MC Cartridge Capacitative Loading

[Ali Tait]

Have read in several places that this has minimal effect with MC's, however having a play around last night I have found that not to be the case!

Are there rules of thumb for calculating this correctly?

Can't find much on the net regarding MC's..

I am using a Benz Gullwing SLR, half metre of Yannis cable into Firebottle head amp, into Firebottle phono stage. Loading on the head amp is currently the 1000 ohm default, as that is sounding the best so far, though I will try 750 ohm at some point. Yes, that is high for an MC, but Benz recommend 400 and up.

[struth]

Dont think it has to be spot on, but as close as poss is best, and will make a big difference in many cases.

[Ali Tait]

Yeah, but as close as possible to what?

[struth]

Think the cap variance is more noticable on mm, or so im told but can affect phase on mc s as well. You have to remember to add the capacitance of cables used too. As to levels if they are not published then it would be trial and error to your ears, or do a freq response curve . Ive heard 300pf is ideal for mm

[Arkless Electronics]

MC loading does indeed have minimal effect with MC carts. The Benz has unusually high output impedance for an MC and so will be effected more than usual... I would presume no loading was correct and increasing loading will (incorrectly) reduce the top end.
We would be talking much more capacitance than with an MM here of course... 10 X more at very least...
It doesn't effect phase any more than would be expected .
I would be VERY surprised if anything other than zero capacitive loading was optimum.

[Firebottle]

In my readings 1nF appears to be a 'default', possibly just as a protection against rfi.
In the Quad 34 they fit 22nF, I have always thought that to be excessive.

:)

[Arkless Electronics]

Yeah I often fit 1n for just the same reason....
I believe Naim also fit high values of C.

[Ali Tait]

So stick with 1n then?

Tried 220pf and it sounded better I thought.

[struth]

If it sounds better, then its better Ali. End of story.

[Firebottle]

Stick with 220pF if it sounds better.

I'm fitting 100pF in the KIN, that is shared by the MM setting.

[Ali Tait]

Yes, intended to do so anyway, but what I was going to do was buy a range of values to try. Guess a range up to 1nf would be good to try?

[Greg2010]

Have a look here Ali.

http://www.hagtech.com/loading.html

Greg

[Ali Tait]

Thanks Greg, yes have seen that.

[AlfaGTV]

I'm very interested in hearing about your final choice on this matter Ali. My latest phono stage have got loading options between 100pf up to 500pf and so far i haven't delved into any experiments.
I also use a few Benz' carts!

[Ali Tait]

Have ordered a range of values, as well as 750 ohm loading resistors. Will let you know how it goes.

I was really surprised how much of a difference 220pf made.

[mac72]

I have "simulated" how different load affect freq response of your Benz , bear in mind its very loose approximation at best as Benz doesn't publish inductance and I have assumed it must be fairly high (5mH) as published resistance is quite high 38ohm as for MC cartridge - it doesnt take into account many more variables is just something close to electrical model of your cart.
Total C loading 250pF (100pF for phono stage , 150pF cable)
colors represent different laod :
blue -400ohm
green -500ohm
red -750ohm
light blue -1k
pink -2k
grey -3k
dark green -5k
it seems like higher load 3k smooth response nicely , going too high >5k will bring subsonic freq peak closer to audible range.

http://i1174.photobucket.com/albums/r614/slawekt/Benz%20R%20loading_zpsczazkmq0.png

Here is what would happen if you kept 1k resistive loading and changed C loading :
grey -250pF
green -400pF
blue -1nF
red -10nF
light blue -100nF
dark green -5k

up to 1nF not much difference , probably something 2.5nF would be best (with 1k load) , if you go higher , again subsonic peak is getting closer to audible range .
http://i1174.photobucket.com/albums/r614/slawekt/Benz%20Cloading_zpsoyen5tch.png

[Ali Tait]

Wow, great info, thanks for taking the time, much appreciated.

