My Phono stage's Input Impedance is 3 Ohm. I very much doubt that is correct. Phono stage input impedances are much higher, commonly 100 ohms for moving coil stages, and sometimes much more, and 47,000 ohms for moving magnets. But to answer your question, assuming it is a moving coil cartridge: Overall volume would be severely attenuated, and the upper treble would be sharply rolled off. Regards, -- Al |
Hmm, yes I took a look at the ESE Labs website pages on the Nibiru, and it indeed specifies 3 ohms. It seems to be oriented towards extremely low output moving coil cartridges, which would presumably have very few turns in the coils, and therefore very low resistance and inductance, which would in turn improve compatibility with heavy (low-value) loading. The unusually low input impedance seems to derive from what they describe as a current sink/current domain/transimpedance design approach. I have no idea how to reconcile that, though, with their statement that it is suitable for cartridges of up to 40 ohms impedance, if severe volume attenuation is to be avoided. And such cartridges are also likely to have considerable coil inductance, resulting in the severe treble rolloff that I mentioned, in combination with the severe loading. You might find the following to be of interest: http://www.hagtech.com/loading.html Regards, -- Al |
Don't ask me to explain the technical side of it (I'm only spewing out what I've read about current mode phono preamps as I own the Aqvox), but current mode phono preamplifiers like the Nibiru, Aqvox and Dynavector in phono enhancer mode use a type of "automatic" (perhaps not the best choice of words) short circuit loading by sensing the amount of current the cartridge outputs. Resistive loading in these types of phono preamps when used with moving coil cartridges becomes a non-issue as the "short circuit" means the cartridge is inherently damped. In theory, I think these types of phono preamps offer particularly good performance with low output moving coils that also have a very low internal impedance (I use the Aqvox with a Denon 103R with a 14 ohm impedance) mainly because many phono preamps will not allow you to load down into the 20-50 ohm range which may be an ideal setting for a very low impedance cartridge. My guess is that the Nibiru will work like a charm with a MC with a low internal impedance of 16 ohms. The lower the better probably with that phono stage. |
OK, well after thinking about a bit further I can see that the fact that the phono stage input is sensing current flow, rather than voltage, that the volume attenuation I spoke of would be avoided. With a more typical voltage-sensing phono stage, the sensed input voltage would be divided down for the 16 ohm cartridge by a factor 3/(3+16), or 0.16, but that would not occur if current were being sensed. But you still may get into trouble with upper treble rolloff. To determine that you would have to know the inductance of the cartridge, which some manufacturers specify but some don't, and plug it into the calculator in the reference I linked to (shown towards the bottom of the page under the heading "mc cartridges"). Hope that helps, -- Al |
