Dedicated phono-pre for MM only?

Hi Tom
you say:
>>> it may necessitate a range of dedicated MC phono stages if someone wants to listen to a variety of LOMC cartridges <<<
I can not support that logic as e.g.: all women are people, there for all people are women? :-)

Loading with MC stages and to some smaller degree loading of SUTs (secondary and primary side) takes care of the variations in MC's DCR and output voltage. Of course a mismatched SUT/cart can not be made to work by loading e.g. if it would overload the phono-stage.

Greetings,
Axel

Kirkus

Thanks for that, I will have a more careful look at the design calculations for my MM only phono amp. The input stage is currently using 2SK389BL as diff amps with simple resistive loads (balanced inputs, there's no need for a feedback connection to the diffamp 'cos there isn't any feedback).

It will be easy enough to change these to cascode.

Mark Kelly

Axel and Tom, if you can change load resistors, I see no reason to lust for a separate MC phono section for each cartridge. The LOMCs are not identical to each other, but they are similar enough. Anyway, IF one needed a different circuit for every different LOMC, that is where I would draw the line. I would not ever do that.

Mark, If I understood Kirkus correctly, he maintains that a balanced input is not optimal for an MM cartridge, which was news to me. The Aqvox preamp makers make a similar claim; their product is balanced for MC cartridges and SE for MM cartridges, because the latter are "voltage generators", in their parlance. Yes, MM cartridges are voltage generators as compared to LOMCs, but why does that negate the positive attributes of a balanced input? (Apparently you chose a balanced input for your MM phono stage, for example.)

Hi, Axel and Lewm. My comment on the need for separate MC phono stages is based on Axel's comment that a SUT degrades the signal, thus my assumption that a dedicated phono preamp (for a specific range of LOMC parameters) would be a better way to handle the amplification and loading requirements. One gain/loading setting probably isn't the best way to handle a wide range of LOMC cartridges, not if optimal performance is desired. And if switches must be used to optimize the LOMC signal, it is not acceptable for a high end preamp, which was the premise of this thread. So, it appears that if the logic is used that a dedicated MM stage is needed (to avoid having additional switching for MC cartridge requirements) then dedicated LOMC stages are needed to avoid having additional switching.

I bring this up because it seems that what is implied, Axel, is that MM is inherently a better cartridge because it doesn't require additional switching or transformers. But a dedicated LOMC phono stage would eliminate the need for switching or a transformers as well. Wouldn't that put a MC cartridge on par with a MM cartridge?

Tom

Tom,
I guess 'switching' means loading in your context, yes?

Loading an MC with 100, 500, 1k ohm for example makes little difference as to the phono-pre used as such.
The mechanical issues involved will.
Soldered Rs are best, than clamped in some binding posts, then the 'mouse-piano' i.e. the switching you seem to refer to.
The same would apply (to the phono-pre) using 47k, 50k, 75k or 100k phono-pre input impedance 'switching/changing' for MMs only.

The issue with MCs is rather to have a phono-pre that "can count electrons" (if no SUT is used).
Apparently only few designs are THAT good after all. Mostly noticeable in the difference of those parameters I mentioned that are improved, when an SUT is used with a Low MC.
Often a lack of dynamics is noted if an MCs output is on the low side - use an SUT, and THAT problem is GONE.

When using an MM there are different things at work.
Mainly due to the 'high' cart voltage output --- BUT also because they are a more 'reactive' load, usually 600 - 3.5 ohm DCR, 700mH as ~ 20uH with an MC and compared to only ~ 2 - 6 ohm with LOMCs).

That is why a TOP MM stage would ask for a different design if strictly dedicated to MMs.
No SUT can be used, single ended (SE) MIGHT be better. I'm as little sure about this as Lewm is and it might have to do with the 3-6dB lesser noise in SE design --- which then again might just be made worse by using common ground that can be noisy.
Also 'floating RIAA' as in a differential circuit between +/- is not an option either.

Greetings,
Axel