Why don't phono preamp manufacturers 'standardise' input capacitance?

G'day all, this one has always really annoyed me as the already high default input capacitance of many otherwise excellent commercially made compromises the potentially good performance of many moving magnet phono cartridges.

220 picofarads seems to be a relatively common value, and that value when added to even quite low interconnect and other cable capacitance can easily push the overall load capacitance to well beyond 300 picofarads, way too high for many 'typical' moving magnet phono cartridges.

The, to me anyway ridiculous loading capacitance recommendations of many Audio Technica moving magnet phono cartridges of 100 to 200 picofarads can never be met with such an inherently high input capacitance value of 220 picofarads....and I have seen other commercially made phono stages with even higher input capacitance!

Thankfully there are some excellent phono stages around with flexible and adjustable input loading arrangements and I applaud those, but there are still an awful lot of good phono stages with unacceptably high default input capacitance. Examples are the Cambridge 640P and the budget but potentially excellent TCC TC-750, both factory set at 220 picofarads.

I have actually changed the factory installed ceramic 220 picofarad input loading capacitors back to 100 picofarad WIMA's on my TCC TC-750. In my opinion 100 picofarads would be an ideal 'real world' default input capacitance value and one of my phono stages (the ANT Kora 3T SE), is indeed factory set at 100 picofarads.

Is there some sort of EMC requirement that 'forces' manufacturers to use these clearly unacceptably high value input loading capacitors? At least in my DIY work I can pick any value of an input loading capacitor that I wish, and 100 picofarads fits the bill 99 per cent of the time! Regards, Felix.

 

There is a lot more to cartridge design than simply capacitance. Trying to standardize the output values of all the cartridges on the planet would be like throwing the baby out with the bathwater. You couldn't have the supreme detail and fantastic frequency extremes of the moving coil cartridge, for example, if all cartridges had the same output capacitance.

 

I agree that input capacitance values varies and are many times too high. The best is to have switchable capacitances but that makes the amp a bit more expensive, if it should be done well. Mine has 33pF input capacitance so I end up below 100pF as a total, and that suits me. As the capcitance formes a resonance circuit with the pickup´s inductance, to get the best out of the pickup this frequency is important to know, and also measure the response as this seldom is cut and dry, IMO.

 

G'day all. Paul Saldana: maybe so, but many moving magnet cartridges 'are' affected by load capacitance. Wouldn't you rather listen to a phono cartridge matched optimally to its connected phono stage? I would.

At least with 100 picofarads you can always add additional capacitance if required and I've certainly done that. It's a little difficult to do if the load capacitance is already too high. Regards, Felix.

 

It depends what we mean by effected when it comes to MCs, all pickups are of course effected but way high up in frequency, where it has no influence below 30kHz. A 100pF cap would be too large for me.

 

The idea of having all carts work with the same capacitance seems as wrong minded to me as demanding all loudspeakers have the same impedance. I don't want my electrostatic or planar magnetic speakers to sound anything like a Klipschorn.

 

They might standardize phono preamp input capacitance if there were a cartridge output capacitance standard they could adhere to.

There isn't.

In the many cartridges I have tried on various systems new and old I have never had a problem with capacitive loading (that I was aware of or able to hear). I spend more time listening than wondering though.

 

G'day all, I'm not saying that all MM cartridges should be optimised for 100 picofarads but at least that value gives one the option to optimise if deemed necessary. Regards, Felix.

 

I'd be happy if the preamp manufacturers just a) consistently included capacitance info in their product specs (and the same goes for tonearm and arm cable makers) and b) included 2 or 3 different settings. If a phono stage is meant to be used with MM carts and has only one set input capacitance, then it should be a low one; if the preamp has a single high setting, then it should be clearly labeled as an MC phono stage in its product name and advertising.

 

I would agree with Felix that it´s better with a standard than no standard at all. I´m not sure about what cap value it should be though. And the best would be switchable caps.

 

G'day all, I am 'comfortable' with 100 picofarads as that is a generally 'workable' value once interconnect and tonearm wiring capacitance are included into the 'overall' capacitance value. Regards, Felix.

 

Talking with Michael Yee, he says RF rejection is related to cap., so some of that is to manage noise issues more associated with MC carts.

