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Need to be educated re: MC Step-up transformers

I recently purchased the EAR MC-4 Step-up transformer. I was having some noise problems with my analog rig. I spoke with Tim de Paravicini of EAR directly in the UK. He answered all the system matching questions and pronounced the MC-4 a fit with my system. He is very direct, extraordinarily knowledgeable, and seemed very sincere and honest.

I still don't understand the "How" though. Here's what I do understand and relayed to Tim:

1. I use the ClearAudio Stradivari, a MC at 0.7mV output.

2. Currently, my phono stage provides a total of 57 dB of gain: 20 in the MC mode using a JFET and 37 in the MM mode using all tubes. My tube line stage provides 12 dB of gain SE, which is how I run it. So, currently without the MC-4, I have a total of 69 dB gain when running my phono stage in MC mode (20 + 37 + 12).

3. The MC-4 has four taps – I was told by Tim to use the 40 ohm tap which provides a 10x gain in voltage and is compatible with the 32 ohm impedance of my cartridge. This would change the output voltage my phono stage “sees” from 0.7mV to 7.0mV.

4. The phono stage must be run in MM mode, bypassing the JFET in the MC mode.

5. Given all this, then, my phono stage will receive as input a 7.0mV cartridge output from the MC-4. This signal will run through the MM mode and receive 37 dB gain and then another 12 dB gain from the line stage SE for a total of 49 dB gain, down from 69 dB, as we are no longer “gaining” the additional 20 dB from the JFET MC mode.

6. I need to remove the 600 ohm Vishay resistors and get the phono stage back to the stock 47 kohm setting, as the MC-4 will reduce the resistance by the square of the voltage gain or 10^2 or 100: 47,000/100 = 470. That is within the range recommended by Clearaudio of 320 – 900, preferably toward the lower end, though let your ears be your guide.

It was based on this information (which I provided) that the MC-4 was pronounced a fit - I certainly don't doubt that.

Here's my confusion: Am I to understand that 7.0mV of cartridge output from the MC-4 is so much more voltage that all I need is the 49 dB the system provides in its new configuration for low noise and analog bliss?

I just don’t understand the science, I guess. I appreciate the education.

Brent
flyfish2002

Showing 7 responses by flyfish2002

flyfish2002's avatar
flyfish2002 OP
94 posts
 
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
flyfish2002's avatar
flyfish2002 OP
94 posts
 
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
flyfish2002's avatar
flyfish2002 OP
94 posts
 
Thanks, John. When the MC-4 finally is in my system, the load will be at 470 ohms due to the SUT "loading down" the cartridge by the square of the volatege gain (47000/10^2). Thanks for posting your experience - it helps to give me some confidence in my starting point.

Brent
flyfish2002's avatar
flyfish2002 OP
94 posts
 
Thanks. Garth Lear of Musical Surroundings had suggested 300 - 400 for the Stradivari.

My speakers are 85dB sensitivy and 4 ohm - may be the culprit.

Good listening.
flyfish2002's avatar
flyfish2002 OP
94 posts
 
Rccc - glad it worked out for you. As I mentioned above, Tim de P told me that 12.6mV is a bit high, but a decent phono stage in MM mode won't get overloaded until you hit 14 or so. I didn't believe him, at first.

My future plans are to replace my monoblocks so I can run the line stage to monoblocks balanced - currently I am SE. The gain on my line stage is 20 balanced and 12 SE. When I do this, I might not need the gain of the 12 ohm tap and I may need to go back to the 40ohm tap.

Future plans...

Enjoy.
flyfish2002's avatar
flyfish2002 OP
94 posts
 
Today is August 5th - the EAR MC-4 finally arrived! Hoorah!

I had a chance to insert the MC-4 into my system and change my phono stage by re-setting the resistance back to the stock 47kohms and switching to MM mode. The results - dead quiet.

Now, the line stage still needs to be up around the same gain value for similar volume levels as before - I didn't "gain" any additional gain, if that made any sense. I swapped out 20 dB of JFET for 20 dB of EAR MC-4.

The difference is that I replaced a 1994 year old JFET (Bill Thalmann completely modded the phono stage, but, of course, did not replace the 15 year old JFET) with a 2009 SUT. Very quiet.

Another very welcome, but unexpected benefit is that the sound is markedly improved. I realize it is trite and overused, but it is as if a "veil" has been removed. Listening to just a few albums suggests a more natural sound, as if I was present at a concert.

While I had no intention of buying an SUT and did not want to spend the $$, I am very pleased with the purchase and cannot speak highly enough of EAR's work and Tim de Paravicini's absolute attention to customer service and build quality.

Brent
flyfish2002's avatar
flyfish2002 OP
94 posts
 
One month later...

I have settled in with the EAR MC-4 more. I have adjusted the set-up. I now use the 12 ohm tap instead of the 40 ohm tap on the MC-4. The 12 ohm tap provides 18x voltage gain instead of the 10x of the 40 ohm tap.

While the EAR MC-4 is MUCH quieter than the JFET in the MC stage of the phono stage (actually this is an understatement - the EAR is dead quiet), the 40 ohm tap presents two problems:

1) It gives me the same 20dB gain as I get when I used the MC stage - I don't gain any gain. With my line stage providing only 12dB in SE mode, I still had to turn the line stage to the same volume level for similar gain. At "fun" listening levels, this produces surface noise even on immaculately clean LPs; and

2) My Clearaudio cartridge likes to see 150 - 200 resistance from the phono stage. Clearaudio actually sets their phono stages to a factory stock of 200ohms. Using the 40 ohm tap, I am at 499; using the 12 ohm tap, I am at 154 - a much more musical presentation for my ears.

I realize that with a cartridge impedance of 32 ohms, I am "breaking" the rules - I was told to use the tap nearest the cartridge impedance. In addition, the all tube MM stage is seeing a cartridge output of about 12.6mV - a tad high (though Tim de Paravicini told me you had to get to around 14 before you typically had any issues).

To date, I have had no problems and I use less gain at the line stage, producing a vastly quiet system even at "fun" volume levels.

I guess the lesson is read, learn, ask questions and then experiment.

Thanks everyone.
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