For loading of MC carts, you need to know the input resistance of the preamp and you need to know the output impedance of your cartridge, or at least the DCR of its coils.
Generally speaking, you want the input resistance of your preamp to be about 10X the output impedance of your cartridge.
In the case of a Denon DL103 with about 40 ohm output impedance, you'd want about a 400 ohm input resistance (load) at the preamp.
To get there, let's say your preamp has the standard 47k input resistance. If you put a 470 ohm resistor in parallel with the 47k load resistor, you'll get 396.6 ohms. That's really close enough.
desired R = R1 x R2 / R1 + R2
How do you put a 470 ohm resistor in parallel with the input resistance? Well, you could solder a little 1/8 watt metal film resistor between the signal and ground leads of the RCA plug that goes into the phono preamp's input jack. Or you could make up a female-to-female RCA connector, and solder that little resistor between signal and ground inside. You could make a bunch of these connectors, each with different resistor values. Some signal loss from the additional connections would theoretically be there, but I think they'd be infinitesimal in practice.
So not having switchable load resistors is not terminal.
Has anyone compared the Mani to an expensive phono preamp? Does it compare well? I've only seen comments from those who've just started with vinyl or have only had other very cheap phono preamps (like the ART, etc.).
Edited by rongon - 2/18/15 at 12:14pm