Dedicated phono-pre for MM only?

Axel, perhaps one reason you don't have "hum" is that the noise that might result from Kirkus' theorem would not necessarily be in the spectrum that we recognize as hum (60Hz or 120Hz, in the US; 50Hz or 100Hz in Germany). The noise he is talking about could be random in frequency (I think) and might not be audible as noise until one took steps to eliminate it and listened for the difference.

Lewm,
yes, I think this could be right.
It again would explain that even some well noted/quoted phono-stage designer(s) like SE.
There was Lamm's Vladimir Shushurin? that stated his clear and decided preference for SE -- but I think he then uses a trannie to change the output to balanced.
His main argument also was 'noise' and could well be what you just mentioned.

The new PassLabs-X15 seem very well regarded (best ever, etc.) would be most interesting to know what circuit it uses.

Axel

Hi Kirkus,
during an earlier part of the MM, balanced vs unbalanced and common-mode rejection posting the SUT subject came up shortly.

It may not fully relate to this thread, but let me try.

You mentioned in your example a 50 ohm SUT input impedance with a 5 ohm DCR MC cart. Explaining some advantages with regard to hum rejection, and how this of course can not be realised in an MM specific phono-pre (as a trannie cannot be used etc.)

Would you share your explanation, why with the use of an SUT (in my listening) some other parameters then hum are notably changed/improved i.e.

- more dynamic depth (better hi/low SPL differentiation)
- more powerful bass
- more hall/room information, stage depth

I could add some more, but it should do for this example.

Cart parameters:
3 ohm DCR
0.3mV output @ 5cm/sec

SUT parameters:
1:31.6 ratio (30dB, i.e. natural impedance 47ohm with 47k)
- primary DCR 1.5 ohm
- secondary DCR ~ 65 ohm (as I recall)
- primary loading 13 ohm (paral. with 47 ohm nat. imp.) i.e. 10 ohm that the cart sees.

If nothing else, it could high-light how very different a MC stage might just be as compared to an MM stage. So we'd be back at the subject, of sorts.

Many thanks,
Axel

Hi Axel . . . well, the first question is understanding as much as possible all of the different factors that change between your comparisons with/without the SUT. I'm speculating that some of them are:

-Cartridge loading is slightly different, i.e. more inductive with the transformer
-SUT presents a different source impedance to the phono stage than the cartridge directly
-Phono stage loading switches/plugs/resistors/caps are different
-Phono stage gain is different, likely affecting noise, bandwidth, and distorion
-Of course, the SUT itself has a sonic/performance signature

And some of the likely causes of what you observe:

- more dynamic depth (better hi/low SPL differentiation)

I think this usually corresponds to better headroom, and lower noise floor. The SUT will most likely gives a better En/In match to the cartridge, and better RFI rejection. The phono stage may also have more headroom at the lower gain.

- more powerful bass

Cartridge loading differences, possibly a little bit of low-frequency 3rd-harmonic distortion from the transformer

- more hall/room information, stage depth

I associate this with more high-frequency extension, or different high-frequency phase response. Cartridge loading differences, the transformer's sonic signiture, or better phono-stage performance at the lower gain

Anyway hope this helps a bit, without re-opening the whole SUT/non-SUT debate.

Hi Kirkus,
thank you.
??? >>> ...without re-opening the whole SUT/non-SUT debate. <<<

Not aware of that debate. Is there a thread I can look up you'd recall?

At least as far as MMs are concerned: THERE IS NOT DEBATE ABOUT SUTs :-)
Axel