Cartridge options for current gain phonostages (47 Labs)

I know nothing about the Phono Cube, but what Chak says is interesting.  In voltage world, 75db gain ought to be more than enough for even the MC2000.  I can't imagine what cartridge needs 90db.
pcosta, What you say about the 75db vs the 90db versions of the Phono Cube is interesting and surprising to me, because one would think that MC cartridges with higher internal impedances would be those with higher voltage output, because higher impedance is associated with more turns of wire in the coil, which usually means higher output.  But since I know nothing about the Phono Cube, I'll take your word for it.

I've done a bit of studying on "current-driven" phono since you started this thread, Pani.  Do you or does Chakster know what is the input resistance/impedance of the Miyabi cartridge that makes it such a good candidate for current drive?  Cartridge output is also a factor.   According to one recommended criterion, the Ortofon MC2000 for example is not a great candidate for current drive despite its very low internal resistance of 2 ohms.  This is due to its very very low output of .05mV.  So, you'd want a cartridge with at least 0.2mV output and less than 10 ohms internal resistance. (There is a minimal recommended ratio between these two parameters, but I cannot recall the value.) These rules can be broken, but the result might not be optimal. The manufacturers like to say that the input resistance of their current drive phono is 0, but that cannot be true, I think, because in that case the signal would go directly to ground, thus "muting" the output.  The input resistance must be at least a few ohms above ground.  If I am wrong, I am interested to be corrected. Also,from what I can tell, current driven phono stages simply use (typically) a solid state gain device which can thrive with a very low input resistance as the first stage of amplification.  The output from that stage is then fed to a conventional RIAA circuit for filtering and further gain if needed.  It's not magic.  In fact, it's kind of an alternative to using a SUT or a conventional outboard active gain stage in lieu of a SUT, except for that exceeding low input resistance which therefore sees the cartridge as a current producing device.

Pani, The only criteria for performing with your phonocube or some other current-driven phono stage are internal resistance/impedance and inductance. Ideally also you want a cartridge with very low voltage output. But since all these parameters go hand in hand, it’s easy. I would stick with LOMCs that have a published internal resistance of less than 10 ohms; the lower, the better. I read elsewhere that, yes, the Transfiguration LOMCs ought to work (but I don't know offhand how they measure). Note that HOMC cartridges are not a good bet, by the same tokens.

I'd welcome the input of others with conventional phono stages, like all of mine, but my experience with mono, derived by paralleling the two stereo channels, is the opposite of yours in terms of the effect on apparent hf reproduction.  High frequency response always seems to improve, compared to playing the same (mono) LP in stereo.  This is when I use the mono switch on my preamplifier, and therefore the cartridge remains the same stereo type used in stereo.  Maybe there is some intrinsic difference for current vs voltage driven phono stages.  I have never quite understood, anyway, the difference between current vs voltage drive in phono, because when you use a very low value load resistor, as is typical for LOMC cartridges, in effect you have enhanced the proportion by which the stage is driven with current.  However, if there is zero load resistance with your current-drive phono stage, that condition usually cannot be achieved with conventional stages.

I can't get my mind around the idea of hooking up the two channels in series for mono output.  I don't doubt that it works, but I am not sure I understand why.  Also, if you wire in series, is it not the case that internal resistance/impedance doubles (as you already noted) but also the output current remains the same?  (I am thinking of Kirchoff's Law.)

What is your impression of the effect on mono performance, if you've tried it both ways (series vs parallel) with the same stereo cartridge?

"My Sonic Labs Eminent, the Air Tight PC series, and, especially, the super-low-inductance Haniwa HCTR01 work extremely well with current amplification type phono preamplifiers." I found this statement online in a review of another phono stage that works by current amplification. Sadly, these are all in the category of "expensive". Other cartridges with very low inductance and very low internal resistance also will tend to be expensive. LOMCs with the lowest voltage output also tend to be those with the lowest internal impedance/inductance, because very low output is synonymous, in the case of an MC, with having a very low number of turns of wire in the coils, which leads to low resistance and low output. The good thing, in your case, is that low output (in terms of voltage) is irrelevant; your phono stage can handle it. You only have to worry about cost.

PS: The reviewer in the article cited above also mentioned the Ortofon Quintet Black.  I think that one is about $1000 or near to it.  I once spoke to the Haniwa designer at a show; he was adamant about the virtues of current amplification and that is what drove his design.  Ortofon MC2000 should work well too, if you can find a decent used one.

HDM, It seems to me that paralleling the two stereo channels of your Denon to produce mono would result in halving of its internal resistance/impedance, not doubling.