Cartridge Loading.....Part II

Ultimately it depends on your ears. There really isn’t a “right or wrong”. Personally, like others I have found 47k to be way to bright/harsh when tried. I have usually settled into more of a “loaded” sound than “unloaded” as I prefer the generally beefier low end. That’s my preference. Have fun with it. One day you might like X loading, the next Y… makes it fun.

Just to share: my Lyra Kleos sounds best anywhere between 60 to 500 ohms depending on recordings (overly dark ones at 500, overly bright ones at 60 and 400 for most, that's why I love the PS audio stellar phono preamp with its instant ohms adjustment on the remote). However the changes are not very significant. On the other hand, my new Sumiko Starling sounds best between 100 and 280 but changes are much more significant. Anything 300 and higher, count me out since it loses its slam. BTW, love this cart, much more fitted to my "head banger" style of music than the Kleos. Term often referred to here by some and always by my wife at home 🙂 That's why I built the house of stereo. Now you know.

Kleos for acoustic and classical, Starling for everything else in my setup.

I am running a Benz Micro Wood SL and have it loaded at 150 Ohms which I thought sounded best after some trial and error. The specs for the cartridge list >100 Ohms. I tried 47K Ohms and as others have experienced I found that setting to be harsh and the music lacked cohesiveness. My Phono Stage is a Herron VTPH-2A and has load resistors that plug in the back so experimenting is easy as long as I have the proper loaded RCA's to experiment with. I also have the ability to custom make different load resistors if I am so inclined. 

Chuck 

I don't know what implications there would be with a SUT.  

I suppose this is all variable, depending on the capabilities of the phono stage, as Ralph @atmasphere seemingly explained in the previous thread.  

Normally you have a rather prodigious electrical peak (resonance) with a LOMC cartridge. It might be as high as 5MHz or as low as 100KHz. Generally speaking if a lower frequency the peak will be less prodigious; this depends on the Q (Quality) of the coil in the cartridge. Lower output cartridges tend to have a higher Q since the windings are shorter and wider with respect to their length; this done to keep their mass down.

That peak can be a good 30dB (1000x) higher than the signal! So if you have a 0.5mV output, perhaps half a volt at 2-5MHz is presented to the input of the preamp. Some preamps don't like that (and might sound bright or weird as a result)! For example, if the phono section employs high quality opamps, its quite possible that the circuit will have some bandwidth that that frequency and so could be overloaded (if overloaded, you'll get ticks and pops) or otherwise affected by an RF signal that powerful at its input!

That's why the loading resistor can be so important (its used to detune that peak, thus eliminating the RFI it generates)! Its certainly not to change the bandwidth or frequency response of the cartridge; at least with all the LOMC cartridges I've tested, all showed no ringing at audio frequencies- quite simply their inductance is too low for that, which implies that the load isn't needed to roll them off to prevent brightness- therefore something else is causing the brightness.

When you use an SUT, it simply lacks the kind of bandwidth to pass RFI at 200KHz or 3MHz- whatever the cartridge might be generating. The only thing with SUTs is that since they have a fairly high inductance, they need to be loaded to prevent ringing ('ringing' is distortion, caused by overshoot of the signal and causes brightness and harshness). If you have an SUT designed for your cartridge, the 47K might be a proper load so no worries. 'After market' SUTs like those made by Jensen Transformers are a different matter. They require specific loading that varies according to the source impedance of the cartridge (since a transformer transforms impedance, the correct load at the output will vary depending on the source impedance). They publish the values needed for a particular cartridge in a pdf file available off of their website. IMO Jensen Transformers make some of the best SUTs available.

I suspect that since the RFI issue is conveniently eliminated when using an SUT that this is why some people say that cartridges sound better when played thru them. Personally I don't find this to be the case, but the preamp I use has no issues if RFI is present at its input and can't be overloaded by that RFI, even if its at 0.5 Volts.

So where this is going: If you have no SUT and 47K sounds bright, you need a loading resistor to eliminate the RFI at the input of the phono section. IOW the brightness isn't the cartridge being bright.

If you have an SUT you do need to investigate the issue of its loading, which might be satisfied by the stock 47K input load of your phono section. BTW, if the SUT is designed for that and you try to drive a 100 Ohm load, you'll find it quite rolled off! There is something called 'critical damping' that applies to things like SUTs (and other interstage or line level audio transformers). If you are loading above critical damping there will be ringing causing the transformer to be bright; if you load with a resistive value too low the transformer will be rolled off.

All phono cartridges are generators, having a coil that interacts with a magnetic field. If you have a regular generator making AC power, for example a portable Honda generator for backup use or camping, you'll notice that when you load it more the engine has to work harder to keep the generator (or alternator) spinning. This is because electrical energy has to come from somewhere ('free energy' is still the stuff of conspiracy theories) so the generator presents a harder load to the engine when its asked to make more current.

The same thing happens in a phono cartridge- the lower the resistive load it drives, the harder it becomes to move the stylus since that is where the mechanical energy is input to be converted to electrical energy. IOW the cantilever becomes stiffer. If you have a means of testing the mechanical resonance of your arm/cartridge combination, you can see that this affects the mechanical resonance since in essence you are reducing the compliance of the cartridge.

@atmasphere 

Thanks for the detailed explanation.  It's going to take me a while to digest all that information!