Resistor in phono stage

Using the a supex step up transformer of course.

Ah! Which of course explains how the 54 db gain of the phono stage suffices for use with a 0.2 mv cartridge.

But it also adds to the possibility that either resistors or capacitors a previous user might have installed in the phono stage could be an issue. For example, suppose a previous user had installed 1K resistors, for use with a cartridge having a rated output in the upper part of the LOMC range. And let’s assume that your SUT provides a gain of 10:1. That would mean your cartridge would be seeing a load of only 10 ohms, which stands a very good chance of being low enough to result in the adverse effects Lew referred to in his previous post that can occur when load resistance becomes excessively low.

From the perspective of the cartridge, use of a SUT also greatly increases the effects of any capacitors that might have been installed on the loading terminals within the phono stage. Which as I mentioned earlier could conceivably have been done to conform to the loading requirements of some moving magnet cartridges.

So I would definitely open up the unit and take a look at what if anything has been installed on those terminals.

Regards,
-- Al

It looks like that cartridge is an LOMC having a rated output of 0.2 mv. It’s surprising that 54 db of gain is adequate with such a cartridge, but on the other hand the noise specs on your phono stage seem quite good ("0.1µV equivalent input noise, IHF weighted, shorted input; 80 dB below 1mV 1kHz input"), which figures to be helping.

In any event, with a 0.2 mv cartridge it’s hard to predict how sonics would be affected by variations in load resistance, as it would be highly dependent on the design of the particular phono stage, and specifically on the sensitivity of the phono stage to RF frequencies. (The interaction of the relatively low inductance of such a cartridge with the capacitances of the phono cable and phono stage input will result in a resonant peak in frequency response somewhere in the RF region, whose amplitude will be affected by the load resistance).

So I suspect that the only way to determine an optimal load resistance would be to try a few different values, although it’s possible that you would find it to not be particularly critical. One thing I would make a point of doing, though, is opening up the unit and seeing if someone has put capacitors on the loading terminals that are indicated in the manual. That might have been done if the phono stage had been used with a moving magnet cartridge having a relatively high recommended load capacitance. If you find that capacitors have been added, it would be best to remove them given that an LOMC is being used.

Regards,
-- Al

Lew, when you said "resistors wired in parallel will always result in a net value lower than that of the highest value of any one of the resistors," you probably meant to say "resistors wired in parallel will always result in a net value lower than that of the LOWEST value of any one of the resistors." Both statements are of course true, but the second one is more meaningful.

Also, Mofi, the manual you linked to talks about using the phono stage in conjunction with moving coil as well as moving magnet cartridges. While 54 db gain is of course too low for many LOMCs in many applications, depending on the noise performance of the phono stage and the gains and sensitivities in the rest of the signal path I suppose it could sometimes be suitable for use with cartridges having relatively high outputs within the LOMC category.

In any event, as Lew indicated further info from the OP is needed before his questions can be answered.

Best regards,
-- Al