Capacitance: Set Me Straight Once and For All!

[jnjansen]

I have been trying to improve the sound of my system as of late and have opted to make sure that, before trying to upgrade components, I have all other variables for sound quality accounted for. The one thing that confuses the hell out of me is capacitance. My understanding of it is non-technical but I know that I should use low capacitance cables between by turntable and phono preamp. This is especially true for the fact that I use the AT-95 and AT-120, which recommends 100-200pf. I have a Technics SL-1200mk5, which has 125pf interconnects. My phono stage is a Musical Fidelity V-LPS, which has 75pf. So with the addition of the tonearm wiring, I am already over the manufacturing recommendations.

Anyway, my question is this: does high capacitance lead to a brighter sound that accentuates surface noise or is it the other way around? I read this article a few months ago that lead me to believe that high capacitance "rolls off" or diminishes highs:
http://daddarioinc.blogspot.com/2009/03 ... es-it.html
However, after reading many posts on this forum and elsewhere, the opposite has been said, that high capacitance leads to a brighter sound and can accentuate surface noise. So can someone set me straight once and for all?

[hoolio]

Just to add to the topic, here is a view from the pro audio community:

http://www.soundonsound.com/sos/nov09/a ... cables.htm

[abril]

Shows the effect of extra capacitance,although what can happen depending on the cartridge is it can accentuate the hf peak,and if the peak is in the audio spectrum (not on this cart)it can give a nasty spitty effect.

Top image is just an extra 100pf in this case.

[HT Performance]

Capacitance itself won´t lead you anywhere.

We look for capacitance, to calculate impedance, so it means that inductance is also a necessary parameter to know.

The AT120E has about 350mH inductance, and if your Technics has 125pF on connects, this will tell you that your cartridge will resonate at 24.1KHz and the optimum resistive loading is 52.9KOhm.

And I can tell you that playing with the resistive loading can really change the sound. Too much capacitive loading may cause ringing below the resonance frequency.

Check here: http://www.vinylengine.com/cartridge_database_tools.php#ResonanceCalculator

All that matters in the total capacitance seen at the pre-amplifier front-end.

I don´t understand your concern with the 75pF... Does your pre-amplifier has input cables with 75pF and you´re connecting to the TT ???

[dlaloum]

To try to keep it simple...

The capacitance combined with the inductance of the cartridge will define the "rollover point" - the frequency at which the response starts to drop...

The Resistive load will then define exactly what happens at that rollover point and how steep the dropoff will be after the rollover point.

If the resistive load is "subcritical" - the rollover will be a gentle curve, and the slope will be relatively gentle.
As resistance load rises, the rollover curve point becomes sharper and the slope steeper, after the critical point, additional resistance starts to generate a resonance peak at the rollover curve frequency - this is a bell shaped boost in amplitude... followed by an even steeper dropoff. Further increases in resistance will make the boost resonance more extreme and the subsequent slope even steeper.

Raising capacitance (or inductance) lowers the frequency at which the rollover point happens - if the load is subcritical, you will effectively be "rolling off" the high end by increasing the capacitance (or vice versa)

But if you are at a resistive load where a resonance is generated, then lowering capacitance will shift the frequency which is boosted to a higher frequency...

All cantilevers show a dip in performance due to mechanical imperfections somewhere between 2k and 10k Hz, many cartridges have their intended capacitance/inductance/resistance designed so that the resonant peak fills out the standard mid-high dip.

But if the capacitance is lower than expected, that will shift the boost to the wrong frequency.... making the cartridge sound "bright", and the dip in the mid-highs will merely exaggerate this.

If the capacitance is higher than expected, the highs could be exageratedly rolled off, and the boost shifted too low down the range, boosting the midrange and presence zone...

the whole equation as described above is best visualised as a plot... changing any one of the parameters (resistance, capacitance, inductance) - changes the shape of the frequency response both in terms of rollover frequency point, slope after that point and resonant peak height and width (if over the critical resistive load).

This makes it a NON SIMPLE thing! - but if you can get your head around it, it can become very very versatile in adjusting the voicing of any MM/MI cartridge.

