficient to avoid hum pickup from ground-currents flowing between the turntable and preamp, provided no mistakes are made. Suceptibility to RF interference is determined by the design of the input stage itself. That leaves magnetic hum pickup as the main type of noise that we're designing the balanced input to reject.
The effectiveness of the hum-rejection in a balanced-input system is directly related to how closely matched the positive and negative conductors are impedance-matched to ground - that is, if the + and - conductors on the input have different impedances, the magnetic field will cause different amounts of interference in each one, which in turn will manifest itself as signal voltage. This is why (IMO all decent) balanced-signal cables use twisted-pair or star-quad configurations - the tight twisting keeps the impedance very much the same between the conductors, for good hum rejection.
But in a tonearm, the wiring is very rarely twisted-pair . . . they're usually just stuck side-by-side through the tonearm tube. And this isn't necessarily a bad thing, because the side-effect of the twisting is an increase in cable capacitance, which is exactly what we DON'T want for our MM cartridge. And if you want to minimise capacitance in the leads between the tonearm and the preamplifier, then you're also probably looking at simple coaxial cable types instead of shielded twisted-pair. Then there's the matter that having carefully-balanced output impedances is probably only very rarely considered in the design of the phono cartridge . . . because the vast majority of phono preamps over the years have unbalanced inputs.
So in any case when we're designing a phono preamplifier, we CANNOT assume that the impedances coming from the + and - leads of the cartridge will be well-balanced, impedance-wise. So if we want magnetic hum rejection, we need to build a balanced input that is fairly insensitive to these imbalances. And the way to do this is to keep the differential-mode (cartridge loading impedance) as low as possible, and keep the common-mode impedance as high as possible, as it's the ratio of these two that determine the effect of the source imbalance.
So for a traditional, say 5-ohm LOMC cartridge driving a 50-ohm transformer input, this is pretty easy to obtain, because the transformer will have a common-mode impedance in the tens of megohms, say 50 Meg. The ratio between the common-mode and differential-mode input impedances is thus 1,000,000,000 . . . and since the cartridge source impedance is so low, the maximum impedance imbalance will be a fraction of an ohm anyway. So hum rejection can be reasonably effective, regardless of the type of wiring used.
If we're to do this with an all-active input, we would still have the same 50-ohm loading resistor, but to effectively manage i.e. input-bias currents and offset, the input impedance of each side to ground would be probably at the highest maybe 470K, making the common-mode input impedance 235K, and our impedance ratio 4700. Not as good as the transformer, but still worth it.
But when we go to an MM cartridge, the source impedance is usually something like 1.5K and rises with frequency, so the impedance imbalance of the cable is then more likely to be a handful of ohms, and also rising with frequency. Per our earlier discussions, the differential-mode input impedance needs to be about 100K. And assuming JFET inputs, the very highest you can probably get away with for common-mode (without having the offset go through the roof, or cap-coupling) is 2 Meg resistors . . . making the common-mode impedance 1 Meg, and our impedance ratio is at 10.
So the endgame: the higher output impedance of an MM cartridge will make the impedance mismatches in the wiring more apparant, and at the same time makes the necessary design criteria in the phono preamp more suceptable to these imbalances. And the most effective way to reduce the imbalances in the wiring (twisted-pair construction) raises the capacitance, which is exactly what we DON'T want for our MM cartridge.
So then there's implementation - for MM cartridges, we can't use transformers, which leaves us with active realizations, which have a couple of major disadvantages over unbalanced inputs. The first is noise . . . you usually end up with twice as many uncorrelated noise sources, and can only make up for it by the fact that each side will see half of the impedance, giving a minimum 3dB noise penalty. The second is that many input stage designs don't work as well in the presence of significant common-mode voltage (which if we're trying to reject it, means it exists), and with high common-mode impedances, some sort of protection diodes, series resistors, etc. will probably be necessary to keep the input stage from getting fried when a ground wire gets disconnected and suddently there's 30V of common-mode voltage.
While I won't pretend that my conclusions on the matter are definitive, all of the above makes me think that for an MM cartridge, active balanced inputs are unlikely to deliver enough hum rejection to be worth the complications.
