Tube Preamp Paired with Tube Phono Stage?

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.

Thanks, yeah, that's what I'm trying to get a grip on, if we're talking about a resonant peak way up above the audio band....maybe 600 khz a the low end or even pushing 2 Mhz at the high end; where presumably it's far enough above the audio band also to have limited if any impact on the phase performance of the audio signal, and even if it's basically undamped or at least certainly underdamped by the cartridge impedance loading (in many instances it seems like even 100 ohm loading would leave the ultrasonic peak underdamped), what precisely is the expected impact in the audio band?

I also realize that these aren't just electrical devices but also mechanical ones and the actual in-use performance isn't always perfectly predicted from trying to model the performance based on a circuit model of the device.

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.

Right, I get that, it's an RLC circuit and the capacitance is tuning the resonant frequency, and the lower the capacitance the higher the frequency (and the R is damping it).

So what does it take in terms of good design for the phono stage to be stage be be stable at RFs or to RFs -- I assume there's some kind of RC filter at the input of the phono stage that's a low pass filter typically, to reject RF generally, no? Just trying to understand. Thanks for your help.

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.