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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
128x128flyfish2002
jafox
1,452 posts
 
Flyfish, I am going to stay clear of all the technical discussion here. As valuable as it can be, the bottom line is how it all sounds to you.

I have been running with a Clearaudio Accurate for several years now. With this previously straight into an Aesthetix Io phono stage, I ultimately found the "best" load to be between the 500 and 1kohm jumpers. When I changed to the Aria WV preamp with Sowter SUTs, the 200, 300 and 500 ohm jumpers were so close that any of these would have been fine. Running without any of these defaults the input to 1k and this was just a touch too "hot". And now with the cartridge running into a rebuilt Counterpoint SA-2, I have found that a 500 ohm resistor in the load terminals is a great balance. So your drop way down to 700 ohms is close to my own experience here.

John
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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
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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
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almarg
9,670 posts
 
Outstanding, Brent! Thanks for the well written update.

Regards,
-- Al
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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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