2channel8 & Ericsch, it is true that the sonics of LOMCs themselves are essentially insensitive to reasonable amounts of load capacitance. However, note the statement by Lyra cartridge designer Jonathan Carr that I quoted early in this thread: I should now debunk another myth regarding loading, which is that low-impedance MC cartridges are insensitive to capacitive loading. OK, the MC cartridges themselves aren’t particularly sensitive to capacitance, but the inductance of the cartridge coils will resonate with the distributed capacitance of the coils and the capacitance of the tonearm cable to create a high-frequency spike, and this spike certainly is sensitive to capacitance. In general, the less the capacitance the better. Having more capacitance (across the plus and minus cartridge outputs) will increase the magnitude of the high-frequency spike and lower its frequency, neither of which is good news for phono stage stability or phase response.
Generally speaking, the greater the capacitance across the plus and minus cartridge outputs, the heavier the resistive loading needs to be to control the resulting high-frequency spike. Conversely, less capacitance allows the resistive load on the cartridge to be reduced, which will benefit dynamic range, resolution and transient impact. Also see the link Jonathan ("JCarr" at Audiogon) provided in his post in this thread dated 5-28-2018: http://www.whatsbestforum.com/showthread.php?15077-Cartridge-Loading-A-Misnomer&p=258578&vie...That is why Ralph (Atmasphere) stated above that "it is advantageous to keep the resonant frequency as high as possible." It's all about the phono stage. Regards, -- Al |
Bill (Wrm57), thank you kindly :-)
Best regards,
-- Al
|
Great info, Wyn; thanks! And thanks also to Catcher10 for his inputs. So, perhaps the answer to the loading question is, no matter how unlikely it seems- it depends on the architecture of your phono amplifier! This is exactly what Ralph (Atmasphere) has said in more than a few prior threads here, as well as in this one, that optimal loading is primarily dependent on the design of the phono stage. BTW, the Herron phono stage I own, which as I previously mentioned I (and also some other members here) run with essentially no resistive load whatsoever (just the input resistance of a FET stage, which is nearly infinite) uses passive RIAA equalization. As do the phono stages that are built into Ralph’s preamps. Thanks again. Best regards, -- Al |
Hi Wyn,
Yes, that is of interest. And I agree with your math, of course, while having two comments:
First, I’m not sure that "back EMF" would be the best terminology to apply to what you are calculating, or the best way of considering it (see the next paragraph for my perspective on that). As you no doubt realize, that term is commonly used in the context of speakers, where a signal is applied by an external source, and back EMF is generated by the speaker as motion of a driver coil in its surrounding magnetic field continues beyond what is called for by the signal. In this case, of course, it is motion of the cartridge’s coil which generates the signal, as opposed to coil motion that occurs in response to an applied signal.
Second, I believe that what your calculation reflects is simply the high frequency rolloff which occurs as a result of the interaction of cartridge inductance and load resistance, putting aside the effects of capacitance. In your example, 2 x pi x f x L (i.e., inductive reactance) would become equal to the 100 ohm load impedance at a frequency of about 1.35 MHz, resulting in a 3 db bandwidth equal to that amount. So the error you are calculating, if indeed it can be considered to be an error, would seem to be insignificant at audible frequencies.
Regards,
-- Al
|
Thanks for providing the comprehensive simulations, Wyn. Regarding: Now 1000 pF. 0mdB at 20kHz, -32dB at 10MHz, 0.5dB peak at 1MHz.
Now 10nF. 10mdB at 20kHz, -52dB at 10MHz, 3dB peak at 400kHz.
Now 22nF. 20mdB at 20kHz, -59dB at 10MHz, 2.2dB peak at 270kHz.
Now 47nF. 27mdB at 20kHz, -65dB at 10MHz, 0.8dB peak at 147kHz.
Now 0.1uF. -12mdB at 20kHz, -72dB at 10MHz. No peaking, -3dB at 150kHz.
Am I correct in interpreting that these results are all with a 100 ohm load resistance? If so, and given these results: With the measured cartridge/minimum input cap (85pF) the response with a 47K R has a 29dB resonant peak at 4.3MHz and is -12dB at 10MHz.
With a 1k load it’s 4.2MHz and 9.5dB.
