I was not stating... just quoting what I found in the net. I will be much more carefull from now on.
I would also like your comment on the following text:
(The load of MC cartridge does not really affect the frequency response - however it does affect two other things - the output and the mechanical damping of the coils - the lower the load, the higher the current through the coils and consequently higher the damping, as the magnetic field created by the current will produce a force trying to slow down coils movement. In this respect some cartridges may benefit from increased damping and some will not.)
I found it on MC cartridge loading [Archive] - The Art of Sound Forum
Hi John,
Just what part of this is off the mark? Please be specific.
Have you ever actually measure the inductance of a moving coil cartridge?
Can you point to a manufacturer's spec sheet that is available today that specifies MC cartridge inductance?
Thanks,
Bob
Once again John, where do you get the basis for firmly saying that the typical inductance is 10 uH? How many have you measured? It is extremely doubtful that there is much of a typical number when MC cartridge outputs (other than high-output ones) have nominal output ranges from less than 100uV to over 500uV, and while they have DCRs of 3 ohms to 50 ohms.
You're the expert, tell us what you have measured: L, DCR, rated output. Your vast experience with MC cartridges over 40 years puts you in perhaps the best position to share with us these results for a wide range of cartridges.
Cheers,
Bob
Hi Scott,
I pointed out that the inductance of an MC cartridge may affect frequency response to an audible extent, especially in the case where an MC cartridge is terminated into a virtual ground. In that case you get a corner at the frequency represented by cartridge DCR and cartridge inductance.
If John is right that even an MC cartridge with 500uV output has an inductance of only about 10uH, then the point is very academic. Ortofon states that most of their MC cartridges have DCR of about 5-6 ohms and between 14 and 28 turns of wire. However, I have no idea whether they have a ferrous core or not.
Might you know the inductances and DCR of your MC cartridges?
Cheers,
Bob
Hi kevinkr,
Thanks very much for this information. If it is reasonably correct, it looks like John's assertion about inductance being only 10uH is wrong - way wrong.
He should be more careful about his sweeping generalizations, especially when he does it in his condescending way.
Cheers,
Bob
Hi John,
Did you not read my whole post? I very clearly pointed out that the inductance value must be viewed in the context of the DCR, as it creates a pole with DCR when the cartridge sees a load much lower than its DCR, such as a virtual ground.
Cheers,
Bob
Bob, you cannot just pick an inductance 'out of the air' so to speak and then analyze it and declare a solution. This is called a 'straw man' in public discourse, and it just creates more confusion than necessary.
Now, I hate to state it, again, but I have been trying to use summing type inputs for the last 38 years. I thought of it, its usefulness, and I used it in the Levinson JC-1 phono step-up, first introduced in 1973. It is even included in my patent schematic. However, THIS application, while an attempt to make a summing junction, did not have much feedback to make it truly a summing type input, AND the alternative advantage of the summing junction was very important to lower the gain of the pre-preamp, with high output, re high R phono cartridges. This secondary advantage gave a limited dynamic range circuit a chance with higher output cartridges. In those days, cartridge output resistances ranged from 2 ohms (Ortofon), 3-10 ohms (Supex, etc), 30 ohms (EMT), and finally 40 ohms (Denon). For all practical purposes the 'quasi' summing input designed into the JC-1 worked pretty well, BUT I wanted to do better.
So with the JC-1 AC, and the JC-1 DC, I went to full push pull common base drive that compares well to many phono preamp designs shown here, recently, and you can find the schematic for the JC-1 DC, on this thread with a previous link. Now, my effective input impedance was a few ohms, and I thought this to be an improvement. In the meantime, I contacted Ortorfon and got back that the inductance was only a few uH's.
So I at least attempted, even 35 years ago, to get REAL info from the manufacturer.
However, in LISTENING with my favorite cartridges, perhaps a Supex at the time, I found that this NEW loading approach tended to sound 'overdamped'. Mark Levinson, himself, did a measurement with a CBS test record with 10 ohms, to 50K ohms and while the plots were just spot frequencies, there was NO significant difference in frequency response with a Supex cartridge. This is how WE determined loading changes. You might try it yourself.
Now, outside of my own opinion, you might listen to the manufacturers themselves. Ortofon, in the early days, had no opinion, and recommended 75 ohms to me, mostly just to give me a number. However Lyra, a company that makes MY personal choice in phono cartridges, recommends a MINIMUM of 91 ohms for its entire range of phono cartridges. If you look at manufacturers literature, including Denon, you will find a recommended loading of 100 ohms with the vast majority, and 47K ohms with the VERY high output ones, that you cite here. This is far from a summing input.
