Possibly ridiculous low capacitance phono cables

[RetroStereo]

Since I have way too much time on my hands now that I'm retired, and to keep myself occupied, and since I've gone completely dodo bird crazy with my hybrid vintage audio system, I now have a variety of cartridges that have different capacitive loading requirements and an absolutely wonderful phono preamp that has a fixed capacitance of 120pF. To resolve this problem I dreamed up the following possibly impractical solution:

• A pair of 30-inch LC-2 (Blue Jeans Cable) coaxial cables (RCA male-male) = 35pF each
• A pair of 6-inch LC-2 coaxial cables (RCA female-male) = 13pF each
• A pair of 6-inch LC-2 coaxial cables (RCA female-male - with a hand-picked 13pF cap inside the female connector) = 26 pF
• A pair of 6-inch LC-2 coaxial cables (RCA female-male - with a hand-picked 39pF cap inside the female connector) = 52 pF
• I used Amphenol RCA connectors because the cable diameter is too large for Rean NYS373 connectors (my usual choice) & I could squeeze in the cap.
• I had great fun going through several dozen wima caps with an LCR to get ones that exactly matched what I wanted.

By combining none, one, two or all three of the 6-inch "pigtail" cables with the original 30-inch cable, I can have an adjustable cable capacitance of 35pF to 126pF in 13pF steps. Total cable length maxes out at 4 feet.

Is there a fatal flaw to my reasoning? It appears to work and I can't detect any additional noise.

 

[JP]

That 120pF on the phono stage can be a deal breaker. A good number of carts that want low capacitance want ~100pF total. Depends on your goals, though.

 

[RetroStereo]

the only cartridge i have that requires that low a capacitance is my nagaoka -- i could build a custom pigtail for it with a resistor of about 68K ohms (if my math is correct) instead of a capacitor that would effectively drop michael fidler's set capacitance.

 

[Chrispy]

Good grief so much work for a cartridge of limited capability. Good luck, tho.

 

[RetroStereo]

What's wrong with Nagaoka cartridges (other that their 100pF spec)?

 

[jkasch]

You also need to account for the capacitance of the tonearm wire. Likely in the neighborhood of 50pf, if you’re nitpicking.