PF SETTING FOR MC CARTRIDGE WITH SUT

When caps are put in series with the circuit the total capacitance drops just like resistance drops when resistors are put in parallel. You can use ohms law to determine what value of capacitance u need to put in series with the phono leads. I have never tried this yet, but it sounds believable according to theory. But in audio theory is not always right!

Don't put a capacitor in series! A low value capacitor (e.g., tens or hundreds of pf's) will have an extremely high impedance at low and mid audio frequencies and will essentially kill the signal that is seen by the phono stage. A high value capacitor in series will not reduce total capacitance significantly, and will degrade the signal due to non-ideal behavior.

The statement about how the values of capacitors in series combine is correct in itself, but is being misapplied.

Concerning the relevance of load capacitance to low output moving coil cartridges, the response of the cartridge itself within the audible spectrum will be pretty much insensitive to load capacitance. However, greater load capacitance will increase the amplitude and lower the frequency of an ultrasonic resonant peak, which may result in phono stage distortion products that fall within the audible spectrum. See the excellent post by preamp and cartridge designer Jonathan Carr (JCarr) dated 8/14/10 in this thread:

http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1281468389&openflup&18&4#18

In this case, the presence of the SUT complicates the issue somewhat. While the SUT may reduce interaction between phono stage input capacitance and the cartridge to some degree, it will introduce the possibility of interaction between that capacitance and the transformer itself, most likely with adverse consequences if any.

So the bottom line, as others have said, is that best results are most likely to occur with the capacitance setting at its minimum position.

Regards,
-- Al

07-07-11: Bifwynne
As an aside, while I enjoy the hobby for the music and relation aspects, I find the technical side to be fascinating. Maybe I'm a just frustrated "EE" who wound up in the wrong profession????

Hi Bruce,

Could be. You do ask intelligent questions, that seem to indicate having the right instincts. :-)

I think I understand what Jonathan is saying about LP noise (hiss and pops), but could you put a little more "flesh on the bones."

What Jonathan is saying about tics and pops is that they include spectral components at ultrasonic frequencies (i.e., above 20kHz), which may be boosted by the frequency response peak which occurs at ultrasonic frequencies due to the interaction of cartridge inductance and load capacitance. As I indicated earlier higher load capacitance will, under typical circumstances, increase the amplitude of that frequency response peak (resonance), and lower the frequency at which it occurs.

The phono stage may in turn have difficulty gracefully handling the resulting increase in non-musical ultrasonic energy, with consequences at audible frequencies.

I thought it was because the stylus of my new cartridge (VPI Zephyr) was shaped a little differently than whatever I used before. As a result, perhaps it was tracking the grooves in a less worn spot, thus reducing noise (hiss and pops).

That can certainly be an important factor, as well.

Best regards,
-- Al