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

Showing 5 responses by twl

Bwhite, I personally think that you should try a slight raising of your VTA, and leave it at 100 ohms. Recessed mids are a trait of a too-low VTA. Raise it up, a little. If there is a percieved brightness, it's probably in the Cube. Running the cart "unloaded" at 47k is just compensating for other errors, that are causing the problem. I know that raising the VTA can cause some brightness, but in this case I think you need to. The Shelter could not be considered a "bright" cart, so if you are having "brightness" problems, it is somewhere else. You might try a little self-stick black felt, from the crafts section in Walmart, on the headshell. The Ittok could be "ringing" a little. That is a high-energy cart, and sends alot of energy back into the arm.
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.
Viridian, we can't help unless we post what we think, right? There are conflicting posts on just about every thread on the forum, including the Digital page. It's not just analog that is suffering from this problem of conflicting answers.

Bwhite, at least with the TT, you CAN adjust something to change the sound. With a CD player all you can do is buy a new one.
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.
Consttraveler, if you can find a used Cotter Mk2, that would be your best bet, but they are sometimes too expensive due to demand. Alternatives are a Peerless, or Jensen, or more expensive ones like Audio Note, Shelter, or ET SU-1. Or a head amp like the Denon, etc. Mimimum will be about $100, if you are lucky. The SU-1 is about $3.5k used.