So roughly speaking...

Higher capacitance will not strictly speaking make things brighter - but by shifting the rollover frequency and its associated boost, it may make a particular set of frequencies more prominent, giving an impression of "brightness".

As a starting point you are working within the suggested range from AT... your Total capacitance being 200pf is quite good really!

My own experience with AT cartridges tends to show that they sound better with the resistive load a little below the standard 47k... and I would suggest you make up some parallel R plugs and experiment with lowering the resistive load - somewhere between 42k and 32k is where I think you will find the optimum setup.

hope that helps

bye for now

David

[jnjansen]

Thanks for the replies--it has gone a long way to helping me understand this issue but I still have some questions. David perhaps hit the nail on the head when he says this is a "NON SIMPLE thing!"

What has motivated this post, in part, is that I feel the high frequencies in my system are a little too bright and that, depending on the recording, a bit thin. I have a friend with a Ortofon 2M Red with a Cambridge 641 and a PL-570. I've played albums with a good amount of surface noise on my system but on his system the snap, crackle, and pops seem to be rolled off or not as pronounced, as if he had a high/scratch filter on. I know other things come into play here (such as his speakers), but I've read that the 2M Red should have 150pf of capacitance for optimum performance. The 641 apparently has 250pf of input capacitance. I have no idea what the capacitance is on the stock interconnects on the PL-570 but they must be over 125pf. So he is already over 400pf total. He always boasts how everyone of his lps that he buys is "flawless with no surface noise whatsoever." Over the years, I have learned how to clean my albums very well and set up my cartridge properly, so I am, perhaps, wrongly attributing too much of these boosted hf to low capacitance in my setup. But given what I have told you so far, does this seem to be a good explanation?

In regard to restive loading, I have been reading about how to do this and may try to bring it down between 42 and 32k, as you suggest. I am intrigued because I have a Kenwood Basic C2 preamp that has some selections for loading: MM: 100 and 47K; MC: 100, 30, and 10K. To make a long story short, the phono input was giving me static and in the process of trying to fix it I broke a thin metal sheet inside. I tried to repair it but the only way I could get it to output sound was at a much boosted gain level but with a sound that made my AT-95 extremely punchy and quick. As long as I played it at low volumes I just went with it and kind of enjoyed it. So I'm thinking: was this loaded for MC (this accounts for the extra gain) and at 30K (the punchiness)? Anyway, sorry for the long response.

[dlaloum]

As you said, his 2M Red is being run substantially over the optimum capacitance... Ortofon spec is 150 to 300pf - so nominal is 225pf - he is most likely running at close to double that capacitance - so his high end is rolled off, effectively making LP Noise "inaudible" - but it will also be affecting air/space/imaging and other aspects related to high frequency response.
The sound is probably also "meatier" more bassy - which is the perceived result of having slightly depressed top end.

The Kenwood Basic preamp should be excellent - and worth while getting working correctly again!

For resistive loading, you can only ever lower the total R using parallel plugs - you cannot raise it. - But if your preamps has a 100k setting, then anything down from 100k is possible.
This won't be required for AT cartridges, but increased R is often beneficial for Shure cartridges (which at default settings have a slightly depressed high end).

I definitely think you are on the right track.
Remotely diagnosing your preamp issues is..... fraught! - may be worthwhile trying to track down a reputable local tech to help you with it!

bye for now

David

[Ldg]

As you said, his 2M Red is being run substantially over the optimum capacitance... Ortofon spec is 150 to 300pf - so nominal is 225pf - he is most likely running at close to double that capacitance - so his high end is rolled off, effectively making LP Noise "inaudible"

Surely it's the other way round, increased capacitance in this case would boost the c 8kHz range leading to brighter sound and all the psycho-acoustic oddities that go with lifting/suppressing that range ? In my experience, and for good theoretical reasons, reducing 2M loading capacitance generally produces a less pronounced top end sound......despite theoretically lifting the extreme hf as DL posts, which is more classically associated with the impression of 'air' if done in isolation.

Unfortunately, loading variation is surrogate eq. Issues of taste, the rest of the system, the room, and programme material are factors in arriving at a setting one enjoys. Put it another way, there are other influences which might interact in someone else's system and obtain a different overall results.

