FWIW I'm loading my Zyx Airy 3 at 100 ohms. I would trust my ears and not worry too much about what others are doing as all systems are different. Listen and have fun.
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Dear Bryan: The load impedance in a MC cartridge is a critical isuue for the quality sound reproduction of any cartridge.
The ZYX manufacturer is the " person " that can tell you with which load impedance the frecuency response of that cartridge will be flat. Then, if you set your preamp with that manufacturer impedance advise and does not like what you are hearing, then something is wrong in other link on the audio chain in your audio system.
Please don't try to use the different load impedance value like an equalizer to conpensate for other deficiency elsewhere: this is a wrong way to make things, many peoples in this forum do that: all them are wrong.
Regards and enjoy the music.
FWIW (I've gone into more detail as to 'why' elsewhere in these threads) I've found that the best baseline (starting point) for then establishing the optimum (best for your ears and your system) cartridge loading is 25 times the internal coil resistance (sometimes referred to as output impedance) Then try your listening tests within a +/_ 50% range of that number.
For example, the Airy 3 SH is 8 ohms (the SL is 4 ohms, but you didn't say which one you have.) So 25 x 8 = 200 ohms is your center point. (And until your cartridge has broken in for at least 100 hours, don't bother screwing around, just leave it at 200 ohms) The range to explore after break-in would be from 100 ohms to 300 ohms.
First make sure VTF, anti-skate, overhang, and SRA are correct. Then I always start at the lower end of the range and work up, to make sure I don't miss anything. At the lower end, you can basically expect the bass to be there OK, but it will be a little muddy or undefined. At the upper end of the range (and beyond), the bass will be lacking, and the mids and highs will stand out, maybe even a little glarey or grainy. Then you back down 'til the bass just comes back full and tight, and you're there. This will be the point at which your cartridge is giving the best energy transfer and the flattest response.
My pet peeve is with those who set the load too high. Sometimes as high as the standard MM 47,000 ohms! I often find these are the folks who tilt their tonearms backward because (though they probably don't realize it) doing so will roll off some of the high frequency imbalance they've created with too high a load setting. Now honestly, what cartridge maker in their right mind would install the stylus in the cantilever such that in order to attain the correct Stylus Rake Angle, you'd have to tilt the cartidge backward? Really!!
Thank you all for your input.
I have the low output Airy 3-S with silver base (.24).
I moved the rear of the arm up one turn on the VLA adjuster and the highs came back.
This is the best the ZYX has sounding in my system.
The other question I have is why did the volume decease when I installed the 3.3K resistors in the pre-amp?
The system is also quitter with the resistors in place then with them out.
If you are using a step-up transformer before the preamp, then the transformer INPUT impedance should be equal to or higher than the cartridge OUTPUT impedance (in your case 4 ohms.) However your preamp's PHONO SECTION INPUT IMPEDANCE should be equal to or higher than the transformer's OUTPUT impedance.
Your preamp's phono section has (I'm guessing) a default input impedance of 47K (for MM cartridges.) By inserting the 3.3K resistors, you are reducing the input impedance the transformer is looking at, which shunts some of it's power. I wouldn't use any additional resistors on the preamp side of the transformer. Doing so has no effect on the impedance the cartridge is looking at.
Some step-up transformers do provide for the use of cartridge loading resistors on the INPUT side of the transformer. I don't know if yours does.
I'm not sure what you mean by "quieter" with the resistors
I'm afraid there's a lot of confused information being posted here.
The resistor sockets on the secondary side of your BentAudio Mu's are not there simply to show your phono inputs a particular impedance. Nor is BentAudio assuming you're using an MC phono stage. If you were, you probably wouldn't need a transformer in the first place. Bent is assuming you're using a MM input with 47K ohms input impedance. The page you linked is correct.
1) Resistance on the secondary side of a transformer IS reflected back to the primary side. Your transformer's primary is connected with the cartridge coils in a closed AC circuit. The resistance reflected from the secondary is seen as impedance by the cartridge. Adjusting that is the purpose of the Mu's resistor sockets.
2) Impedance on any AC circuit does act as a frequency tone control, as Raul said, but in this application it also acts as impedance on the electro-mechanical motors in the cartridge. If circuit impedance is too high the cantilever will be under-damped and excessive HFs will result. (You may also get higher output, which is probably what you were hearing before you inserted the resistors.) If impedance is too low the cantilever will be over-damped. HF response and overall dynamics will suffer.
2) The formula "25 times coil resistance" is for MC's feeding a voltage gain stage. It has nothing to do with transformers. When playing through stepup trannies most MC's like to see a reflected impedance somewhere between 1x and 5x the coil resistance. IME low output ZYX's usually prefer something between 1.5x and 2x their 4 ohm coil resistance, ie, 6-8 ohms. (You're actually in this range now, stay with me.)
3) When using a tranny the impedance "seen" by the primary = the resistance on the secondary side divided by the SQUARE of the tranny's turns ratio. Your 26db trannies have a 1:20 turns ratio, so those 3.3K resistors are "seen" by the cartridge as an impedance of 3300/20^2 = 8.25 ohms.
4) Any resistor you place in the Mu's socket is in parallel with the resistance of your phono inputs. With a 47K ohm MM phono stage, the actual resistance on your secondary side can be calculated with the formula for resistors wired in parallel:
1/R = 1/ra + 1/rb...
R = total resistance on secondary side
ra = resistance value "a" (eg, phono inputs)
rb = resistance value "b" (eg, resistor in Mu socket)
For your present setup, the formula is:
1/R = 1/47K + 1/3.3K
R = 3083 ohms
Dividing this figure by 400 (the square of your turns ratio) gives us 7.71 ohms. That is the actual impedance your ZYX is presently seeing (not counting the trivial additional impedance of your phono cable and the Mu's wiring).
5) IME, MC's playing through a stepup are EXTREMELY sensitive to VERY small changes in reflected impedance. A change of 0.1 ohms will be more audible than a change of 25 ohms when using an MC gain stage. In one demo I took a ZYX UNIverse from dull to perfect to bright by going from 6.54 to 6.65 to 6.71 ohms of reflected impedance.
This sensitivity is both a blessing and a curse of course.
How do you make these tiny impedance adjustments? Simple. You put two resistors in each socket of the Mu. You can calculate the total impedance on the secondary side by extending the formula above to:
1/R = 1/ra + 1/rb + 1/rc
Divide R by 400 to get the impedance seen by the cartridge.
For my low output ZYX I'm current using a 680 ohm and a 27Kohm resistor in each socket of my (20db, 1:10) Mu's. That works out like this:
1/R = 1/47K + 1/680 + 1/27K
R = 654 ohms
654/10^2 = 6.54 ohms
In my system with this cartrige, 6.50 ohms is too low, 6.62 ohms is too high. That's how touchy this is. I'd suggest buying some cheap resistors and experimenting. IME the same cartridge will need slightly different values in different systems.
Unfortunately, asking the manufacturer will get you nowhere. Few MC makers offer more than general impedance guidelines, and even fewer offer any guidelines at all when using a tranny. How could they? The turns ratios of trannies vary all over the lot, and as you can see from the formula above that has a major impact on the impedance actually seen by the cartridge.
Hope this helps more than confuses,