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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
salavat
37 posts
 
Sorry for jumping into the discussion, the main subject was never clear to me, even after reading many posts and detailed explanation on vinylengine article for example.
I have Fidelity Research AGT-5X SUT, which can accept loading of the carts from 3 to 10 ohms, with respective gain from 31 to 29 db. If I look at the carts produced at the time SUT was made, carts by FR, they all fall into 3 to 10 ohms load impedance (with 2 carts as exception), which would make a lot of sense to me - mfrg making SUT to fit their carts, why would they make incompatible SUT at all (I presume that they making SUT primarly for their carts, not just for the market).
Now I have Transfiguration Phoenix, which has impedance of 7 ohms, and requires loading higher than 7 ohms. That should almost perfect match between SUT and cart.
But I am reading not for the first time about 3X or 10X rule of thumb ratio between cart impedance and SUT loading, which makes me confused again.
My Phono stage is Audion Phono (which requires impedance of 47 kOhm which SUT has), volume of playing at the same level as say from CD, not different.

Can someone clarify?
axelwahl
788 posts
 
Hi Salavat,
your Phoenix has 0.4mV output, yes?
A 30 dB SUT has a 31.6:1 voltage ratio. Therefore 0.4mV*31.6 = 12.64mV output of SUT secondary to your phono-pre ---- and that will pretty surly OVERLOAD your phono-pre input stage, usually starting to overload already if the above calculation gets to ~ 8.5mV

So, before you want to work on the impedance side of things, the first thing is to make sure you will not get into OVERLOADING the phono-pre input --- all else comes next.
Mid spec for phono-pre input is actually 4.7mV. Check any MM/MI cart output and it will give you a pretty good idea what seems an acceptable range: 3mV - 6mV, so 12.6mV is too much by far.
Only if you consider SUT primary or secondary resistive loading will this value it come down somewhat, but not enough by far for the above example.

Greetings,
Axel
rccc
216 posts
 
After reading this post I swapped my 1:10 sut for 1:18 with my strad. This should make the output to hot for the phono stage, also it reduces the load to around 140 ohms. I hadnt been using this xfrmr (4722) because the math didnt work for this cartridge (I use this sut for my denon). Man was that wrong. This is my new preferred setup. There is no sign of overload with the several phonopres I tried it with and the sound is beautiful. I tried this set up very briefly when I first got the cartridge and didnt like it but at that time the cart was not broken in and it is a completely different cart now. This brings up another point for strad buyers or new owners. This cart takes a full 100+ hours to break in and changes dramatically during that process. If I hadnt discovered that earlier with several other CA carts I may have bailed on it early on but it is definitely worth waiting. CA suggests breaking it in with a 47k ohm load which only exacerbated its shrillness during the break in period. Its worth the wait, Im very happy now and thanks to Brent Ive discovered something new for it.
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.
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