So what's the problem?
24 responses Add your response
As you approach 30 ohms from higher values, you may notice at some point that you have less apparent phono stage gain, due to loss of signal from hot to ground. If that is happening, then go up at least one notch from the value that affected gain. This will give you a near approximation of "critical damping". Or just use 100 ohms, which is pretty standard for cartridges with an internal resistance of <10 ohms.
There is no specific recommended loading for any cartridge -- a lot depends on your phonostage, your personal taste, etc. With well behaved phonostages that don't freak out and overload from the ultrasonic peak, it is possible for most moving coils to be operated almost unloaded (the higher the number the LOWER the loading, e.g., 47K or 100K). That would give the most open top end, but it could also mean excessive brightness and sibilance and an anemic bass response which is why some loading may be required.
The recommended 30 ohm minimum value represents an extreme amount of loading for most cartridges. When too much loading is applied (very LOW value resistor), overall signal level is reduced, the top end sounds shut down and the cartridge will sound bass heavy, slow and lifeless.
As a very rough guide, I would start at 15 times the internal impedance of the cartridge (90 ohms, in this case) as the low end and expect to find the ideal value somewhere above that number. As a pure guess, I bet something around 125-250 will work well.
>30 is the right answer. In most systems, the number has been in the 100-150 range. In some rare configurations, I've found 35-50 works best.
Now, with my Atma-sphere MP-1, I am running wide open (no loading resistors). Just when you think you have it nailed down, your world turns upside down.
I'm beginning to think that we're not hearing so much the ultrasonic resonance peak direcly as much as we're hearing how this peak gives some phono stages fits (throws them into resonance).
I'd be curious to hear the thoughts of some preamp designers on this.
Thom @ Galibier
Thank you all for taking the time to post. I had initially used 700 ohm when the cartridge was new since I wasn't too concerned about loading until I had a few hours on it.
I still only have 40 hours on it and it actually sounds quite nice with the current load but I will definitely try different values as I put more hours on the cartridge.
Thom, Allen Wright (a noted preamp designer) is very outspoken on this subject, over on the TubeDIY forum. He has insisted for a long time that LOMC cartridges sound best with a 47K ohm load. I've got an MP1, too, albeit a highly modified one. For me, 47K is a bit too bright with my Ortofon MC7500 or Koetsu Urushi. My guess is that one's preference will depend upon one's listening bias and the amplifiers and speakers downstream from the phono stage.
And they may well sound better at 47 kOhms, on Allen's phono stages. But it is a valid point to make that it will be somewhat system dependent. I have heard my xv-1s on a friend's maxed out K&K and it sounded better up around 500. But my Alaap seems to prefer 100 to my ears. IMO, YMMV, and all that.
I've played around with loading quite a bit (though not on an XV-1S), trying loading on the primary vs. the secondary, various types of load resistors, different SUTs, etc. It's all guesswork in my opinion, and completely system dependent. When I've had different tonearms on the deck using the same cartridge, I've noticed I've had to tinker with loading - sometimes the difference is subtle, sometimes night and day (ahem). One of the better explanations as to why this is the case came a while ago from Jonathan Carr of Lyra in this thread (the pertinent excerpt from it is below):
>>You are very crisp with your technical specifications, however, you openly offer a wide range for cartridge loading (100 Ohms to 47 kOhms). Why such a range?
First, because the loading of a low-impedance MC is not really an issue for the cartridge itself. An MC cartridge is a mechanically-driven electrical generator, and a not-very-efficient one at that. Unlike loudspeaker drivers, the meager efficiency of a low-impedance MC cartridge implies that loading applied in the electrical domain will have relatively little effect in the mechanical domain (which is where you will see effects on aspects like tracking performance and distortion). Also, due to the very low inductance of the signal coils, electrical loading will have practically no effect on any signals in the audible range, and this has other benefits in keeping a relatively flat phase response in the audible domain (a general rule of thumb for good phase response out to 20kHz is that the electrical frequency range should extend to at least 200kHz). This is a completely different situation with high-inductance MMs and MIs, where changing the loading will affect the frequency response in the audible range, and the phase response even more so.
So, if electrical loading doesn't change the behavior of the phono cartridge in the audible frequency range by much, why does the sound change so dramatically? The answer is that the inductance of the cartridge coils will resonate with the capacitance of the tonearm cable (and distributed capacitance of the coil windings) and create a high-frequency spike. The magnitude of this spike can be extremely high, and may give many phono stages outright problems if it isn't damped with loading measures at the phono stage input. I don't have my lab notes at hand, but from memory loading a Delos with 47kohm can result in a 28dB spike at 6~7MHz. Some phono stages will have been designed so that they remain unflustered by this, but many phono stages will not be happy with such brutal treatment, and will not sound good because of this. >>
Hope this is of some use. Happy hunting!
Dear Frank: I think that with 40 hours in yor cartridge right now is not the time for cartridge fine tunning. IMHO you need at least other 20-30 hours and then along the load impedance you will need to revise the cartridge set up: VTA/SRA, VTF, overhang, etc, etc.
You need that the XV-1 be settle down before any " serious " listening or set up changes.