Hi Kirkus VERY insightful, thank you. I'll have to chew over all of this with my 'consultant engineer':-) But now one question: Common mode rejection, yes well... everybody points this out on the differential circuits, and nobody is running 20m or more ICs (other then in the professional world).
But it was the OTHER item: The inevitable and unavoidable 'ground contamination' influences of capacitors etc. that makes the other argument for differential/balanced vs. unbalanced.
It seems this (at least to my current take) is to be weighted against the ~ 'imbalance(s)' in a balanced design.
A lot could be said about some renown reviewers / testers having found, that even in a balanced design (not pseudo) the single-ended still sounded more 'natural'.
Why? It is that the differential circuit also cancels even-order harmonics in the process of common mode rejection, so you wind up with a bias toward odd-order harmonics, and that is not so 'natural' to our ear.
Hi, Axel, it was this comment that I probably misunderstood: "I have the idea that Raul will be the person to explain to you in his words why he has opted for two **dedicated** phono-pre option in his 3160 and NOT a one-serves-all (just with a jumper to switch from 40 to 60dB)." I understood the portion within the parentheses to mean that the 3160 does not use switches except for a jumper to set gain. My mistake.
Kirkus, I would like to try to re-state your argument in short form, to see if I understand it:
For the reasons cited, it is much more difficult to obtain a true balanced signal from an MM cartridge as compared to an MC one. Feeding a signal with an imbalance of noise on one phase vs the other to the balanced gain stage will result in the amplification of that noise, i.e., it will not be rejected because it is not identically present on both phases.
Is that more or less correct? Why is the noise to which you refer not similarly amplified by an SE topology? (It's that "3 db" boost of the noise that I don't quite get.) Noise is noise(?) In a good SE phono stage for MM, is the "ground" isolated from chassis or earth ground? That would seem to be a good idea.
Dear Axel: +++++ " some renown reviewers / testers having found, that even in a balanced design (not pseudo) the single-ended still sounded more 'natural'. " +++++
the main subject here IMHO is the kind of topology in the design, there are very good balanced designs and there are too not so good balanced designs. This not so good balanced designs performs a " step " down the unbalanced good design performance but IMHO not because the unbalanced is better.
As in other audio areas here there are good, regular and bad designs.
For the reasons cited, it is much more difficult to obtain a true balanced signal from an MM cartridge as compared to an MC one. Feeding a signal with an imbalance of noise on one phase vs the other to the balanced gain stage will result in the amplification of that noise, i.e., it will not be rejected because it is not identically present on both phases.
Lewm, this is a fair approximation of most of what I was saying. Maybe add to that . . . if the "balanced" input stage doesn't do a bangup job of eliminating magnetically-induced hum in the real world, then does it really need to be "balanced"? This is of course a question that each circuit designer will have to answer for him/herself. Right now, I'm personally leaning toward "no" . . . but it wouldn't suprise me if I changed my mind in the future.
Why is the noise to which you refer not similarly amplified by an SE topology? (It's that "3 db" boost of the noise that I don't quite get.) Noise is noise(?) In a good SE phono stage for MM, is the "ground" isolated from chassis or earth ground? That would seem to be a good idea.
Well, in this case "noise is not noise". The noise to be avoided in poor grounding is a result of the amplification of ground currents flowing across ground connections of finitely-low resistance (that is, everything except superconductors), and should be completely eliminated in a good design. This is what I am referring to in response to Axel's comment below.
But the 3dB minimum noise increase from an actively-realized "balanced" input stage is a different noise source altogether - here I am referring to the (mainly) thermal noise from the input semiconductors/tubes and their associated passive components. In a differential "balanced" input, there are double the number of devices, each producing their own uncorrelated noise, acting in series. When combined, they will produce double the noise voltage, which is 6dB higher. That can usually be offset by the fact that each side of the differential input stage is now looking at half the source impedance, which can reduce the noise by 3dB . . . so that's where the net 3dB noise increase comes from. This is a big reason why the vast majority of low-noise preamplifiers for ANY kind of low-impedance (hence low-noise-voltage) transducer is usually unbalanced in architecture. But IMO there can be plenty of logic to the idea of swallowing 3dB higher thermal noise (especially if the circuit is still very quiet), for improved hum rejection from a balanced input stage.