So, I trust manufacturer's recommendations these days, for the most part, having 'been there, done that' with summing type input, in the past. In fact, I will offer a range of loading in subsequent phono stages, but I will now avoid summing input, for good reason.
Now, I hate to state it, again, but I have been trying to use summing type inputs for the last 38 years. I thought of it, its usefulness, and I used it in the Levinson JC-1 phono step-up, first introduced in 1973. It is even included in my patent schematic. However, THIS application, while an attempt to make a summing junction, did not have much feedback to make it truly a summing type input, AND the alternative advantage of the summing junction was very important to lower the gain of the pre-preamp, with high output, re high R phono cartridges. This secondary advantage gave a limited dynamic range circuit a chance with higher output cartridges. In those days, cartridge output resistances ranged from 2 ohms (Ortofon), 3-10 ohms (Supex, etc), 30 ohms (EMT), and finally 40 ohms (Denon). For all practical purposes the 'quasi' summing input designed into the JC-1 worked pretty well, BUT I wanted to do better.
So with the JC-1 AC, and the JC-1 DC, I went to full push pull common base drive that compares well to many phono preamp designs shown here, recently, and you can find the schematic for the JC-1 DC, on this thread with a previous link. Now, my effective input impedance was a few ohms, and I thought this to be an improvement. In the meantime, I contacted Ortorfon and got back that the inductance was only a few uH's.
So I at least attempted, even 35 years ago, to get REAL info from the manufacturer.
However, in LISTENING with my favorite cartridges, perhaps a Supex at the time, I found that this NEW loading approach tended to sound 'overdamped'. Mark Levinson, himself, did a measurement with a CBS test record with 10 ohms, to 50K ohms and while the plots were just spot frequencies, there was NO significant difference in frequency response with a Supex cartridge. This is how WE determined loading changes. You might try it yourself.
Now, outside of my own opinion, you might listen to the manufacturers themselves. Ortofon, in the early days, had no opinion, and recommended 75 ohms to me, mostly just to give me a number. However Lyra, a company that makes MY personal choice in phono cartridges, recommends a MINIMUM of 91 ohms for its entire range of phono cartridges. If you look at manufacturers literature, including Denon, you will find a recommended loading of 100 ohms with the vast majority, and 47K ohms with the VERY high output ones, that you cite here. This is far from a summing input.
So, I trust manufacturer's recommendations these days, for the most part, having 'been there, done that' with summing type input, in the past. In fact, I will offer a range of loading in subsequent phono stages, but I will now avoid summing input, for good reason.
Thanks GK7, you are on track. I tried to say that the VAST majority of moving coil cartridges follow the 10uH, 10 ohm track. Some will have lower inductance, with lower resistance as well, some will have higher inductance, but the resistance will be higher. That is WHY you need both numbers to make any sense. Kevinkr, was helpful, but we also NEED the corresponding resistance to EACH cartridge to make sense of what he put down, AND certainly at least one was a TYPO, (manufacturer's mistake).
I am not taking about VERY HIGH OUTPUT, cheaper MC phono cartridges to mimic moving magnet cartridges, and PLEASE NOTE their RECOMMENDED LOADING by the manufacturer.
I am not taking about VERY HIGH OUTPUT, cheaper MC phono cartridges to mimic moving magnet cartridges, and PLEASE NOTE their RECOMMENDED LOADING by the manufacturer.
Sorry Bob I was really only considering the very LO ones as candidates for virtual ground use since there the conventional feedback impedances get difficult to drive. I and others I'm sure have toyed with MM in current mode with a recomputing of RIAA to account for it. you could do the same for any cartridge.
So as I understand it it sounds "overdamped" or as Mr. Risch put it "under water" and there is no measureable FR abberation. That's what I thought in the first place. So Mark determined that it made no difference and you the opposite, does that make a WE.
If memory serves, there was a commercial MM preamp back in the early '70s that was run that way (Bravura?). It could only be used with one cartridge...
Scott, quibbling will get us nowhere. Of course, ANY change in loading will often make some change in frequency response. BUT is it enough at ALL TIMES to be the REASON that it sounds 'under water'? Maybe, sometimes, but not in any OBVIOUS way. When Mark Levinson made his tests, he used a 'spot noise' test record. Had he, as I had at one time, a full playback setup with an Ortofon Sweep Record, and a B&K graphic recorder, he might have found SOME small deviation in frequency response, especially above 20KHz. Still, at the time, there appeared to be virtually no change, and it was a surprise to us, to be sure.
