MM Phono Input impedance change 47k to 100k ohms

Hi Erik,

I don't think it's possible to say without having a schematic and/or being familiar with the details of the design. There could very well be a 47K resistor between the input for each channel and ground, that could be changed to 100K. But even if that were the case, without knowing the details of the design I would not have confidence that the change would not result in unwanted side-effects.

Also, see my post here. Contrary to widespread belief, 47K could very possibly be a suitable load for the F9 cartridges.

Best regards,
-- Al

I agree with Al. I have sold, (I was a Grace dealer) and personally owned many various F9 cartridges and have found that in most cases, the 47K setting is perfect. I currently have several F9E's and have tried many different phono stages with them.

I have owned a couple different phono stages that allowed the 100k setting, but I always went back to 47K. IMHO, the 47K setting is just fine.

I've had a Grace F9E in my collection and system, non-stop for over 30 years now.

Thanks to both Al and Mofimadness, really appreciate the response and will stick with 47k ohms. Incidently the Grace F9Ruby seems to mate very well with the Herbies Most Excellent mat

FWIW, I have a Grace Ruby which I load at 100K, and I love that cartridge. However, I would not say that 47K is not also appropriate, only that I perceive no downside to using 100K. Now I have to go read Al's treatise on why he prefers 47K.

OK. Now I know that Al actually uses 100K, too, and with a SS phono stage, whereas mine is tube-based. Actually, I never knew that there was any written statement from Grace to the effect that 100K is preferred; I am using 100K because that's the load resistor that In installed in my phono stage input.

As to Elunkenheimer's question, I cannot imagine how the circuit could be harmed, if you were to change the 47K load resistor for a 100K one. If you know how to solder, get some high quality 100K resistors and go for it. Most phono stages I have ever seen will use a 47K resistor between hot and ground to set the input impedance. Since the grid of the tube or the gate of a transistor have a very high impedance, in the megohm range, 47K will become the dominant value at all audio frequencies. Likewise if you change to 100K. The issue is a bit more complicated if you have a true balanced input; let us know. Beware of dangerous voltages; always unplug your device, and leave it off power for at least a full day before doing any soldering. (A full day does not make it perfectly safe, however.)