The inevitable and unavoidable 'ground contamination' influences of capacitors etc. that makes the other argument for differential/balanced vs. unbalanced.
Hi again Axel :) - There should be no such "ground comtamination", regardless, in a good circuit design and layout. This is "simply" a matter of the designer carefully analyzing the ground current flow in each part of the circuit, and understanding and considering the subtleties of such things as careful local bypassing, power-supply impedances, and ground-trace routing. But judging by many of the commercial products I see, this seems to be a particular challange, and differential-balanced circuits can sometimes be more forgiving of these sorts of faults.
Why? It is that the differential circuit also cancels even-order harmonics in the process of common mode rejection, so you wind up with a bias toward odd-order harmonics, and that is not so 'natural' to our ear.
I'm of the opinion that while low-distortion is only one of several required characteristics for a good-sounding circuit . . . I feel that in a high-quality phono preamplifier, ALL harmonic and IM distortion should be completely and totally buried in the noise floor, which in itself should be very low. Yes, low-order and even-order products are less disconcerting to the ear . . . but who wants any of it at all?
because the side-effect of the twisting is an increase in cable capacitance, which is exactly what we DON'T want for our MM cartridge.
This is fascinating for me right at this moment due to the fact that I have just mounted a Garrott P77 MM cartridge to my Continuum Copperhead arm which has balanced input terminations into the Halcro DM10 preamp. The tonearm wiring is fine gold (or copper) uninsulated Litz type wiring (I think), which is very tightly wound together to reject the noise (hum) to which you refer. This seemed to work for LOMC cartridges such as the DV1s and Universe (which only produced a slight hum when the volume was turned up considerably), but fails miserably with the MM which produces an incessant hum at any volume. The question has been asked of Mark Doehmann if he has listened to any MM cartridges through the Cobra and Copperhead arms as none of the dealers believe anyone has actually mounted a modest MM in such exotic and expensive arms? We are still awaiting the answers but your statements are intriguing indeed. What do you venture, would be a solution to this problem? Regards Halcro
Kirkus, Thanks for your patience in preparing a detailed response to my questions. Your take is very interesting and thoughtful. Meantime, I am wondering whether we should all be beating the bushes for vintage phono stages to use with these vintage MMs. But that would partially negate the premise that we can get more out of them now than ever before with modern well designed preamplification. Here are low-priced products that jump out at me as being possibly well suited to MMs: the new K&K, the Aqvox (SE for MMs, balanced for MCs), the Herron dedicated to MM and now out of production, any of the Hagerman products (I have high respect for his design capabilities), the Allnic products (they add on a SUT for MCs, so maybe they would work well for MMs, especially the H1200), the Whest2.0, possibly older Audio Research phono stages (maybe a tweaked SP3 would be great). Raul's 3160 may be at the top of the heap if price is no object. Any other ideas, guys?
Kirkus, y.s.: >>> I feel that in a high-quality phono preamplifier, ALL harmonic and IM distortion should be completely and totally buried in the noise floor, which in itself should be very low. Yes, low-order and even-order products are less disconcerting to the ear . . . but who wants any of it at all?"
Some would not agree with this necessarily, since other then in digital designs, harmonic distortion is never buried in the noise floor completely. It seem current understanding that harmonic distortion should rather RISE evenly (even- and odd-order equally) with increasing output, rather than then decreasing with higher output. (Output rise as from cart input rise)
Two notable designs come to mind by PassLabs (SUSY, Super Symmetry) and the 'cyclotron' (re-invention) by the Thorens TEM-3200 mono blocks have proved that to be correct.
Item: 'ground contamination' as you pointed out is more of a challenge then maybe generally accepted? And we are not talking of major ground loops. I is VERY difficult if not impossible to prevent some potential differences occurring in components (and amongst each other) during all states of operation. So they best possible directed by use of e.g. star-ground schemes. The point is, there are still caps (to ground) involved and caps have power factors, creating a far less 'clean' signal path then the dedicated (-) in a balanced design.
The noise floor of my ML326S is below 90dB (balanced). I think the issue is the 'tonality', influenced by 'combing out' harmonic distortion selectively. It is why even a MUCH noisier single-ended design often will sound 'better, more natural' then does a balanced one. (I speak from experience) The trade-off is most always balanced = more dynamic, and 'cleaner' vs. unbalanced = better harmonic completeness, more natural sounding.
