Dedicated phono-pre for MM only?

Tom and Axel, I heretofore have had only one LOMC cartridge, which seeems optimally loaded by a 100R resistor, which I soldered in place myself. But I recently purchased a (third) LOMC that will probably do best with 1000R. I have contemplated installing a switch, so I can change between 100R and 1000R, when I want to change cartridges. Obviously there is a risk of introducing noise at the switch. But in practice, have either of you, or anyone else, actually perceived degradation of the sound with such an arrangement? Many commercial products incorporate such switches in this critical part of the circuit, so most people would not know if they are losing anything in the way of S/N ratio as a result.

But this is off-topic. With an MM phono stage, we should all be using a 100K load, according to Raul. Based on very limited data, I have to agree with him; several years ago, I made a similar accidental observation with whatever MM I owned at that time. It sounded better with a 98K load compared to the standard 47K load, and the diff was not subtle.

Hi Lewm,
>>> With an MM phono stage, we should all be using a 100K load <<<
Another reason for this thread's subject.
I mean, WHICH phono-pre, of one-serves-all, has a 70k and/or 100k ohm input impedance option I ask?
I know Raul's Essential 3160 has, but that is a non-main-stream item.

As to 'switching degradation' I had a PS Audio GCPH using some pretty convenient switching, and now a pain-in-the-butt ML phono-module using internal binding posts or some jumpers.

But as you say, how could I have tested the GCPH's performance without the switches for gain and loading?

All I know is, that the ML modules sound better --- but because of the switches?

Raul and Co. might have some contribution in sharing their findings, wouldn't they?

Axel

Hi Mark - FWIW, my experimentation with discrete JFET MM stages included both the 2SK389 dual, and a pair of 2SK369 singles. I cascoded them with 2N5089 NPN bipolars, and loaded the collectors with 1K . . . there was also a single 2N5089 used as a simple current source for the tail. Rails were +/- 20V, and I put about 8mA through the tail (4mA through each JFET). VDS across the JFETS was about 5V.

I used this circuit in an unbalanced-input feedback amplifier, in the classic "hybrid-amplifier" (JFET-frontend feeds opamp) topology. Instead of a monolithic, I used a 990 discrete opamp, driving a low-impedance EQ network for the 318uS and 3180uS time-constants, with about 20dB of gain at 1KC. This fed a passive 75uS network and another 990 for 20dB more gain, same as my MC design.

I never really put in the time to fully optimize the circuit, but it was very low-distortion, and CRAZY quiet . . . like greater than -90dBV at the output when looking at a 1K source impedance. I think that the 2SK269s had a little better 1/F noise, and even though the offset on the 2SK389 was much better, it didn't really matter for my application. Of course, YMMV.

Hi Lewm - I will add my vote as well to the higher-loading approach, I think that 100K with minimal capacitance is much better (with virtually every cartridge that I've tried) than the common 47K/150pF.

But as far as commercially-available phono stages go . . . I don't really see enough of them anymore to have really strong opinions. I do think that in general, getting the subtle details right makes more difference than any generalisations about whether it uses JFETs, tubes, bipolars, opamps, etc. etc. There are certainly an unlimited number of ways to screw things up, or to avoid doing so.

I'm currently using my Beogram 4002/MMC20CL with a little phono preamp that's an opamp design, made on a Vectorboard . . . and the case and power-supply from a Lehmann Black Cube. Its a two-stage topology like my MC phono unit, with active 318/3180 in the first stage, passive 75uS, then more gain in the output stage. Opamps are AD745 (input) followed by AD797 (output), both of them use complementary discrete JFET buffers for high-current output, within each feedback loop.

Daer Axel: I can speak about that switch subject. During our researh and tests on the deign of the Esential 3160 and due that this PHonolinepreamp was/is designed for our ( José and I. ) specifics need in one of the prototypes ( the one battery powered. ) we have six phono inputs through a switch that I use it for several months till I decided to hear the same cartridges with out that switch where every change on tonearm/cartridge means disconnect/connect in manual way each time, well there is a quality improvement with out that switch and we decided to go in this " fashion ".

But the Essential 3160 is not a product thinking on commercial subjects ( facilities for the customer: using switchs instead that manual changes, switchs for impedance changes instead solder resistors, etc, et. ) but with targets of absolut quality performace where less means more and with no trade-offs or trade-offs at minimum. Many times this approach ( no trade-offs on quality performace. ) means that the Essential user has less facilities: switchs.

Regards and enjoy the music,
Raul.