[Ali Tait]

If it's not too much trouble, what C would be ideal with 3K loading?

[mac72]

If it's not too much trouble, what C would be ideal with 3K loading?
Give me few minutes I plug some numbers in

[mac72]

With 3k load
blue-150pF
green-250pF
red-400pF
light blue -1nF

150pF is probably as low as you can go , TBH I would try different resistive loading first and see what you like best (keep C load at minimum), what looks good on the grapf might sound crap in real life as simulation is not perfect plus we all love bit of coloration in the sound , you might find whats flat would sound almost CD like .
But is quite clear from 1st graph in previous post why Benz advice is to go above 400ohm.
http://i1174.photobucket.com/albums/r614/slawekt/Benz%20C_loading_zpsdreb5owh.png

[Ali Tait]

Yes indeed it is. Great, thanks for that, I will experiment when I get the time.

[mac72]

Yes indeed it is. Great, thanks for that, I will experiment when I get the time.

My pleasure, it would be great if someone could measure Benz's inductance , it would give closer approximation -5mH in simulation might be way out , best to experiment and see what sounds best .

[walpurgis]

Be careful measuring cartridges with a meter. The fine coil lead out wires can fuse.

Deccas and Entre MCs were known to blow very easily. I've had two examples of each come my way damaged like this. Not done by me I might add.

[mac72]

Be careful measuring cartridges with a meter. The fine coil lead out wires can fuse.

Deccas and Entre MCs were known to blow very easily. I've had two examples of each come my way damaged like this. Not done by me I might add.

Oh no , I wouldn't use standard LCR meter to do that ,
Benz might survive , most of MM's as well but its too crude for most MC's

[Ali Tait]

LOL, no chance of that Geoff, I wouldn't let a meter anywhere near my Benz!

[sq225917]

I run my BenzLp at 2.2n and 720r. arrived at by measuring 20-20k sweep.

[mac72]

I run my BenzLp at 2.2n and 720r. arrived at by measuring 20-20k sweep.



up to 1nF not much difference , probably something 2.5nF would be best (with 1k load) , if you go higher , again subsonic peak is getting closer to audible range .


As I said simulation is very simplified and represents only "rough" electrical model of cartridge ,I might also be a decimal place out when it comes to induktance.
I assume you measured output on phono stage , I didn't take RIAA eq into the equation ,
f.responce 20-22kHz :
blue - 250pF/3k
green - 2.2nF/720R
"trilion" combinations and all might sound good , plug&play&listen
http://i1174.photobucket.com/albums/r614/slawekt/Benz%20loading%2020%2022k_zpsh4qmhkeg.png

[RothwellAudio]

I have "simulated" how different load affect freq response of your Benz , bear in mind its very loose approximation at best as Benz doesn't publish inductance and I have assumed it must be fairly high (5mH) as published resistance is quite high 38ohm as for MC cartridge.
I think that might be quite a high estimate of the inductance. Audio Technica's OC9 is specified at 25uH (and 12 ohms). That's 200 times lower than your estimate for the Benz, though I agree that the higher resistance implies more turns of wire and more inductance.
Everything will look considerably different with an inductance of, say, 50uH.

[mac72]

Yes , I might be (probably am) out but by how much is difficult to say , unfortunately induktance is not a function of resistance , it could depend on number of turns , coil radius , number of turns , lenght of the wire , etc..

[Arkless Electronics]

It would be safe to resonate the thing with a known capacitor value, say 10n, from a low level RF source via a resistor of lets say 10K and that will give the inductance from some simple maths;) Of course this needs someone with both the test gear and a Benz cart.....
Or an email to Benz may prove easier:D

[mac72]

Is bit annoying that some manufacturers don't give a ... about publishing all specs , it would be much easier to determine "ideal" conditions ,
Model I made is very crude as it doesn't include mechanical properties but to do it properly one would need consider it as oscilating device with high resonance and create electro-mechanical model, maybe next weekend:)