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MM capacitive loading with stock Technics SL-1200GR or SL-1500C

Anj

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This being my first post on the forum, and in the spirit of objective measurement, I measured the stock connecting cable and tonearm cable without the headshell using a capacitance meter. The error for the range I used is + or - 1%. The SL-1200GR connecting cable alone measured 80 pf. When connected to the turntable the measurement rose to 106 pf. Therefore the tonearm cable only presents approximately 26 pf. The SL-1500C connecting cable measured differently for each channel: 115 and 109. Tonearm cable alone is approximately 32 pf. These measurements will hopefully be useful when calculating total load on a particular cartridge.

In practical application it helps a great deal to know the load presented by the phono input. I don’t have a way to determine the load presented by the internal phono preamp on the SL-1500C. My guess is that it is optimized for the stock Ortofon 2m Red cartridge. Ortofon specifies a desired range of 150-300 pf for the 2m series. Tonearm/headshell cable aside, can we conclude that the capacitance of the internal preamp is between 118 and 268 pf? Your guess is as good as mine but that seems reasonable.

In the days when Shure (250 pf for the M9x and V15typeVmr, and 400-500 pf for the V15typeIII) and Stanton (275 pf for the 681eee and 881s) cartridges were available, higher specified capacitive loads were common. Even the Ortofon OM series which is about 3 decades old specifies 200-500 pf as a suitable range. Audio Technica was an outlier with 100-200 pf and have remained consistent to this day. Sumiko currently specifies 100-200 pf for the Oyster series. Nagaoka does not list values on their website. Therefore, when combined with the phono input capacitance, the use of the stock Technics connecting cable is likely to bring the load out of range for certain brands.

My guess is that 47 pf at the phono input (Rogue RP-5, Schiit Mani 2) is an exception; values of 100 pf and higher are more common. How, then, can the load be brought into range? Faced with this problem I ordered a Blue Jeans LC-1 cable in a 2 foot length which measures 32 pf (terminated). Therefore, I was able to interface my SL-1500C with my phono input of 100 pf and come up with a total load of approx. 164 pf. This works for the Audio Technica and Sumiko cartridges. The stock Technics cables will likely be suitable for Ortofon. The jury is out on Nagaoka.
 

mike70

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Thanks for sharing ... I can say that in ebay you can find RCA terminated cables with Mogami low capacitance for 1/2 or 1/3 the blue jeans price
 

Digby

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Audio Technica was an outlier with 100-200 pf and have remained consistent to this day.
I tried to start a thread about this, asking why AT are outliers in this. Is there a technical reason? It doesn't make sense, at least with cheaper gear, where the consumer is unlikely to know about/be able to adjust loading, to go with a very different spec than most everyone else. Do you have any insight into why this may be?
 

DSJR

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Before my ears became terminally bad, I did some brief experiments with a phono preamp able to flick dip switches for loading. I'd ask respectfully PLEASE not to worry overmuch these days with more modern designs (Ortofon in the case of the SL1500C and AT VM95 with the SL100C). The 2M designs (based on the OM inners I gather) don't seem as fussy on loading as their VMS ancestors were and the VM95's seem pretty ok as well with a typical 200pF loading. Fine tuning the VTA and tracking force will almost certainly do more I think. not sure you need ot lok at other MM types although Grado and Nagaoka as well as the old fashioned but beefy toned Sumiko MM's have their fans still in more retro systems.

As for Shures, the last ones (V15V and descendants, 97XE and so on) gave you a choice. Low capacitance meant a gentle 5dB downtilt from 1kHz to 20kHz and increasing it tended to flatten the response to 10khz after which it also fell to -5dB at 20kHz. My V15 III (new old VN35E stylus) is as hard toned as it always was (the VN35HE was a revelation once it came over here) and changing capacitance doesn't alter this characteristic I remember when I tried.
 

Digby

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@DSJR From what you say, it sounds like things are going in the right direction then, in that loading is less of a factor with modern carts and they are happy with typical ranges available from any sensible equipment you may use. I wonder why this took so long for manufacturers to figure out and somewhat standardise? It seems to me the kind of thing you want a standard for 99% of the time, save at a high price point where people will have knowledge of, and access to equipment that can easily accommodate different loading.
 

DSJR

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@DSJR From what you say, it sounds like things are going in the right direction then, in that loading is less of a factor with modern carts and they are happy with typical ranges available from any sensible equipment you may use. I wonder why this took so long for manufacturers to figure out and somewhat standardise? It seems to me the kind of thing you want a standard for 99% of the time, save at a high price point where people will have knowledge of, and access to equipment that can easily accommodate different loading.
I'm way out of it now, but I believe that 'digital' as in CD to start with, was th ebest thing that ever happened to vinyl record reproduction, as at last, 'we' had a proper easily verifiable reference to aim for. I appreciate the vinyl diehards still sniff and even sneer at digital, but that's their ignorance (intentional or otherwise) talking there.

If my stash of old turntables (Duals, Garrard autos and Duals and a Lenco or two and a Thorens 160mk2 sans arm) went up in smoke, much as I 'ought to' buy a Rega 6, I'd probably go to an SL100C or maybe the full-kit 1210mk7 as they'd see me out and be easily usable for any descendants or inheritors... I'm also a 2M and AT fan as well and can pick and choose without angst here :)
 

dlaloum

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If you can find the circuit diagram for the SL1500C inbuilt phono stage, you might be able to identify the C loading...

You can change the "voicing" of a cartridge by adjusting the parameters - the H of the cartridge body, the C and R of the loading adds up to an EQ curve.

This is balanced against the resonance that all stylus cantilevers have - the better the cantilever the higher the frequency at which the 1st resonance happens - at that frequency you get a bell curve of rising sensitivity/output (along with rising distortion, reduced tracking ability etc...) - and after the resonance bell curve, you typically have rapidly dropping sensitivity (as it starts to get beyond the needles ability to track the modulations due to its effective mass)

Basically you use the loading EQ to balance out the resonance and try to achieve a relatively flat frequency response.

The very best exotic cantilevers, with ultra low effective mass, can move the resonance frequency beyond the audible range - making the whole loading process much easier...(Shure V15VMR moved it out to around 32kHz - leaving nothing but a hint of a rise around 20Khz, easily compensated for by light loading)

Today, exotic cantilevers are rare on MM's - and the standard aluminium cantilevers have resonances which range from around 10khz to 15khz followed by a steep drop off

You can model the EQ curve, and then deduct it from a cartridges measure response to identify (roughly) the core cantilever response...

You can then vary the EQ curve model (try various loadings) - the identify the optimal FR - before applying it to the cartridge and seeing how the system responds.

Yes it is a rough estimate - but you can get surprisingly good results with a wide variety of cartridges using this method.

Another interesting thing - various manufacturers have had "families" of cartridges with styli interchangeable between them (Shure, AT, Stanton, JVC)... the differing bodies in that family typically have different inductances - sometimes the trick to getting the optimal combination for a given stylus is to vary all 3 (H/C/R).
 
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