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Cartridge loading

Presently I am using a ZU/Denon DL103 mc cartridge with ZU Audio's highest tolerances.  I had this cartridge mounted on my VPI Prime and after going through all the various loading combinations, I settled on 200 ohms.  I was always satisfied with my choice of setting.  I no longer have the Prime and now use the Technics SL1200G turntable.  After having the same cartridge mounted and aligned by the dealer, I inserted it into my system and enjoyed the sound immensely, never touching the 200 ohm setting.

Yesterday I was listening to vinyl most of the day and for some reason I found the sound to be better than ever, mostly in the treble area.  The highs had shimmer when needed and I had played the same records many times before on the Prime and they never sounded as good as they did yesterday.  Just for the heck of it, I checked the cartridge loading and found it was now set at 1000 ohms.  As I said, when I put the Technics into the system, I never bothered changing the loading which was at 200 ohms as it was the same cartridge, just a different turntable.

I believe I know what happened, when I last used the tone controls on my McIntosh preamp, (you have to shuffle through a menu) I must have inadvertently put the cartridge loading at 1000 ohms.  It truly sounds fantastic, better than I ever thought possible.  The Bass is still very deep and taut, midrange is the same but the treble, oh my, so much better.  Now the million dollar question is why should it now sound better at 1000 ohms, when it sounded great before at 200 ohms?  Can the tonearm on the Technics have an effect on cartridge loading?  I always thought it was all dependent on the preamp, amp and speakers.  What am I missing here?  I am very curious to know.  The specs for my cartridge say greater than 50 ohms for loading.

Thanks
128x128stereo5
antinn
408 posts
 
All,
Re-reading my response above, I failed to address the actual question.  So, did some more research and came upon the site,  http://pspatialaudio.com/index_help.htm which has a wealth of historical data, with detailed info, lots of calculations, and this article  http://pspatialaudio.com/analogy.htm presents an interesting model of the equivalent circuit of the dynamic system of a phono cartridge.  While it does not clearly show that harmonic distortion can mimic unloading, the mechanical resonances are not so simple".  Depending on the design of electrical circuit, harmonic distortion can saturate capacitors and inductors thus shifting the electrical resonance frequencies, and if they coincide with the mechanical resonances, there should be no reason that the circuit in the presence of the high harmonic current behaves as if the cartridge is unloaded. 
bydlo
142 posts
 
@antinn Fantastic source, thanks Antinn for sharing! But the cart model of Shure brothers analyzed there is *unloaded* (plus the current source is strangely drawn with series (??) instead of parallel source impedance). The R on the schematics is the mechanical damping of the suspension, not the loading R.
atmasphere's avatar
atmasphere
11,970 posts
 
When you say, RFI, are you talking radio frequency interference, or in general, electro-magnetic interference (EMI)?
@antinn Thanks for your comments!

RFI, not EMI. The RFI is caused by the tank circuit created by the cartridge inductance and tone arm cable capacitance. It is driven into excitation by the cartridge energy.
Don’t really buy the RFI argumentation, sorry. Putting aside simple and super cheap solutions like grid stoppers existing for decades, I cannot see how the RFI conspires to always give the effects exactly mimicking underloaded (high R) cartridge.
@bydlo

Grid stoppers amazingly are not used in all phono preamps! Some designers have ’not heard the gospel’ so to speak ;( But more to your point, I’ve yet to see an audio circuit that sounds right if it is having problems with RFI. The ’cartridge loading resistor’ detunes the tank circuit at the input of the preamp. With most preamps if they are RFI sensitive, this will cause them to be less bright as there will be less intermodulation. Intermodulation contributes to brightness as the ear converts all forms of distortion into tonality.

the cart model of Shure brothers analyzed there is *unloaded* (plus the current source is strangely drawn with series (??) instead of parallel source impedance). The R on the schematics is the mechanical damping of the suspension, not the loading R.
Shure to my knowledge never made a LOMC cartridge. My comments about RFI relate only to low output cartridges. MM cartridges are an entirely different matter, as the resonant peak is often at or near the top of the audio band. They are also capable of ringing at audio frequencies as their inductance is so much higher, so to use a MM effectively, proper loading **is** required.

antinn
408 posts
 
Bydlo,

That article was modeling the mechanical resonances as an equivalent electrical circuit.  I was trying to show that the mechanical resonances were more complex than I originally thought, and if the cartridge goes into physical resonance (which is more likely at high frequency), then there will be a high harmonic distortion (EMI/RFI) produced.  Its my understanding that LOMC, are poor voltage generators, but good current generators which is why the new generation of LOMC preamps are current sensing.  If a capacitor saturates because of the high harmonic current, and there is no dampening resistor, the only thing that is left is the capacitor equivalent series resistance (ESR). If the circuit current suddenly increases, this will by the back emf, dampen the motion of the cartridge armature (stylus-cantilever-suspension), and may depending on where on the record this is occuring (i.e. radial velocity), cause miss tracking.  So long as the current was not outrageous and the capacitor is not damaged, and most will self-heal, once the current drops, the capacitor returns to function.  So the event can be very transient.  
danvignau's avatar
danvignau
935 posts
 
Around 1980, the B&W and Audire Florida rep was my neighbor near my family's St Augustine beach house.  He turned me on to both brands, and suggested a Supex 900 E+ M/C to replace my Ortophon.  I bought an Audire Diffet 1A  preamp, which had a three position impedance selector.  He changed the 40 ohm input resistor to a 10, really opening up that cartridge.  BTW, I had thought my Phase Linear Stacked Advent system was good, which is was for my grad student party system, but he enlightened me. 
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