As to hum caused by 'unbalanced' MM cart output impedance. Well, I think that the more expensive carts we are speaking of (Raul mostly), those have always excellent channel balance, often better than more main-stream MCs with an e.g. <1.5dB spec.
I run MMs into my (balanced) ML phono-board and have no discernable noise (ear to the speaker)! This at elevated listing level setting ~ 45 (max = 80, grading in dB steps). Adding 35dB (level 80, that would destroy my ears first, and speakers next!) I can practically NOT hear noise from the listening position (this @ 60dB 'normal' daytime background noise).
I guess, ML is very good at what they do with their balanced designs ---- however, tonality and 'live like' emotionality is not exactly their forte. One always seems to find that with 'noisier' and most always single-ended designs. That's where I see the trade off. Balanced = Hyper-clean and dynamic vs. unbalanced = naturalness, less clean, and better harmonic completeness.
All is of course subject to some generalisations and subject to levels of degree.
This seemed to work for LOMC cartridges such as the DV1s and Universe (which only produced a slight hum when the volume was turned up considerably), but fails miserably with the MM which produces an incessant hum at any volume.
Halcro, please understand that I mean no disrespect to Bruce Candy or the namesake of your moniker . . . but unless the Continuum tonearm's wiring scheme is unconventional (in a connection sense, not just in a twisted-wiring sense) or defective (i.e some metal tonearm parts accidentally ungrounded) . . . then the problem is your preamplifier, and the manner in which its input stage is designed.
There seem to be many designers who look at balanced input stages (both line, phono, and microphone) purely as a pair of opposing voltages, not balanced impedances . . . and its amazing how many otherwise top-notch pieces of professional and consumer audio gear are very intolerant of the slight impedance mismatches that I describe. Another example of this would be the work of Douglas Self . . . a designer who I greatly admire and find much of his work invaluable . . . but simply cannot agree with his approch to designing balanced input stages.
But hopefully its just something silly like an a missing/loose ground wire somewhere, and my little diatribe is all for nought.
Some would not agree with this necessarily, since other then in digital designs, harmonic distortion is never buried in the noise floor completely.
Sure it is - just about any datasheet-derived single-NE5534 phono stage will do it, for reasonable signal levels and output current. I obviously don't feel that such circuits are ultimate expression of what's possible in a phono preamp, but the only reason to tolerate measureable harmonic distortion in these circuits is if the designer feels that there are benefits to choosing certain types of parts or topologies - and these choices make it impossible to eliminate distortion. I have no problem with that . . . every designer is free to decide what parameters meet their goals - ultra-low distortion just happens to be one of mine.
It seem current understanding that harmonic distortion should rather RISE evenly (even- and odd-order equally) with increasing output, rather than then decreasing with higher output. (Output rise as from cart input rise)
I believe that what you're referring to is a specific type fault that many feel can occur as a result of crossover distortion in Class B power amplifiers. Again, a phono preamplifier can and should be completely free from these types of anaomolies.
I is VERY difficult if not impossible to prevent some potential differences occurring in components (and amongst each other) during all states of operation. So they best possible directed by use of e.g. star-ground schemes. The point is, there are still caps (to ground) involved and caps have power factors, creating a far less 'clean' signal path then the dedicated (-) in a balanced design.
If you re-consider Kirkhoff's laws and look at the signal CURRENT, it always must flow between the power-supply rails, period. The purpose of local bypassing capacitors is twofold - first, to remove the effects of power-supply wiring and traces from the circuit, and second, to prevent different stages' current draw from affecting each other. These functions are necessary in both differential and non-differential circuits, and regardless of whether or not the signal VOLTAGE is defined in relation to ground, at least a portion of the signal CURRENT will always flow through the bypass capacitors . . . and that's the way its supposed to be. It is up to the designer to keep these signal and supply currents separate from each other, regardless of whether or not they flow through a node we call "ground". In fact, it can sometimes be more of a problem in differential circuits, where each side of the circuit has separate bypass capacitors to ground . . . in which the signal current has to flow through a minimum of two capacitors and a ground trace to return to the supply.
