Step Up Transformer Question

One other way from recollection used by myself as a method to discover what might be contributing to producing Hum, is to put a finger on the Metal of the Input RCA. Use the Spare Finger to touch the other Metal Parts, other RCA's, SUT Chassis, SUT Covers is external mounted, Phon' Chassis, Pre RCA's and any visible screw heads on any device local to the finger in contact with the RCA. 

If one of the contacts being made substantially reduces Hum and it is in-line, a small gauge wire used as a earth bridge might make the Hum inaudible at listening levels with a ear about a metre from a speaker. 

I have a single wire removed from a Telephone Extension Cable used as a Earth Bridge, a friend soes very similar, but also has pure copper crocodile clips attached to make an improved contact that a loose wrap.  

Ralph from Atma-Sphere also mentioned, as did Roger, that a lower ratio will be less prone to noise. I'm waiting on some new cables to come next week to see if I can eliminate some of the hum I'm getting with the Bellari. As you said, might need to try different grounding schemes. I feel like that's a whole other thread, lol

@rmdmoore  I enthusiastically disagree with this part. With a SUT, it's a given that you absolutely have to get the grounding and cable shielding right - whatever the ratio. Once you do, hum noise will disappear and the only noise you should be hearing is a "hisssssss" or "shhhhhh" noise from the active RIAA stage of your phono (the noise part of its signal-to-noise spec). Using a higher ratio SUT allows you to lower preamp volume while attaining the same signal SPL, which pushes this noise DOWN. It's not so much a matter of total gain (yes everyone agrees 70dB is high), as it is about optimizing the *structure* of that gain. The actual signal levels hitting each part of your analog chain up to the preamp volume control - this is what matters!

Of course it's a balancing act - if you push SUT ratio too high you risk loading the cartridge too heavily (which will cause loss of signal), overloading your RIAA stage (bad distortion), and of course the SUT itself will distort more at higher ratios (all else being equal). Higher quality SUTs will distort less at the same ratio. A good rule of thumb, for most MC cartridges (coils wound on iron), is to choose a SUT so that your "calculated" signal coming out of it is ideally 5mV (this is what hits your MM / RIAA stage). But anywhere in the range of 3.5mV - 7.5mV is usually considered good (I listen loud and like to ride on the high side of that, personally). So your 0.2mV Windfeld into a 10X SUT is only 2mV. That sucks, IMO. I can't believe people are recommending that lol. A 20X would give you 4mV and a 30X would be 6mV. I'd choose the 30X there, but either would work great. 

If your 2nd wood cartridge is also 0.2mV that would be great, and the same SUT would likely be optimal for both. But that's also why many SUTs come with 2 or 3 taps. The Sky 30/15 for example, would work great with a 0.2mV cart at 30X and a 0.4mV at 15X.

@mulveling it's funny, that's what I was initially thinking. I messaged Ned Clayton about an SUT that would have some adjustability so I can play with different gan ratios and then I can adjust my tubes in my phono pre accordingly. I'll probably end up doing that. 

dogberry

thanks, i'll check them periodically

@mulveling Your dislike of Lundahls is interesting. I only have experience with the 1931 Ag, and it sounds pretty good when stepping up my Koetsu.. Not quite as clean or warm as my differential amplifier stage, but close.

Now that I'm using a Grado as my primary stereo cartridge, it's a moot point.