Einstein The Perfect Match phono pre and My Sonic Labs cartridge
My Sonic Lab's Cart's are quite an attractive Cart' to be under consideration. Learning about matching one of the MSL models to the available ancillary equipment is a worthwhile pursuit. Recent info made known on the 'Gon', and the 'Elephant in the Room', has also shown that when purchasing the Brands Cart's through a US Importer Service, learning the After Sales Support on offer from the service, will also be a very worthwhile pursuit. |
@lewm I’m just curious how that works - doesn’t a "transimpedance" stage’s effective gain rise as the source’s (cartridge coils) DC resistance lowers? So for an MSL with super low < 1 ohm coils and high 0.3 - 0.5mV output (usually typical of 5 - 15 ohm coils), does that not risk overload somewhere? If not that sort of sounds like a magic gain generator 😅 Besides the "magic" core material MSL markets, isn’t the secret of their low impedance simply using a larger gauge coil wire (meaning more mass for same # of turns)? I’ve been playing with a fairly new Frog Gold and MSL Eminent Ex in my office rig. Strangely, the Frog loves my EAR MC-4 SUT and hates the JFET MC stage (active voltage amplification) of Herron VTPH-2A or Hagerman Trumpet Reference. The MSL is exactly the opposite, preferring JFET MC. Despite the Frog listing 0.85mV output and MSL 0.4mV, they have the same perceived output levels. When either cartridge doesn’t get its "preferred" MC stage, its soundstage shrinks; furthermore the MSL becomes dull and boring while the Frog gets a piercing harsh treble. On their preferred MC, both are wonderful. |
Yes, that was my concern, that I might overload the circuit somehow with that low of an impedance. I was surprised that I didn't have to put it on hi gain for my Transfiguration Phoenix, but now I think I understand why.
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I think it is a dangerous game for amateurs like us (me included) to toss around these terms. First of all, "gain" is a term associated with an increase in the voltage component of an audio signal. The decibel (db) is defined by a certain amount of change (up or down) of voltage, not current. For a cartridge, an approximation of its current output can be arrived at by dividing its signal voltage output by its internal resistance, which is just Ohm’s Law. The MSL with a 0.3mV output and its internal R of 0.6 ohms would then have a current output of about 500 microamperes, at the standard stylus velocity. You can use that number to compare it to other LOMC cartridges in terms of how the cartridge might drive a current mode phono stage. (I don’t use the term "transimpedance" as it suggests impedance is not a consideration at all, but I think it IS a consideration.) I have done this for a few cartridges, and the MSL would rank among those that make "a lot" of current. For another example, my Ortofon MC2000 has an output of 0.05mV with an internal Z of 2 ohms. That suggests the current output is 25 microamperes. Then you look at the particular current drive phono stage; they all have a finite input impedance greater than zero, where zero is the theoretical desired impedance for pure current drive. Fact is, the actual input impedance of various current driven phono stages seems to range from 2-3 ohms to as much as 20 ohms, where the data are even available. Most makers hide that information. This finite input impedance causes a very specific interaction of each LOMC with each of the many different current driven phono stages. In the case of the MSL driving the Einstein, I cannot find for sure the input impedance of the Einstein, but there is one spec on their website that suggests it might be 12 ohms. In that case, the MSL is going to be driving the Einstein as if in voltage mode, because the input impedance of the phono stage (12 ohms) is way more than 10X the output impedance of the cartridge (0.6 ohms). I have done such a thing with my MC2000; I have an outboard current drive gain stage (gain only; it does not do RIAA) that has a high-ish input Z similar to the Einstein, and the ratio of its input Z to the output Z of the MC2000 looks more like voltage drive than current drive. It works great in conjunction with connecting it to the MM input of a phono stage. I also use the MC2000 with a BMC MCCI current drive phono (2-3 ohms input Z); that works fine too, once I set the gain in the MCCI to +11db. What’s going on in these current drive phono stages, I think, is the input stage senses current or voltage depending upon impedance matching and immediately converts it to voltage. After the input stage, it’s all in voltage mode, including RIAA correction. At its output, I think the MCCI has an additional voltage mode gain stage that can either be bypassed ("0db" setting) or set to add various amounts of voltage gain (+7db, +11db, or +14db). The net result is I think every combo of LOMC cartridge and current gain phono will have a unique sound. |
@lewm, thank you for this excellent, informative post on a topic that’s been murky to me. |
+1 thanks @lewm very interesting! |