Its not that I don't like the differential approach, in fact my linestage is designed this way. But I will confess that I'm especially proud of the bypassing scheme - there are separate, unambiguous AC return paths for both differential signal current and signal current that flows to ground (i.e. from an impedance imbalance in the output cable or the amplifier that follows it).
The trade-off is most always balanced = more dynamic, and 'cleaner' vs. unbalanced = better harmonic completeness, more natural sounding.
I firmly believe that as we improve our art . . . it IS possible to have all of what you describe, without tradeoffs. And not everybody will see it the same way, but hopefully we will all end up with a more fulfilling experience from our recorded music.
Axel, You wrote: "As to hum caused by 'unbalanced' MM cart output impedance. Well, I think that the more expensive carts we are speaking of (Raul mostly), those have always excellent channel balance, often better than more main-stream MCs with an e.g. <1.5dB spec."
I am pretty sure that Kirkus was not referring to differences between channels in his comments on the impedance properties of MM cartridges. I think he was referring to the generally much higher and more reactive impedance of MMs and the fact that these parameters may not be identical for each phase of the output in a SINGLE channel, using a balanced circuit. This creates a noise that cannot be cancelled by the balanced topology and is instead amplified. Channel balance has nothing to do with it. If I am full of baloney, perhaps Kirkus will correct me.
Lewm, of course you are right! We are talking one channel at a time, sorry. >>> ... he was referring to the generally much higher and more reactive impedance of MMs and the fact that these parameters may not be identical for each phase of the output in a SINGLE channel, using a balanced circuit <<<
I see, but then this would be a GENERAL issue with every kind of MM?! They ALL have a much higher reactive component than any MC.
Now why do you think, do I have NO hum what so ever with a FULLY opened pre, going balanced into a balanced phono-line-pre?
Maybe the answer lies with ML's balanced design then?
I think he was referring to the generally much higher and more reactive impedance of MMs and the fact that these parameters may not be identical for each phase of the output in a SINGLE channel, using a balanced circuit. This creates a noise that cannot be cancelled by the balanced topology and is instead amplified. Channel balance has nothing to do with it. If I am full of baloney, perhaps Kirkus will correct me.
Actually Lewm, you got it exactly.
Now why do you think, do I have NO hum what so ever with a FULLY opened pre, going balanced into a balanced phono-line-pre?
Well I'd say that you happen to have good synergy between the cartridge, tonearm wiring, and preamp input stage, at least in the sense that its noise-rejection happens to be sufficient to completely eliminate interference from the particular amount of mains-frequency magnetic flux to which it is being subjected.
Now whether or not the ML engineers anticipated/designed for a similar level of performance in other situations or environments, I have no idea . . . but for yours, they got it right.
Thanks Kirkus, gotta get lucky once in a while in this here Audio game.
But as you mention as well, noise is only one facet of it all. As I noted - tonality is yet another thing. In fact, funny enough it also seem very high on Raul's list of evaluation criteria too :-)
Axel, perhaps one reason you don't have "hum" is that the noise that might result from Kirkus' theorem would not necessarily be in the spectrum that we recognize as hum (60Hz or 120Hz, in the US; 50Hz or 100Hz in Germany). The noise he is talking about could be random in frequency (I think) and might not be audible as noise until one took steps to eliminate it and listened for the difference.
Lewm, yes, I think this could be right. It again would explain that even some well noted/quoted phono-stage designer(s) like SE. There was Lamm's Vladimir Shushurin? that stated his clear and decided preference for SE -- but I think he then uses a trannie to change the output to balanced. His main argument also was 'noise' and could well be what you just mentioned.
The new PassLabs-X15 seem very well regarded (best ever, etc.) would be most interesting to know what circuit it uses.
Hi Kirkus, during an earlier part of the MM, balanced vs unbalanced and common-mode rejection posting the SUT subject came up shortly.
It may not fully relate to this thread, but let me try.
You mentioned in your example a 50 ohm SUT input impedance with a 5 ohm DCR MC cart. Explaining some advantages with regard to hum rejection, and how this of course can not be realised in an MM specific phono-pre (as a trannie cannot be used etc.)
