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Capacitance loading for AT 150 mlx cart

I am considering an Audio Technica 150 mlx cartridge for my resurrected vinyl system. Arm is an ADC LMF carbon fiber arm (8 gr effective mass) on a Technics SL-150 MKII table. Phono pre-amp is PS Audio GCPH.

My concern is capacitance loading, as some report too much capacitance can make the 150 mlx sound bright. AT recommends 100-200 pF. I am assuming this is total capacitance, including cables and pre-amp input.

The GCPH has an input capacitance (at 47 K) of 100 pF. Problem is my cables are 250 pF. They are ADC versions that came with the arm, and have the 5 pin DIN connector. I got some reasonably priced teflon insulated silver plated CU cables from an Isreali manufacturer, but they are also about 200 pF.

So can I use these cables or do I have to make ones that are 100 pF? I have priced various aftermarket versions and I do not want to spend more for the cables than the arm and cartridge are worth.

Or do I have to forgo using this cartrigde in the first place?

A salesperson at Needledoctor had suggested that the AT spec for 100-200 pF was for the pre-amp input loading only, and did not include the cable loading. Is this possible? I would have thought the spec was for the total loading, although it is very difficult to find 3 meter phono cables at 100 pF total loading.

Any input would be appreciated.
dhl93449
fleib
1,124 posts
 
Blue Jeans Cables has interconnects that are 12.2 pF/ft. They might make you a set with DIN plug, or you could buy a set and incorporate them. They are relatively inexpensive, but many people report excellent, good-sounding results.

Some people also change the input capacitance on their MM input. 25 or 50 pF should help, of course you'd have to modify your pre. It's not only AT, some other mfg also recommend total load of < 200pF.
Regards,
johnnyb53
3,510 posts
 
When I was shopping for a phono pre a year ago, I came across a great deal on a demo Musical Surroundings Phonomena II. However, I also found out that the lowest input capacitance setting on that phono pre is 200 pF for a total of 300 with TT cable, so I passed. I got the Jolida instead and its wide range of capacitance (for MM), resistance (for MC), and gain settings made it easy to dial in my current rig and any LOMC, HOMC, MI, or MM I may get in the future.

And yes, the Needledoctor guy was wrong. The 150MLX wants to see 100-200 pF total including the tonearm cable. At least, in my case, knowing the Technics cabling is spec'd at 100 pF, I get the best sound when the loading into the phono stage ranges from 0 to 100 pF, and preferably 50-ish.
dhl93449 OP
455 posts
 
Thanks for everyone's feedback. Incredibly useful.

Looks like no matter what cartdridge I end up with, low capacitance cables may still be required. As Al rightly points out, large low Q resonant peaks at 40KHz can be just as damaging as ones at 15 KHz.

Its also clear that Needledoctor sales folks may be more interested in selling cartridges that providing correct information.

Thanks to Johnnyb for the cable suggestions, esp the Cardas versions. The Golden Presence has an incredibly low capacitance of 12 pF/ft x 4.1 ft (1.2 m) for a total of 50 pF. They are still a bit pricey but good know they are available as a fallback. Not sure the Blue Jeans stuff meets my criteria. I would like to stay with silver plated Cu/Teflon insulation which may mean I'm building my own. I have some DH Labs BL-1 Silversonic cable that is 17 pF/ft which may work.
dhl93449 OP
455 posts
 
Just got another wild idea, actually from another post where the Soundsmith folks are recommending the use of attenuators between the cartridge and pre-amp. As I posted there, in the late 70's we did this with MM cartridges to increase the effective phono overloads of pre-amps. The sound improvement was very noticable.

It occurs to me that a 5:1 attenuator would isolate the pre-amp input capacitance from the cartridge, leaving only the cable capacitance. This would give me another 100 pF to play with, at the expense of more required gain, which is in adequate supply with the GCPH. This would also isolate the very high impedance of the cartridge at the LC resonant point, another issue that affects the stability of the phono preamp input stages. With the attenuator, the phono pre-amp sees a pretty constant 10 K source impedance throughout the frequency range, not the nonlinear 1k to 25K it sees unattenuated.
almarg's avatar
Ag insider logo xs@2x
almarg
9,670 posts
 
Interesting thought about the 5:1 attenuator. It seems to me that it might very well do the trick, but I would have some concerns.

One concern is the possibility that the higher source impedance seen by the phono stage at low and mid frequencies, compared to direct connection of the cartridge, would result in some degradation of the phono stage's signal-to-noise performance, as well as increased susceptibility to hum pickup in the phono stage input circuit. Note in one of the links I provided earlier that the cartridge's DC resistance is spec'd at 530 ohms.

Also, obviously, the attenuator would have to be constructed so as to provide good shielding.

Finally, stray capacitance in the attenuator and its input connector would reduce the 100 pf saving at least a little bit, perhaps by 10 pf or so as a rough ballpark guess.

Best regards,
-- Al
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