The Shure M97 is a high inductance cartride with a specified inductance of 650 mH. High inductance cartridges require very low capacitive loading to obtain the proper Q with a 47k load resistor, typically around 100pF. This is the total capacity in the cartridge, tone arm wires, interconnects and preamp. You want the capacitive loading to resonate the inductance above the audio band and you want the Q between 0.5 (critically damped resonance) or 0.7 for a maximally flat magnitude response. An approximate formula for estimating the Q is Q=Rl*SQRT(C/L) where Rl is the load resistor, Cis the load capicitor and L is the cartridge inductance. SQRT means take the square root. This is the formula for the Q of a parallel resonant RLC circuit. I have a Shure V15-V and to obtain low capacitive loading I used a Leach jfet preamp with a specified input capacity of 20 pF, mounted in the turntable base and connected to the tonearm with 4 inch wires.
Mr. Hagerman has a good explanation of loading here. Hagerman Technology LLC: Cartridge Loading.
Ray
Mr. Hagerman has a good explanation of loading here. Hagerman Technology LLC: Cartridge Loading.
Ray
O yes, thanks. I know the patent since the eighties, so I did not look at it again today. I wondered where I saw a more detailed Grodinsky's schematics....
I do not find the whole idea, with its half-passive/half active RIAA equalisation, very original, since I saw it in a french magazine around 1975, I think.
G'day all, interesting comments re the Shure M97xE loading. The Shure recommendation for capacitance loading at 47 k is 200 to 300 picofarads and I can certainly confirm (from actual listening evaluations) that this general range is optimum into 47 k. Too high or too low input capacitance at 47 k severely diminishes the apparent upper treble response.
From my own listening observations at 62 k, lower input capacitance (150 picofarads) is desirable. Regards, Felix.
From my own listening observations at 62 k, lower input capacitance (150 picofarads) is desirable. Regards, Felix.
The only circuit that I've personally seen that used an input buffer was the jfet srpp phono preamp detailed in Elektor magazine. Since that circuit used a high capacitance jfet in the initial srpp stage (with resulting amplified Miller capacitance) putting a buffer in front of it made a perverse sort of sense. Using a jfet with lower capacitance in the first place would have made more sense.
Fap,
I still claim 200-300 pF is way too high for 650 mH inductance. The resonant frequency would be about 13 kHz and the Q would be about 1 so you would have a peak in the response.
Here is a link to a phono cartridge frequency response calculator. You can see the effect the terminating values have on the frequency response.
Website of Wayne Stegall - Phono Termination Calculations and Calculator
Ray
I still claim 200-300 pF is way too high for 650 mH inductance. The resonant frequency would be about 13 kHz and the Q would be about 1 so you would have a peak in the response.
Here is a link to a phono cartridge frequency response calculator. You can see the effect the terminating values have on the frequency response.
Website of Wayne Stegall - Phono Termination Calculations and Calculator
Ray
G'day all, yes the 'electrical resonance' is definitely needed to extend the upper frequency response with a great many moving magnet cartridges. In the case of the Shure M97xE, the manufacturers recommended loading is 47 k with 200 to 300 picofarads input shunt capacitance, which appears to be pretty spot on. http://www.tnt-audio.com/sorgenti/shure_m97xe_e.html
The overall frequency response of a typical moving magnet cartridge is a complex thing with many variables involved like stylus and cantilever resonance, tonearm compatibility and electrical loading (both input resistance and input capacitance). I've proven that for myself. Regards, Felix.
The overall frequency response of a typical moving magnet cartridge is a complex thing with many variables involved like stylus and cantilever resonance, tonearm compatibility and electrical loading (both input resistance and input capacitance). I've proven that for myself. Regards, Felix.
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I have always thought that the cart manufacturers' recommended 47k resistance loading could never be bettered. I also thought that the only tuning available was weight and capacitance and arm angle.
Now having read that earlier Hagerman link in post22, I realise I completely misunderstood the resonance and damping and what could be done with that peaky treble response. Yes, for all of 44years.
It appears from Hagerman, if his paper can be relied on, that low capacitance is always best for an extended audio bandwidth. And further that the peak can be removed by adjusting the resonance damping. This damping adjustment is done by changing the resistive loading.
If I have understood Hagerman correctly then the generally adopted 47k that is usually recommended by the manufacturers is plain wrong.
Can someone read Hagerman and see if I have interpreted the paper correctly?
And secondly, is the Hagerman paper correct in stating that the response can be smoothed to a Butterworth or similar type of roll off by adjusting the load resistance?
Now having read that earlier Hagerman link in post22, I realise I completely misunderstood the resonance and damping and what could be done with that peaky treble response. Yes, for all of 44years.
It appears from Hagerman, if his paper can be relied on, that low capacitance is always best for an extended audio bandwidth. And further that the peak can be removed by adjusting the resonance damping. This damping adjustment is done by changing the resistive loading.
If I have understood Hagerman correctly then the generally adopted 47k that is usually recommended by the manufacturers is plain wrong.
Can someone read Hagerman and see if I have interpreted the paper correctly?
And secondly, is the Hagerman paper correct in stating that the response can be smoothed to a Butterworth or similar type of roll off by adjusting the load resistance?
Beware, that analysis does not take into account any of the mechanical response. It is useful to compute the noise in a solely electrical sense. Here is a model from Graham Slee http://www.gspaudio-community.activeboards.net/topic964_post7158.html#7158
EDIT - The whole thread is about this subject.
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When you model the cartridge as a low pass filter the Q is determined by both the terminating capacitor and resistor. See post 22. The capacitor mainly determines the filter cutoff frequency and you can play around with the R-C values to adjust the Q and cutoff frequency. It is not required to use a 47k terminating resistor. The cartridge resistance and load resistor form a voltage divider (Rl/(Rs+Rl) where Rs is the cartridge resistance and Rl the load resistance, which gives you a loss. As long as Rl is much larger than Rs this loss is small. In a single section filter, the type of response ( phase linear, Bessel, Butterworth) is completely determined by the Q of the L-C section.