I am sure, that someone, somewhere, will find sonic 'nirvana' with the right combination of a summing type input and a SPECIFIC phono cartridge and playback system. I'm not going to bet on it, however, because with a Vendetta Research input stage, most serious users find an 'optimum loading' by manually adjusting the input pots while playing their favorite musical selections. That is WHY we offered this facility in the Vendetta Research SCP-2 phono stage. Usually this will be between 50 and 500 ohms, 100 ohms being a good compromise. Summing is WAY off the mark these days.
I am sure, that someone, somewhere, will find sonic 'nirvana' with the right combination of a summing type input and a SPECIFIC phono cartridge and playback system. I'm not going to bet on it, however, because with a Vendetta Research input stage, most serious users find an 'optimum loading' by manually adjusting the input pots while playing their favorite musical selections. That is WHY we offered this facility in the Vendetta Research SCP-2 phono stage. Usually this will be between 50 and 500 ohms, 100 ohms being a good compromise. Summing is WAY off the mark these days.
Hi John,
I was not just picking numbers out of the air and was not making a straw-man argument. I certainly agree that hi-output MC cartridges should not be part of this specific discussion, but several of the low-output cartridges listed in the post above had inductance in the neighborhood of 50uH, which is one of the values I used as an example. 50uH is a very long way from your "firm" assertion that the majority are in the 10uH range.
I was also not trying to criticise anyone's design, especially yours. I was just trying to show that frequency response can be a contributing factor in the "under water" sound described as occurring sometimes with an MC cartridge driving a virtual ground.
Of course, any mention of L in an MC cartridge should be accompanied by mention of DCR and nomianl output as well. We are certainly in agreement on this.
You still have not answered how many MC cartridges you have measured, and where any current MC manufacturer's documentation specs inductance. I still think that your assertion that most MC cartridges are only 10 uH is completely unspupported and wrong.
Cheers,
Bob
Moving Coil Cartridges - Goldring
These are manufacturer´s specs, and none of them (except for the high output one) is above 12uH. The have specs for DC resistance too.
For the other carts mentioned I could not find manufacturer data so these informations should be seen as "unconfirmed".
These are manufacturer´s specs, and none of them (except for the high output one) is above 12uH. The have specs for DC resistance too.
For the other carts mentioned I could not find manufacturer data so these informations should be seen as "unconfirmed".
Sort of universal input stage...
Sorry to break up the discussion about cart loading. Inspired by the Lux circuit and Johns designs i came up with the following basic design for a riaa input stage. It does fulfill the basic criteria of being non inverting and n-channel input only.
BR,
Anders
Sorry to break up the discussion about cart loading. Inspired by the Lux circuit and Johns designs i came up with the following basic design for a riaa input stage. It does fulfill the basic criteria of being non inverting and n-channel input only.
BR,
Anders
Hi bappe,
I like this design. I have been a fan of N-channel JFET differential input stages, even though they do not produce as low a noise level as single-ended designs. Even in an MC design, four paralleled LSK389 dual JFETs will yield 1 nV/rt Hz or better noise performance. BTW, my simulations show that 1 nV/rt Hz will achieve a 77 dB SNR RIAA equalized and A-weighted with respect to a 400uV nominal cartridge input voltage. For reference, I believe that the excellent JC-3 is rated at 75 dB SNR under the same conditions.
The differential input stage lends itself nicely to running with no NFB or with NFB. No NFB in the input stage is OK in this application because of the small input levels involved and the use of the differential input stage to keep distortion down. Also, the no-NFB stage makes it easy to go balanced at the input if desired.
Going no NFB does involve some gain and channel balance uncertainty due to the JFET device-to-device characteristics unless they are chosen carefully and matched, but this is reasonable in a high-performance design.
There is still the option of NFB or no NFB in the output stage, given that the levels will be higher. This may be more of an issue for the MM stage than the MC stage.
It looks like you are running the input JFETs a bit on the high side in regard to Vds; this could cause you to incur a noise penalty. If you wish to keep the output portion having as much voltage swing capability, you might consider adding a conventional cascode between the input drains and the folded cascodes.
If you are concerned about JFET input capacitance, you can use a driven cascode.
Cheers,
Bob
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