advertisement


phono leads pico farads

If it is to be used as line level interconnect over normal distance runs then less than anything like enough to bother worrying about.

On the other hand, if it is being considered as tonearm interconnect between an RCA socket equipped turntable with MM cartridge fitted and phono stage, then possibly just enough to be concerned about.
 
Varies a lot, but anything from around 70pF to >200pF. That is obviously more than enough to dramatically change the capacitive loading and frequency response of a MM cart. It all needs factoring-in. Don’t forget to add a bit on for what is in the arm itself.

If you disconnect the cartridge you can measure the capacitance of the full arm-loom from headshell through to amp-end RCA plugs with a good multimeter. Don’t do it with the cart in place though as a multimeter does send a signal/voltage down the wires.
 
As many SL1200 enthusiasts will recall, back in 2008/2009 Technics inadvertently began supplying Mk2 and Mk5 decks with 325pF tonearm leads (i.e. the same capacitance, in fact the same cable, as their then standard RCA to RCA interconnect). This was first detailed by Technics deck and mods/accessories dealer KAB Electro Acoustics (scroll down here). Both prior and subsequent to this, Technics turntable interconnects typically measured circa 120pF.
 
Hi am using a shure m75ed into a nad 3130 phono stage from a sme 3009 s2 arm phono stage is 100 pf but cartridge load recommens 400-500pf
i think im getting about 250pf total so just wondered if there would be much difference adding more pf,
Regards, Peter
 
Unless the Shure is sounding somewhat rolled off and or 'shut in' within the mid through top end then I wouldn't bother.

Without sufficient capacitance a MM will begin rolling off well within the audible range due to coil inductance. Capacitance is restorative here, therefore, one can 'dial up' the upper midrange through high frequencies as one wishes, especially so, with such as these old Shure models. These also allow for an easy experimental path toward finding out exactly how much capacitance sounds right with your system, room, ears, taste, etc. via inserting various value resistors into the chain (i.e. rather than faffing about with numerous different cables). Much easier than the opposite case of having to reduce total capacitance in order to eliminate a shrill and/or sibilant, surface noisy sound from cartridges that 'want' to see less pico-Farads.

Let me know if you'd like to give this a go and I'll forward on a 'recipe' including a calculator.
 
As Tony says above, if you remove the cartridge, you can measure the capacitance of the full cable and arm assembly. I measured my Hadcock GH242, which has a 1 metre Integra cable, to be 150pF. I used a (dirt cheap) Multi-function Tester-TC1, which has short leads that can clip anywhere that’s exposed, along the length of the cable.

I removed the 100pF loading capacitors from my phono-preamp, which would have made 250pF in total. It gave a reduction of about 1/2dB at 8kHz, and about 3/4dB at the 12kHz peak. Cartridge is an AT-VM95ML. 150pF puts it in the middle of the recommended range. I didn’t expect that reduction to be very noticeable, but the sound is now much more realistic. The shrill sound seems to reside at around 6 to 8kHz I think.

Obviously I had exactly the opposite problem that you have.
 
Just as an FYI here, part of the reason why I suggested leaving well enough alone "unless the Shure is sounding somewhat rolled off and/or 'shut in' within the mid through top end" is that SME began fitting tiny ceramic capacitors within the RCA plugs of their tonearm cables sometime round the time they began co-marketing these under Shure-SME in North America. By the time 3009 Series III/IIIS came along, combined internal/external tonearm wiring capacitance was down to 73pF (19pF internal + 54pF external) sans caps in; with the fitted 220pF caps bringing this up to 293pF, just about perfect for old Shure (and Ortofon*) models once the capacitance of one's phono input was added in.

This bit of trivia should explain a lot to those who've rewired and/or re-shod their old SME with new plugs. Then again, perhaps not.

* Some may remember Ortofon VMS models coming with CAP210 which fit across the pins out back should one need pad the capacitance.
 
Last edited:
I have a 3009 SII that had ceramic capacitors inside the cable connector shells
Yes, I recall having seen your post over on vinylengine re your having found 220pF caps within your SME lead.

I don't post over there, else I would have long ago chimed in re: how this proved most suitable for contemporary Shure and Ortofon, etc. models.

The only official word I've come across from SME was within the III/IIIS flyer, specifically...
  • 4' (1.22 metres) length audio lead. Total capacitance with arm 293 pF per channel,
    arm alone 19 pF. Lead incorporates 220 pF padding capacitors which can be removed
    or replaced by other values for special requirements.
 
Last edited:


advertisement


Back
Top