Ray
Ray
Hagerman says "Obviously, real-life conditions are far more complex, but general trends and first order results can be realized." As Scott says, he only covers the electrical resonance but in real life this interacts with the mechanical response. This means that the Hagerman analysis is correct as far as it goes, but it doesn't go far enough so his conclusion is flawed. The peak in electrical response compensates for a mechanical drop.
i seen this kind of analysis before and thought that what scott says was the case.
also wondered if the cartridge manufacturers actually factored in the mechanical response as part of their published recommendations for R & C loading.
i always thought it would be pretty amusing if a manufacturer published something like the following in the data sheets: "follow alternate loading recommendations at your auditory peril. in addition to listening evaluations, our recommendations take into account mechanical details which the average audiophile does not have access to without special equipment."
i'm still waiting ...
mlloyd1
also wondered if the cartridge manufacturers actually factored in the mechanical response as part of their published recommendations for R & C loading.
i always thought it would be pretty amusing if a manufacturer published something like the following in the data sheets: "follow alternate loading recommendations at your auditory peril. in addition to listening evaluations, our recommendations take into account mechanical details which the average audiophile does not have access to without special equipment."
i'm still waiting ...
mlloyd1
As the TNT-Audio review shows, you can compensate for the falling mechanical response by peaking the electrical response. The electrical peaking will however cause overshoot and ringing on transients. It also reduced the bandwidth in this case. I am not in favor of fixing one problem and creating another.
I usually use Grado moving iron carts which are a special case. An analysis of ticks and pops does not show much overshoot or ringing but that would be expected, never checked a Shure.
If the electrical response exactly compensates for the mechanical response then there will be no ringing, because this will be compensated too. You just have two filters cascaded together. The fact that one is mechanical makes no difference. In real life no compensation is perfect, but the fact that the electrical network will ring on its own does not mean the combination will necessarily ring too.
As a first order approximation i agree. Maybe it is not a good example but a Bose 901 would virtually have no treble without EQ. I talk since years to manufacturer of cartridges if they are interested in a phono stage that does exactly that: make the total response including arm and cartridge flat, so far without success. I listen with a Phono Stage like that and it works very well.
Hi Joachim,
For most people, simply having a good sounding phono stage would be a huge plus. Never mind the assorted mechanical effects. Now, I mentioned "assorted mechanical effects", and they are just that ... assorted. On top of this, from long experience in the consumer audio field, you can't even expect audio dealers or repair shops to get the capacitance loading figured out correctly. There is no shortage of phono replacement cables that have been installed with no adjustment in loading - or even any mention of padding in the phono section to compensate.
What this means (to me anyway) is that your interest in compensating the entire chain from the cartridge / arm and cables back (including anything else that might have an effect) isn't going to fly. Never mind those of us who change phono cartridges from time to time. Some people even swap cartridges to suit the music style. I can't see how this would work for the masses of audiophiles. Never mind the new crop of USB tables! That would represent the closest thing to a fixed system with few variables (but they are very cheap).
Now, regarding that horrid combination called the Bose 901, I have to agree with you. Not only do these not have any highs without the EQ, but they also strongly lack in bass output. The last EQ I looked at (Mark IV) used a terrible power supply. Cheap to the point where all they can be sure of is that the op amps are not subjected to high supply voltages. Noise performance would be a joke, but I'm not laughing. The op amps used are inexpensive to be nicely put, same as the passive components. But then, there are far more issues with the 901 speaker system than mere frequency response.
I think you picked about the worst audio component to use as an example! But I get your point, and it might be better suited to custom work or individual audiophiles to execute. First and foremost though, the phono EQ amp stage itself needs to be improved over what you would commonly see out there. Otherwise, your changes are probably the least of the problems in a turntable sound chain.
Interesting concept. Can you possibly outline the benefits someone could expect by doing this?
-Chris
For most people, simply having a good sounding phono stage would be a huge plus. Never mind the assorted mechanical effects. Now, I mentioned "assorted mechanical effects", and they are just that ... assorted. On top of this, from long experience in the consumer audio field, you can't even expect audio dealers or repair shops to get the capacitance loading figured out correctly. There is no shortage of phono replacement cables that have been installed with no adjustment in loading - or even any mention of padding in the phono section to compensate.
What this means (to me anyway) is that your interest in compensating the entire chain from the cartridge / arm and cables back (including anything else that might have an effect) isn't going to fly. Never mind those of us who change phono cartridges from time to time. Some people even swap cartridges to suit the music style. I can't see how this would work for the masses of audiophiles. Never mind the new crop of USB tables! That would represent the closest thing to a fixed system with few variables (but they are very cheap).
Now, regarding that horrid combination called the Bose 901, I have to agree with you. Not only do these not have any highs without the EQ, but they also strongly lack in bass output. The last EQ I looked at (Mark IV) used a terrible power supply. Cheap to the point where all they can be sure of is that the op amps are not subjected to high supply voltages. Noise performance would be a joke, but I'm not laughing. The op amps used are inexpensive to be nicely put, same as the passive components. But then, there are far more issues with the 901 speaker system than mere frequency response.
I think you picked about the worst audio component to use as an example! But I get your point, and it might be better suited to custom work or individual audiophiles to execute. First and foremost though, the phono EQ amp stage itself needs to be improved over what you would commonly see out there. Otherwise, your changes are probably the least of the problems in a turntable sound chain.
Interesting concept. Can you possibly outline the benefits someone could expect by doing this?
-Chris
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