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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!
 
 
128x128xceilidhx
18 responses Add your response
tablejockey
3,978 posts
 

Whew! Post is a little run on...

Try the Red into the PL. It’s not going to hurt anythingng.

I use the same model with a .4mv into a tube integrated

On paper, a little low, suggesting I may be loosing out on full potential dynamics. In my setup and my ears, no need to bump volume. I hear nuances of familiar cuts. Maybe the cart/PL specs isn’t exact, who knows/cares-whatever.

Linestage typically add 10+ dB gain, so you’re at 70dbs or so. I don't know what/if the Marantz adds?

Are you aware there is a FREE Upscale mod for the PL?

I haven’t bothered with it. Inquire and they’ll give details.

mulveling's avatar
mulveling
2,096 posts
 

The Hana into PL’s 60dB MC mode might sound good...but yeah, it’s probably going to be a bit nosier than alternatives, and you might also prefer to have a bit more gain on tap.

If you’re wanting to try the SUT way (which I personally love), you might as well go all-in and use the PL’s MM mode (40dB, 47kOhm input) with a ~ 15x SUT (e.g. Bob’s Sky 30x / 15x - I have one, it’s great). A 20x would also work, a little on the "hot" side for overload, but should yield lowest noise floor. Forget about trying to tap into the premium MC tubes. That’s what I’d do.

However, let’s say you want to mix a low ratio SUT with PL’s 52dB mode. Yes, a 5x SUT (e.g. the Sky 10x / 5x - I have one of these too) is most appropriate, because 2.0 mV (0.4 mV * 5) hitting 52dB gain is just about perfect. The problem, however, is PrimaLuna’s highest 1000 ohm load setting in MC mode. This nets you ((1000 / 5) / 5) = 40 ohms load. The Hana has 6 ohms coils and recommends a load of greater than 60 ohms. A 40 ohm load will certainly work, but it’s edging into marginal territory. This would work a lot better if the PL had a 2000 ohm load option for MC.

You could sort of try both with the 10x / 5x, though 10x might be a *little* low to observe full benefit of the SUT - or it could work great! I'd just go for the 15x / 30x, though. Then if you get a lower output MC later (e.g. 0.2mV), you'll be set :) 

xceilidhx's avatar
xceilidhx OP
6 posts
 

You guys rock. Thanks so much for the thoughtful replies. Much food for thought and extremely helpful.

So if you have a 40 ohm load for for a 60+ rated cart, what is the (theoretical or actual) sonic impact of that being on the low side, AKA marginal territory? Forgive my ignorance. Just not sure what the downside of that is in practice.

The included math is very much appreciated.

 

And the Marantz is adding nothing because i'm passing though it with a regular line input on pure audio mode so it shuts off everything else that could interfere inside the pre/pro and I'm not using the Marantz phono input.  So the PrimaLuna is currently doing all the work +/- SUT which I'm trying to consider how to integrate. 

 

Cheers

 

mulveling's avatar
mulveling
2,096 posts
 

So if you have a 40 ohm load for for a 60+ rated cart, what is the (theoretical or actual) sonic impact of that being on the low side, AKA marginal territory? Forgive my ignorance. Just not sure what the downside of that is in practice.

@xceilidhx  As you plunge into lower load impedances, proportionally more of the cartridge signal "burns up" in resistance before hitting the phono stage. Hence, you lose some amount of signal. This setup is essentially a voltage divider, with the coil’s DC ohms on one side, and the phono stage load impedance on the other. To preserve signal, you need "a lot" more of the total resistance, proportionally, on the phono stage side.

Of course, this is just a simplification, because with AC signals (music) the cartridge might not measure at a constant impedance across all frequencies (20Hz - 20kHz). And in THAT case, the impedance curve could start to influence and change the resulting frequency response, again increasingly as your load impedance gets lower.

But anyways, taking the "simplified" approach, you can calculate losses in dB:

6 ohm coils (DC) into 40 ohms gives us a voltage divider such that (40 / (40 + 6)) * 100% = 86.9% of the original signal voltage is preserved.

Then you have to remember logarithms to convert this to dB:

20 * log(86.9 / 100) = -1.21 dB

So we’ve lost 1.2 decibels of signal from the voltage divider. Now if we had a 100 ohms load:

(100 / (100 + 6)) * 100% = 94.3%

20 * log(0.943) = -0.51

We lose half a dB into 100 ohms. So relatively, it’s about 0.7dB louder than into a 40 ohms load. From THAT perspective, it’s not "that bad". But the 40ohm load could come with a little bit of FR aberration, and that extra 0.7dB is also penalty to the signal/noise ratio.

