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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
dhl93449 OP
455 posts
 
Al:

Thanks for your input. Since posting I have done more digging into this and it's a bit more complex than I first thought.

The site you reference is a bit misleading because his plots don't take into account the effect of the series resistor on the shape of the peaking (he assumes a Q factor of 1).

I found this reference by Rod Elliot to be a bit more realisitic:

http://sound.westhost.com/articles/cartridge-loading.html

The problem is that some manufacturers use the electronic tuning response to compensate for mechanical resonances of the stylus tip/cantalever/motor devices in the cartridge, so that the overall actual response is not just predicted by the RLC network of the elctrical components. See, for example:

http://www.tnt-audio.com/sorgenti/load_the_magnets_e.html

So the electrical modeling would suggest that the lower the capacitance, the better. But for some MM carts this might result in a reduced high end response due to mechanical effects.

Not sure how any of this is related to the performance of the AT 150 mlx, but I am begiining to remember why I don't like the concept of MM carts, and may re-consider using them. MCs don't have this issue due to the much lower inductances and impedances. They are tolerant of higher cap loading because of this.
johnnyb53
3,510 posts
 
Swap to a 100 pF arm cable if you can. I've been using an AT150MLX for 4 years and love it. I currently have a JoLiDa phono stage with highly adjustable capacitance. I have a Technics SL1210 M5G TT whose arm cable capacitance is 100 pF. I have played with the input capacitance in my preamp and found that 0 through 100 pF works OK, but my personal preference is an input of 47 for a total of 147 pF (or 150). However, 200 total is good enough that it could come down to system matching. I definitely wouldn't want to run it into 300 pF or above.

I hope you can get it to work for you. The AT150MLX has a very musical balance of robustness and body on the one hand and spatial cues and detail on the other. It's also an excellent tracker.
dhl93449 OP
455 posts
 
Johnyb:

Where can I get a 100 pF RCA/DIN phono cable? Most manufacturers of aftermarket versions don't spec the capacitance. ADC made a 100 pF special version back in the day, but this is NLA and I have never seen a used one.

FYI the ADC arm's internal wiring is 30 pF (headshell to DIN in the arm), so the DIN/RCA cable has to be about 70 pF to have a total interconnect of 100 pF. The input capacitance on the GCPH is fixed at 100 pF. They use all surface mount capacitors so exchanging or modding input caps in this phono preamp is near impossible.

I think your setup with a total of 147 pF is right on the money, as the references indicate the lower the better.

To get to 70 pF in the interconnect would mean I have to build my own cable, or build an interface box with a short cable to the arm/DIN and RCA bulkhead connectors. I have low cap RCA/RCA interconnects I can use from the box to the pre-amp. Or I could shorten the cables I have to under 12" and mount new RCAs. But that limits where I can place the preamp; it would need to be immediately adjacent to the turntable.

A lot of work just to use this cartridge though. I am leaning back to a HO MC or maybe MI

johnnyb53
3,510 posts
 
04-17-12: Dhl93449
Johnyb:

Where can I get a 100 pF RCA/DIN phono cable? Most manufacturers of aftermarket versions don't spec the capacitance. ADC made a 100 pF special version back in the day, but this is NLA and I have never seen a used one.

FYI the ADC arm's internal wiring is 30 pF (headshell to DIN in the arm), so the DIN/RCA cable has to be about 70 pF to have a total interconnect of 100 pF. The input capacitance on the GCPH is fixed at 100 pF.

If your tonearm cable is already 30 pF and the GCPH input is 100 pF, then you want the phono interconnect to be 70 or less.

Kimber Kable gives the capacitance specs for *all* their interconnects including phono interconnects. Their TAK Cu is 47.1 pF, so that would make your entire phono signal chain 171 pF, which is nearly ideal. All the phono cables in their standard line are 1M long and 47 fP, give or take a couple tenths of a picofarad.

Nordost also publishes specs, and their Frey 2 is 25 pF per foot.

Cardas also publishes specs. Their Neutral Reference is 20 pF per foot.

So here are a few off the top of my head that offer low enough capacitance to dial in the right overall total for your phono signal chain. I'm sure there are more makers that publish, but I knew that Nordost and Kimber interconnects tend to have low capacitance. I was pleasantly surprised by the Cardas. That may explain why his wire is popular for tonearms.
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almarg
9,670 posts
 
DHL, thanks for providing the references and the additional comments. Yes, the Hagerman paper is somewhat simplistic, most notably in not addressing the fact that for MM's too little capacitance can result in too little upper treble.

Good inputs from Johnny. His finding that optimal results occurred with 147 pf, right in the middle of the recommended range, would seem to further confirm that the salesperson you spoke with was mistaken.

Re MC's, the response of the cartridge at audible frequencies will of course be pretty much insensitive to load capacitance. A point to keep in mind, though, is that the amount of load capacitance may still have significant audible consequences (with lower capacitance generally being better), due to effects that the ultrasonic resonant peak may have on the phono stage, and due to constraints that it may impose on the choice of resistive loading. See the post by preamp and cartridge designer Jonathan Carr (JCarr) dated 8/14/10 in this thread.

Regards,
-- Al
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