Voltage mode vs current mode phono stages

Boothroyd, LOMC cartridges, like the Lyra cartridges you mention, will have inductance in the low micro-Henry range.  The low output MI cartridges made and marketed by SS have an inductance in the low milli-Henry range.  In other words, the inductance of their LOMI cartridges is about 1000X higher than that of a Lyra or other typical LOMC.  (This is no attempt to critique the SS cartridges; I actually prefer MI cartridges over most other types, and I am grateful to SS for carrying the MI banner.) The point is that level of inductance might affect the cartridge's capacity to produce signal as current, especially at high frequencies. Thus I am curious about what happens when you mate a Sussuro, for example, with a current driven phono stage.

@lewm Since the cartridge functions as the input resistor to the opamp, the impedance of the cartridge affects the gain of the circuit (as you probably know, the gain of an opamp will be the ratio between the feedback resistor and the input resistor). This suggests that as the impedance of the cartridge goes up, the gain of the circuit goes down, which is probably good since the output of the cartridge will be higher.

I've not messed with this circuit to any great degree, so I don't know what constraints might exist, but I'm sure there are limitations- there always are. I just thought I'd point this first bit out.

Hi Ralph, You wrote, "This suggests that as the impedance of the cartridge goes up, the gain of the circuit goes down, which is probably good since the output of the cartridge will be higher."  The linear relationship between voltage output and stylus velocity (higher at higher frequencies) is accounted for by the RIAA correction.  Would you want the cartridge to alter that relationship by virtue of an upgoing internal impedance? Also, the paradigm for current drive is you want the cartridge to have a very low internal resistance/impedance to begin with, which makes it a decent current generator.  Obviously, I am parroting ideas that are in the air without much depth of knowledge. But this question points out how consumers are a bit confused by "current drive" or a term like "transimpedance".  I think there are an array of products that each may do it differently enough to defy generalization.

Boothroyd,

I found this in the Sussuro cartridge owners manual:

"Please also note that some designs of “current amplifier” preamp circuits will not allow loading in the range required, causing the Sussurro MK II ES to sound very dull – caused by improper loading, resulting in loss of high frequencies."

What I could not find was a spec for the inductance of the Sussuro, but if memory serves it is about 50 mH.  This would give an impedance of 314 ohms at 1000Hz.  Let's say it's only 10mH; then divide 314 by 5.  Still high for a typical current driven phono.  Add the impedance due to inductance to the coil resistance of only 10 ohms.  I emphasize again that I love MI cartridges as a rule.  This is more about the usefulness of most current driven phonos stages.

lewm,

I would reach out to PL for clarification. FWIW, he was using a Loco with one of his LOMI pickups when he indicated the results were very encouraging as long as proper cables were used.