Benz Micro Glider Loading

@lewm,

Thanks for your response. I now dropped the MoFi phono pre down to 900 ohms. I know not much of a difference but it’s a start. Next down (or is it referred to as up?) is 500 ohms.

It would be nice to go with a phono pre with as many options as possible though.

Makes me wonder why a lot of them don’t have at least 7 or 8 options for loading.

I once had the HO version, yeah, the original 2mv, actual rating 1.9mv.  This I ran like an MM, at 47.5K.

I personally would use 47K ohms for a load with a HOMC cartridge.  I agree.  Reason why not many phono stages offer multiple choices for cartridge loading is that the switching mechanism itself, unless done rigorously, can add noise, etc.  It's a purist approach not to use switching (also cheaper for the manufacturer, of course).

@nicktheknife When dealing with a cartridge of this type the loading is for the benefit of the preamp, not the cartridge!

What is going on is the inductance of the cartridge is in parallel with the capacitance of the tonearm cable. Whenever inductance is in parallel with capacitance you get a resonance. In this case it can be from about 50KHz up to about 1 MHz depending on the capacitance of the cable and the inductance of the cartridge. If it goes into 'excitation' (a Radio Frequency term meaning that the resonance is oscillating and is making a signal) then that signal is injected into the preamp. Audio information can send the resonance into excitation even though its not the same frequency!

The result is RFI is being injected directly into the preamp and could be overloading it. This would cause distortion (brightness). By 'loading' the cartridge, you detune that resonance and excitation can't occur- the problem goes away.

If the phono section designer understood how this happens, the phono section won't be sensitive to RFI at these frequencies and so won't care about the loading either- it won't affect the sound.

However, when the loading is used, you are asking the cartridge to do more work! Normally it has to drive 47,000 Ohms but now its only 1000. nearly 5x over a magnitude more work- and that work comes with a price- the cantilever, which does the work, becomes harder to move. This causes the cartridge to have a lower compliance than the spec sheet says and may lead to tracking difficulties if you were paying attention to that when the cartridge was bought and set up in your arm!

In addition the stiffer cantilever may make higher frequencies harder to trace.

The bottom line is when you see a preamp that has loading options on a switch it means the designer did not think about the implications of an inductor in parallel with a capacitance (which is your first week of electronics 101 class). Take that for what its worth...

So not having such a provision is not always a bad thing. It might mean the designer knows what he's doing 🙂

@atmasphere

I don’t want to appear ignorant but I’m not sure how the info you provided helps me in deciding what phono pre I should look for other than listening of course which really isn't an option when buying used.   One with a 1k loading option or not?

In my previous phono pre’s 1k or close seemed to work the best. Some phono pre’s don’t have this option as I’m sure you know.

I have two MC cartridges and one MM. I like to swap them out fairly often.

I guess I should be looking for something that’s more flexible/adjustable than some of the others out there.