With 250 ohms it’s basically flat to 5MHz, with -14dB at 10MHz.
with 100 ohms it’s 1mdB down at 20kHz, with -17dB at 10MHz. ... It appears to me that these and the rest of your results are reasonably consistent with statements I, Atmasphere, and JCarr have made, and with what is illustrated in the plots provided in the post Jonathan linked to, that in the absence of a relatively heavy resistive load a large resonant peak will occur at an RF frequency, and (as can be predicted theoretically) at progressively lower frequencies as the amount of capacitance increases. But as your simulations show, even if extremely large amounts of capacitance are present, e.g. 1,000 to 100,000 pf, a load resistance in the vicinity of 100 ohms will cause frequency response to be reasonably well behaved, at least for the particular cartridge parameters you chose. However there is only one phono stage I am aware of which has an input capacitance within that very high range, that being the AcousTech PH-1, which in LOMC mode provides a load of 100 ohms in parallel with 10,000 pf. I believe that the great majority of other phono stages having active input stages have input capacitances in the area of perhaps 50 to 250 pf or so. I would expect that there are reasons for that. And I would expect that in many cases those reasons, in addition to making it possible to provide a wide range of choices of resistive loading, are along the lines of what Jonathan has said in the post he linked to. Namely that heavy resistive loading "reduces the cartridge’s dynamics and resolution, and can also worsen tracking ability." As well as what I quoted him as saying in an earlier thread here, namely that "less capacitance allows the resistive load on the cartridge to be reduced, which will benefit dynamic range, resolution and transient impact." Perhaps he or Ralph (Atmasphere) will elaborate on that, as they are much more expert in this area than I am. Regards, -- Al |
By the way, I still have no idea what you mean by energy of the cartridge itself etc. I didn’t say "energy of the cartridge itself." I said energy "generated by the cartridge itself," and I was referring to energy "generated by the cartridge itself" at RF frequencies. Which I was distinguishing from Radio Frequency Interference, which appeared to be the focus of your analyses. Surely it must be more than obvious to you that a cartridge generates an electrical signal when it is playing a record, and electrical signals contain energy, and: Energy = Power x Time And for a resistive load: Power = Voltage x Current = Voltage Squared / Resistance = Current Squared x Resistance Not sure why what I meant by energy "generated by the cartridge itself" would not have been clear. Regards, -- Al |
Thank you for joining the thread, Jonathan, and for providing the link. The text to the right of the last figure in the post Jonathan linked to is particularly relevant. Some excerpts [words in brackets are mine]: The resonant peaks have too high of a frequency to hear directly, but the magnitude of the peaks and their high frequencies are likely to cause decreased stability and increased distortion and noise in many phono stages. Some phono stages will be fairly insensitive to these ultrasonic peaks, while other phono stages will show bigger effects....
... No additional capacitive loading was used [in the simulations] at the phono stage input.
Comparing the simulations of the 3 cables shows that higher capacitances of the tonearm-to-phono stage interconnect cable demand lower resistor values at the phono stage input to control the resonant high-frequency peaks. This, in turn, reduces the cartridge’s dynamics and resolution, and can also worsen tracking ability. Also, regarding Wyn’s simulations, I would reiterate a point I made in an earlier post: Almarg 5-26-2018
I believe what underlies the differing perspectives between your [Wyn’s] analysis and what I, Atmasphere, and JCarr have maintained is that while your analysis focuses on rejection of RFI per se, as reflected in your choice of 10 MHz in the analysis, I and the others have focused on energy that may be generated by the cartridge itself, at and near the resonant frequency. Best regards, -- Al |
Are you perhaps stating that the increased current generated by the lower resistive load increases distortion? No, I was not saying that or implying that. And for that matter I have no particular knowledge of how the distortion performance of phono cartridges tends to vary as a function of load impedance. Regards, -- Al |
Hi Wyn, Thanks for providing the excellent and thought-provoking analysis. I see no flaws in it as far as it goes. And in fact the manual for the OP’s phono stage states that the higher capacitance setting (570 pf) can sometimes be beneficial with respect to "interference rejection," when used with LOMCs. However I believe what underlies the differing perspectives between your analysis and what I, Atmasphere, and JCarr have maintained is that while your analysis focuses on rejection of RFI per se, as reflected in your choice of 10 MHz in the analysis, I and the others have focused on energy that may be generated by the cartridge itself, at and near the resonant frequency. Not directly in response to musical information, which is presumably not present at frequencies of hundreds of kHz and above, but rather in response to "surface noise," tics and pops, and other causes of unwanted high frequency modulation of the output of the cartridge. Or (and I’m just speculating here) perhaps as a result of upper order harmonic distortion components that may be generated by the cartridge in response to musical information at lower frequencies. As Atmasphere stated in a post in this thread on 5-21-2018: ... the cartridge inductance combined with the tone arm cable capacitance forms a tuned RF circuit- which is energized by the cartridge signal. It can be over 30 db higher than the phono signal- thats about 1000x more powerful! Note the words "which is energized by the cartridge signal." I guess the bottom line, though, is that as is usual in audio there are many complexities and competing tradeoffs involved, as well as many system dependencies, and consequently there are multiple paths to an optimal setup, and multiple paths to setups that are less than optimal to varying degrees. And speaking of complexities and competing tradeoffs, your mention of SUTs certainly brings many more into play. As I’m sure you realize, optimal loading with a SUT will usually be different than when a cartridge is driving an active circuit, in part because of the need to optimize loading of the transformer itself, to minimize ringing and resonances. Another consideration being that capacitance that is present on the secondary side of the SUT will be presented to the cartridge multiplied by the square of the turns ratio. BTW, was the AD797 one of the integrated circuits you mentioned having designed? If so, or even if they were anything comparable, I’m truly impressed! Best regards, -- Al P.S: @terry9 ;-) |
Thank you for the nice words, Raul. As far as the usefulness of an understanding of LOMC capacitive loading is concerned, for one thing it has provided guidance to the OP as to which of the two settings of the capacitive loading switch on his phono stage is likely to provide best results. And that in turn perhaps saves him the trouble of having to evaluate a number of different resistive loading settings twice, once for each of the two capacitance settings. And the experience reported by Catcher10 certainly serves to illustrate that knowledge of this issue can be helpful to other audiophiles as well. Finally, while I certainly agree with your concluding statement that... ... I always try to make things in the best way and in an easy way because at the end what I and we want is to enjoy the MUSIC and always is system dependent.