Regrads and enjoy the music,
Yes, 28dB is a lot! (25 times greater energy than the flat-response amplitude)
My experience has been that when a low-impedance MC cartridges changes in sound and energy balance due to different electrical loading, what we are hearing are mainly the effects of altered distortion characteristics (particularly intermodulation distortion) in the phono stage, and to some extent, dynamic compression of the cartridge (which is what too-heavy loading will do). The oft-repeated mantra that loading-induced alterations in the sound and energy balance are due to the frequency response in the audible frequency range changing is a myth, because there is no measurable sign of this happening. OTOH, factors that I don't see normally mentioned will cause significant changes in the measured frequency response, such as when the ambient temperature changes by a few degrees, or where on the LP the cartridge happens to be tracking (groove radius).
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.
From the above we can deduce that tonearm cables for low-impedance MCs should have low capacitance. As a test, some time ago I built some 5-pin low-capacitance tonearm cables of 1.2m length (configured for use with a Graham Phantom). Including 5-pin and RCA connectors, the smallest-capacitance versions got down to 32pF, there was an intermediate version at 42pF, and the highest-capacitance version had 50pF. I felt that these low-capacitance tonearm cables resulted in greater flexibility in loading, a more natural tonal balance with better dynamics and resolution, and were a worthwhile upgrade.
hth, jonathan carr (preamp and cartridge designer)
PS. The possible frequency range occupied by the high-frequency resonant spike also includes the frequency range encompassed by LP pops and ticks, and these can likewise be of quite large magnitude (larger than any music signal inside the groove). Just as with the high-frequency resonant spike, controlling pop and tick energy is the task of the phono stage (although it is a big help if the cartridge has a low-mass moving assembly). The phono stage and cartridge can have an immense influence on how "noisy" your LPs appear to be.
The load will generally reduce capacitive effects in the cable, so I have been an advocate of cartridge loading on this account, so long as the load does not over-damp the cartridge.
If handled correctly, this means that the phono cable will not have any significant contribution or degradation in the sound of the phono!
I am thankful to Jcarr's for his last post; its an uphill battle getting people to understand that the preamp does indeed play a role in the severity of ticks and pops, so its nice to hear a cartridge manufacturer acknowledge that.
Jonathan, Ralph ... thanks, as always, for jumping in. You always force me to get back to the raw numbers that always explain what I'm hearing.
I think the best we can hope to accomplish, in advising our customers, is to outline the general principles (as we have all done) - providing basic guidelines for fine tuning.
Both of your comments serve to me as objective validation of what I'm hearing, and justify the obtuse answer I always on give loading: "it depends".
So, what we've (re)learned here:
1. All of the capacitances in the cartridge to preamp path (interconnect, Miller capacitance, etc.) contribute to, and interact with the inductance of the coils to create a resonant tank circuit (look it up, if you're interested). This tank circuit can challenge some RIAA stages more than others, and we run the risk of shooting the messanger (the cartridge), instead of the overall solution.
2. The capacitive component of this tank circuit can be altered with a resistive load (look up "RC filter" and "time constant"). Loading can either be the "correct" solution, or a Band-aid.
3. "Just enough" is always the best solution to all of your adjustments. Exercise a delicate hand in applying any adjustment, whether it's loading, anti-skate, tracking force ... whatever.
4. Re-visit your adjustments when you apply a system change. This element was (obviously) most responsible for the wild variance I've experienced with the XV1s loading (anywhere from 35 ohms, to wide open at 47K). Re-investigate whether or not you were using loading as a Band-aid.
5. RIAA stages can go into hissy-fits (pun intentded) if they're not up to the task of handling any of the above. A good design will be more immune to much of the above, but again, the designer has to have a light touch with his implementation, because the "just enough" philosophy applies here as well as it does with the end user in his analog adjustments.
6. This is a great forum, and I learn a lot here, by thinking out loud, and in public. We should not however, underestimte the value of a good dealer to help you save time and money in navigating this minefield we call analog reproduction. They can save you countless experimental iterations (dealer disclaimer) Sharing anecdotal information is extemely helpful, but it is highly unlikely that any two audiophiles will have every element in their signal path identical to one another, so this advice needs to be understood in that light.
Thom @ Galibier
Oooo ... wait a minute! I re-visited items 1 & 2 (resonant tank circuit).
The formula for resonant frequency is given by:
res. freq. = 1 / [2 * pi * sqrt (L * C) ].
I believe this is the net capacitance, but what I'm not clear on is whether the resistive load is taken into account - whether we're talking about the net capacitance as defined by the RC circuit (including the resistive load), or whether the only effect is the raw capacitive elements - without taking the "R" (resistive load) into account.
I believe it takes the resistive load into account, but perhaps Ralph can answer this question for us.
Thom @ Galibier
The formula for resonant frequency is given by:Thom, I believe that the resonant frequency is determined purely by L and C, per the equation you cited. R will affect the degree of damping of that resonant peak.
If R is very high, say 47K, that peak will be relatively large. If R is excessively low, the low pass filter formed by L and R will cause the overall frequency response to roll off before the frequency of the resonant peak is reached. If R is optimal (with respect to damping of the resonant peak, which may or may not be optimal in terms of overall system synergy), then the response will be essentially flat up to the area of resonance, and above that frequency a smooth rolloff will occur.
As you aptly stated, "'just enough' is always the best solution."
Great thread, btw!
Tuning - reminds me of one of my other loves - guitars.
As it applies to analog, I recall an instance at a music shop where the mother wanted to return the guitar she bought for her son ... because it was out of tune!
Fortunately, our analog front ends are more stable than that (grin).
Thom @ Galibier