Matching the cartridge to the phono stage

@jcarr +1

Most phono pre designers seem to build around 100 ohms, but the SL is an outlier at being both low-output MC and recommending >400 ohms. Interesting. 

@paulburnett There's actually a standard for phono inputs, which is 47K. A cartridge designer might recommend a 100 Ohm load or the like because he has no way of knowing what preamp its going to drive. So he recommends a 'worst case' scenario. 

@ajones82 The Technics SL1200G has a pretty decent arm and the 'table is one of the better ones made at any price. Its weak spot it its platter pad, easily replaced.

@ajones82 One of the issues with the Rega arms is an adjustment called VTA is tricky or impossible to set, at least the ones I've seen. But if you use a Rega cartridge its spot on. IMO if you have a Rega arm a Rega cartridge is your best bet. If you want to do better you likely will want to move to a different machine.

As for your last point about how the preamp design deals with the RFI, isn't some level of variability in load resistance needed? The market for MC carts presents a lot of options, all of which have very different specs. Or am I not understanding your point?

The short answer is 'no'. People use the loading as a tone control with many preamps, on account of without it the preamp sounds bright. This is usually due to distortion as I mentioned prior. Get rid of the RFI and the distortion goes away.

So if your phono section is properly designed, you'll find the loading makes little difference. That remaining difference will be because the cantilever is less supple tracing the groove when the cartridge is loaded. The specs the cartridge manufacturer posts about compliance are usually when the cartridge is driving a 47KOhm load, not 100 Ohms or the like.

Put another way, if the phono section is properly designed its plug and play.

The Hana SL has been on my table for the past two years, running into a Parasound JC3 Jr. (which allows me to adjust MC load using a variable pot that runs from 50-550 ohms). I can say that the differences in load between 100-400 are subtle, but there is a more pronounced treble "edge" and a more brittle sound on certain vinyl when running below 300 ohms. This is likely due to a drop out of the upper mids below that 300 ohm load.

@mrmojo 

The loading has nothing to do with the cartridge sounding different and everything to do with the phono section making less distortion. Also, a lower resistance might load the cartridge so much that the cantilever becomes so stiff it might have difficulty responding to higher frequencies.

The reason this is so has to do with the inductance of the cartridge. Its quite low! In fact its so low that if you pass a 10KHz squarewave through it (put the cartridge in series with the squarewave) you'll see on an oscilloscope that the output looks just like the input- no rolloff at all!

So the change in tonality is something else. There are two things to affect that. One is that the inductance is in parallel with the tonearm cable and its capacitance. That sets up an electrical resonance that is probably at 1 or 2MHz. That resonant peak is likely about 25dB (based on the Q of the inductance of the cartridge); when energized by the cartridge tracking an LP the resulting RFI can easily overload many phono sections, resulting in distortion which is perceived as brightness.

The loading resistor detunes the resonance. Brightness is gone.

But a 100 Ohm loading resistor is going to force the cartridge to do 2 orders of magnitude more work as opposed to the stock industry standard of 47KOhms. So the cantilever will be stiffer just as an alternator shaft gets harder to turn when its loaded. A cartridge is a kind of alternator. The decreased compliance can result in less high frequency energy and may affect how the cartridge tracks in the tonearm.

If the preamp is designed to deal with the RFI generated, you'll find that the loading resistor makes far less difference! When the phono section has a loading resistor switch, its a pretty good sign that the designer did not take the implication of an inductance in parallel with a capacitance (electronics 101, 1st week) into account.