Would you share your explanation, why with the use of an SUT (in my listening) some other parameters then hum are notably changed/improved i.e.
- more dynamic depth (better hi/low SPL differentiation) - more powerful bass - more hall/room information, stage depth
I could add some more, but it should do for this example.
Cart parameters: 3 ohm DCR 0.3mV output @ 5cm/sec
SUT parameters: 1:31.6 ratio (30dB, i.e. natural impedance 47ohm with 47k) - primary DCR 1.5 ohm - secondary DCR ~ 65 ohm (as I recall) - primary loading 13 ohm (paral. with 47 ohm nat. imp.) i.e. 10 ohm that the cart sees.
If nothing else, it could high-light how very different a MC stage might just be as compared to an MM stage. So we'd be back at the subject, of sorts.
Hi Axel . . . well, the first question is understanding as much as possible all of the different factors that change between your comparisons with/without the SUT. I'm speculating that some of them are:
-Cartridge loading is slightly different, i.e. more inductive with the transformer -SUT presents a different source impedance to the phono stage than the cartridge directly -Phono stage loading switches/plugs/resistors/caps are different -Phono stage gain is different, likely affecting noise, bandwidth, and distorion -Of course, the SUT itself has a sonic/performance signature
And some of the likely causes of what you observe:
- more dynamic depth (better hi/low SPL differentiation)
I think this usually corresponds to better headroom, and lower noise floor. The SUT will most likely gives a better En/In match to the cartridge, and better RFI rejection. The phono stage may also have more headroom at the lower gain.
- more powerful bass
Cartridge loading differences, possibly a little bit of low-frequency 3rd-harmonic distortion from the transformer
- more hall/room information, stage depth
I associate this with more high-frequency extension, or different high-frequency phase response. Cartridge loading differences, the transformer's sonic signiture, or better phono-stage performance at the lower gain
Anyway hope this helps a bit, without re-opening the whole SUT/non-SUT debate.
Kirkus, since I was rather too curious, I did some back-tracking on the subject in some related A'gon threads. What I come up with is, for best sound for the $$$:
1) 'affordable' phono-stage with MM 2) good stage with MM 3) good stage with SUT and MC 4) top stage with MC
2) and 3) mybe on par, and MC = LO MC > 0.4mV
Raul has his take on what comprises a 'good' stage (3160)and 0.01dB deviation in RIAA --------- other then the one he uses, I've never as yet seen one measured that could do this. So I can at best call my own lot 'affordable'. ML claims +/- 1dB deviation, my previous GCPH claimed 0.25dB deviation. Interestingly, the ML sounds better, and maybe due to using the 326S power supply.
Also some other acclaimed stages do rather poorly in this particular measurement.
I noticed earlier that someone recommended Juicy Music. They are very very good, but unfortunately Mark has retired but will still service all of his equipment.
Hi, Raul, I was wondering about the design of the 3160: What level of gain is bult into the LOMC side of the preamp? It seems that 60 dB or so is the typical level of gain for many (most?) LOMC stages and I was curious what you use in the 3160. Thank you for your time.
Dear Tom: Yes we use 60 db too in the MC phono stage circuit and we can get, on the whole/overall Phonolinepreamplifier, ( changing the line stage gain ) easy 90 db, I never have the necessity to go to a higher total gain.
Normally 60 db is enough for almost any LOMC cartridge. I own the Ortofon MC- 2000 that is very low output ( 0.05 mv. ) and I can handle very good with very low noise/distortions, yes the Esential attenuators has to be around 3.0 o'clock for around 83-84db on SPL in my system.
Thank you for the reply, Raul. You and the others have been kind in answering all my questions. Based on what I've learned here I feel comfortable that I can make more informed decisions in future phono preamp purchases. Compromises abound in audio components to meet the needs of price, performance, and convenience, and I'm getting a better sense of what to look for.