... in a hobby where a lot of audiophiles concern themselves with dubious and unexplainable minutiae such as which way a fuse is oriented an explainable and potentially significant phenomenon such as this seems to me to be a reasonable thing for audiophiles to be aware of. In any event, thanks again for the nice words. Regards, -- Al |
Wynpalmer4 5-25-2018
The non-inverting amplifiers used in an RIAA stage never have a gain below unity unless an additional pole is added. It’s hard to see why adding a capacitance of significant value to the input of a phono stage helps when the self resonant frequency of most larger value caps is well below the RF region of interest. Indeed, if that is your concern, then adding several caps of scaled value 1-2 orders of magnitude apart, say 0.1uF//3300pF//100pF as the cartridge load would be the way to go, and who does that- except as an extra pole in a non-inverting RIAA stage.
I’m a believer in fixing the problem where it exists and not by adding an additional parameter to an already over-constrained problem. Thank you for your responses. I must say, though, that despite being a highly experienced electrical engineer myself (in my case analog and digital circuit design for defense electronics), I don’t see the relevance of this statement. What I, Atmasphere, and Jonathan Carr have said in regard to load capacitance, and which the Hagtech calculators you referred to will confirm, is that in the case of LOMC cartridges **minimizing** load capacitance will increase the frequency and reduce the amplitude of the resonant peak which occurs at RF frequencies as a consequence of the interaction of cartridge inductance and load capacitance. Both of which are desirable goals, although it presumably won’t matter much if at all in the case of **some** phono stages (such as my Herron and I would assume the phono stages that are built into Atmasphere’s preamps). But in the case of phono stages whose design is such that RF energy received at their inputs may have audible consequences keeping that resonant peak as small as possible and at as high a frequency as possible will mean that less resistive loading will be necessary to tame that peak. Which in turn can often be beneficial sonically, as has often been attested to by many highly experienced and astute audiophiles. A notable example being Larryi, who posted earlier in this thread. So I’m not understanding why your statement that I quoted refers to adding capacitance, rather than minimizing it, or what the relevance of that statement’s concluding sentence may be. Regards, -- Al |
Wynpalmer4 5-25-2018
Contrary to what has been said, for LOMC the capacitance, unless it is quite large (in the order of .1uF), is essentially irrelevant .... As explained earlier by me, and by Atmasphere (Ralph Karsten of Atma-Sphere Music Systems), and in the statement I quoted by Jonathan Carr (Lyra cartridge designer), while load capacitance is indeed essentially irrelevant to the cartridge, it is not irrelevant to phono stages whose design is such that RF frequencies received at their inputs can have audible consequences. Regards, -- Al |
I took a look at the manual, which can be found at the Plinius site. On page 11 (pdf page 13) it can be seen that the capacitance switch is to the left of the resistive loading switches, and appears to be identified as switch "1", and it should be set to the "Up" position for 100 pf. Enjoy! Regards, -- Al |
Did you read my earlier posts? Almarg 5-22-2018
I see that the Koru provides two selections for input capacitance, namely 100 pf and 570 pf. You are likely to find that the 100 pf setting will allow you to use lighter loading (i.e., higher resistance values) than the 570 pf setting.... [And quoting Lyra cartridge designer Jonathan Carr]: "Less capacitance allows the resistive load on the cartridge to be reduced [i.e., the number of ohms to be increased], which will benefit dynamic range, resolution and transient impact."
