Cartridge loading explained

the thin end of the wedge
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dirkwright
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Re: Cartridge loading explained

Post by dirkwright » 17 Jan 2015 16:55

Thank you everyone for your detailed replies. Here is the article about using huge capacitors with MC cartridges:
http://www.extremephono.com/Loading.htm

Obviously, since the R and L are so low, then the C has to be huge to bring the time constant into the audio range. As a designer, I am having difficulty with adding a separate C loading for MC cartridges, though I can do it. It just makes the board larger and more complex. They don't make trimmers that large either, so I would have to have something like a 1uF fixed value. What's the opinions out there on this?

What about typical R values? What's the maximum that you'd use? Is 1 kohm big enough?

There are going to be two trim pots for the R, one for MC and one for MM. The MM is 100k and I'm guessing that the MC should be 1k. The reason for the separate pots is that the resolution down below 1k is not very good on the 100k pot, even when it's a multiturn model. So, to provide good resolution, I need a separate pot at a lower value for the MC loading. Each pot will be switch selectable, obviously.

dirkwright
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Re: Cartridge loading explained

Post by dirkwright » 17 Jan 2015 17:26

It looks like the MC trim pot should be 500 ohms. I can put a 10 ohm resistor in series with it to prevent the use from making it zero. I suppose I could put a 1k in series with the 100k trim pot also.

The 1 uF polypropylene capacitor is huge... sigh.

andyr
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Re: Cartridge loading explained

Post by andyr » 17 Jan 2015 20:51

dirkwright wrote: It looks like the MC trim pot should be 500 ohms. I can put a 10 ohm resistor in series with it to prevent the use from making it zero. I suppose I could put a 1k in series with the 100k trim pot also.

The 1 uF polypropylene capacitor is huge... sigh.
I suggest you will be in more trouble trying to set 'R' values for MC than you will be with MM values - at least the latter is probably going to be only 47K or 33-38K (to allow for Grado wood-bodies). Whereas MC can vary from:
* 22ohms (for some Ortofons)
* 100ohms (which is a common value for DL103 owners)
* 220-470ohms (which some DL103 owners prefer)
* to 2K2 (which is what I use on the my Benz LP)
* through to 47K (which is what Benz recommends).

This is the reason I use parallel RCA sockets, to permit an infinite value adjustment.

And I note for 'C' load, the graph in that article you linked to only references 1.5uF with 2 low 'R' values which are completely unsuitable for my Benz. I suspect at 2K2, the optimal value of 'C' will be lower - which David and I will find out. :D

Regards,

Andy

dirkwright
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Re: Cartridge loading explained

Post by dirkwright » 17 Jan 2015 22:00

To each their own.

It's still no problem with my setup. If the owner wants a high impedance for their MC cartridge, then they just leave it in the MM position and adjust accordingly.

dlaloum
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Re: Cartridge loading explained

Post by dlaloum » 18 Jan 2015 00:14

I would not worry too much about super high C for MC's - very few people are even aware of this, I would call it a "nice to have" - and those aware of it who want it will easily find an external means of providing it...

When I had my phono stage built I specced it with high internal R and low internal C, as both can easily be provided externally - internally it has no additional C other than the circuits own, and internal R is 500kohm - which is high enough that anything I connect externally becomes the actual R (47k becomes 46k.... close enough!)

dirkwright
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Re: Cartridge loading explained

Post by dirkwright » 18 Jan 2015 17:23

The boards have been redesigned already. I have Hi and Lo input Z, each adjustable for R but only Hi adjustable for C. The Lo Z has a fixed 1uF poly capacitor. Total range of adjustment for R is going to be 10 ohms to 100kohms across the two ranges.

