Dedicated phono-pre for MM only?

Raul, Do you mean to say that every time you change from an MC that likes to see, for example, ~100R to one that needs significantly higher R, you actually take the 3160 to the workbench and solder in the required higher R? Or do you use some plug-in system that obviates the need for a switch but still puts mechanical (i.e., unsoldered, pressure-based) contact points in the signal path? Or do you still have a switch for load resistance? (Your post suggests you eliminated switching between input jacks, rather than between load resistors. Even with a single pair of inputs it would be desirable to be able to switch load resistors.)

Kirkus, I just paid too much for a B&O MMC20CL off eBay. I hope I will be happy. The AD797 is one of the ICs I had in mind when I noted that the op amp-based schematic that was posted above might be upgraded with later, better chips. (The schematic used TL072, I think.)

I just paid too much for a B&O MMC20CL off eBay. I hope I will be happy.

I think that I was looking at that one too . . . glad you got it. If it's in good shape, then you didn't overpay. Stellar cartridge.

On the AD797 - this opamp is capable of extremely high performance, but it's definately NOT one to swap into an existing circuit without careful consideration, especially if it originally uses TL072s! The AD797 really shines with low source impedances (not MM cartridges), but on the other hand, it can be limited in its useable output current . . . so it doesn't necessarily do the best job of driving the low-impedance feedback network that suits its low eN characteristics. That's why I used the discrete JFETs as a buffer, and why I used it in the second stage, where it can be driven from the low source impedance of the first. The AD745 is FET-input, so it works great with an MM cartridge . . . but it's not stable at lower gains, so stability and phase margin have to be carefully considered in application. Then there's the fact that the TL072 is a dual, and AD797 and AD745 are singles.

For general TL072 replacement, try OP249.

Dear Lewm: That's right, if I need a different load impedance then I soldered a new resistor value, no switch. Normaly almost all the LOMC cartridges comes with a very low internal resistance where 100 Ohms can cope all them. The other subject is that due to the Ponolinepreamplifier characteristics you don't need to change the load impedance, only in extreme very extreme cases.

Lewm, one way or the other normaly a switch makes a degradation to the cartridge signal so you have to make a decision on trade-offs between quality or convenience, we choose for quality performance.

Regards and enjoy the music,
Raul.

Raul, Just another one of life's compromises.

Kirkus, Would you care to comment in more detail on your earlier statement that a balanced input is per se not ideal for an MM cartridge? At least I think that is what you meant to say.

By the way, thanks largely to Kirkus' input I am beginning to learn some things about MM phono stages and phono stages in general that I did not know.

This thread has been informative and I'm better understanding some of the nuances of phono stage design, both MM and MC architecture.

And I'm beginning to see the value in having a dedicated MC phono preamplifier if LOMC cartridges are preferred. Why bother with 40 dB gain and 47K loading for MM cartridges. The design would, at most, have binding posts to change loading resistors. Being able to change the amplification (gain) would be handy but not necessary if the output voltages of the preferred cartridges were within a fairly close range.

Is such a phono preamplifier available?

Tom