In my list of candidate MM phono stages posted 6/26, I neglected to include the Graham Slee Gold Era Reflex (hope I got the long name right). The Reflex was specifically designed for MM and HOMC. Further, it got great reviews from some respected sources, including M Fremer. It's a bit odd in that it uses active RIAA equalization, but Kirkus has espoused that approach also. (The more common gospel is that passive RIAA is better sounding than active.) Earlier in this thread, someone dismissed this or one of the other Graham phono pres as not being "as good as" a Jadis, without naming the particular Jadis preamp he was referrring to. As I have never been a fan of any Jadis product, I am keeping an open mind on the Graham. Has anyone been able to audition this product (the Gold Reflex) in a system driven by an MM cartridge? (There is an optional accessory, the Elevator, which adds the necessary gain for an LOMC. One would prefer to know what the Reflex sounds like without this add-on.) Thanks for any comments.
I have both the Reflex and the Elevator. I first used the Reflex alone with an Ortofon 2M Black. It sounded great! Then, I added the Elevator and Ortofon Kontrapunkt B. This is an outstanding setup and is highly detailed and refined sounding. To my ears, this combination is transparent across the frequency spectrum, very dynamic, and with no detectable glare, distortion, or other audible anomolies. The Reflex and 2M Black are certainly a nice pairing and I could live happily with them, but adding the Elevator and Kontrapunkt B sounds even better to me and is worth the money. The Elevator is nice in that it has easily accessible switches on the front panel for adjusting MC loading. I have settled on 100 ohms for my MC cartridge. I should also state that Graham Slee himself is very responsive to any questions you may have. You can contact him via the Graham Slee web site's link to their own discussion board. I am very pleased with my Graham Slee units and have no desire to look elsewhere.
Hi, Lewm, it was my first reply to Axel that mentioned the Reflex as a dedicated MM phono preamp. And it was also me that too quickly dismissed the Reflex as not being in the same league as a preamp costing multiples of the Reflex. After seeing where the discussion was going I put the Reflex back in the mix. But apparently it's not what Axel considered "top end" when he asked the original question.
I had, at one time, considered the Reflex as the basis for a phono stage configuration, intending to use a headamp such as the Elevator or a step-up transformer, of which there are many, to run LOMC cartridges. I ended up with a phono preamp that has a relatively simple architecture but handles both MM and LOMC cartridges using jumpers and resistor screw posts.
You might ask over at the Vinyl Asylum about the Reflex and MM cartridges.
Tom, re.: Reflex & Elevator... >>> But apparently it's not what Axel considered "top end" when he asked the original question.<<<
Actually I'm not really in a position to be the 'judge' on what a "top-end" MM-stage comprises (other than $$$/hear-say/etc...)
But what I did say earlier on is:
- "What I come up with is, for best sound for the $$$:
1) affordable phono-stage with MM (Reflex?) 2) good stage with MM 3) good stage with SUT and MC (Note: not mentioned headamps i.e. Elevator) 4) top stage with MC
2) and 3) maybe on par, and MC = LO MC > 0.4mV " -
This would be in favour, $$$wise, of using MM with MM-only stage. I think we'll struggle to get an answer to whether a "top-end" MM stage even exists (other than 3160), AND if it makes actually as big a difference in sound, compared to the more affordable ones (e.g. Reflex)
Note: There is absolutely NO DOUBT in my mind, that due to the low output voltage of MCs, only the-best-of-the-best MC-stage will actually be good enough to do justice to an MC's potential.
Maybe, because good MM's, due to the higher output, make for simpler, less costly, yet top performance stage designs?
Like: Single ended, JFET & tube (2 gain stages only), ~ 1dB RIAA error, good clean power supply ---- finito?
If that was so, there'd be plenty to pick from, and it would 'sink' plenty of MC set-ups with only so-so MC-stage. Everyone can get back to vinyl, without another mortgage on the house :-)
Rockinrobin, I am going to guess that your experience is an overall endorsement of the Reflex. If it were not doing a good job, you might not hear a big difference between the two cartridges. Now you should try the Reflex alone driven by a Grace Ruby, Garrott P77, AKG, AT, B&O, or etc. Let us know how such a combo compares to the Elevator/Kontrapunkt source. Maybe some one of us can lend you one of those gems. (Just kidding...., but it would help the cause.)
Tom, what Jadis preamp did you have in mind? The last top end product from them that I am aware of was the JP80. By now there must be newer models. They have been really quiet in the US market, as in "absent".