Almarg 5-22-2018
The point, generally speaking, is that minimizing the capacitive load seen by an LOMC cartridge is likely to result in optimal resistive loading being lighter than the resistive load that would be optimal if the capacitive load is higher. And in turn the lighter resistive load is likely to be sonically beneficial.
Almarg 5-23-2018
With regard to the OP’s situation, all I was basically saying is that he is likely to obtain better results using the 100 pf setting of his phono stage rather than the 570 pf setting, assuming that he optimizes the resistive loading that is used with the 100 pf setting by listening. Regards, -- Al |
Hi Raul,
With regard to the OP's situation, all I was basically saying is that he is likely to obtain better results using the 100 pf setting of his phono stage rather than the 570 pf setting, assuming that he optimizes the resistive loading that is used with the 100 pf setting by listening.
Regards,
-- Al
|
Rauliruegas 5-22-2018
@almarg , I read in the past that from J.Carr. Now, please tell me if you have first hand experiences where you can attest it. Attest to what? I don’t see any inconsistency between what I said, what Mr. Carr’s post that I quoted said, and what you quoted from the Lyra website. The point, generally speaking, is that minimizing the capacitive load seen by an LOMC cartridge is likely to result in optimal resistive loading being lighter than the resistive load that would be optimal if the capacitive load is higher. And in turn the lighter resistive load is likely to be sonically beneficial. That makes sense based on theoretical analysis that can be performed, and is backed up by statements by Mr. Carr and by Ralph (Atmasphere), who collectively probably have more relevant expertise than the rest of us put together. And for that matter it is consistent with suggestions provided by Keith Herron for his VTPH-2 phono stage, which I use. From its manual: We highly recommend trying the VTPH-2 in the no load configuration as the unit is supplied for many moving coil cartridges. 47,000 (47K) ohm RCA load plugs are supplied with the unit for optional use. Additional user specified loading plugs can also be purchased with the unit.
The input resistance of the VTPH-2 is nearly infinite when no loading plug is used, yet Mr. Herron suggests trying that configuration when his phono stage is used with "many moving coil cartridges." And that is how I use mine with my Audio Technica AT-ART9 cartridge, after having also tried 1K and 47K. Audio Technica’s load recommendation for the ART9 is "100 ohms minimum." And contrary to what you seem to be implying, none of this is in any way inconsistent with a recommendation to "determine by listening." It is a general guideline which can provide a useful starting point, and in some cases what can turn out to be an ending point. Regards, -- Al |
Atmasphere 5-21-2018
This is because the cartridge inductance combined with the tone arm cable capacitance forms a tuned RF circuit- which is energized by the cartridge signal. It can be over 30 db higher than the phono signal- thats about 1000x more powerful! To add to Ralph’s (Atmasphere’s) response, with which I of course agree, the input capacitance of the phono stage will add to the capacitance of the phono cable. And I see that the Koru provides two selections for input capacitance, namely 100 pf and 570 pf. You are likely to find that the 100 pf setting will allow you to use lighter loading (i.e., higher resistance values) than the 570 pf setting. Also, related to all of this the following excerpt from a post dated 8-14-2010 in this thread, by Lyra cartridge designer Jonathan Carr, will be of interest: I should now debunk another myth regarding loading, which is that low-impedance MC cartridges are insensitive to capacitive loading. OK, the MC cartridges themselves aren’t particularly sensitive to capacitance, but the inductance of the cartridge coils will resonate with the distributed capacitance of the coils and the capacitance of the tonearm cable to create a high-frequency spike, and this spike certainly is sensitive to capacitance. In general, the less the capacitance the better. Having more capacitance (across the plus and minus cartridge outputs) will increase the magnitude of the high-frequency spike and lower its frequency, neither of which is good news for phono stage stability or phase response.
Generally speaking, the greater the capacitance across the plus and minus cartridge outputs, the heavier the resistive loading needs to be to control the resulting high-frequency spike. Conversely, less capacitance allows the resistive load on the cartridge to be reduced, which will benefit dynamic range, resolution and transient impact.
Good luck. Regards, -- Al |
2channel8 6-1-2018
I haven't been able to measure my phono cable's capacitance. My multimeter just reads 0.0 F, even though it has a uF range. As a rough ballpark approximation, a typical phono cable may have a capacitance in the vicinity or 25 pF (picoFarads) per foot or so, corresponding to 125 pf for a five foot length. 125 pF is 0.000125 uF (microFarads), and 0.000000000125 F (Farads), so it would be understandable that your meter indicates 0.0 F. Regards, -- Al |
