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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
psychicanimal
1,738 posts
 
Ortofon sells a step up transformer (it's in their website). Pretty beefy unit and it can be purchased through Hong Kong for less than $500. You'll save so much it will be worth to send it to vapor cryo treatment...
mamba
18 posts
 
You have to always properly optimize input load according to the type of cartridge (MM/MC) or you either baffle the signal too little or too much. You should'n forget to add a interconnect capacitance and deduct this value on the phono stage settings if you want to have it optimized accurately. The standard setting are 47k/220pF for MM and 100ohm for MC. MC type cartridge gives less output voltage and due to low resistance you don't need to use any capacitor, it's recommended to bypass the cap. if possible. A lot of manufactures don't allow you to change all values, they allow you to choose between MC or MM type of load, and they rely on luck that it's gonna be suitable. It will be suitable in most cases, but if you have some unusual or special type of cartridge, you will probably loose the low or high sound edge and that's the problem if you can not set it accurately.
mamba
18 posts
 
Guys, unfortunately, I have to disagree with step up transformers used in phono preamp. Yes, it's possible to use them but it won't give you the best resolution. There are semiconductors those are suitable for this kind of applications (to amplify low level signals),and believe or not they do their job much better. Using of step up transformers in phono stage (nowadays) is a marketing trick or lack of knowledge when someone tells you that it's gonna give you better sound.
twl
3,251 posts
 
Mamba, I don't think you are entirely correct about the step up transformer thing. We don't like semiconductors in our signal paths. About the lack of knowledge part, maybe you should discuss this with Kondo, who specifies only step up transformers be used in his pickup systems. I personally use a step up transformer with a tube phono section, and it gives me better sound than any "semiconductor" would hope to give.
zaikesman
3,017 posts
 
Consttraveler - Sorry, I'm not going to be of much help for specific recommendations, as I've never owned a super-low output MC that required a transformer (though I have read that Wright Sound offers a decent one for about $350). Maybe do a forum search on the topic 'phono step-up transformer' or such. The other option would be to just switch to a very high-gain capable phonostage that doesn't need transformer assistance (or has one built-in) to provide adequate gain (probably >66dB I should think), rather than keeping the one you own and also investing in a separate trannie, but I can't suggest which approach would potentially give better sound or be more cost effective for you (not forgetting the extra set of IC's you'll need for the stand-alone option). Best of luck, Z.
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