Step Up Transformer Question

Yes, I posted a photo of the SUT I use above: Fidelity Research FRT-4

Zero Noise at any setting, or arm selection.

My friend had some hum, Steve at VAS diagnosed it, the Grado cartridge that came with the Vintage JVC Turntable was the cause. He said MANY Grado's Hum. My Grado Mono (using PASS thru the SUT does not hum here.

My friend changed to a different cartridge on a spare similar headshell, nothing else, hum gone.

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One of the advantages of a SUT with multiple tonearm inputs, is you do not change the output cable or which preamp's input, it sends any selected arm out to preamp or phono stage.

Something wrong with the numbers

0.2 mv into 10x transformer is only 2mv signal out, that's too low for some/many phono inputs. Would cause volume controls near max, perhaps the volume control/circuit is noisy when raised so much.

10x is only +20db.

do you mean SUT xFactor 10 combined with the MM Phono gain will be 70db?

If something is great, but it hums, it ain't great.

I have and had several SUT - and there is difference- not sure why -

I had an inexpensive Denon AU-300LC- that was thin sounding...

I use now an E.A.R MC 3 (there is a newer model MC4) which is great. Also a Dynavector SUP-200  which is still in a box but apparently also good. but I can attest firmly to the E.A.R. . the Phono is in a nu-vista Preamp with mm Phono.

Cartridge is MC Ortofon Kontrapunkt b

YMMV of course - but this is my experience

mdmoore, I advised against replacing a 12AX7 with a 12AU7 first and foremost because those two tubes are electrically very different from one another. Upon further thought, I do seem to recall that there is something out there where the manufacturer officially OKs such a tube swap. I can conceive of doing it if there is some sort of switch that changes the load resistor and other parameters, when the user makes such a drastic change in tube types. Is that so, in the case of your unit? Do I recall correctly that you have a Bellari? The second reason I reacted so negatively is that I and many other hobbyists do not much like the sound of a 12AU7, when it is used for gain, typically in a linestage. Using a 12AU7 in a phono gain stage seems impossible; you would get very little phono gain, nowhere near even the 40db typically associated with MM stages. So, to sum up, the 12AU7 would be current starved in a 12AX7 socket, would result in very inadequate gain even for an MM cartridge, and would sound bad even if changes were made to the circuit so the 12AU7 would run properly. Better candidates would be 5751 (check me on the numerical designation of this tube, which is a standard replacement for 12AX7 when users want slightly less gain), 12AT7 (which also would run better if the circuit for a 12AX7 was slightly modified), and those are your best bet. There are some others in the 12A?7 series, e.g., 12AY7 and 12AV7 that might work, especially 12AY7, but the circuit really ought to be re-worked for such swaps.

@rmdmoore When using a SUT there is a possibility Hum can occur.

One cause of this can be using a RCA Connection that does not have a good bite.

The most simple method to try to remove/ substantially reduce a Hum, is to move the SUT around in relation to the Phon' and TT. Typically a movement away from both will start to create a change to the level being heard.

As short Cables are recommended between SUT > Phon' the movement of the SUT with a short cable may not be enough to have an effective control.

It has been a very long time since I done this, but in the past have also had good success using a very small gauge earth wire to bridge across connectors on the SUT. From recollection the Bridging has been done in line and not across channels. 

As for Cable selection, for quite some time now I have been an advocate of a Cable using PC Triple C wire for the Signal Path. My recommendation for RCA Connectors are outlined in a earlier post.