It's being comfortable and enjoying long term listening that is the goal with overall eq, IMO.

[jnjansen]

Thanks again for the help and the encouragement. Yes, I would love to get the Kenwood up and running again. I have a Shure v15 iv and a 91ed, so your suggestion of starting off with the 100k setting and putting in some parallel resistance plugs to get it to optimal performance is something I would never have thought of.

In regard to the AT-120, I used the calculator that HT Performance cited above, and I came up with the following numbers: 19kHz resonance and 41.8ohm optimal loading. I am going to contact db Systems today and see if I can get some custom loading plugs so that I can load at 42 and 36 ohms.

The only question I have now, is that if I get a resonance at 19kHz, I am doing pretty good right, since that is at a frequency most of us have trouble hearing?

[dlaloum]

Depends... the resonance will generate a bell shaped amplitude curve - depending on the level of damping (resistance) that will be wider or narrower - if it is very wide it can have an influence on frequencies up to 2 octaves away (which would be circa 4kHz)

The other thing is you also need to take into account the cantilever response and its own losses and gains - specifically the cantilever will also have its own resonance - with a similar effect.

But you are right, the higher the resonances are in general the better the sound becomes - and the very best setups generally place the resonances well above 20kHz.... but 19KHz is not so bad! (especially considering the AT120 is a budget cartridge...)

bye for now

David

[Ldg]

Yes, there's far too much focus generally on frequencies which are at, or beyond, the threshold of hearing at normal programme levels IMO.

The appearance of brightness mostly relates to content in the 6-12kHz frequency range, perhaps even lower, and its relation to other programme content levels.

The reason resonant responses, even at say 19kHz, might affect perception of brightness is that artifacts of the resonant system can extend well below the resonant f, as DL posts. And a general 'shape' to the profile implying some lift in the 8-12kHz range infers some effect on brightness. But much depends on specifics, about the depth and 'Q' of the resonance.

In the case of a 2M body and the RC values posted in play, the primary electrical resonance is square bang in the range likely to affect perception of brightness, c 8KHz. Then changes to C and R are pretty likely to bring abut changes to how bright things sound overall. It really is a bit of a mixed muddle of eq contour. A matter of fit to the rest of the system and taste. IMO, R loading plugs are the way to fly with the 2M range, and keeping C below 200pf total IME gives enough range likely to find something which suits.

Fiddling about with 12kHz+ frequencies might change the perception of 'air', and this is also worth getting right for long term listening too, but probably won't drive you nuts, whereas a gross-out in perception of brightness just probably would

HTH !

[jaspar]

I'm still a bit confused about this too. Any help would be greatly appreciated. I recently acquired a Signet Tk3Ea cartridge and paired it with a new AT125LC stylus. This should be a nice combination, but I think it could sound much better if I experiment with loading.

How exactly do I use the load/resonance calculator? Do I need to enter the capacitance of the cabling only, or do I include the intrinsic capacitance of the phono input as well?

Also, does anyone know what the recommended capacitance range for the Signet Tk3Ea cartridge might be?

[jnjansen]

Someone with more knowledge than I should chime in here, but since I just ran through the procedure for my AT-120 and 95e, I think I can help. From everything I read, you should include everything up and through the phono stage for calculating capacitance (tonearm wire, interconnects, and phono stage).

I found the owners manual for your cart here:
http://www.vinylengine.com/library/signet/tk3ea.shtml
It's coil inductance is 490mH. I would then do some research to calculate your capacitance to the best of your ability. Just playing with the numbers on the VE calculator, if you can keep your capacitance to around 225pf, you would not have to change anything on your load, that is, if you have the standard 47kohm phono stage. If you can't reach that level, then you may have to alter the restive load.

I am still waiting to hear back from David at db Systems for loading plugs. I don't have the time to diy me a pair. Hope that helps.

[jnjansen]

BTW, I too just bought the AT125LC for my AT-120 and it's just starting to open up after about 20hrs of playtime. I would wait until you break that sucker in before you start to experiment with the sound.