2. analog
  3. 184437-182089

Which SUT to match Koetsu Rosewood Standard in my system?

Howdy everyone,

I’m about to move to to my first MC cartridge, and I’d be grateful for your advice in choosing a step-up transformer. First, here’s my current system:

  • Table: Thorens TD-124 (mk I, with a few upgrades from Hanze HiFi)
  • Arm: Ortofon TA-110
  • Cartridge: AT-540ML
  • Amp: Audio Note Soro Phono SE Signature
  • Phono stage: Built-in MC phono preamp in the Audio Note Soro
  • Speakers: Klipsch Forte IV
  • Interconnects: Ortofon 6NX-TSW-1010L (came with the tone arm)
  • Speaker cables: 14 gauge Audio Note bulk wire (planning to upgrade this at some point, but not until I finalize the analog front end)
  • Room: I live in a city townhouse, so my listening room isn’t huge—about 15 feet long by 12 feet wide. It has been sound treated a bit: absorption at the first reflection points, front corners, and on the ceiling slightly in front of the listening position, and diffusion + absorption along the back wall.

It seems to me that the clear mismatch now is the cartridge, and after auditioning several contenders, I’ve settled on the Koetsu Rosewood Standard. At least in my system and to me ears, it gives me the most of what I want: a rich, organic, natural sound. When I auditioned it, the dealer lent me an Audio Note AN-S8 SUT. A fantastic piece of gear, but well above my budget at this stage.

So I need some help choosing an SUT. Here are a few priorities:

  • Maximizing the natural, organic sound of the Koetsu and amplifier, which seems to balance so well with my speakers—retaining the dynamism and drive of high-efficiency horns while taming stridency that sometimes also comes along, especially in my relatively small space.
  • Favor emotional impact over technical accuracy: “good” distortion can be fine with me.
  • That said, minimize noise. I rent a city townhouse, so there’s old wiring that I can do only so much to fix, and a healthy bit of RF noise. My turntable, while about as quiet as an idler wheel can be, isn’t as quiet as the best designs of today. My amp is great, but also not silent. And at 99 db sensitivity, those horns pick up everything. So it’s important that the SUT be well shielded from RF noise and have an effective grounding scheme.
  • Favor an ideal match with cartridge, amp, speakers, etc. rather than future flexibility. I don’t mind swapping the SUT out for something else if I decide to change cartridges sometime in the future. I prefer optimizing it to what I have now, not what I might have
  • A 1:8 step up ratio, if possible. The cartridge is 0.4mv; the amp’s phono input is 3mv. 
  • Budget: $3k or less, ideally 

I really look forward to your thoughts. Please don’t hesitate to ask for any other info that might be helpful. Thank you!

zazu22

Showing 2 responses by elliottbnewcombjr

elliottbnewcombjr
5,139 posts
 

IMO: for that cartridge: you need a unit that has separate control of GAIN (x factor) and separate control of impedance shown to the amp's phono input.

.................................

Your intended Cartridge (KR) is 0.4mv signal strength; 5 ohm resistance.

1:8 gain ratio (x factor 8) is not right for that cartridge, it is too low for two reasons. 

Your Amp's phono specification: phono input sensitivity 3.0mv. Not Ideal, not preferred: That is the MINIMUM signal strength it needs IN to boost the signal up to line level. These amp's phono inputs also have MAXIMUM _____ mv, (before overload occurs) I cannot find what your amp's max phono signal strength  is. You can write the maker and ask. 

X factor directly effects the resulting IMPEDANCE SHOWN to your amp's phono input's impedance, (presumably 47k).

There is a 'guidance formula' for any cartridge's Impedance Shown: cartridge coil impedance x 10 (KR 5 ohms x 10 = 50 ohms). Thus guidance for IMPEDANCE SHOWN is 50 ohms, or a bit more. 

Impedance Shown Calculation: x-factor. x-factor squared. Divide phono input's impedance (presumably typical 47,000) by x-factor squared = impedance shown to phono input.

x factor 8 = x factor squared 64. 47,000 divided by 64 is: 734 ohms impedance shown to amps phono input. (over 14 times guidance of 50 ohms)

It is inverse: the higher the x factor, the lower the Impedance Shown.

x factor 16 = x factor squared 256. 47,000 divided by 256 is 183 ohms shown to the amp's phono input. (over 3 times guidance of 50 ohms)

Meanwhile, signal strength is getting higher, 0.4mv x 16 = 6.4, allow some loss, say 6.2 mv. More may be too high signal strength. i.e. KR 0.4mv x 20 x factor = 8.0. allow some loss, say 7.7 mv signal. Close to overload?.

IF you increase x factor, to lower impedance shown, the signal strength will be too high.

That is why this KR cartridge would be best with a unit with independent gain and independent impedance controls. 

Note: the other reason 1:8 x factor is not ideal: you want a phono signal strength that does NOT require a lot of gain from your preamp, BECAUSE, some (not all) preamps get noisy when you have to raise the gain control a lot. KR 0.4mv x 8 = 3.umv, allow some loss, say 3.0 mv. 

elliottbnewcombjr
5,139 posts
 

Hegel V10 is exactly the kind of unit I thought you would need: independent gain control and independent impedance control.

I have 3 tonearms, but if you have 1 arm and several cartridges, it is nice if they have similar output regarding the positioning of your volume control when you switch them

Me, I would go for anything in a range 1:12 1:14, no higher than 1:16

KR 0.4 x 12 = 4.8mv. That is close or higher than many MM cartridges: mine range from 3.2mv to 5.0mv

Several Grados are 5.0mv

All my Audio Technica’s are 4.0mv including your 540ml

My Shure’s: V15V is 3.2mv

97xe is 4.0mv

Ortofon range is 4.0 to 5.0 to 5.5mv

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