Which SUT? .... for .3mv/10 ohms MC cartridge into 3mv MM input sensitivity

Please help me choose a SUT for my 1st MC cartridge.

Now I have more than enough volume using my existing MM cartridges thru my mx110z MM Phono input which says sensitivity 3mv/47k ohms impedance.

AT440ml is 3mv.
Shure 97xe is 4mv
Shure V15VxMR is 5mv
Grado ME+ Mono is 5mv.

coming tomorrow: AT33PTG/2 MC .3mv/10 ohm coil impedance/dc resistance


signal boost, am I getting it right?

1. Is 3mv a MINIMUM strength for the mx110z input?

2. .3mv x 10 = 3mv (+20db correct?) (minimum boost therefore x10/+20db)?

3, if correct, is .3 x 20 = 6mv equiv to +40db?

4. if so, a SUT providing +40db is more than enough for the .3mv and any likely future MC?

impedance/loading: I am not getting it.

I read about a general rule: coil impedance x 10 for ____?
A33PTG/2: 10 ohm coil x 10 = 100 ohm

too high impedance sounds thin? bright?
too low impedance sounds dull?

(how?) (minimum?) (where?)

Thanks as always, and this time I will definitely wait for advice before getting anything. I am not in a hurry for this, Bill will loan me one of his SUT’s until I get my own.


In a word, no.  Re-read Almarg's post.Also, you are making this much more difficult than it needs to be.Start with the turns ratio of the SUT, which is another way of stating the boost in voltage it provides.  A 1:10 SUT will boost voltage by 10X, in other words.  The reflected impedance afforded by that or any SUT will be equal to the value of the input resistance of the phono stage (47K in the case of nearly all MM stages) divided by the square of the turns ratio (10^2 = 100).  So, with a 1:10 SUT and a 47K resistor, your cartridge will "see" a 470 ohm nominal impedance.  Since we know your cartridge has a 10 ohm internal resistance, you will be fine with a 1:10 SUT.  The ratio 470/10 = 47, is way higher than the minimum goal of 10X.  There is no problem with having a ratio of these parameters that is >>10. With your cartridge, you can also use a 1:20 SUT; the same 47K ohm input resistor is then seen by the cartridge as 47K/400 = ~117 ohms, which is still more than 10X the internal resistance of your cartridge.
In your final paragraph, you seem to be asking what happens when you parallel 100K with 47K.  I don't know where you got that idea, but maybe someone else talked about REPLACING the 47K ohm input resistor with 100K ohm (not paralleling the two resistors; replacing one with the other).  This is a little trick that one can do if one wants to use a particular SUT with a turns ratio that is not compatible with the internal resistance of a cartridge that has a relatively high internal resistance (e.g., >30 ohms) but a low output voltage.  For example, do the math for using a 1:20 SUT with a cartridge having a 20-ohm internal resistance; you'd want to use a 100K ohm resistor on the phono input side to achieve the desired minimum ratio of cartridge output to phono input resistances. With your cartridge, you don't have to think about doing that.  You can use 1:10 or 1:20, and there is absolutely no reason to wish you could fine tune the turns ratio between those two choices.
I don't want to confuse you further, but the 10X rule is "soft".  You can even get away with ratios a bit lower than 10X but not much lower.  For now, think of it as a hard rule.
I wouldn’t worry about 6 mV signal after the SUT being "too high" - most decent MM stages will handle that perfectly fine, and personally I don’t like being in the reverse situation where I’m pushing my preamp volume control too high and still wanting more volume. And keep in mind you will often lose around 0.5 - 1 dB or so from the cartridge being loaded by the SUT - depending on its coil impedance and SUT ratio - so in the case of 20x and 10 ohms coils you lose 0.7 dB of signal from the loading, so that’s actually netting you about a 5.5 mV signal (down from 6 mV) anyways. 5.5 mV is pretty close to ideal for most MM stages.

Heck, my 0.3 Koetsu into a Sky 40 sound awesome on my VAC MM stage, and that’s netting over 10 mV of signal after the SUT! You certainly don’t want to overload the MM stage input, but good stages have lots of margin and will still sound good until you’re way off base.

I also wouldn’t worry too much about hitting a specific target loading number with a SUT. You definitely want to avoid loading the cartridge down too much, keep the load at least 6x - 10x the coil impedance. But beyond that, it’s mostly about choosing a ratio to the right output level. It’s not like active MC stages where you can get obsessed with finding the "perfect" load number. Once you get a good SUT match you will hear it and be happy! Recommendations from those who have your particular cartridge can be very valuable. But like I said before, the Bob’s Devices Sky have been great all-’rounders from what I’ve thrown at them.
impedance is what effects the sound
too low = dull. too high = too bright
As a general rule of thumb that is often true in the case of low output moving coil cartridges. But the effect is also dependent on the phono stage, and for that matter on the capacitance of the cable connecting the output of the SUT to the preamp. (The shorter that cable is and the lower its capacitance per unit length is the better, assuming accuracy is the goal).

.3mv cartridge x 21.5 = 6.45mv = TOO HIGH SIGNAL STRENGTH

Nope. See below.

.3mv x 10 is 3mv, TOO LOW? (mx100z phono sensitivity is 3mv)
.3mv x 20 is 6mv" TOO HIGH?


While sensitivity specs for power amplifiers can be useful, I suggest that you completely ignore such numbers in the case of preamps. All it means in the case of a preamp is what I described in my initial post, and pretty much all it is useful for is calculating the gains of the phono and line sections of the preamp (if they are not explicitly specified), as I did in that post.

A 20x (26 db) SUT will boost the rated output of the 0.3 mv cartridge to 6 mv, as you indicated. 6 mv is only about 1.6 db greater than the 5 mv ratings of two of your present MM cartridges. For a single-turn rotary volume control (as is provided on your MX110Z) a 1.6 db change in volume typically corresponds to around 10 degrees of rotation, and perhaps even less. So with the new cartridge and a 20x SUT you would simply be setting the volume control a tiny bit lower than the settings you presently use with those two cartridges, to achieve the same volume.  (This assumes that the specs are reasonably accurate, of course).

-- Al

AU-320 at 40 ohm position the step-up ratio: 1:10  and at 3 ohm position ( if I remember. ) : 1:33.

 When you have it you can try it both positions and decide which works better for you. I t think the 40 ohm position but......


Cartridge just delivered, ordered 2 days ago. Amazon Prime is a waste of a lot of fuel for single item deliveries, but nice when you want it quick.

I jerk myself around when learning new stuff, so thanks for all your patience. And I always imagine others learning like myself following along

certainly I like the features of the Denon AU-320, and you have all given me confidence,

not to mention, Bill will be bringing his Denon SUT, that's what I will hear for the first time.

Nice to know 6mv is not too high. Changing the volume is easy, using 11 o'clock with 5mv shure now.

I just found an Ortofon ST-7 (single input, no bypass) it's specs:
Frequency response: 15-45 kHz (+0 dB -2,5 dB)
Gain: 24 dB at 1 kHz
Recommended cartridge impedance: 2 Ω - 60 Ω
Recommended load: 47 kΩ // 200 pF

chart I found converted +24db to 15:81x
result then 4.75mv (before loss); 188 ohms

I like how many Denon's are for sale, not too costly.

Yes, Bob's Devices Sky looks awesome, I am hoping to keep the cost down

AT-650, I like the three options 3, 20, 40 and it has Pass, the 20 input gives an optional/potentially preferable sounding choice. (for this or future MC after I get hooked, the Pandemic never goes away, I keep wearing out cartridges!!!