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Phono Preamp Help - 47K Ohms - 100 Ohms .. Huh?

I am relatively new to analog and therefore have little experience matching a cartridge with a phono preamp. I currently have a Shelter 901 which the user manual specs at "within 100 Ohms" as the recommended load impedance for the head amp. I've been shopping for a new phono pre and find that many top phono pre's are all rated at 47K Ohms and are not switchable.

This got me thinking that maybe 47K Ohms was the right setting for ALL phono stages and sounds the best... So since I currently use a Black Cube which IS switchable between 47K Ohms and 100 Ohms I decided to play around.

When in the 100 Ohm setting, I feel the sound is crystal clear - nearly perfect - yet the midrange seems recessed ever so slightly causing some recordings which I know should have heft and body to be somewhat recessed sounding and maybe thin. Also, at 100 Ohms, the sound is not quite as involving as I like. It's not exactly bright but quite close.... really close - in fact, as extended as I've ever heard a system be without being able to confirm it as being bright.

Switching das cube over to 47K Ohms gives a dynamite midrange. Very impressive vocals. Solo instruments seem incredibly lifelike - highs are ever-so-slightly rolled when compared to the 100 Ohm but during complex music, and even not-so-complex music the mids seem somehow congested as if the notes are bumping into one another slightly - perhaps muddy - more or less "confused". This sucks because everything else seems to be close to perfect.

Each setting has its virtues but I feel the 47K Ohm setting would be ideal without the midrange confusion.

Now for the questions...

If my Shelter 901 is designed for "within 100 Ohms" what the heck does that mean? Within? Does this mean I need to stay at 100 Ohms for the best match to the cartridge?

When switching to 47K as I said above, there are some advantages and clearly a few disadvantages. Are the downfalls more related to the phono preamp, the cartridge or even the impedance match? I mean, could the congestion be a result of the black cube itself vs. a direct result of the impedance settings?

What's more important - the preamp or the impedance setting?
bwhite
bwhite OP
807 posts
 
Okay... I messed with the VTA. Quite frankly I don't know if it went up or down but the bass is better, the highs are nice and the mids are much more accurate. This is what I was trying to acheive.

Thanks all who helped!

This brings me to the phono stage question regarding various loadings. I guess from what I've read, its best to match the output of the cartridge however it is difficult to find a better phono pre (the kind without the toggle switches) that is at 100 Ohms. The Linn Linto is at 150, the LAMM is at 40, Jadis is at 47K, The Joule's are at 47K, the Lukaschek is at 22K.... I cannot find one at 100 Ohms What gives?
gregm
3,021 posts
 
As Oldears notes, fixed 47k is usual for MM phonos. For Mc carts, most phonos allow a variety of settings; mine goes from 25-1000. I would very surprised if Jadis et alia don't allow variable settings nowadays -- even if changes are not user friendly (i.e. involve finicking with solder). I assume you've checked that those loadings refer to low-output MC phonos... Cheers
bwhite OP
807 posts
 
Gregm, I was looking at getting a Jadis and the guy told me, "It is fixed at 47K. Every modern moving coil is optimized for 47K". That was VERY confusing for me and the catalyst which sent me into my latest fervor regarding my analog rig.

All my research tells me that his comment, "Every modern moving coil is optimized for 47K" is asinine. Perhaps he blundered by saying moving coil vs. moving magnet but given we were discussing the DPMC I presumed he knew what he was talking about. The name DP"MC", kind of implies its for MC cartridges but I could perhaps be wrong.
twl
3,251 posts
 
Bwhite, many of the better MC phono stages have plug-in resistors to match the value that you want to load your cartridge to. This is the type of phono stage to get. Selector switches are ok, if they have the right values for you, but as you found out, they often do not. The best ones also allow capacitance loading, which is another can of worms, but can give even better results if you are willing to mess with it. My MFA Magus preamp has a plug built into the back for plug-in resistors, for cartridge loading. Do some more research on different brands of phono sections, and you will find some that have the plug-in resistor feature.

The guy who told you that all MC carts are designed to work into 47k was either confused, or doesn't know what he's talking about.
zaikesman
3,017 posts
 
I have found that the recommended loading can be pretty useless as a guide to what sounds best. It seems to me you would probably prefer a loading somewhat higher than the low 100 ohm setting, but not essentially unloaded like 47k ohms. The correct setting could prove to be in somewhere in the low to mid hundreds, or even up to a couple of thousand ohms, depending on both the cart and the rest of the system. Since you don't have the ability right now to easily test many values in order to find your favorite before wielding the soldering iron on your Black Cube (unless it has socketed resistors - I'm not familiar with it), you might want to try giving your cart's importer a call and see what they recommend using. BTW, if you do install custom value loading resistors, be sure to look into getting premium quality replacements - this might run you $20 instead of $2, but the improvement is well worth the small difference.
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