In practice, I’ve found that a load impedance ~ 6x the coil ohms is the practical "lower limit" before things go to pot. So again, from that perspective - 6 ohms * 6 = 36 ohms, and 40 ohms would be (just) above that.

Subjectively, sonically - lower impedances generally make for a softer wamer sound, and higher load impedances are sharper / faster / brighter sound. If you go too far in either direction, you’ll know it. For me, this has been very dependant on the phono stage in question. For the same cartridge, I’ve preferred 50 ohms on one stage and 200 ohms on another (though in MOST cases, 50 - 100 ohms was best for that example). SUTs are another matter, and generally I find that you need to focus on picking the right ratio for your cartridge’s output level, use a 47kOhm load, and FORGET about the net load impedance - with SUT’s it only comes into play for cartridges that aren’t a good match to SUT’s anyways (high coil ohms versus outout level). Your Hana Red is electrically a good mach for SUTs in the 10x - 20x range. Not too far off the Air Tight PC-7 which I love, and was also made by the same maker (Excel Sound) :)

xceilidhx's avatar
xceilidhx OP
6 posts
 

Wow.  Thanks for taking the time to type that all out.  You just summarized a lot of cart physics in a way I can actually grasp.  Bravo.  You may have just achieved the impossible :)  And I appreciate the specific recommendations for my kit because going back to practical application, now I have some real food for thought and numbers I can use to compare products depending on how I want to try and tweak this to get a little less noise and a little more dynamics / soundstage.   

 

Cheers again. 

xceilidhx's avatar
xceilidhx OP
6 posts
 

@mulveling : What do you think about pairing my kit with Bob’s Sky 20-S? There is no 30-S at this time as far as I know but the 10 and 20 ratio SUT is also pretty much in the range you are recommending (rather than 15 and 30) and offers improved quality (in theory). Just wondering if you have an opinion.

 

Cheers

mulveling's avatar
mulveling
2,096 posts
 

What do you think about pairing my kit with Bob’s Sky 20-S? There is no 30-S at this time as far as I know but the 10 and 20 ratio SUT is also pretty much in the range you are recommending (rather than 15 and 30) and offers improved quality (in theory). Just wondering if you have an opinion.

I think that's fine. 20x * 0.4mV = 8mV into MM is a little in the high side, but I've personally used that level and liked it a lot. It's really good for minimizing a tube phono stage's noise floor. You also get the 10x, which could also work great here (4.0 mV into MM), and you can simply choose which you like better. A 10x / 20x SUT is really handy to cover a very wide range of low-to-medium output MC cartridges. Seems like a great choice to me. The Sky SUTs have a warm, meaty, bold sound that pairs well to most systems and gives a very nice counterpoint to the (sometimes) relatively lean-sounding active MC gain stages! I haven't heard the improved "S" versions yet, but I've owned a few of the regular Skys and the older 1131 - all great.

billstevenson
462 posts
 

FWIW, Bob recently explained comparing my Sky 10, which I described as having a warm sound, that the improved "S" versions are more neutral.  I am tempted to order one out of curiosity, although I need another SUT like another hole in my head.  As usual mulveling, you did a great job breaking this down for the OP. 

xceilidhx's avatar
xceilidhx OP
6 posts
 

Indeed.  And thank you for chiming in as well.  I really appreciate the time you all took to respond.  

mulveling's avatar
mulveling
2,096 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
22 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
13,421 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
457 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!

lewm
13,421 posts
 

Priceless advice is worth what you pay for it.

xceilidhx's avatar
xceilidhx OP
6 posts
 

Ah... but sometimes you get more than you bargained for :)

tablejockey
3,978 posts
 

The Google AI response:

"For a .4mV output moving coil (MC) cartridge, you'll typically need a phono stage with around 60-62dB of gain. "

As mentioned, I use the same PL unit as the OP and use a .4mv cart. 

The OP should demo something and compare straight thru(no step up) and let the ears decide. 

Audio end results are always YMMV.

 

 

 

 

audioguy85's avatar
audioguy85
2,028 posts
 

I’ve had a Jensen SUT for several years now, used with my Hana and denon 103. Sounds great to me. Made in USA.

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