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Specific SUT with unusual case scenario question from a LOMC N00b

I tried posting this over at Steve Hoffman forums and got crickets so I am trying my luck here as well as I am also new to this forum for posting although i have been reading off of it for years so nice to finally meet you all and I would like to thank you for your time as my question is kind of specific and a bit numbers nerdy beyond my physics calculation capabilities so I am hoping I can get some expert opinions here. To ask this question I have to give the details on my system setup and the vinyl wing of it is a new addition I am putting together but haven’t yet been able to assemble because the salamander designs AV furniture it will be sitting on in my living room is on backorder which is kind of an exercise in patience I hadn’t planned on… leading me to obsess over ideas and post on forums like this one in the meantime while I wait.

So my system has to do double duty as home theater and audiophile listening meaning some of my choices had to blend the two along with the WAF since it is in my living room but here’s the phono path in it’s entirety as it stands:

Hana Umami Red LOMC Cart (with wallytools custom brass mounting shim) —>
Bergmann Magne turntable / tonearm —>
Morrow Audio series 5 DIN to RCA phono interconnect cable —>
PrimaLuna EVO 100 tube phono preamp (with upgraded tubes) —>
Morrow Audio series 5 RCA interconnect —>
Marantz AV10 preamp/processor —>
XLR balanced output —>
Emotiva XPA HC-1 Monoblock SS Amps —>
DIY assembled 10 awg speaker wire —>
Martin Logan hybrid electostat speakers paired with a Deep Sea Sound Mariana 18” subwoofer

So the primaluna phono preamp has all tubes including the gain boost for the MC cart before it enters the signal pathway like a MM cart would through the rest of the tubes. It has 3 selectable gain settings for the MC mode but it’s right at the limit for my Hana Umami Red. I haven’t heard this combo yet due to the furniture backorder snafu but from what I have read online others that have paired that cart and phonostage seem overall satisfied. I upgraded all the tubes in the phonostage including the quietest I could get from Uncle Kevin at Upscale Audio for the MC gain tube complement.

So with all that in mind, here is my question:

If i want to retain the upgraded MC tubes in my signal pathway but minimize (if even possible) how much gain i need to apply with that to keep the noise to a minimum, is there any role for a small SUT boost between my turntable and the phonostage but into the MC (not the MM as would be more typical) signal pathway? My rationale is that a small boost from a SUT might allow me to continue to use these tubes in the pathway but minimize the gain i have to apply with them and possibly keep noise down while expanding the soundstage. I was thinking something like the Bob’s Devices Sky 10 SUT might be suitable for this if it is possible. But maybe I have no idea what I’m talking about here and that won’t work at all which is why I’m asking.

Any thoughts from those more experienced with SUTs and that know how to crunch the numbers applicable to my setup would be much appreciated. If exactly which tubes I got matters I could list them but i was thinking that’s probably unnecessary detail for this calculation but again maybe I know nothing (John Snow). Any thoughts on this or recommended SUTs that would work in that (apparently) uncommon usage scenario? I couldn’t find much info about if you can (carefully) feed a SUT into the MC pathway if you want to retain those tubes in the path in an all tube phonostage.

I know that was rather long-winded so again I appreciate anyone taking the time to read all of that.

Cheers & Thank you!
 
 
xceilidhx
mulveling's avatar
mulveling
2,154 posts
 

You're welcome @xceilidhx !

Sorry about your wait on the Salamander rack. Man that's frustrating! Really nice cart you've got waiting, for when that all comes together. 

