Need to be educated re: MC Step-up transformers

Thanks for all the input. Re: loading the MC cartridge. I had been running it at 47 kohms (don't laugh), and found the sound a bit harsh. My original dealer (now out of business) never educated me on matching and I never educated myself until the sound just didn't feel right.

I contacted Garth at Musical Surroundings, and he suggested the range I indicated above as a starting point, but cautioned that I may choose to go lower - let my ears be my guide. His thoughts were based on:

1. His personal experience
2. His contact with other ClearAudio customers and
3. His personal preference to make less of a reduction than more, given I was starting at 47kohms!

He did mention ClearAudio's preferred phono stage settings during our conversation, but he mentioned 800 ohms. Here's an excerpt from his e-mail:

"Yes 10x coil impedance is the rule for minimum resistive loading, thus you can go as low as 350 ohms. Clearaudio phono stages load at 800 ohms, one reason I suggested it. And 350 is a very radical change from your 49k ohm load. If your system is on the ultra bright side, yes go for 350."

My phono stage requires that the resistors be soldered in - so to me it is a bit of a hassle. I chose 600 ohms because I felt my system was not THAT bright and it was in the middle - a sort of compromise/place to start.

I have to tell you to my stone ears, I was satisfied, save for the noise I mentioned.

As I let the MC-4 settle in, I plan to listen and let my ears be my guide. I just may make some adjustments in the future.

Thanks to everyone.

Brent

Brent,
are still talking SUT? Please note that the values you had discussed related to non-SUT, straight into your phono-pre gain stage, the way I understand it, and the values look to me. I do not know your specific cart but ~ 500ohm could be fine to give you some "air" without getting the sound too "fluffed out", loose, chirpy, uncontrolled, what ever you want to label it.

There are not no many carts that go OK with 47k, as it seems to depend on the internal damping of the typical MC rise in the treble.
Only some MC designs are OK with 47k, and some would argue NONE at all.
Again, if you talk SUT, and specifically truly low output ones then the loading values for SUT use change drastically in my experience, but we have already gone into all of that, no?
Cheers,

Flyfish, The others have subverted your post into a discussion of loading. Bear in mind that this is a "loaded" question; there are "front-loaders" (those who urge you to add a resistor to the primary side) and back-loaders (the more common method of loading the cartridge only on the secondary side) in two opposing camps. On this question, I can only add that Tim de Paravicini might know a little bit more about cartridge loading than some of the others here who are telling you that loading the secondary is "wrong". But what I am interested in is whether you got rid of the noise by switching from your MC input stage to using the SUT. I am not clear on what happened to the noise when you made the switch.

Brent -- Regarding using a 47K load, iirc correctly even the estimable Harry Pearson (founder of "The Absolute Sound") wrote many years ago of preferring the sound of some particular mc cartridge when loaded (or perhaps I should say "unloaded") with 47K! But as Axel indicates, that would be optimal only for a small minority of mc's.

Basically, what the typical lower value load does is to dampen what would otherwise be a large high frequency (usually ultrasonic) resonant peak. You can find an explanation of that here:

http://www.hagtech.com/loading.html

The degree to which that peak would produce adverse audible consequences, such as brittleness or edginess, would depend on its amplitude, its frequency, the bandwidth of the rest of the system, and the intermodulation and other effects that may be produced in the rest of the system by ultrasonic or very high frequency spectral components, as well as on the mechanical damping provided in the cartridge itself, as Axel points out.

Axel & Saudio -- Thank you for your comments. I don't question your experienced-based comments, and I think we all agree that mc cartridge matching necessitates that listening be the final arbiter even more so than with the rest of an audio system.

I haven't seen any good explanations of why use of a step-up transformer would typically call for heavier loading than would be the case if a high gain phono stage or head amp were used. After giving it some thought, I've developed the following theory:

A real-world transformer can be modeled as an ideal transformer in parallel with an inductor on the primary side, representing "magnetizing inductance," as well as other resistive and inductive elements representing loss mechanisms. See the diagram around the middle of this page:

http://en.wikipedia.org/wiki/Transformer

Referring to that diagram, if we assume that the series leakage inductance Xp is relatively insignificant compared to the cartridge's inductance, then by Thevenin's Theorem the magnetizing inductance Xm can be considered as combining in parallel with the cartridge inductance. That will result in a lower total inductance, and therefore an ultrasonic resonant peak which is higher in amplitude if a heavier load is not applied to damp it.

Although the peak will be higher in frequency as well, and it will also be affected by the bandwidth limitations of the transformer, all of which sufficiently muddles the situation such that, again, listening would seem to be the only way reach any meaningful conclusions.

Regards,
-- Al

Thanks again for the posts. In my second posting, I was discussing loading my phono stage, or what I have just learned is referred to as "back loading". I never even knew one could "front load". I apologize to Axelwahl for any confusiuon. In my phone conversations with Tim, he felt I could use the MC-4 "as is", just remove the two 600 ohm resistors I use to "back-load" and I should be good to go.

Did I remove the noise - can't answer that, yet. Neither the US importer nor EAR carry any inventory on the MC-4. Each is made as an order is placed. From e-mails, I understand my MC-4 just made it out of testing in the UK and should be shipped to the US either Monday or Tuesday of next week.

I will post again with results.

Again, this is wonderful info for me.

Brent