Tube Preamp Paired with Tube Phono Stage?

If you can get an all-tube recording as well as playback, then its even better :)

This is almost as frustrating as John Curl's JC-3 phono preamp offering only one impedance setting of 100 Ohms for MC. That one I'll never understand.

The reason is if the preamp is resistant to RF at its input, the load on the LOMC is not critical. Its only there to reduce RF caused by the inductance of the cartridge interacting with the capacitance of the interconnect cable, which can form a tuned RF circuit. The resistor destroys the 'Q' of the circuit. IOW if the preamp works right, the value of the resistor is not important since it only works at RF frequencies.

This says to me that Mr. Curl's preamp must be pretty resistant to RF issues.

Actusreus, (in case its not clear from Al's comments) the reason some preamps offer more loading settings, and that they are audible has to do with the fact that such preamps are not 'graceful', as Al put it, when dealing with RF energy. IOW, the RF energy affects the way those preamps sound.

All we ever found with loading (our preamps have a loading strip above the phono connectors so you can put anything there you want) is there is a slight change in the noise floor.

If you have a moving magnet cartridge, the loading can affect the sound of it directly, IOW the effects are occurring at audio frequencies.

Actusreus, if Fremer is not 'full of it', he was hearing those differences due to issues with the **phono section(s)** rather than the cartridges. 47K, 100 ohms, the cartridge does not care. I run my cartridges (Transfiguration Orpheus, ZYX Universe) at 47k with no worries, can't really tell the difference if I use 100 ohms. But our stuff is stable in the presence of Radio Frequency energy, which is in fact what this is about.

Jonathan Carr's comments can be trusted regardless of the LOMC.

You are partially correct with your summary in your last post. The entire summary should read: "So to summarize, it depends on the preamp."

Odd that Boulder would suggest 100 ohms generically for all moving coils.

Chervokas, read my posts above and you will see why this is not odd at all.

Actusreus, the Atma-Sphere preamps are intended as stand-alone phono reproducers. People ask us all the time why we don't have a separate phono section; the reason has to do with interconnect cables. The idea behind our preamps is to reduce the signature of the interconnect cable between the amp and preamp. Without special circuity this cannot be done. It is included in our preamps. This allows the phono section to be more neutral.

Chervokas, to be clear: if you load the cartridge with a lower resistance than your 10:1 or 11:1 ratio, all that happens at audio frequencies is you may reduce the output voltage of the cartridge. Its bandwidth will be unchanged.

So in theory you would want to load it as lightly as possible such that the RF issues are managed. The RF issues *can and do* act like changes in tonality. I admit that its confusing, but if you study this stuff on the test bench the fact of it comes out in spades.

Chervokas, As far as an undamped LOMC goes, there is no effect whatsoever in the audio band, other than the voltage output- with no load its output will be a little higher, not much.

The issue is that the coils in the cartridge have so little inductance that the ringing issues that often affect inductive devices do not come into play until you are at very high frequencies, well into the MHz region. It is this ringing that supplies energy for the tuned circuit that results from the cartridge and the interconnect cable. Note that the capacitance of the cable always plays a role, the lower it is the higher the frequency of the resulting tuned circuit. So its rare that this can be solved by reducing the capacitance of the cable!

What is paramount, IOW, is that the phono section be stable with RF at its input.

Chervokas, one of the problems with RF is it can be rectified by elements of the preamp circuit itself. Tubes often tend to be a little less susceptible on account of transistor junctions can rectify the RF energy fairly efficiently if not properly set up. Tubes don't do that nearly so easily. Mechanical connections can also be a problem.

If the RF can get in at sufficient level, non-linearities caused by overloading the circuit can drive any preamp into conniptions, so the trick to do things that limit that; shielding at RF frequencies (aluminum is often better than steel for this), correct use of 'RF beads' that limit how much RF can enter the input connectors, proper 'grid stop' resistors in tube circuits ('gate stop' resistors in solid state gear), layout and grounding all play a role.

IOW its all in the design and the designer's attention/awareness of this as an issue.