MC Cartridge loading with a step-up ... Attn. John

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andyr

MC Cartridge loading with a step-up ... Attn. John
« on: 26 Dec 2003, 10:32 am »
John,

I would be grateful if you could explain the cartridge loading issues when you use a step-up transformer like your MU step-up kit.

1.  I understand the fact that the 47Kohm input load of a typical MM phono stage looks like 470 ohms to an MC cartridge, if you have a 1:10 turns ratio in the step-up transformer.  (That's actually just perfect for my Benz Ebony LP!)

And your web site shows how to adjust this downwards if your MC cartridge prefers to see a lower 'R' loading.

2.  What about 'C' loading for an MC cartridge?  Could you explain, please:

a)  whether an MC cartridge likes to have a capacitive loading (I know MM cartridges like to have some ... including the capacitance inherent in the phono cable); and

b)  how you produce such a 'C' loading, if this IS required by an MC cartridge??

For a MM cartridge, I understand that you simply have a small (maybe 100pF?) cap connected from the input signal pin of the MM phono stage to ground.  Fancy phono stages allow you to alter this loading with a flick of a switch!

When the MC cartridge is connected to a step-up transformer, where do you put a capacitor for the load?  Do you create a cap loading for the MC cartridge by keeping the cap across the input signal pin of the MM phono stage to ground ... or is it better not to have any cap at all?

Thanks,

Andy

John Chapman

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MC Cartridge loading with a step-up ... Attn. John
« Reply #1 on: 28 Dec 2003, 02:03 am »
Hello!

Sorry for the delayed reply. I have mostly been drinking heavily and watching the Christmas Goat webcam. Pretty busy time right now.

You seem to have a good handle on the resistive loading. I have not played with Capacitive loading yet and from everything I see there is no reason to with MC cartridges. There is some cap load from the interconnect and from the phono stage input capacitance already and no reason to add more. I did some digging around and this seems to be the conclusion. My loading article is done to be as non techie as possible but Jim Haggerman has a great loading article that gets a bit more techie and goes into cap loading (and why it is not a good thing for MC carts!) here:

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


If anyone with more info on the subject could post it would be most appreciated!

Many Thansk!

John Chapman
www.bentaudio.com

Marbles

MC Cartridge loading with a step-up ... Attn. John
« Reply #2 on: 28 Dec 2003, 02:35 am »
Quote from: John Chapman
Hello!

 I have mostly been drinking heavily and watching the Christmas Goat webcam. Pretty busy time right now.

...


YOU TOO?

You don't know how many times I've said that exact same thing  :lol:  :rotflmao:

andyr

MC Cartridge loading with a step-up ... Attn. John
« Reply #3 on: 4 Jan 2004, 12:40 pm »
Quote from: John Chapman
Hello!

Sorry for the delayed reply. I have mostly been drinking heavily and watching the Christmas Goat webcam. Pretty busy time right now.

You seem to have a good handle on the resistive loading. I have not played with Capacitive loading yet and from everything I see there is no reason to with MC cartridges. There is some cap load from the interconnect and from the phono stage input capacitance already and no reason to add more....  Jim Hagerman has a great loading article that gets a bit more techie and goes into cap loading (and why it is not a good thing for MC carts!) here:

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

 ...
John, Thanks for your reply.

I have read Jim's article and he has also been kind enough to answer a couple of my email Qs .... but .... I still cannot make sense of what is supposed to be best for a MC cartridge (wrt whether a capacitative load is advisable or not!!).  I see these descriptions of phono stages like the Manley "Steelhead" which go into great detail about how you can basically infinitely vary the C and R loading for your cartridge .... yet the blurb is not specific wrt the cartridges which can be used with it, in terms of them being MM or MC!!

I would be very grateful if you would treat me as if I were an ignorant dumbo and explain it from first principles.  IE.:

*  assume one has a MC cartridge.

*  assume one's phono IC has some capacitance.

*  first example:
a) assume one has one of your step-up transformers feeding a MM phono stage which has NO additional cap loading;
b) assume one has one of your step-up transformers feeding a MM phono stage which has some additional cap loading.

A)  What difference in sound will be heard from the above two??
B)  How will the cap loading on the MM phono stage affect the MC cartridge??

*  second example:
a) assume one has an active head-amp which feeds a MM phono stage which has NO additional cap loading;
b) assume one has an active head-amp which feeds a MM phono stage which has some additional cap loading.

A)  What difference in sound will be heard from the above two??
B)  How will the cap loading on the MM phono stage affect the MC cartridge??


BTW, what is this "Christmas Goat webcam" you people in the US seem to watch at this time of the year??  Another poster mentioned he was watching it too (we don't get it in Oz!!).

Regards,

Andy

Marbles


John Chapman

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MC Cartridge loading with a step-up ... Attn. John
« Reply #5 on: 5 Jan 2004, 01:35 am »
Hello!

As I mentioned I have not played with cap loading myself so I am not likely the best one to ask! I can guess a bit - it always bugs me how many posts on these forums are just guesses rather than actual experience but I'll take a go at it anyway.

Basically adding capacitance will roll off the high frequencies. There is always a small capacitance in the cables and in the input circuits - even though there may not be any 'capacitor' installed.

Think of the effect that happens when you run a long length of high capacitance cable as an interconnect. Search fro Jon R.  and his cable notes at the asylum for why you want low capacitance for interconnect cables. I can't see why this is necessarily a good thing but I can see that in certain cases it would maybe  get rid of some ultrasonic distortion - just one of those guesses.

The resistive loading helps to tame any ultrasonic peaks the MC cart may have while capacitive loading will tend to lower the frequency that the high frequencies will start to roll off and I think it would  change the frequency that the ultrasonic peak occurs at.  Keep in mind that with low values of capacitance (like just the short capacitance in the stub cable from a MU step-up) we are talking HIGH frequencies - way above 20Khz and likely as much as a couple hundred Khz. In this respect my gut says that typically the inherent capacitance has a value that is just about right to roll away any garbage that might be riding up there.

I have an open mind with this stuff so I would not be surprised if cap loading would have a similar (good) effect when applied modestly if the capacitance of the circuit was extremely low. This is more likely to be needed with a solid state high gain phono stage or a head amp than when a transformer is used. The transformer has the effect of raising the naturally connected capacitance and also has a bandwidth of it's own that will strip away any noise way way up high in frequency.  

The transformer will translate the impedance it is connected back through to the cart by trhe square of the turns ratio. This is why a 10K resistor at the seconday looks like a 100 ohm load to the cartridge connected to the primary. The same principle is at work when capacitance is applied so I think the effect would be the same for a headamp or a transformer IF you adjust the cap values so the EFFECTIVE capacitance ends up the same from the cartridges point of view.  


The only way to find out for sure what the effect is would be to measure with a test record and do a series of listenning tests. I am afraid I haven't time right now to dig any further into it so I can't get a test setup and all that....

Please report back what you find out from others or via testing done yourself.

Many Thansk!

John Chapman
www.bentaudio.com

andyr

MC Cartridge loading with a step-up ... Attn. John
« Reply #6 on: 5 Jan 2004, 03:02 am »
Thanks, John, for your detailed discussion.

Makes sense ... plenty to think about there!

Regards,

Andy