Thanks for everyone's input.

carlosfm
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Re: Cartridge loading explained

Post by carlosfm » 24 Feb 2015 21:58

Hi guys

This thread is already 9 years old, I've just remembered it and came for a visit.
It is sad for me to see that the links for the images on the first posts are not working anymore ("This image does not exist.").
It is very important for the understanding of the whole matter that the images are available and it has given me quite some work back then to put all this together.
I may not have those images anymore...
Well, take care and go load some carts, will ya? :mrgreen:

madis64
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Re: Cartridge loading explained

Post by madis64 » 14 Mar 2015 20:18

Hello everybody who has contributed to this thread throughout the years.

The question about how the measurement graphs are to be created in a standard and proper manner (last occurrance is some pages back) is still waiting for a step by step howto.
Obviously one of the first steps is powering up the gear and taking the test record from the shelf but after that?

Can anybody post a link to a process description ("for dummies" style) or post it here in few lines?

tubewade

Re: Cartridge loading explained

Post by tubewade » 14 Mar 2015 21:18

Carlos, I hope you still check back occasionally, thank you for making this incredibly useful thread. Yes, I can't believe it is nine years old! It has been a terrific help to many people, including me, over those years.

Madis, I cannot answer your query. Hopefully someone else who can will come along shortly.

bcarso
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a nice thread

Post by bcarso » 02 Aug 2015 23:23

Hello to all. It has been a while. It is good that this comes up readily on a search on the subject.

There are a few things that could be added, although the material is pretty comprehensive already. I am glad to see mention of the mechanical behavior separated from the electrical, and an acknowledgement that the reciprocity is very small.

There is an interesting effect for low inductance and low resistance cartridges when the capacitive loading is large. The load resistance can be increased indefinitely, which is to say that for a large enough capacitance the internal cartridge resistance dominates the electrical damping. For one example, for the tabulated values of the Eroica LX, which are 12uH and 8 ohms, 360nF loading yields an unpeaked electrical response that is -3dB at about 79kHz, rolling off at 40dB/decade in the stopband. The potential advantage of terminating this way is the elimination of midband attenuation and as well the thermal noise of any terminating resistor. So aside from the bulk of the capacitor, and possible piezoelectric effects, it seems an appealing approach. It also has the feature of rendering any realistic cable capacitance a tiny effect.

Another remark, in the context of MM/MI configurations, is that one can compensate for excess cable capacitance using a synthetic negative capacitance. Stability against oscillations must be carefully assessed and adjusted for, but it seems feasible. Has anyone ever heard of this being done in a commercial preamp?

Brad

jmchrislip
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Re: Cartridge loading explained

Post by jmchrislip » 03 Aug 2015 23:03

Check out the DB Systems cartridge kits for MC and MM. You can fine tune your cartridge loading. They will also make custom plugs for you at $7 per set of plugs. Best thing I've purchased recently.

bcarso
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Re: Cartridge loading explained

Post by bcarso » 15 Sep 2015 20:17

I also did some additional explorations and note that a series R-C network works best for some medium inductance and resistance MC terminations. The resistor contributes a little noise at high audio frequencies, but the network has the other advantages of low attenuation at low and mid audio frequencies. The response can be tailored for a little rise at high frequencies, which may be advantageous.

mkane77g
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Re: Cartridge loading explained

Post by mkane77g » 24 Jun 2016 17:08

Read every page, again and thanks.

Tube Radio
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Re: Cartridge loading explained

Post by Tube Radio » 14 Oct 2016 17:12

carlosfm wrote:Bauzace (Carlos),


- If the cartridge sounds too smooth and shut in, with lack of high treble, it needs a higher value shunt impedance.

Leave capacitance alone, low, the cabling is enough, and just change the resistors.
Thanks for this.

I did not know the load resistance could be changed to alter the upper treble response.

KarlBaj
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Re: Cartridge loading explained

Post by KarlBaj » 15 Oct 2016 14:56

Astonishing how all this mingling with resistors and capacitors looks like a primitive, manual and extremely awkward way of doing exactly what is happening inside that nowadays much- maligned HiFi seperate that we were told back in the Eighties no one could live without: the equaliser.

Yes, I know:

[-X [-X [-X

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