Hi, Axel, it makes sense that newcomers to vinyl would benefit from using MM cartridges initially. And having a high quality, affordable (but dedicated) MM phono stage would be something they could continue to use as they upgraded the turntable and other components. The Graham Slee Reflex and Elevator appears to be one option that fits the upgrade path. I don't have the experience to offer an opinion as to whether it's high end or not.
But I think that for many people starting out, committing to MM cartridges due to a specialized phono preamp is not a comfortable decision. I know when I purchased my first "real" phono preamp, I chose one that had a wide range of gain and loading options because I wanted to be able to experiment with different cartridges without having to purchase additional components; i.e., a SUT or headamp.
But it seems (based on the discussions of this thread) that a dedicated MM phono preamp may not be the best design for adding LOMC capabilities, thus requiring a completely different LOMC preamp to get optimal sound. There's no simple (or affordable?) solution. '-)
Hi, Lewm, I didn't offer the Jadis as a reference, Axel mentioned it in his initial post. I checked some prices and one their premium designs (JP80MC) was approaching $20,000 USD. That's when I retracted my suggestion of the Reflex as an example of a high quality dedicated MM stage. Not really fair to compare a $1300 USD phono preamp with one costing more than ten times that. Or maybe it is... '-)
Hi Saudio EAR 324, a good one in the context of MM - alas it showed some issues with too little head-room in the 20Hz region. Not a lot going on down there mostly, but still.
The 88PB would be more ===> MC targeted I'd guess.
1) affordable phono-stage with MM (Reflex?) 2) good stage with MM 3) good stage with SUT and MC (Note: not mentioned headamps i.e. Elevator) 4) top stage with MC
2) and 3) maybe on par, and MC = LO MC > 0.4mV "
Hi Axel - I think its really difficult to make these kinds of general heirarchical statements about performance, price and topology . . . for a few reasons:
- You can't assume that providing the additional required voltage gain is always going to be the biggest challenge when designing a phono preamp for use with an MC cartridge . . . it may be for some designs, but definately not all.
- The usual axiom of "price and performance don't always go together" . . . even though they do frequently, we must always be skeptical here.
- I think that the implementation of an external SUT will always be a compromise - mainly because the transformer will have to be designed in a specific way to provide a "standard" step-up ratio that works well (in terms of voltage gain and output impedance) with a "standard" MM phono input. In a phono stage such as my own, the transformer (a Jensen JT-346) has a turns ratio that is much lower than a typical SUT (thus much higher performance) and provides a perfect En/In match to the electronics that follow it, which in turn have had their gain adjusted to suit the paramters of the SUT. That is, the transformer and electronics have been designed specifically to work together, not as a "universal" add-on solution.
On the subject of accurate RIAA . . . I was actually inspired by Raul's postings to take this matter very seriously in my own design. This isn't an easy thing . . . there are specific challanges to even measuring it to better than +/- 0.01dB across a 40-dB-ish range of signal level, as most test equipment must either generate or measure it through several output/input measurement ranges. For this, I was lucky to have an APx 525 on loan as an extra test set to verify the results against the AP2700's measurements . . . suffice it to say there needs to be some very careful hand-selection of parts to even begin to come close to this level of accuracy.
And there's the question of . . . why should the preamp be so precise, when no cartridge is anywhere close to this? Well, error is error . . . and it's always statistically additive in this case. After all, our CD players and amplifiers should have extremely precise response, even though a loudspeaker can't come anywhere close . . .
I was following the thread the last few days for a different reason than most of the previous participants. I have a Supratek Chenin that has only a MC input and I want to experiment with one of the Moving Irons made by Soundsmith that require a MM input. Currently mi analogue rig is Teres 255/Triplanar VII/Zyx Airy 3 and I am puting together a second analogue rig that would be finished in a couple of weeks. I bought a Townshend Rock III with a Moerch DP-6 and a totally refurbished Lenco L 75 (with a 70 pound plinth) with a Micro Seiki MA 505. I want to install the Soundsmith The Voice in both of those tables and see how it sounds. I can even install the Moerch in the Lenco and see what happens. That is the reason I am looking for a dedicated MM pre-pre. Thank you very much for this very informative thread and the options that you are considering. I will look for the K&K, Whest, Aqvox, Haberman and Allnic here on Audiogon and buy one of them. Regards, Pablo.
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