Why does input loading resistor quality matter?

[tpatton]

I know from experience with four or five phono preamps that the quality of the 47K ohms (or close) input loading resistors greatly influences the sound.  I use TX2352 Vishays, and sent a pair to the buyer I sold a Wright Sound two-chassis phono preamp to, part of the deal.  After replacing the Audio Note Japan tants I had in before, he emailed me, "Wow!  What a difference!", and went on to describe the improvement.

Yet that resistor goes straight from input to ground, so one might think that it just "wastes", throws away, part of the input signal, and isn't itself in the signal path.  So, on those premises, its quality shouldn't matter.

I have a guess as to why it does matter, but would love to hear from someone who wouldn't be guessing.

[ssssly]

My guess would be magnetics. Those AN Tants are very magnetic, the Vishays less so. In my, purely subjective, experience the less magnetic a resistor is, particularly load resistors, the better the sound.

Again purely subjective experience from swapping out parts to see what makes a difference where.

[Paul Joppa]

The signal current passes through the resistor on its way back to the phono cartridge. Pretty much all the signal current goes through that resistor - just the tiny high frequency current goes through the paralel path of the grid-to-other-electrodes capacitance. This is the same reason (IMHO) that power supply capacitors are important sonically. I maintain the "signal path" is  a sort of fiction; it's the signal voltages and the signal current loops that are sonically important.

I'll speculate that there are some noises generated by the passage of current - this is a known effect in carbon composition at least. The suggestion of magnetic effects is also plausible, especially motion of the resistor in response to magnetic fields inside the amplifier. Any motion of a conductor in the presence of a magnetic field generates a corresponding signal, just as a current through the conductor produces a mechanical force.

Hmm... this suggests an experiment. What if a magnetic resistor were shielded in mumetal?  :^)

I've never seen or heard of any of these effects (outside the carbon composition noise) being measured or quantified.

[tpatton]

Thanks for these ideas, both of you.  Very roughly, Paul J's first sentence would have been my guess, though I would have expressed it worse: it's alternating current that we're dealing with, and the implication of that.  Back to the phono cartridge is really part of "the circuit path".  But it isn't just ANJ tantalums that are greatly improved on by the TX2352 Vishays--it's "ordinary" resistors too, even ones considered pretty good, like original Holco's, for example.  So I don't think it's just magnetism that's an issue.

Thanks to advice from Grainger, I do my best to improve power supply capacitors too, with good film cap bypasses as well as good electrolytic caps to begin with.  But I was totally vague on why this should work.

[ssssly]

Guess I should have payed attention to the part number as well as the manufacturer. Used to people just referring to those as Nakeds.

Hard to find a better sounding resistor than those for low voltage applications IMO. I still like Shinkoh Tants better for higher voltages. Again completely subjective.

If you like the tx2352 you should try the tx2575 "naked zfoil".

[tpatton]

Thanks ssssly, for the idea.  I've priced the TX2575's--about 30% more than TX2352's, so not totally unaffordable.  Knowing me, I'll probably try some in future, though right now nowhere to put them without taking TX2352's out, and it would pain me to do that.

[ssssly]

Yeah they are pretty fragile.

Basically I think it is pretty much like PJ said in the other post. I don't think anyone knows why some sound better to some people than others. Much like caps. For myself I have spent the better part of 10 years randomly trying different resistors and caps. So I know what sounds good to me. Couldn't tell you why scientifically though.

I stopped trying to figure out the why things sound good after a long post war over if it was worth building speakers that could put out below 50hz. Was a gang of people swearing that because of the long wavelength of the frequency that it was impossible to hear below 50hz. Certainly don't want to get into the debate again, but needless to say I build my speakers with the intent of producing sound at frequencies lower than 50hz.

Also why I always use words like "like" "think" "guess" and "subjective" in topics like this.

Be well