Cartridge Loading.....Part II

I have two complete systems in two different listening areas in my house. The Steelhead runs a system in my basement based on Beveridge 2SW speakers driven by Beveridge direct-drive amplifiers. The Beveridge outboard woofer system is long gone; I use a pair of Transmission Line cabinets employing KEF B139 woofers for frequencies below 80Hz. That system is single-ended all the way, as is the Steelhead. My upstairs system consists of Sound Lab 845PX speakers with modified crossovers driven by Atma-sphere amplifiers. The preamp is either an Atma MP1 or the 3160 Phonolinepreamp that was conceived and designed by Raul and his engineer friend. The entire system is all balanced from cartridge to speakers. The BMC was made for balanced operation, so I felt constrained to test it in the balanced system. To do that, I had to remove my CDP from its shelf and replace it with the BMC. The BMC goes into a balanced line level input on the 3160, right now. I can already tell the BMC is good, but what would make you think necessarily that the Steelhead would be better? Right now, I cannot make a direct comparison, at any rate.

@lewm 

how does the BMC compare to the 3160 phono stage ?

Don’t have a formed opinion yet.

Plus, db are units expressing the ratios of voltages, having nothing to do with current. Anyone?

DeciBels refer to voltage, yes.

The higher gain settings must invoke downstream gain stages that add to signal voltage output by the indicated db’s. Is that correct?

Yes. Transimpedance phono sections have cartridge-dependent gain as you point out. There's a limit to this, for example you really don't want to push most opamps past about 20dB of gain and since the cartridge is an uncontrolled variable in this, you will need to change the gain somehow downstream.

Using the ZYX Universe, which has an output of 0.24mV and an internal R of 4 ohms, the gain is as much as you’d want, at the 0db setting. So, if you estimate the current output of the ZYX as 0.24mV/4 ohms or ~60uA (micro-amps), it would seem that any LOMC that makes significantly more current might be pushing too hard. But I also notice there is a certain unpredictability or non-linearity (in the sense of overall SPLs per estimated current) to what really happens. Anyway, there is no problem mating the MCCI with any typical LOMC. (If the current is much less than 60uA or if the voltage output of the unit is not resulting in satisfying drive, then of course one can add +7, +11, or +14db by activating gain circuits under the hood.) I found that the ART7, with 0.12mV output and an internal R of 12 ohms (which calculates to much less current at standard stylus velocity), also can drive the MCCI at the 0db setting very handily, but I think it sounds a bit better at the +7db of gain setting. This is all well and good. The question in my mind remains, is the result really "special" or just very good at the level of any other very good voltage gain phono stage. Or as Cole Porter wrote, "Is it the good turtle soup or merely the mock."