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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
cpdunn99's avatar
cpdunn99
639 posts
 
This is one of those "holy grail" issues that has no set answer; it is all so personal!

My Goldring Excel VX is rated at 100 ohm and is a low- to medium-output MC cartridge (0.5mv) Using an EAR/Yoshino 834P tube phono stage works very, although I don't know its specs.

However, the Blue Circle solid state BC23 phono stage, like many other makes, has DIP switches and adjustable gain that can make a huge sonic difference. Setting the BC23 to anything other than 100 ohm is a waste. For one thing, I have to turn up the volume on my amp to almost 2 o'clock! Setting it to 100 ohm sounds better. Adding the extra 10pF DIP switch clears things up a little more. Then, setting the toggle switches to 61db results in magic!

With these setting, the results are wonderful. I must say, however, that although I'm happier with the BC than with the EAR, both are very fine for under $1000. With the BC, one must remove the cover and set the switches (no big deal), whereas the EAR simply has a button on the rear that changes from MC to MM output (much easier, but does not allow for tweaking).
zaikesman
3,017 posts
 
Consttraveler, with a cart output so low as .23mv, many (most?) phono preamps will need the assistance of a phono step-up transformer to provide a sufficient amount of quiet gain, and that sounds to be the case with your system.
consttraveler
250 posts
 
Zaikesman:

That's what I was afraid of, and where my next purchase will be. Do you (or anyone else) have a recommendation? I've been reading about the EAR MC3, which seems to be the likely candidate.

Dave
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.
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