 

Are we talking about an RC filter made from the load resistor and the load capacitor that rolls off RF? I could see, yeah, in that case, with a 100 ohm load resistor and 100 pF or less of capacitance, the potential, I guess for problems in the VHF range, although the resonant frequency of a typical low output MC in that kind of set up would be more in the ELF range and is there much if anything there that the system is going to act as an antenna for that's going to create noise? I don't know enough about the science and engineering here, maybe someone could explain?

I does seem like the best design offers capacitance adjustment as well as resistance load adjustment because the needs of higher inductance MMs and lower inductance MCs are just very different, so setting a single standard is tough.

 

That may very well be what he was referencing.

From the designer:

 

This was brought up in another thread, but "Moving Magnet Capacitance Loading Fatigue" has gotten the best of me and I've "moved on" to moving coil.

 

I am about to be done with it, but am happy to have cracked the Mac nut, so to speak, in finding a free software measurement situation.

This is looking pretty useful.

 

That hump still looks like too high capacitance presented to your cart. Are you leaning that way?

 

A three db lift on the top is characteristic of this cart, and typical of the 50K loading. That is what the owners of the cart strive to fix. After I test my test LPs against each other and suss out the issues as best I can with the source, I’ll test the cart @ 38K, 50K and 61.5K and compare. 38K is where I listen most of the time. This has already been done by other users, so I am really trying to work out a procedure for myself.

In terms of the capacitance, the preamp has 68pF and the cable from the cart to the pre is 33pF. I don’t think I will shorter the cables again or be able to find a lower mass RCA.

 

I've seen it mentioned elsewhere that the 440's mechanical cantilever resonance is around 14 kHz, so even with the electrical resonance out of the way like here, there would still be a top end lift.

 

I'm not up on the details, Felix, but I'm certain that for CE labeled products there are such requirements.

 

Interesting. The corresponding fast rolloff to 20kHz looks like what I have seen when the capacitance is too high. But then again, it could be the rolloff on the cutting of the pink noise itself. My understanding is that the high end of pink noise really heats up the cutting head so they tend to roll it off aggressively around 20kHz or so.

 

It would be interesting to see it run through a phono pre with no capacitance, in my case @ 33pF for the cable. In general, the response looks much better @ 32-38K. With the flexibility of this particular plug-in, you can alter the slope and tailor every aspect of the chart so you can visually emphasize the variation.

I think the gap in the market is for good budget phono preamps designed specifically for MM carts that have all the versatility needed to fine tune. The Budgie is an interesting example. My speakers roll off at the top, so I can tollerate a little boost. It is very nice to be able to tailor the cap and resistance to maximize the synergy.

 

I also have seen this mentioned. I´m a bit sceptical to this though, seems far too low as I see it.

 

They tried a somewhat similar scheme back in the 80s with P-Mount cartridges. Every parameter of those cartridges had to meet a rigorous set of committee-designed specifications. And I've yet to see anybody rave on and on about the incredible sound out of their p-mount equipped phono setup. Why is this? Because making such design constraints necessarily imposes compromise on other aspects of a design which often cannot be overcome. Why? Because things which are designed by committee will never, ever represent the best that is possible.

Its sort of like saying: "Why doesn't Ferrari design a car with the exact same performance which fits into the exact same footprint of a prius?" Now perhaps some people would like their new prius-shaped Ferraris, but I'd pass (even if I could afford one, which I can't).

That said, I agree that any phono preamp which has high input capacitance is by its nature sub-optimal. But it is/was the designer's decision to make whatever design compromises that they see/saw fit. And its your right not to buy it.

But let me turn this around on you for a minute:

How about we make it illegal for phono-cartirges to require optimum reistance loadings greater than 47k? If we did this, then we could eliminate non-conforming products such as that Sure 97 because they would fail to conform to the standard input impedance requirements for every single phono preamp made for the past 60 years.

 

Here are some interesting findings from Jonathan Carr (Lyra cartridges) regarding capacitance loading affecting even MC cartridges. To paraphrase him, though the frequency bumps are well above the audible threshold those ultrasonic spikes increase intermodulation distortion in the phono-stage making it "grating to the ear" his words. I believe his opinion is to have the lowest possible capacitance before (cable)/in the phono-stage.