flash56
31 posts
 

I am a huge fan of SUTs. I agree with mulveling's first suggestion. Forget about using the PL100's MC stage. Go through an SUT into the MM section. I know that you spent a bunch of money upgrading the MC tubes and don't want them to go to waste. However, I find that the simpler that you can keep the signal path, for the most part, is for the better. The MC tubes may give it color, but they will also add noise. Also, you are entering a problematic area trying to interface an SUT with the MC input. I would be very worried about loading down your cartridge and dropping your input voltage right out of the gate. The MM stage will have the standard 47KΩ input impedance. With a simple SUT. Which I also believe in. The reflective impedance that your cartridge will see is calculated by taking the output impedance of the secondary and dividing that by the square of the winding ratio. So for a simple example. A 1:10 SUT into a 47KΩ load will be 47,000/100 = 470Ω. That is the highest reflective input impedance that you can achieve. However, you can lower that value by putting a resistor across the secondary in parallel with the 47K. It is possible to load the primary input, however that makes things much more complicated. You will cause ringing in your output waveform, unless you design it correctly to stop that from happening. And I fail to see the point of having a fixed input impedance, with all of the issues that that implies, when you can achieve the same result by adding a resistor across the secondary in parallel with the 47KΩ impedance of the MM input. With no complications what-so-ever. If your cartridge requires a higher impedance load than 470Ω. You must reduce the winding ratio. Thus sacrificing gain. But the specs of your cartridge give you a lot of range. I doubt that you will need more than 470Ω. More than likely less.

If you are interested in experimenting with using a SUT. I would bypass the active MC tube section altogether. That is basically what a SUT is for. It is a passive gain device that gives a cleaner simpler signal path. That is why they are used. I find them to be much quieter, and they give a much more open sound to the music. People will tell you that they are difficult because they are prone to EMF humming and must be placed in the right spot. I haven't found that to be much of an issue. However, the interconnects between the SUT and the MM inputs should be a low capacitance cable as short as is reasonable for your situation. Because the MM input is very sensitive to capacitance. I would go with that experiment. If you find that you prefer the active tube step up. You can always use that. But trying to interface the two, is problematic at best. And probably will not give you what you are looking for. There is a company that will custom make you whatever SUT fits your needs for a very reasonable price. Even cheaper if you are willing to assemble it yourself. They use Lundahl transformers. Check them out. https://www.erhard-audio.com They came highly recommended by Peter Lederman of Soundsmith cartridges. I believe mine cost me under $400 assembled. And it sounds great! It is a simple task to swap out resistors to fine tune the loading of your cartridge. I will never go back to active MC step ups. Even if they are tubes. I am using a SUT into an Icon MM tube phono pre, into a PrimaLuna EVO 300 integrated and I love the synergy. I am sure that the MM section of the PL100 will give you all of the tube sound that you are looking for. I believe that it also uses a tube rectifier. An SUT will give you a nice quiet open soundstage that I think that you may appreciate. And you can always use the MC stage in the PL100 if you find that you prefer that.

lewm
13,519 posts
 

I would suggest you try to listen without any SUT if your phono stage permits, before committing to a SUT. Too many of these discussions begin and end with the supposition that a SUT per se is beneficial to sonics. From what I read here, there is the idea that one ought to "bend over backwards" to figure out how to insert a SUT, and in this thread, there is also the idea that a higher turns ratio may be preferable to a lower turns ratio (in this case, 1:20 vs 1:10). I think you have to take it on a case by case basis. Some/many high gain phono stages are a better choice than using a SUT; some are not.  If a SUT is the choice, then the lowest workable turns ratio ought to be preferred, at least to start.

bubba12's avatar
bubba12
462 posts
 

It seems like the easier solution is getting a cartridge that matches the phono stage better OR a phono stage that matches the cartridge better. The gain on the PL is the reason I stayed away from  it. I love PL but it should play nice with just about every cartridge at that price point. 

xceilidhx's avatar
xceilidhx OP
6 posts
 

Thanks again all for this truly priceless advice and your time and effort in replying.  It is helpful to hear from fellow listeners with experience as I dive back into high end analog so i don’t just waste my time and money on components that won’t give me what I am looking for.  Of note, it looks like Bob’s actually recently did release the 30-S so if i did go that route and wanted to buy from him i would have the 1:15 option now that may be more of a sweet spot for my cart but of course in the end there is a subjective listening aspect fudge factor that is hard to anticipate ahead of time before purchase.  

Also, thanks for the link to the Lundahls. I’ll check them out as well.

Cheers!

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