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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
tablejockey
3,979 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
2,107 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
2,107 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. 

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