PF SETTING FOR MC CARTRIDGE WITH SUT

I understand (I think) why the capacitance should be as low as possible for a moving coil cartridge plugged directly into an active gain stage. The OP said he has his cartridge plugged into a step up transformer and the SUT into the MM input on his phono stage. Is it the case that the phono still sees a moving coil cartridge and that the SUT is "invisible" so to speak?

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

Hi Al: Thanks again for the cartridge lesson on impedance, capacitance and inductance. I've tried to apply your advice, both that which you and I shared privately and here on A'gon. I think my phono stage sounds all the better because of your help. Now, I also read Jonathan Carr's post. In particular, Jonathan wrote the following:

"PS. The possible frequency range occupied by the high-frequency resonant spike also includes the frequency range encompassed by LP pops and ticks, and these can likewise be of quite large magnitude (larger than any music signal inside the groove). Just as with the high-frequency resonant spike, controlling pop and tick energy is the task of the phono stage (although it is a big help if the cartridge has a low-mass moving assembly). The phono stage and cartridge can have an immense influence on how "noisy" your LPs appear to be."

Al, 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."

FWIW, after applying your advice, it came to my attention that normally occurring record noise (hiss and pops)decreased by a significant amount. 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).

Instead, it may be that this improvement has an electronic rather than a mechanical explanation. Very interesting. As an aside, while I enjoy the hobby for the music and relation asspects, I find the technical side to be fascinating. Maybe I'm a just frustrated "EE" who wound up in the wrong profession????

Cheers!

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

Hey Al, I guess that's what synergy is all about, i.e., the interaction of a number of factors that combine to effect a better outcome.

In the present case, the factors being: (A) electrical ("higher load capacitance will, under typical circumstances, increase the amplitude of that frequency response peak (resonance), and lower the frequency at which it occurs" and vice versa); and (B) mechanical ("stylus of my new cartridge . . . shaped a little differently than whatever I used before. As a result, perhaps it [is] tracking the grooves in a less worn spot, thus reducing noise).

Regardless of the reasons, my LP playback sounds almost as quiet as my CDP, but better for all the reasons that vinyl sounds better than "redbook" CD. I wish someone could figure out how to use a remote clicker to change tracks and automatically flip the record. Oh well, maybe Harry Weisfeld can figure that problem out by the time he releases the 60th anniversary version of the Classic.

Regards,

Bruce