Playing with Cartirdge loading on my phono stage

Thanks @atmasphere - Ralph you are a gentleman, and your thoughts, and guidance, are very much appreciated.

@holmz That is going to depend on how the phono section reacts to the RFI and IME that depends largely on the circuit itself so a blanket answer will be inaccurate. If it were me I would be looking at all those things. Its also worth noting that the electrical resonance may not always be in excitation- so it will come and go in certain circumstances.

It would be better to use a distortion analyzer, but this would only be of benefit if the phono section can't deal with the RFI on its own. If the phono section does deal with the RFI properly, you'll see no benefit from the loading in terms of distortion.

@atmasphere thanks Ralph - what would the distortion look like? IMD, noise, or HD.

I am guessing it might look like IMD beating an RF tone against the audio signal??

Asking because I can digitise the TT signal, and look at it spectrally and do some math on it. Just need to know what to look for… (Like everything other than the specific test record tone freq?)

does that mean we can just select the load with an o-scope?
and select the highest resistant value possible?

It would be better to use a distortion analyzer, but this would only be of benefit if the phono section can't deal with the RFI on its own. If the phono section does deal with the RFI properly, you'll see no benefit from the loading in terms of distortion.

No. The reason the sound changes is due to distortion- LOMC cartridges and the tonearm cable together form an electrical resonance that generates Radio Frequency Interference which is injected directly into the phono section and can cause distortion. The loading resistor detunes the electrical resonance, thus eliminating the RFI.

However if your preamp was designed by someone that knows about this phenomena, you'll find that the highest load impedance (47,000 Ohms) is the right one, with little or no effect at lower resistances other than the tracking ability is reduced.

@atmasphere does that mean we can just select the load with an o-scope?
and select the highest resistant value possible?

Would it not depend on the frequency response of your speakers in your listening room with your tastes for sound in mind?

No. The reason the sound changes is due to distortion- LOMC cartridges and the tonearm cable together form an electrical resonance that generates Radio Frequency Interference which is injected directly into the phono section and can cause distortion. The loading resistor detunes the electrical resonance, thus eliminating the RFI.

However if your preamp was designed by someone that knows about this phenomena, you'll find that the highest load impedance (47,000 Ohms) is the right one, with little or no effect at lower resistances other than the tracking ability is reduced.

Would it not depend on the frequency response of your speakers in your listening room with your tastes for sound in mind?

There are only two settings available that fall within the specified 100-200 Ohm range…100 and 170.  Try both and decide if you prefer one or the other…leave the capacitance at 470pF.  

Tuning by ear is the way to go here, as others have said. 10x the internal resistance of the cartridge puts you on the edge of pinching the signal - that is decreasing the volume by resistance instead decreasing it by lowering the gain. Once you get down to 5x, this is noticeable. Downstream volume pots can be opened up if you pinch the signal at the phono pre, which may be preferable. I’ve always thought most systems have too much gain. Some carts I have (Miyajima Zero and Denon 103R) sound better to me when pinched at the phono pre. Some (Hana) are the opposite and sound better opened up.  The differences are subtle and in my system come down to bloom vs transients - or to say it another way - fullness of the instruments vs separation of the instruments. When the resistance is pinched, tones fill up with more bloom. When opened up, instruments have more space between them. I’ve tried recording A/B to DSD and then compared playback - that didn’t work. Best to work from a recording you are very familiar with. 

In general, higher ohms mean leaner sound and better tracking. My phono does 10R to 47K, and I usually run the Koetsu at about 1k. But there are times when I prefer it at 30R, or even 47K. Depends on source, mood, and how long the electronics have been warming up.

I recently acquired a Sumiko Starling and between 100 ohms and 200 ohms there is a HUGE difference. With Lyra Kleos, a 100ohms difference is hardly noticeable. Just play with it. Don't listen to anyone about that but your ears.

I have been surprised that sometimes loading makes virtually no difference and then on some cartridges it makes a small difference. Surprisingly to me I have never gone: “something sounds wrong” and traced it to accidentally changing loading. 
 

You just have to flip through them. 

The bottom line is you cannot hurt anything by experimenting with a wide range of different loads and selecting the one you like best. You could even start at 47K ohms and go down from there in logarithmic steps. But it is probably wise not to go lower than the manufacturers lowest recommendation. Ideally, you want to maintain a 1 to 10 ratio between the internal resistance of your cartridge and the load resistance.

When you go lower ohms - I hate saying lower load because technically that’s a tougher load for the cartridge - you can start to lose noticeable signal, like 1 dB and more as you slide down below a 10x coil-to-load ratio (about half a dB at a 20x ratio).

This is because of the voltage divider formed between the cartridge coil and load. This only applies to voltage-amplification mode phono stages and SUTs, as intactaudio will point out (though current mode stages are still much less common).

So you may need to adjust the volume slightly on different loads, to be fully fair in your comparisons. You can often notice the difference going from say 50 ohms to 200 ohms (e.g. adjust the volume up almost a dB for 50 ohms load) or vice versa. But at some point, throwing away too much signal (too low of a load resistance) is definitely bad - you’re lowering signal-to-noise ratio for one.

The manufacturers usually know their own products best. I always stick with their recommendation. You will not notice much when you play around.

Which means that you can take some bigs steps.
If they say 50-200 ohms, then you could try 40 or 50 and 1k to bound the problem… If you cannot hear much change from that, then just stay at 200.

Or try 50, 100 and 200 and see if there is much in it.

@jemmer01 , flip through the values and you tell us.

The manufacturers usually know their own products best. I always stick with their recommendation. You will not notice much when you play around.